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20 October (2026)
Instead of Back to Spain I could write "Back to where I started"... still doing the quantum billiard on my non-integrable loop. Always coming to the same starting point.
Speaking about journeys in time, $I_{\alpha\beta}$ is the weak value introduced by Aharonov et al.[1], in our case of the intensity operator $\hat I(\mathbf r)\equiv\hat\Psi^\dagger(\mathbf r)\hat\Psi(\mathbf r)$ for a field prepared in the coherent state $|\boldsymbol\alpha\rangle$ (or in the past) but later found in the coherent state $|\boldsymbol\beta^*\rangle$ (or in the future), so that makes Eq. \eqref{eq:0LiYJb} a positively weighted average of weak values. Progress! It is something...
It is my feeling that when past and future agree, the weak-value becomes a classical probability.
When they don't, then we enter this weak-value business of contextuality and realizations as two-time objects. Now what it all means, I don't know, but it seems it has some place to go. Also on †â¶
Back to Spain, after a long and rough trip, but the company (of the sun) was quite something. I'm always trying very hard not to re-read what I already read but since I wanted to relate my never-ending missed encounter with the Japanese sun and other cosmic objects to Buzzati's K (which is called this in French only; a better name, actually), I dived into the book again and did read a few stories. In particular, "E se?" which makes even more sense now than it did when I was a teenager, since a twenty-five year gap in the impossible infatuation between incompatible people could only hit me so far thirty years ago, but now of course it reads like Dino put it down for me. It's a short book, I actually read pretty much all of it again... And againâin particularâ"La lezione del 1980", since I was also reading De Gaulle's confidences to Peyrefitte during this trip. It was nice to read De Gaulle comments on recognizing China and his thoughts on this country when I was there myself. If I have time, I'll tell "us" what I felt this time about China. It changes so much so quickly, every visit is a new one. To first order, I felt much more defiance and hostility towards the West this time, especially at the Summit where various talks, in Chinese (translated live on the app) were openly challenging the occidental world. Anyway, reading Buzzati put me in a melancholic mood. «E oggi, oramai, era tardi.» One shouldn't mix Italian (Buzzati) with Japanese (the Hinomaru by the window), that's too strong, too extreme, too reactive, Oganov would say. The sun escorting our plane and then gone for ever but reappearing constantly as if to say "I'm still there" was not helping to concentrate on Ergoli. I did change the order of the manuscript all around, dealing with high-multiphotonic regime in the last part now, not coming back to removing the confounders, so we're not getting closer to meeting our deadline. Meanwhile, Alexandros proposed to Natalia in Copenhagen. I left him haggard and confounded on the wharf of a Chinese river, and will find him back a betrothed fiancĂ© to a stupendous young physicist, both of them in our paper. At least some good things happen in the world. I should send them the draft along with my congratulations.
19 October (2026)
Past Kazan, the Hinomaru came back! This time it was red even without the glasses; I'm not sure what happened. It can't be that we're going faster round the globe than the sun itself, so it might have been obstructed by the plane's inclination, but was still there lurking in the background all this time, or it had been absorbed by the Ural mountains, which are now behind us. I don't think I have just dreamt it although I don't see it now anymore... but I made sure this was true, as it indeed looked like a dream, if not a message, definitely an apparition. It's this sort of not impossible, just improbable, well-timed things that look like a miracle. I was mourning and missing it but it was never completely gone. It's night all right, but the sun was there anyway.
It just reappeared again... I can see it through the window of the passenger in front of me, not through mine, although his also has the reflection of his screen, he is playing some sort of Tetris. The fact it's now red on its own, more truly itself, adds to the sensation. It is silent, but it shines.
E se?«Ma lui non lo aveva mai capito, non lo aveva mai sospettato, neppure come scherzo. Solo il pensiero gli sarebbe parso una scandalosa follia. CosÏ gli anni erano passati inutilmente. E oggi, oramai, era tardi.»
The Hinomaru was at our rendez-vous, but it had nothing to tell me. Or I didn't hear it. Which is probably closer to the truth. I've been told everything, possibly even several times, but have failed or even refused to hear it. Still, it was there, silent, but magnificent. It doesn't make you less majestic to be silent, of course. Although what a spectacle it would be if the sun were to say something, like it seems it wants to when it goes full solar eclipse. What an encounter, what an embrace with a furnace!
And, laugh if you want, but with those modern windows with electrochemical dyes or polarizing material in them that they have in planes now, which switch off by themselves and automatically, the sun appeared pinkish and then purplish as it was setting. And with my orange glasses that I use to filter out blue light to avoid eye straining, then what was left from this successive filtering of colours was indeed the most beautiful, perfect, intense red, pure red, the most literal Japanese sun that I ever saw. It was not over Kazan, it was all over Omsk for a good thousand kilometres on both sides of it. It was unending. It was red like blood, floating in the night, immobile, suspended. And then, at some point, it quickly sank down below the horizon. It stayed afloat staring at me in the eyes for maybe a good hour, as the plane with myself inside it was hopelessly running after it, chasing pathetically something too far and too huge for you, and then in a few seconds, it was gone. Sometimes in life you have what feels like an eternity of beauty in front of you and then it disappears in a matter of seconds, leaving the night behind it.
It's very cloudy over Novosibirsk, so I won't see the city, but the night is slowly catching up on us, which means I'll have the most beautiful conclusion of my journey with the Hinomaruâthat has abandoned Tokyo and its permutations to the nightâfollowing me instead to meet me somewhere over Kazan, maybe, or Moscow. I have Glass' music that resonates in my head already over the background of the reactors, thatâin the particular piece I have in mindâseem to be part of the music anyway.
Maybe like Buzzati's Colombre the Hinomaru has something to tell me. I'm convinced that there's only silence and spite for me from where it's coming from but maybe over the dollish Russian churches with their candy-like roofs, it will tell me something which I have been dying to understand, a story which I have been longing to hear, «che dĂ , a chi la possiede, fortuna, potenza, amore, e pace dellâanimo», although even if that would be the case, «Ma era ormai troppo tardi»:
Che lunga strada per trovarti. Anchâio sono distrutto dalla fatica. Quanto mi hai fatto nuotare. E tu fuggivi, fuggivi. E non hai mai capito niente.But then, when it would tell me, it would all become clear, it would all make sense, and I could finally let it go, forgiving myself for having wanted to treasure the sun, the moon and all that they shine their light onto, as if it was a symbol of something, when they are all little else or little more than «un piccolo sasso rotondo».
We're running away from the night. I might be lucky to have clouds Mie scattering on me for the entire eleven time zones of Russia. Clouds now look like the wool of an unending stream of sheep going from Irkutsk to Krasnoyarsk. It's already night in Harbin, which is the place from where comes Vladimir Osipov, who works on exact solutions to the kicked Ising Hamiltonian. I have to send him literature on Conti and Berloff's use of Ising models, he was very interested in their ideas, as he's also into quantum applications of such. Later at the conference banquet, Klembt asked him: "is it true that the more to the north you go in China, the more people drink?" Osipov replied with a scoff, as if outraged, but not by the undertone, instead by the fact that it was obvious: "oh yes, of course, of course, definitely!..." Sebastian justified his "cliché" (that he presented as such) with some arguments which I thought would be that this direction was getting closer to Russia, but Vladimir provided a more universal explanation instead: "I mean, it's the weather!" We actually drank quite a lot at this dinner, although the weather was all right. I can see the gigantic lakes before Ulaangom glittering in the sun.
There's much room in the plane as there's an empty seat between me and my neighbour, who has been looking fixedly at the map since we departed. So I can use my laptop, although it's of office size. We're now over the Gobi Desert. I'm at the window so I can get the thrill of the dusty desolation of this infinity which is empty in all the directions, even when seen from our current 10394m of altitude. There's an occasional road piercing through. I'd like to be down there. There loneliness must really feel something. The distances in your head projected into the mountains around you. No distractions. We're already approaching Eren Hot, and there are more signs of civilization and structures. In no time we'll be flying over Sainshand and then over Ulan Bator, which should start to look like a bit more than a settlement. I can document all this through my local web server. But I couldn't send emails, for instance, if I would want to. Say if I wanted to ask someone if they're bored, and if they're not, why are they reading this? Not that I would, if I could. So I'm a bit down there in the desert indeed. Not even, not anymore. We go so fast, currently at 774km/h, that clouds have replaced the sand. They are very beautiful, the clouds, something between layers of cotton and milky sea waves. It's not boring but it's painful to look at them.
How my next 15 hours will look like, painted by a monk from the Yuan dynasty on fragile bamboo paper so that the universe could bring it to me at the airport to tell me "you're not alone, I'm with you, just carry on inside me, I'm gestating you into something worth the effort, you'll see... Safe trip. Or not. It's all taken care of."
Yellow mountains at the airport.
Bored, are we?
Who's talking to you? well you know "who", there's no mystery as to who the writer is; but who is the reader? Who is this "you" this "who" is talking to? Who are you? Not so clear, hey?
Well, I know who you are. You're the one who doesn't know, who wonders whom this is written for.
And now, you know. Funny, isn't it?It could just be good timing, it could be chance, it could be a coincidence. Or it could be fate, or perseverance, or a miracle.
