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8 October (2026)
Violation of CSI from two $\ell_a\neq\ell_b$ vortices. Never everywhere, always somewhere:
In the plane of radial contrast and angular separation, the CSI is satisfied in a band around equal radii, $r_1=r_2$, whose width oscillates with the angle between zero and a factor $(3+2\sqrt2)^{1/||\ell_b|-|\ell_a||}$ in $r_2/r_1$, and are violated everywhere outside this band. No choice of charges removes the band: $|\ell_b|\neq|\ell_a|$ implies $\ell_b\neq\ell_a$, so the relative phase always reaches $\pi$ somewhere, which fights violation. The band narrows with increasing $\big||\ell_b|-|\ell_a|\big|$.
7 October (2026)
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 fields—still not being single-photon source ones—are able to violate CSI in an environment where standard fluctuations are the thermal ones.
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[1] 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 to—indeed, should not—refer 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.