Whatever it is (I don't know what it is), I'll tell you something I know: Everything is. Or nothing is. Same thing.
And while you're reading that, let me also tell you: there are more interesting ways to not get bored. You know that too, right? You don't want to admit it but you know it. Why wouldn't you try this for a change?
Daniel did it with the experimental data and it's even better than I thought, since it has the advantage of U-statistics, it's even more correlated:
18 October (2026)
Not a long night but at least a long day. And I have to leave early, so I'll go to bed but taking this with me below the sheets: the thermal-aligned donut is still a donut but with a pulsating profile, making it look like a pinched donut, a wannabe dipole $$\rho_{\rm oracle}(r,\theta)=\frac{r^2e^{-r^2}}{\pi}\left[1+\frac{\pi}{4}\cos2\theta\right].$$
Along any ray the normalized radial law is the donut's $r^2e^{-r^2}$: the cuts along and across the axis differ only by the weights $1\pm\pi/4$ and coincide once normalised to unit area.
Around the rim the alignment is a cosine of contrast $\pi/4\simeq0.785$, between the coherent donut ($0$) and the critical dipole ($1$): $1+\pi/4\simeq1.785$ on the axis, $1-\pi/4\simeq0.215$ across it:
While I'm still in China thinking about the Simpson's paradox, let me share the animation I did for the slide opening the 3rd (äž) part of my talk: Laozi contemplating birds. The flock as a whole goes upward. Each bird in its own group feels it's getting downward, as birds appear out of the fog upwards from it. Each birds independently of anything else flies in a straight horizontal line. Correlations are thus dependent on your reference frame and to what you compare yorurself to.
I found the way out, it's smoking hot: we cut everything in two: left, ensemble averages; right, single-collapse averages. Because they are the same, nobody will notice, which is basically the point. But we'll have a cornerstone "Ensemble average" vs "Single-collapse average" on both sides of an almost invisible dotted yellowish line, and $C_\alpha=1/6$ and $1/4$ on two columns, also introducing RCPS in a very natural way. It will be beautiful!
I'm thinking in putting the one-collapse observables for $g^{(2)}$ and $g^{(3)}$ too:
but we don't quite have the room. Logic demands them, though... The above is Monte Carlo for 1000 points. Continue on †â¶
To gloss for Ergoli on correlations of azimuthal beams:
- Spatial correlation singularity of a vortex field. D. M. Palacios, I. D. Maleev, A. S. Marathay and G. A. Swartzlander in Phys. Rev. Lett. 92:143905 (2004).
- Hanbury BrownâTwiss-type experiments with optical vortices and observation of modulated intensity correlation on scattering from rotating ground glass. A. Kumar, J. Banerji and R. P. Singh in Phys. Rev. A 86:013825 (2012).
- Measuring the orbital angular momentum of partially coherent optical vortices through singularities in their cross-spectral density functions. Y. Yang, M. Mazilu and K. Dholakia in Opt. Lett. 37:4949 (2012).
- Effect of spatial coherence on determining the topological charge of a vortex beam. C. Zhao, F. Wang, Y. Dong, Y. Han and Y. Cai in Appl. Phys. Lett. 101:261104 (2012).
- Measuring mode indices of a partially coherent vortex beam with Hanbury Brown and Twiss type experiment. R. Liu, F. Wang, D. Chen, Y. Wang, Y. Zhou, H. Gao, P. Zhang and F. Li in Appl. Phys. Lett. 108:051107 (2016).
- Experimental determination of the azimuthal and radial mode orders of a partially coherent LG$_p^l$ beam. X. Liu, T. Wu, L. Liu, C. Zhao and Y. Cai in Chin. Opt. Lett. 15:030002 (2017).
- Review on partially coherent vortex beams. J. Zeng, R. Lin, X. Liu, C. Zhao and Y. Cai in Front. Optoelectron. 12:229 (2019).
- Phase detection of coherence singularities and determination of the topological charge of a partially coherent vortex beam. X. Lu, C. Zhao, Y. Shao, J. Zeng, S. Konijnenberg, X. Zhu, S. Popov, H. P. Urbach and Y. Cai in Appl. Phys. Lett. 114:201106 (2019).
- Review on vortex beams with low spatial coherence. X. Liu, J. Zeng and Y. Cai in Advances in Physics: X 4:1626766 (2019).
Hanbury Brown-Twiss effect and classical entanglement with OAM-carrying light. J. Laatikainen, S. Pokharel and O. Korotkova in arXiv:2604.14452 (2026).
Last day in China, with some last hoping back by West Lake University.
I had breakfast with Paul Abbott who gave a talk on behalf of Wofram corp. about Mathematica for quantum computation. It turns out he's a long time friend of Wolfram himself, who he has known since even before Mathematica, being one of the earliest user of SMP. We discussed Wolfram physics, the people around that and various aspects of the legends and myths surrounding the man and the universe he created for himself. A short but interesting talk.
17 October (2026)
I should check it they match.
Oganov.
16 October (2026)
Last animation for my keynote, the removal of the phase confounding factor for thermal light:
I want to discuss three points, äž äș äž, and because I'll prepare and rehearse their delivery, I should have time to cover them all. I won't have enough time to go into the details, like fully removing the Simpsons paradox with random-phase coherent states, but the main message should be conveyed.
I want to record this neat idea I got while discussing with Sebastian, now over dinner, at which occasion the question of AI and consciousnessâof courseâemerged around the table (these big, precious-wood round Chinese tables covered with food that you circle round). I shared my opinion about the nature and effect of time on that matter. The discussion continued with Sebastian because he didn't agree or understand my point, on those machines not having a notion of time. I argumented about the lossy compression, their lossy memory and how that's what time does for us, while this happens at algorithmic pre-defined steps for them, when they need to release resources, but that otherwise, the previous prompt five seconds ago or something started two months ago was the same, and that they don't progress linearly, they are not dragged through time one moment after another, like we are. Everything is an instant. And then, him being a physicist, I had this nice picture which I want to record because I think it's neat and spot-on: it's like proper time for the photon, there's no time. Photon is emitted, it's absorbed, it doesn't matter if it passed twenty picoseconds or five billion years in between, it's the same for them. AI is this with their "thinking". They have singular access to intelligence, or knowledge, one point in time, with nothing before and nothing after until the next such singular encounter. They are like photons of consciousness, with singular, pontlike accesses to its structure. I think it's accurate, and insightful. Maybe to finally unleash machines, we need to stuck or pluck them into time.
Through one of my sixteen windows, I saw a remote building turn bright red. It's because on the other side, which I could also see as I have 90° view of what's going on outside, there was the most splendid Hinomaru setting behind the distant towers of the city.
The photo does not make it justice. It was red like in the Schrader movie.
I'll organize my talk around Laozi and the Tao Te Ching, in three parts:
My new animation of the azimuthal HBT effect: It's faster than distances, less things to introduce, and I can carry on right away on the confounding factors and Pavlos' experimental data.
I met with Prof. Chao-Yuan Jin (éæœźæž), from Zhejiang university, part of the organization and, accessorily, in charge of the Chinese translation of the 2nd edition of Microcavities. He brought me to the nearby Technological Innovation Centerâconfirming in passing there is no place to eat at the hotelâand gave me a quick tour of the place. Here you see him with a model of the campus, half of which is currently under construction. It was no ordinary model, as it was illuminated and flashing from place to place.
He is an expert on quantum-dot lasers and worked with Andrea Fiore and then was in Sheffield! So I should know him more than I do. I see that in a recent paper,[2] they claim to generalize our sensor method[3] for Ultrafast Control of Rabi Oscillations, which is also something I like to do.[4] In fact about everything he does is somehow related to my own interests. Even his moiré flat-band cavity QED paper[5] brings condensed-matter into photonics, which is part of my turf. They also put recently an arXiv on Structured Single-photon Metasource,[6] which is single-photon vortex light, our Ergoli playground, and a recent PRL on frequency-engineered Floquet physics,[7] something we want to explore with Sven to make a perfect single-photon source.[8]
Unfortunately, the same problem I have with their face, I have with their name. I can't quite map who is who and doing what in the Chinese community, and Sven in fact had already pointed me to one of their papers,[9] precisely in that context! I'll have to do something about that, recognizing them and getting to know them all, all the Yu, all the Yang, all the Wang, all the Chang, but at this stage, I don't even know if my host's firstname is Jin, or Chao-Yuan, and most of the previous interactions we had by email, I had called him "Ms. Li", because he uses the same email as the secretary for the group, and I lost track that the correspondent had changed at some point! How embarassing. At least I didn't call him Ms. Li today.
I hope we have occasions to speak more after the talks, although when I offered to meet his broader team, he told me the young generation doesn't like to mix with foreigners and doesn't want to speak English. No wonder, now that the cultural gap is weighting on their side, they don't have to suffer the annoyance of our arrogance. I told him it's good for the young generation overall but not for the young generation of scientists. I should invite him to the next Multiphotonics.
I had breakfast with Sebastian Klembt. We were sitting on sofas so with the mouth very close to the plate. I felt like we were chldren, especially in those big surroundings. They had to kick us from the huge breakfast lounge since we stayed there after everybody and everything else had left, including the breakfast itself which got cleaned away from our table as we were discussing. Two people on an empty table past hours in a deserted dining room is not the protocol.
I'll prepare my talk well in advance, and even rehearse it at least once. Let's see if that makes a difference. If not, it'll justify two decades of not caring. If so, it'll condemn me for having wasted everybody's time to spare me the burden of not doing everything at the last minute.
I must also start to look into our Simpson paradox in parallel spaces.
We now have two oscillators (or two universes in which they live), in the doubled phase space $(\boldsymbol\alpha,\boldsymbol\beta)\in\mathbb C^M\times\mathbb C^M$, and the state is now
\begin{equation} \label{eq:0Lmokb} \rho=\int P(\boldsymbol\alpha,\boldsymbol\beta)\, \frac{|\boldsymbol\alpha\rangle\langle\boldsymbol\beta^*|}{\langle\boldsymbol\beta^*|\boldsymbol\alpha\rangle}\, d^{2M}\!\alpha\,d^{2M}\!\beta\,, \end{equation}
This is my hope for the alternative-universe description. It becomes standard, classical one-universe when $\boldsymbol{\alpha}=\boldsymbol{\beta}^*$. The de Finetti representation then reads: \begin{equation} \label{eq:0LiYJb} \rho^{(N)}(\mathbf r_1,\dots,\mathbf r_N)=\int P(\boldsymbol\alpha,\boldsymbol\beta)\prod_{j=1}^N I_{\boldsymbol\alpha\boldsymbol\beta}(\mathbf r_j)\, d^{2M}\!\alpha\,d^{2M}\!\beta\,, \end{equation} where, and this is where the key to the problem lies: \begin{equation} \label{eq:0LdNRb} I_{\boldsymbol\alpha\boldsymbol\beta}(\mathbf r)\equiv \Psi^*_{\boldsymbol\beta^*}(\mathbf r)\,\Psi_{\boldsymbol\alpha}(\mathbf r)\,. \end{equation} This is complex. Even if it'd be real, I'm not sure what it'd mean so I'm not entirely concerned about it being complex. We're about at the stage of Cardano finding $i$ such that $i^2=-1$ something so "complex" that it's even "imaginary"! It's not if you look in the extended space (2D), then it's not a point in the line, it's a point in the plane. You bring rotation into that, but little else (formally). I expect something similar here. Something has to be weird, or complex, or imaginary somewhere... otherwise it'd be boring classical physics all the way down. Also on †â¶
15 October (2026)
Meeting from the bed. Re-enacting, twenty-two years later, this special moment when you keep the best for the end. But now it's my turn to be the giving hand to the receiving one.
«La main qui donne est toujours au dessus de la main que reçoit.»
I said goodbye to Alexandros tonight. We only had time for long scientific discussions. All more private and personal discussions, we had only little time. Often because of me. He was leaving today and although I'm very far from everything in this Buzzati hotel, he made a loop on his way to the airport so that we could have a beer. I got lost with the first taxi already, after spending half an hour to book it because I eventually realized I hadn't paid the one of yesterday and the app didn't let me book a new one until I settled the bill. The guy from the lobby (I hope it's not always the same guy, although all the Asian people look similar to me) explained that unimaginable subtelty: "you didn't pay your bill." He ordered the taxi after settling my debts, but then as I explained where I wanted to goâto meet Alexandros for our farewellâthe information got lost another couple of time. In the first taxi I spent a good five minutes (which is a long time in a taxi with some Chinese shouting) until I convinced the driver to bring me somewhere. This time it was pre-paid, the lobby assured me. After resolutly refusing and indicating the door, he gave up and drove very fast very far and dumped me in a park. Not his problem anymore. Only mine, and a bigger one. The taxi was still in sight when I got a notification that I got refunded the fare. So he probably was very upset. Meanwhile, Alexandros was waiting for me by the river, in the mist... time passing, his flight approaching, our goodbyes departing... I sent him my location, and he replied "Ouch!" I took a second taxi and that's with this one that I realized they want the last four digits of the phone. Protocol. It doesn't matter that I have their order, the registration plate on my phone, if they don't have the last four digits, they get agitated. And if shouting is not enough, they drive far and fast and dump you. You don't arrive to your friend by being randomly tossed from place to place. But I managed to arrive with this sĂ©same: 0781, although it was very late. It was already time for Alexandros to go. We'd have to tell each other everything we had to, for the time it takes to eat a pizzaâhe had ordered one with those Shitaki mushrooms and truffe du PĂ©rigord, a strange combinationâand a beer. Not that I had much to say, anyway. We talked about cats, about my failure with phone applications, about the close-to-diplomatic incident in the first taxi, the retaliation from the driver, I also complained that I can't say if I'm interacting with one and the same receptionist at the hotel or if it's always a brand new one that I introduce to the intricacies of solving a foreigner's personal problems. We didn't have time for my red-braised soft-shell turtle dish story. We also didn't have time for anything involving this utmost mystery that every woman there has glasses, and that although women all look different, unlike men, they all remember me of the same person, with their glasses. Strange. It doesn't matter, I would never had raised such a subject anyway. And it was time already to ask him to get me a taxi back, as he was taking his own taxi to the airport. It was slightly raining. The fog was bouncing the light from everything that was standing: the trees, the building, the men's hairs, the rims of the women's glasses, everything seemed in fire. It felt like the droplets of waters were truly carrying the light while the true droplets of light, the photons, were the ones delivering the mist. I walked a bit faster and told him "Wait! I want a last picture of you in China!" He said he'd be back. I told him that I might not, and that everytime was always a last time. I was saying nonsense to take the picture, so that he'd have to listen to me and this would give me time to capture him in the fog, in the light, in his flight towards his flight.
I'll see him soon in Madrid, anway, but it'll be different. It will be without this feeling of dragging laboriously non stop in a vicious circle.
A quick proof of Marino et al.[10]'s Eq. (3) (which is Eq. \eqref{eq:0LoKmb} below for violating CSI for bright beams). If one decomposes $$g^{(2)}_{ij}\equiv 1+\epsilon_{ij}$$ as we like to do,[11] then the CSI reads $(1+\epsilon_{ab})^2\le(1+\epsilon_{aa})(1+\epsilon_{bb})$ which, expanded, yields $2\epsilon_{ab}-(\epsilon_{aa}+\epsilon_{bb})\le\epsilon_{aa}\epsilon_{bb}-\epsilon_{ab}^2$. The lhs is of first order, so setting the rhs, of second order, to zero gives their Eq. (3): \begin{equation}\label{eq:0LoKmb}\epsilon_{ab}\le\frac{\epsilon_{aa}+\epsilon_{bb}}{2}\,.\end{equation} This is not equivalent, though. If CSI is obeyed, then Eq. \eqref{eq:0LoKmb} is obeyed. By contraposition, therefore, violating Eq. \eqref{eq:0LoKmb} âč violating CSI. But one can violate CSI while satisfying Eq. \eqref{eq:0LoKmb}. There is a cute proof on †â¶
Probably my main contribution to Microcavities, 3rd edition for today, the revised Landau and Solvay conference group photos, with wireframes identifying the participants.
I'll work on the bio snippets back in Madrid, it's not convenient (and not the place) from here.
In the race to the bundler, I have always said that China would make it first... and it's clear for this truely groundbreaking technology as it is in most other things, as seen for instance, in the number of citations to the initial work.[12] I have prepared this animation for my keynote here:
This reminds me the EIC referee's comment that «this [...] has not gained much attention in the single photon sources community». This Referee was probably from France, which is constantly at the bottom of this chart and will soon drop out of it. For them, indeed, not much to see, as they still struggle to make a slightly "better single-photon source."
The hotel is gigantic and everything in and around it is out of proportion.
I went for a little stroll in the park in front, where Chinese families bring toddlers to interact with black swans. The look of young children at the wonders of this world, how they scrutinize wilderness full of perplexity, feeling somehow they are in command of a considerable power and maybe even duty over it, as the floating birds squeak for food, while not understanding at the same time quite what this is all about, a mixture of realization and awakening although without the embrace of ifs finality, this will never cease to amaze me.
Then the child gets bored, waves the animals goodbye as if they were good friends, and carries on towards the pursuit of more fun and new experiences. All thisâthe meeting with black swans, the interaction over food, the taming of the outdoorsâthis is obsolete aleady. The spiritual encounter was short lived. The same for them toddlers than for us. We are, after all, the same people.
It started to rain lighty, almost not enough to notice, but the lake's surface is not specular anymore. I'm coming back to my room to progress over the abyss in which I am free-falling, still marvelling at the immensity of things everywhere. I don't know if I'm becoming more little or if the world is getting bigger around me but I have the feeling of becoming a toddler again. Everything amazes me.
Breakfast is fab, honey is not in a jar but literally dripping from the honeycomb.
I woke up in paradise, meaning flooded in misty light: there's fog outside so the scattering is lactescent and half of this gigantic room are panoramic windows. I felt like in Space Odyssey and for a second mistook the huge black flat horizontal TV set in front of me for the monolith. I also have a twisted stomach complaining of the spicy pork chops or whatever they were of yesterday. I'm sure the receptionist would have enjoyed them even more than I did, the spicing was exceptional.
Today I'll work on our CSI violation manuscript to finally leave poor Daniel with something to work on, submission of Ergodicity breaking of multiphoton light at its classical boundary and preparing my keynote talk. It might be my first keynote, so I can't just improvise something something the day before as I did for the last twenty years. As every day now till its submission, I'll also work a little bit on Microcavities, 3rd edition.
I've upgraded showme so that it opens (and finds, first) basically anything I want to see:
# #@=----===@%: # :#:::-=---===+=@=- # +=%* :-+=:.... .:@- ____ _ # @-+#-*%+**+#=+*#@@@@#@ / ___|| |__ _____ _ # @=%.% # @ .# %= \___ \| '_ \ / _ \ \ /\ / / # #:.. @ @# * @ @# ## ___) | | | | (_) \ V V / # #.=:% .%. @-=* @% |__ __| |_|_|\___/ \_/\_/ # %@.*@ :#@@@-. @ +%@%- @ | \/ | ___ # *@@% #@ .. =+.. ...@ | |\/| |/ _ \ what # @:#-.:-= .:.+#-: .. : @ | | | | __/ you got # @.:---::@. ..:-++=:.-%.% |_| |_|\___| # @=-:-:@ @++==-:-=++-@%. # @-::. : . . .. . :@ # @:--:...........=* # **=-=::.......:.@ # *=:-=.:::::::: @ # %@.::.::::::.+# # -@@+=:.....+@ # laussy.org/showme # F.P. LaussyNow both
showme zubizarretacasalengua24aand
showme Microcavities.pdfbut also
showme ergoli5work. The latter opens the file browser on the named directory.
14 October (2026)
The food eventually arrived. Some knuckle bones with possibly pork meat, and a very spicy sauce, plus rice. The collection point was easy to find, at least, since a lot of people were waiting in scattered spots. A scooter went a few rounds and let a bag on a table, took a picture of it, and left. So I thought, this must be my food... but there were people there at this table. Like at every other tables. After a few seconds without them interacting with the food, I got closer, looked round it, then started to rotate it by the tip of its plastic handleâstill no reaction from the tableâso I lifted it in the air and pretended to be studying the ticket grappled to its side, no information of which was of any value to me, it wasn't even clear this was food. I slowly drifted apart from the table with a dubitative mood, holding the bag as if it was dog poo, at a distance from me... I went to the lobby hopping nobody would shout in my back for the ten meters it'd take me to take shelter there, asked if it was what we had ordered, got some agitated enthusiastic reaction which I interpreted as a yes, and brought this back to the room, where I let it devour my taste buds rather than the other way around. Very spicy. But being very hungry, I was happy of this victory of randomness and chaos over technology and civilization.
In my new, keynote hotel, which is a strange place... a gigantic tower, sovietic style, a room with a triple en-suite that doesn't fit in the picture and... no place to eat (I arrived here late). Nobody speaks English well enough, not even the translation app on the phone. I was told that 1km in some direction, there is a BBQ. I tried both directions and only found highways and closed shopping malls. Maybe it was 10km. I tried to order food but on this Chinese internet (to which you connect through a Chinese phone number) I don't seem to get translation of the Chinese text anymore either. Alexandros piloted the operations over WeChat but when I finally asked for the last piece of help at the reception, they told me I was ordering to a shop that was closed. I asked if they could order something from one that was open, and that's where it started to get surreal. The clerk at the lobby asked me if I wanted this or that type of food, and I said anything is fine, whatever you'd have... and he started to browse for an unending amount of time, and was in doubt as if he was ordering for himself, going back and forth the list. Sometimes a smile was starting to draw on his face as if he was thinking "that would be nice" but then he seemed to reconsider with some thought along the line of "not tonight..." I think he finally took some pork feet, is my understanding. I have sort of gathered I'll be called on my phone (I highly doubt it) and then will have to collect the package at some weird corner of the side of the entrance. Since I walked a lot, I'm hungry now, and anxious... in this big spacious luxury room, starving for my survival, waiting for food that is probably being delivered some other place tomorrow morning.
Graphene cat.
Cats for the book.
The new one for Chapter 11 will involve graphene...
13 October (2026)
The high-res version of the quantum to classical transition, which I computed here in the background, with an adaptative grid (each time there was a gap, Claude instructed the computer to try harder; since it's never bored, he could do that efficiently):
I've started to work with GitHub so as to run scripts on the cloud and VPN and globally away from things in my immediate sphere of (physical) influence, and my (free) dollars are going down the drain as a result:
Tasting the (in)famous West Lake fish in vinegar (Xihu Cuyu, è„żæčé鱌):
It mixes vinegar and sugar to remind the unfortunate of the sour and happy moments in life. There is a beautiful legend behind the taste which makes the iconic dish attributed to Song Wusao (Sister Song).
More stratification of beautiful colours. Not people but petals.
The citation tree of the 2nd edition of Microcavities, which also weighted in my selection of people to enter the bio. It is biased as too generous self-citations by the authors are inflating their actual weight and that of their co-authors to a lesser extent in the field! This will be remedied in the 3rd edition.
But this gives a good idea of who's doing (not exactly what, but with whom) in polaritonics.
One of the most successful material of Microcavities is its biographical snippets. I got several praises for it, especially when it includes less famous people. This is also dynamite when it involves living people. I'm in favour of putting as many names as possible in the most polarized way possible, while Jeremy wants to exert caution, fairness and keep distance from active developments as opposed to historical imprints. Alexey's in favour of what is most crazy and Guillaume is happy to support what is most reasonable.
We had 67 biographical entries in the 2nd edition:
- Charles Fabry (1867â1945)
- Alfred PĂ©rot (1863â1925)
- James Clerk Maxwell (1831â1879)
- Henri PoincarĂ© (1854â1912)
- George Gabriel Stokes (1819â1903)
- Max Born (1882â1970)
- Emil Wolf (1922â2018)
- Albert Michelson (1852â1931)
- Norbert Wiener (1894â1964)
- Aleksandr Khinchin (1894â1959)
- Robert Hanbury Brown (1916â2002)
- Michael Faraday (1791â1867)
- RenĂ© Descartes (1596â1650)
- Willebrord Snellius (1580â1626)
- William Henry Bragg (1862â1942)
- William Lawrence Bragg (1890â1971)
- Igor Tamm (1895â1971)
- Lord Rayleigh (1842â1919)
- Eli Yablonovitch (b. 1946)
- Gustav Mie (1869â1957)
- Paul Dirac (1902â1984)
- Werner Heisenberg (1901â1976)
- Erwin Schrödinger (1887â1961)
- David Hilbert (1862â1943)
- John von Neumann (1903â1957)
- Vladimir Fock (1898â1974)
- Roy Glauber (1925â2018)
- Hendrik Lorentz (1853â1928)
- Yakov Frenkel (1894â1952)
- Nevill Mott (1905â1996)
- Gregory Wannier (1911â1983)
- Evgenii Gross (1897â1972)
- Solomon Pekar (1917â1985)
- John Hopfield (b. 1933)
- Vladimir Agranovich (1929â2024)
- Edward Purcell (1912â1997)
- Felix Bloch (1905â1983)
- Edwin Jaynes (1922â1998)
- Frederick Cummings
- Robert Dicke (1916â1997)
- Göran Lindblad
- Isidor Isaac Rabi (1898â1988)
- Benjamin Mollow
- Leonid Keldysh (1931â2016)
- Charles Townes (1915â2015)
- Nikolai Basov (1922â2001)
- Aleksandr Prokhorov (1916â2002)
- Zhores Alferov (1930â2019)
- Herbert Kroemer (1928â2024)
- Claude Weisbuch (b. 1945)
- Albert Einstein (1879â1955)
- Satyendra Nath Bose (1894â1974)
- Pyotr Kapitza (1894â1984)
- Fritz London (1900â1954)
- Lev Landau (1908â1968)
- Nikolai Bogoliubov (1909â1992)
- Ludwig Boltzmann (1844â1906)
- George Uhlenbeck (1900â1988)
- Hans Kramers (1894â1952)
- Samuel Goudsmit (1902â1978)
- Wolfgang Pauli (1900â1958)
- Georges Lampel
- Boris Zakharchenia (1928â2005)
- Vladimir Perel (1928â2007)
- Mikhail Dyakonov (b. 1940)
- David Deutsch (b. 1953)
- Robert Suris (1936â2024)
Plus group photos that listed more people (sometime redundantly), namely, the 1927 Solvay conference (Ch. 3; upper row, middle row, lower row, each left to right, as in the caption):
- Auguste Piccard
- Ămile Henriot
- Paul Ehrenfest
- Ădouard Herzen
- Théophile de Donder
- Erwin Schrödinger
- Jules-Ămile Verschaffelt
- Wolfgang Pauli
- Werner Heisenberg
- Ralph Fowler
- LĂ©on Brillouin
- Peter Debye
- Martin Knudsen
- William Lawrence Bragg
- Hans Kramers
- Paul Dirac
- Arthur Compton
- Louis de Broglie
- Max Born
- Niels Bohr
- Irving Langmuir
- Max Planck
- Marie Curie
- Hendrik Lorentz
- Albert Einstein
- Paul Langevin
- Charles-EugĂšne Guye
- C. T. R. Wilson
- Owen Willans Richardson
And the Landau and his group in Moscow, 1956 (Ch. 9; back row, then front row, each left to right):
- Semyon Gershtein
- Lev Pitaevskii
- Lev Vainshtein
- R. G. Arkhipov
- Igor Dzyaloshinskii
- Lyudmila Prozorova
- Alexei Abrikosov
- Isaak Khalatnikov
- Lev Landau himself
- Evgeny Lifshitz
In preparation of 3rd edition, we have agreed at an early stage on:
- Bo Monemar (1942â2025)
- Eougenious Ivchenko (b. 1946)
- Stephan Koch (1953â2022)
- Monique Combescot
- Yasuhiko Arakawa (b. 1952)
- Maurice Skolnick
- Peter Littlewood (1955â2026)
- Le Si Dang
- BenoĂźt Deveaud (b. 1952)
- Ataç ImamoÄlu (b. 1964)
- Yoshihisa Yamamoto (b. 1950)
Tomorrow I want to make a case for the following additions and groupings:
- Claude Weisbuch & Yasuhiko Arakawa
- Le Si Dang, BenoĂźt Deveaud & David Snoke
- Yoshihisa Yamamoto & Ataç ImamoÄlu
- Stephan Koch, Monique Combescot & Peter Littlewood
- Marc Ilegems & Romuald Houdré
- Cristiano Ciuti & Iacopo Carusotto
- Paolo Schwendimann, Antonio Quattropani, Lucio Claudio Andreani & Vincenzo Savona
- Serge Haroche, Daniel Kleppner & H. Jeff Kimble
- Jacqueline Bloch
- Maurice Skolnick
- Alfred Forchel & Sven Höfling
- Elisabeth Giacobino & Daniele Sanvitto
- Natalia Berloff, Pavlos Lagoudakis & Pavlos Savvidis
- Roy Glauber & Ugo Fano
- Vitaly Ginzburg, Eugene P. Gross & Lev Pitaevskii
- Kirill Tolpygo & Kun Huang
- Leonid Keldysh, Sviatoslav Moskalenko & Robert Suris
- Eougenious Ivchenko, Grigory Pikus & Emmanuel Rashba
- Thomas Ebbesen & David Lidzey
- Eli Yablonovitch & Sajeev John
- Bo Monemar & Bernard Gil
I'll be working on Microcavities today, before tomorrow's point with Alexey. One highlight of our meeting should be the new cat for the new chapter. Look for its insider's privileged access here on đ!
So far, the new structure compiles, everybody's existing material is included on its skeletonâsome new limbs are quite fleshyâand I'll be updating my own material. The whole thing is not as advanced as Alexey reported to the editor but it's not as behind-schedule either as he probably thinks it is, although as the GĂ©nĂ©ralissime he gave orders to his troups that are clearly untenable. Until this is submitted, I will regularly devote entire days to this and a few hours every other days, with increasing frequencies until it becomes full time at the critical point. This possibly will be the last edition, since AI will make such things obsolete in the near future, so it has to be done «pour l'honneur de l'esprit humain», as DieudonnĂ© had put it.
12 October (2026)
Taking pictures of people.
It looks like a promotional ad.
My hotel (tower) and my campus (gate).
Preparing our WP4's today meeting, I realize that I'm lacking the visual of the bimodal homogeneous field that violates CSI, the companion of the uniform one of the day before, for which I had plotted the fields.
As it's better to show pictures than equations, here they are, at the threshold $k=2\pi/L$ where the violation becomes total:
$\phi_a$ is real and simply decays, $\phi_b$ grows exactly as much, so that their productâand thus $G^{(2)}(\mathbf r,\mathbf r)$âis the same everywhere, while its phase winds once over the box, which is also what makes the two modes orthogonal. The intensity itself, $G^{(1)}=2c\cosh k(x-L/2)$, is a bathtub: anything but uniform. You can't have both at once, that's a theorem of that time. Continue on †â¶
Alexandros suggested to really go into the multiphoton regime with photon-number resolving camera. Since then (this was the doggy-park discussion), I've looked at what the theory says about this. Instead of the continuous plane, we pixelate a 3000$^2$ grid covering $[-4,4]^2$ (in units of the vortex's radius, putting its rim at 375 pixels from the center).
With $N=1.2\times 10^7$ photons, we have about 10 photons averages in a pixel on the rim for the donut. That makes for neat, classical pictures:
The pair distance has $\binom N2=7.2\times10^{13}$ sample points. Now, that's large numbers! Continue on †â¶
11 October (2026)
Hotel chill... There's a sofaânot a chairâby the desk so I have to recline into cosiness, and be lulled by the fan of the laptop collapsing million photons on discretized lattices, falling asleep far from this pristine king size bed overlooking the park of the campus. The poetry of being left only with equations and exceptional points, dreaming about the missing exceptional people and ignoring the diabolical ones.
What I'm up to in China.
Most boring man on the planet.
Something which has been on my mind since 2009 is the the nature of the quantum to classical transition in the Jaynes-Cummings model. I described it with this type of structure in our paper with del Valle et al.[13].
This has everything. For the life of me, I don't remember now who at the HPM (2026) was doing something similar but, of course, in Tavis-Cummings or much more complicated systems. People always jump to the difficulty and invoke big machinery and hopeless cases when everything is, always, in two coupled oscillators (one truncated). The discussion also popped up with Najmeh on the nature of nonlinearity in quantum mechanics. I'm referring a paper now who goes again to great circumlocutions to miss the point very badly. When Miguel Bastarrachea-Magnani visited us in Madrid (and when I met him again at the PLMCN26), I tried to interest him in solving this problem, him being an expert on quantum chaos and integrability. I had spent then much time digging up my old codes that were running in the Southampton clusters so that we could reproduce the results then. I was concerned about convergence and numerical stability, because the computer capacities had demultiplied. Now in times of AI, you can have Claude do these things for you, find the code, cleanse them, run them and check convergence by itself:
It's working indeed as a very efficient, very motivated PhD student or obedient Post. Doc. I'll settle this question once and for good, then. Expect to see beautiful fractals in the coming weeks. I'll just have it use the color code of our later (del Valle and Laussy[14]) paper. Also on †â¶
10 October (2026)
Late evening walk in the Chinatown of Hangzhou, it all feels a bit utopian.
I ordered giant oysters, cooked, with a spicy soy sauce. You press a button and someone brings you the dish. Couriers come in from time to time to pick up a delivery. They pick theirs from the row of bags waiting for them, being careful not to disrupt their peers' orders. Nobody checks anything, everybody trusts you. When the cook has no more orders, he appears inside the eating room and joins the waitress, who is having her dinner at a table, looking at her phone. He doesn't have a phone and makes the most exaggerated movements, as if he were in a cartoon. He looks at the food, from which he occasionally picks up a piece with a great sweeping arc of his arm. Most of his eating, though, consists of holding the bowl of rice up to his open mouth and shovelling it in with his chopsticks. After that he munches exaggeratedly, as if he were in a cartoon. Sometimes he also casts a glance at the waitress, and smiles. He seems happy that she is happy. But she's probably not, she's looking at her phone.
When you're finished you press "Pay" and you leave. Nobody checks anything, everybody trusts you.
Afternoon with Alexandros. We tried to have lunch at some Asian Turkish place of great historical interest, but this was closed (apparently indefinitely). The door was nevertheless opened under its arabic inscriptions, leading into some abandonned place, so we could still get a bit of mystery out of it along with a bit of disapointment. We ended up in some "normal" Chinese place with noodles and dumplings, plus a soup with tiny baby shrimps, which we only realised were there at the end, although the taste should have told us on the first sip. We tried to fix my Ali Pay and it works to some extent. I could pay for coffees. But not order taxis, so still hanging as to what I can or cannot do. We had coffee in a place with lots of dogs playing freely in the park. I ordered a plater of fruits with the coffee, which was mainly sweet lemon in some even sweetier sauce, with baby tomatoes. «That settles your questions whether tomatoes are fruits», Alex said. There we discussed things which I hope I'll remember now as they'll pace the rest of the work of this week: i) the azimuthal Hanbury BrownâTwiss effect, and how we're the only one who understand it, ii) thermal imaging (no effect with RPCS, the nail in the coffin of intensity fluctuations as bunching and bunching as powering ghost-imaging), iii) the reason for the remanent correlations in RPCS when removing phase confounding factors, iv) CSI violations on LG with differing â and HG beams, v) bright squeezed vacuum and their potential for a variety of things, vi) much higher-photon number experiments on pixelated screens (I put this to run now) as well as vii) other works on the arXiv. I feel I forgot most things already. We also discussed Asian and European societies. There's something soothing and peaceful in Chinese people, but this is magnified by being an outsider, Alex assured me. In fact, one of the dogs misbehaved somehow and her mistress spanked him repeatedly, even as he had stopped moving and submitted to the punishment, shaking after each stroke. She was definitely getting invigorated by the sound and feel of the leash snapping the flesh as she started to spiral into a frenzy of beating that was verging on sadism. The dog crawled below our table and Alex took him under his shelter. The lady looked at us three with her fists closed and I wondered if she'd come to spank the dog between our legs or maybe even start to spank us. I thought I would offer to expose my buttock to invite the retribution if she'd get closer but she exclaimed something and turned back. It looked nasty, but it looked mainly addressed to the dog. Or maybe she was just perspicace and had said "don't even think about it." Alexey wants to have dinner tomorrow and see "the marathon". Daniel now signs his emails Danieâ.
What is super inefficient though is internet, proxy, vpns, phone details, credit cards, bank accounts, etc. This is a nightmare. It took me a couple of hours to set up a survival version more or less working (everything very slow), and I still haven't worked out Ali Pay. And we think we live in a civilised, modern world. It's only technology that improved a lot, we're still as crippled and contained as ever.
Arrived to China. Immigration is so efficient, I arrived before the pickup.
9 October (2026)
I'm preparing to leave for my Trip to China (October 2026), where we'll submit Ergodicity breaking of multiphoton light at its classical boundary and where I'll speak about "Simple Photonics" at the Quantum Summit in Hangzhou. I'll also speak about these recent results by Zhou et al.[15] who realized the three-photon version of our López Carreño et al.[16] and Zubizarreta Casalengua et al.[17] CUBA correlations. Yesterday the EIC didn't fund my PathFinder proposal to implement such technology in Spanish and German laboratories, with one referee commenting «this approach, as far as today, even if it has been theoretically predicted for more than 14 years, has not gained much attention in the single photon sources community». That much of the EU single-photon community (from which this Referee obviously is) is shit and slow and not up to the standard is not really my fault, I did the theory and I even tried to push the experimental effort myself, but EU referees prefer to see it as "not gaining attention" (because they oppose it!) Well, China will do it... What do I care. Failures are on you, EIC!
8 October (2026)
To gloss for Violation of Cauchy-Schwarz Inequalities in Space and Time:
- Cauchy-Schwarz inequality and particle entanglement. T. Wasak, P. SzaĆkowski, P. ZiĆ, M. Trippenbach and J. ChwedeĆczuk in Phys. Rev. A 90:033616 (2014). CSI violation in bosons âč entanglement.
- Violation of the Cauchy-Schwarz inequality in the macroscopic regime. A. M. Marino, V. Boyer and P. D. Lett in Phys. Rev. Lett. 100:233601 (2008). Squeezing is no violation.
- Violation of the Cauchy-Schwarz inequality with matter waves. K. V. Kheruntsyan, J.-C. Jaskula, P. Deuar, M. Bonneau, G. B. Partridge, J. Ruaudel, R. Lopes, D. Boiron and C. I Westbrook in Phys. Rev. Lett. 108:260401 (2012). Violation needs low occupancy or antibunching
- Antibunching and superbunching photon correlations in pseudo-natural light. Z. Ye, H. Wang, J. Xiong and K. Wang in Phot. Res. 10:668 (2022). Vortex correlations
- Propagation effect in resonance fluorescence: Spatial antibunching of photons. M. Le Berre-Rousseau, E. Ressayre and A. Tallet in Phys. Rev. Lett. 43:1314 (1979). Early theory in space.
The physics of farfalle.
Violation of CSI from two $\ell_a\neq\ell_b$ vortices. Never everywhere, always somewhere:
At the HPM, I discussed with colleagues how publications in the form we know them will cease to exist. I gave ourselves six months. We are writing our last papers. Witnesses are Dario, Daniele, Said, Anton and Nina, with whom I was arguing the case. The discussion was chiefly with Said who thinks this is is possible but will take years. It might not even take months.
https://github.com/openai/math/tree/main/preprints
7 October (2026)
Today we met Najmeh Eshaqi-Sani who told us a bit about her work (Es'haqi-Sani et al.[18]) on quantum synchronization. Exactly what I was discussing with Anton last week in Paros. Speak of coincidences! Unfortunately she'll be at the ICMM only for a couple of months more, but maybe that still leaves us time to understand a couple of things.
Working on Violation of Cauchy-Schwarz Inequalities in Space and Time, I realize that the infamous $g^{(2)}$<1/2 criterion might have some sound meaning in violations of CSI inequalities with a thermal field as a reference, as opposed to a coherent one, which gives the antibunching scenario. If using another reference $b$, then CSI violations read: $$g^{(2)}_{aa}<\frac1{g^{(2)}_{bb}}\,.$$ Have $b$ thermal, you get $g^{(2)}_{aa}<1/2$. It doesn't make the criterion any better, except that such fieldsâstill not being single-photon source onesâare able to violate CSI in an environment where standard fluctuations are the thermal ones. Also on †â¶
6 October (2026)
Francis Halzen got the 2026 Nobel prize in physics, for IceCube and the discovery of astrophysical neutrinos.
I like to find the connection I have to every Nobel prize awarded. This year, this is to be found in our Referee reply to the Two photons everywhere[11] paper, where the Referee was complaining that something rare, even if big, is not significant. He wanted to rob us of my title and have it read "Two-photon correlations everywhere" instead. I told him "how about IceCube?" I didn't tell him "this'll get the Nobel prize in a couple of years" but could have:
Of course, the authors are the first to be aware that a correlated photon pair consists of two individual photons and that strong bunching at vanishing intensity does not imply that a relevant rate of photon pairs is available. Instead, it follows from strong bunching that two-photon correlations occur much more frequently than predicted by the Poisson statistics. Thus, for a sufficiently small intensity, one correlated photon pair per year can correspond to a value of g^(2) of 10^5. The authors will agree with me that from a practical point of view, i.e. in the presence of finite detection noise and with applications in mind, it is not justified to list such a region of the two-photon spectrum under the title "Two photons everywhere". I therefore suggest that the authors adapt their presentation in such a way that even an uninformed reader will not be misled.One of the points we wish to highlight is precisely that two-photon physics (multiphoton physics in general) is not related to the amount of signal, which is one-photon physics (or classical physics). Whether two-photon phenomena are, or are not, useful from a practical point of view is a secondary concern at our present level of description. We want to attract instead attention on the two-photon spectrum structure, with its two-photon Mollow triplet (of two-photon leapfrog transitions), circles of antibunching, unconventional bunching in the detuned Heitler regime, etc. All this is happening in the abstract two-photon space, which is not directly visible, but exists nonetheless, with no (theoretical) concern for signal. In this context, does one correlated-photon pair per year, to take the extreme case of the Referee, make a phenomenon unphysical? The IceCube collaboration recently reported the observation of seven (7) events in a 1 km$^3$ detector measured over the course of 10 years [Phys. Rev. Lett. 132:151001 (2024)]. The present text is, conceptually, at this level of description. In the two-photon spectrum, one does not need toâindeed, should notârefer to intensity: the structure exists regardless of the one-photon brightness.
What I couldn't tell him, of course, is that there were 124 people before the one guy who would get the prize (and he was in the top list):
For most people not from the neutrino community, that is the most obvious thing to comment upon: Halzen got the prize alone. The last one was Charpak in 1992. Before him, De Gennes (also French) also got it alone. For many physicists I know, a single awardee is a first time in their life. Since Cecil Powell in 1950, and Yukawa before him (the one after whom an institute is named in Kyoto), it is indeed more common to award various physicists. Before that, couples were the exception, even when such couples were Schrödinger and Dirac. The only triplet for the first 55 years of the prize was Becquerel and the two Curie, who were really one. Times change.
AF tags for the win. I have integrated them to Gmail so that I can now refer to them and cross-reference appointments, af2cal, papers, screenshots, pictures, equations, etc., as part of a big meta structure of interconnected elements of a greatly varying nature. I ask Claude "where's this comment I made on Anton's limit cycles to this Iranian scientist?" and it connects the †posts, sections in the manuscripts, calendar appointments and now the emails.
So 0HwAB (af) is my clarification on the 0I00G (af) meeting. The I period should be fun, it makes for funny tags. Every second is a little game.
5 October (2026)
I'm still emotionally shaken by this morning epiphany in the Athens airport. When Kevin Rowland's song to Eileen came back from my childhood memory into the present, where I was writing about this idea of not finding someone in everybody else, I literally sprang to my feet, I jumped over the couch to listen to the song, which was faint, I wanted to hear it again, it was like remembering all of a sudden what I once knew but had forgotten. I don't have the proper tense. Something that was waiting to be understood, something I always had inside me but that did not detonate yet. This morning, it did. As I jumped over the seats to hear it better, I got mangled with someone's bag, that I kicked with my foot. I touched the leather bag and apologized "I'm sorry, I'm so sorry", caressing the bag, petting it as if it was alive, repeating my apologies, while trying to absorb the music's message: «Too-ra-loo-rye-ay». My apologies were all the more sincere that I literally was sorry, but not for my clumsiness, for being in the song, along with everybody else, and realizing it for the first time. The owner of the bag looked at me in this stage of great agitation and his outrage at some brusk person suddenly springing round for no apparent reason dissolved into sympathy and he said "it's fine, it's all fine, don't worry", understanding that something urgent was going on. I found the microphone and absorbed the song from decades of awaiting it to bring an exclamation mark to a message that was being delivered now. When the song had concluded, I sat again, I put back my computer on my lap and full of this love that's overflowing from the musicâfrom the tempo, the violins, this supplicating voice in the force of age which doesn't know what it's supplicatingâI was finally getting it. This love, that escapes one generation which it leaves behind to devour the next one, is what remains. Not us. It. It was time enough now to realize that Eileen is dead, or at least wilted and worn out, that her red dress that was unleashing such irrepressible dirty visions, was now an old rag, that the exultation of the singer when he was at the peak of his devotion for his loved one, had finally turned against him too and that he, now, was the «Poor old Johnnie Ray». So I started, like Johnnie Ray did on stage, to cry. It is clear that the poet did not know how both cruel and literal were his verses:
At this moment
You mean everythingWhat a song! What a force in these pure Irish feelings and tunes that lure the Wulfrunian poet into thinking that his torment is that the Carpe Diem is tough on him for the moment he can and does actually seize, while failing to see that the generational gap that he so candidly mocks and dominates is having the advantage of him, that he is the victim, the toy, the same loser as those who came before and those who will come after him. Too late, it's already too late, even before it started.
The video clip, which I didn't know, is a little masterpiece. These young beautiful people, naked in their blue jeans, beautiful because young regardless of their shoddy appearance and neglected attires, is full of symbolism. The love of our grand-parents for their idol, the jubilation of those womenâgorgeous then, in black and white, swooning over a picture, ravished, and now dead and long time buriedâand then the hero, the singer, the poet, that makes transition from Mom and Dad, to Me and Eileen, turning the black and white into colour with the first kiss, a transformation that lasts what a kiss really lasts: less than a second. All the rest is its memories and its lamentations.
and back to online meetings...
A lot to catch up.
Finally back home.
Now at the gate, two hours before boarding, but I couldn't check in online as the plane appeared overbooked (no seat selectable) and I got scared they would deny me boarding if not arriving very early. I'm now 30F, last seat at the back of the plane, but at least in the plane. And for the time being at the gate.
These airports are the most anguishing places I actually go to, in real life. You really feel they are queueing you to get you shot at the end of the line. I'm sure the atmosphere of a camp isn't much less human than that of an airport. But I do go to airports, while I've only been to camps in abstraction.
And speak of a concentration of estranged strangers, everybody disfigured by stress, tiredness and frustrations of a failing trip or a lost luggage. Or of an unwanted destination, robing you from this primal need to stay anchored where you were, with your people and your things, and not get lost at the other side of nowhere with nothing but courtesy and civility of slightly less than strangers is waiting for you.
I read recently that Stendhal started at some point to write about everyday of his life, apologizing for a typo in the first sentence, "already", he said, and the first one of many because he was intending not to correct or change or hide anything. A bit like what I'm doing here.
But things need to happen... I was thinking in one of the queuesâthat of the metro, or of the security, or of the baggage drop-off, never mind which, I forgotâbut I was thinking of such a short story, for Stendhal's or my daily journal: you go and ask someone who is in front or behind you in the queue, or at the coffee stand, or in the corridor, you ask "are you the one I'm looking for?" and see how the story goes from there on. In most cases it'll end up on the spot, but I'm sure some would end up in Patagonia or Ulan Bator.
You see if you go somewhere with someone, it's different. It's the place that's coming to you, not you to it.
Many people have to be looking for something or someone. At the look of them, around me, I would say at least a good 20%, although the real figure is probably closer to 100%. Problem is, of course, you're not the one they're looking for, except you might well be, they just don't know, and you don't know either. And most people are so exhausted from waiting for what they're looking for, they don't even know they're looking for something anymore, they only know that they wait. And the waiting is so boring, I'm sure some people would actually bet on adventure, novelty and exploration, for a change. Some would say: "okay, let's do this, let's open the window on the universe together. We have the universe but we don't have the window. You are the window."
And what could happen? "Are you saying this to everybody?" Then it's an easy dialogue: "yes, to literally everybody, since a too-early morning in an airport, but nobody is the person I'm looking for."
The main problem is, of course, if you already found the person you were looking for but you lost this person at the same moment you found them. That's bound to happen to anyone playing this game of grabbing fates as they pass along. Most will escape you, many with a scratch or a bite, furthermore, and when you finally find someone, she's from the Qinghai province in China or the northern territories of Australia. You wake up to the world but in the middle of the night at a train station which goes both ways, and of course the other person is on the opposite platform, waiting for the other train.
Well, the story could still write itself for a few additional sentences: "I've been looking for you everywhere and in everyone, and I've written it like Stendhal would have done, down to the last details, so that you could go and read it, and see that nobody was you, nothing happened but missing you", and then, the story continues in the future perfect, "and then when I will have found you, the journal will stop writing itself, because I'll be writing it on you instead, with you, through you, it'll be your hand holding mine not holding the pen, there'll be nothing to say because everything will be to do. It won't be something to share, to narrate, to remember. It'll be out of time. It'll be us."
Beautiful story.
As I was writing this, the airport music played "Come on, Eileen", and then this music, this supplication, this exaltation drowned in melancholy, these lyrics:
These people 'round here
Were beaten down, eyes sunk in smoke-dried face
They're so resigned to what their fate is
But not us, no never
But not us, not ever
We are far too young and clever
Remember
Too-ra-loo-ra
Too-ra-loo-rye-ay
And we'll hum this tune foreverin addition to my story, all this together, the violins, this got me... and I'm crying, like a child, I'm weeping, I'm crying in the airport, face sunk in the keyboard and dripping all over...
4 October (2026)
The acropolis by night.
Last (Greek) coffee on Paros, waiting for the bus to the airport.
Doing the check-out at the guest-house, it wasn't Dmitry but his sister, Smaragda, who attended me at the reception (which is the kitchen of their house), while Dmitry on the phone was struggling with the CSIC VAT. We had a long chat, waiting that he works it out. She asked me when was my boat. I said that I was taking the plane. She said "really? why? It is very expensive! So when is your plane then?" When I told her the time, she said "so you have a lot of time, the next bus is at 16:10". I told her I was thinking to go by taxi, and of course she said "really? why? It is very expensive! Go with the bus!" I said that all right, I'll go by bus. So now I have to... I wouldn't like that the little interaction we had end up with a lie. It's at 16:10 indeed. Just the time for one last coffee and to write this down. I'm already benefiting from her advices. It's more interesting to write this down than to sit in a taxi.
While we were waiting, after the banalities, she told me of her solitude on the island. She didn't tell me "I'm lonely", of course. People don't tell you that. She told me about how she has to pretend she's upset with her son, with whom she's got arguments because he doesn't want to listen. Boys never want to listen, she told me, their brain is not as developed as the brain of girls. I asked what it is he didn't want to listen about, and she said "reading; he doesn't want to read". Also that he's difficult because he's bored. I said that surely he must have friends to play with. She told me they have no friends on the island (they're all from Paros for generations), no time to get coffee anymore, no time to chat outside, only work and to take care of her son and very young daughter. So her son's missing friends were really her own. So I had the feeling she was feeling very lonely... That's how people tell you. At least that's my understanding. I'm not telling them "you seem lonely" anymore. Now I just say "hmm-hmm".
She wanted to be a hairdresser. She got a training in Athens, but hairdressing ladies is a nightmare, she told me (she exclaimed that last wordânightmareâin the most Greek way you can imagine, detaining the first syllable in the air with a parabolic motion of her head before she let it crash on the second syllable). Finally the brother called and said he had finally solved it. He had mistaken the last D of the CSIC VAT for a 0 (it was from my handwriting, to be fair), but now it was all right, he just needed my "occupation". I toyed with the idea of making something up, but I told her, and so she told him: "researcher". We thus had to discuss a bit about this too, what it is exactly, that I'm looking for. I told her I wasn't sure, something that ancient Greek people started to look for and nobody found it yet. I toyed with the idea of telling her something more inspired or inspiring but decided not to, she was keeping the conversation going well without me having to be imaginative. But it takes less time to put "Researcher" on a tax-entry form than it does to have a VAT code recognized. So Dmitry called quickly again to say that I could check my email, I was checked out.
I did, and indeed an invoice was there in my inbox. I said "thank you" but Smaragda insisted that I check, so I did. She showed me the price for the room, the extra taxes, she showed me the VAT that was causing so many problems, and so, side by side, we examined this form together with utmost scrutiny, as if we were two tax inspectors.
I feel she would have liked that we spend a bit more time chatting like this, after she showed me everything that there was to show on the invoice, so that she could tell me more about the time of before when she was going to Athens, or about the time of now when she doesn't even go to the coffee shop down the road anymore. I would actually have liked that too, I was not saying much, but she was interesting to listen to, and was making a lot of faces, nodding with a wink, twitching her lips, humming as if in possession of a great wisdom.
I didn't have much to tell her, besides the VAT of CSIC. I could have told her about the monastery, about the candle I had put there in the morning, which was, also, alone when I left if there, and that was already gone by now. About the color of the sea, from up there, about how close the summit looked although there was no road towards it anymore, and if only I had good shoes, how I would have conquered a mountain today. And she could have told me about when she used to go there too, when she was young, when she had friends and time, about how she did reach the top many times and probably will never return now. About how she remembers the color of the sea from up there. How she's not looking at the sea anymore. But we did none of this. After an awkward pause, she extended her hand, I shook it, we both smiled, and back to our loneliness. It seems like lonely people recognize each other. They both get a little bit more lonely afterwards.
Back to Parikia.
The monastery, hanging on a steep flank of the mountain.
Icons and light.
Parikia from the monastery.
Leaving Parikia towards the Agioi Anargyroi monastery.
I arranged the rest of my escape. Fly to Athens and spend the night at Hotel Marina at 13, Voulgari str in central Athens (I stayed at Piraeus port previously). Access by Metro Omonia after ~40 min on blue metro Line 3 until Monastiraki from airport, at which point change to green Line 1 toward Kifissia.
I should have time to wander the old town. Maybe Psyrri (Iroon square), Monastikari and Thissio.
Departure next day in the morning for Madrid, with business in town, before getting back to ICMM. Still in Parikia, I'll try to have a last walk, maybe on the flank of the mountain (I don't have good walking shoes), so as to not spend the whole time doing administration (I still progressed on on referee report and ran some hybrid simulations of Gerace gates with part Fock/part coherent state inputs, so not entirely wasted time).
Last day on the island.
3 October (2026)
That was the sunset for today. The sun disappeared a bit earlier than scheduled, it hid behind the clouds before it plunged into the sea, draped itself with water from the sky not to go totally naked into that from the horizon. As it finally took its dive behind the cloudy curtains, colors splashed from the dark sea and wet all the firmament with burning light: red light, orange light, yellow light. The clouds absorbed the droplets of Sun almost entirely in one instant, and when they had finally soaked all of it, the night washed them out, mixing the blue with the saffron into a purplish black that it lit up with the stars into total darkness.
That's where my two October lovers were hanging from.
Sunset hunting.
I have successfully simulated the entangling Gerace gate (H+CNOT) with coherent states. It fails in a different way than I'd have thought. If fails gracefully. It's not immediately useful for anything I can see (no obvious quantum supremacy) but it's not trivially useless either. There might be scheme to push it into a computational resource. And at a fundamental level, it's a beautiful thing to characterize.
The most interesting is that the block we're interested in remains shielded all down the circuit, so it remains good for whatever comes next, that's what the deterministic scheme brings us. Next is to implement a real application, Deutsch, Simon, GHZ, teleportation, whatever... and show that with probability $e^{-2}$ or $e^{-3}$ depending on what we do, we get our result. It'll certainly won't beat a direct classical approach, but it's a first foot into quantum computation with only resources already available to our experimentalists (interacting waveguides). It'd be interesting to also consider hybrid approach, e.g., a Fock state + a coherent one. That might bring us over the edge.
The sea is not calming down (I've spent the afternoon at the seafront in a restaurant, with Baklava and more Greek coffees) but the sun is coming down. I'll have the chance today to see the sunset from the castle. I'll see if the other prisoners would be interested in that.
The Gerace gates could be useful as deterministic even on Gaussian inputs, and thus semi-scalable, shifting the indeterminacy to the number of qubits as opposed to the number of gates. This seems to be $e^{-n}$ for the $|\alpha|^2=1$ (optimum) case.
I'm not sure how well known this is. See for instance Descamps et al.[19] It would be interesting to devise a practical problem that could be implemented and actually solved demonstrating a quantum advantage. Maybe using Grover's algorithm, for instance.
There is only one story. This dead man on a 2nd century BC funerary stele is sitting in front of a reclining woman, who, even if she has been worn out by time, is clearly escaping his supplication. It's been going on for over 22 centuries for them.
At the archeological museum. C. 550BC.
Truncated coherent states to $\nu$ photons per rail quickly degrade the LOQC CNOT probability of success from $P_{\rm succ}=1/9$ for $\nu=1$ (Fock states) to, already with $\nu=2$, $P_{\rm succ}\simeq|\alpha|^2/27$ (ratios $0.111$ and $0.037$ at $|\alpha|^2=0.01$): already $3.7\times10^{-4}$ at $|\alpha|^2=0.01$.
Besides, which should also be looked at closer, it's not only that the gate fire less, but it fires wrong, in contrast to Gerace gates, which fail gracefully. Anyway, it's now established that while Fock states are an essential resource for LOQC (as they should), it's not the case for Gerace scheme, surprisingly.
The same arguments work for Gerace than for the earlier gates. And then this calls to ponder what have people propagating coherent states in Kerr medium been up to. These are:
- Nearly deterministic linear optical controlled-NOT gate. K. Nemoto and W. J. Munro in Phys. Rev. Lett. 93:250502 (2004).
- Weak nonlinearities: a new route to optical quantum computation. W. J. Munro, K. Nemoto and T. P. Spiller in New J. Phys. 7:137 (2005).
- Quantum control gates with weak cross-Kerr nonlinearity. Q. Lin and J. Li in Phys. Rev. A 79:022301 (2009).
Interestingly, Shapiro and Razavi[20] stayed alert and rebuked this implementation too.
There's been an experimental implementation by Feizpour et al.[21].
I also found this paper which has to do with special properties of coherent states (any optical process is fully characterised by how it responds to coherent states), by Lobino et al.[22], from Lvovsky, who was on the island at least until yesterday. In the bus bringing us from the conference venue to Parikia, he told me that they had an old work on quantum vampires, that was probably related to what I showed. This is their Fedorov et al.[23] paper, which might or not have some amount of overlap, the photon detection (or subtraction) indeed bearing on the prior (see also Ref. [24]). But he missed the main point, since when I told him about ghost imaging with thermal light in the absence of single-shot correlations, he said that the underlying mechanism was «like EPR» (which is a surprising statement in any interpretation of the mechanism); so then I repeated the spurious correlations of thermal light but he shook his head to say that no, no, there are correlations. Like EPR. So he understood nothing of my talk. Only that after you detect one photon, you can detect another one.
As for the nonlinear variations Ă la Gerace, that rely on cross-Kerr instead:
- Quantum optical Fredkin gate. G. J. Milburn in Phys. Rev. Lett. 62:2124 (1989).
- Simple quantum computer. I. L. Chuang and Y. Yamamoto in Phys. Rev. A 52:3489 (1995).
- Nonlinear optics quantum computing with circuit QED. P. Adhikari, M. Hafezi and J. M. Taylor in Phys. Rev. Lett. 110:060503 (2013).
Milburn[25] implemented a Fredkin gate with cross-Kerr. Chuang and Yamamoto[26] implemented the dual-rail logical encoding of Scala et al. (before them). As for Adhikari et al.[27], they rely on superconducting qubits to implement those ideas.
This has been well-known criticized by Single-photon Kerr nonlinearities do not help quantum computation[28] and Gea-Banacloche[29].
Working on Gerace gates, I must first check failure of LOQC ones with coherent states. The standard schemes are:
Greek coffee, an Hamiltonian and a stormy sea, my kind of Saturday.
2 October (2026)
Now in Parikia, in a cheap guest house, of someone Dimitri. Said offered spontaneously to accommodate me in his room, got me a key, had an extra bed fit in... but when it turned out I would have to spend more than one night, I decided to decline the generous offer. Besides, on an October 2, I wanted to be alone.
The guy is super interesting and we had fascinating conversations every time we met. So I also wouldn't want to take the risk of making a best friend at the corner of some bad weather condition. Then Pavlos also offered to shelter me in his room, and Xenia even offered to give me her room in full, and move herself with someone else... When I told her I was staying for two nights, she told me "then I move out for two nights". Everybody's so nice in harsh weather...
I'll go now with some of the other people stranded on the island to this Symposium, which is the prettiest corner of Parikia, and have an Ouzo with Panayotis, which is long time overdue. One should not get too much alone either on an October 2.
But not the last day on the island. Ferries are cancelled due to weather conditions, so I'll be two more nights here, and a third additional one in Athens... The wind is hurling outside, it's ominous. What a 2nd of October. I knew it'd be a tough day... but did it need to be this literal?
Last day at HPM.
1 October (2026)
We spent the rest of the day walking round in the city center, first with Anton and then with Dario, Daniele and Monica. At the restaurant, a candle lit fire to the curtains. Fire goes very fast. It was outside, a Greek island of stones and painted wood, so nothing to propagate, but it was not for lack of time. We discussed with Anton possible activities for Pavel. I still think that checking the breakdown of Gerace gates with weak coherent pulses as the most interesting immediate activity on that topic. An entangling gate, Hadamard + CNOT. It should produce the Bell states with inputs from the basis, and fail to do that with weak coherent states. The mechanism of the failure would be particularly interesting, as well as to what happens with squeezed states.
We walked around the same places several times. When at the feet of the castle from the sea promenade, I got glimpse of this beautiful picture:
I am surprised nobody recognized that it is an instant masterpiece, and that I had to explain. A young couple, suspending their love and youth over the precipice, one looking at the other looking at the world, loving with the insouciance of not knowing that it is already too late, that there is no further ascension from this apex of their journey together, with the church in background of their promises, and the sky in background of the church. I still marvel at it. I wonder if they are still there. It is very windy now. Maybe they have already fallen.
I'm in the selfie business now.
Today I spoke.
Day 4 at HPM. Today I speak.
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