Anomalous bunching effect in which all photons coalesce into two output beams. Credit: Ursula Cardenas Mamani
In a paper just recently released in Nature Photonics, researchers from the Center for Quantum Information and Communication– Brussels Polytechnic School of the Free University of Brussels report the discovery of an unforeseen counter-example that challenges traditional understanding of photon bunching.
Niels Bohrs principle of complementarity, a fundamental concept in quantum physics, essentially states that items can show either wave-like or particle-like behavior. These two mutually exclusive descriptions are well highlighted in the iconic double-slit experiment, where particles are striking a plate including two slits.
If the trajectory of each particle is not enjoyed, one observes wave-like disturbance fringes when gathering the particles after going through the slits. On the contrary, if the trajectories are seen, then the fringes vanish and everything takes place as if we were dealing with particle-like balls in a classical world.
As coined by physicist Richard Feynman, the disturbance fringes originate from the lack of which-path info, so the fringes must necessarily disappear as soon as the experiment enables us to find out that each particle has actually taken one or the other course through the best or left slit.
Light does not leave this duality: it can either be explained as an electromagnetic wave or it can be comprehended as including massless particles traveling at the speed of light, namely photons. This includes another amazing phenomenon: that of photon bunching. Loosely speaking, if there is no chance to distinguish photons and understand which course they follow in a quantum interference experiment, then they tend to stick.
This behavior can currently be observed with two photons impinging every one on a side of a half-transparent mirror, which splits the inbound light into two possible paths associated with reflected and transferred light. The well known Hong– Ou– Mandel result informs us here that the 2 outgoing photons always exit together on the same side of the mirror, which is a repercussion of a wave-like interference between their courses.
This bunching result can not be understood in a classical worldview where we think about photons as classical balls, every one taking a distinct course. Therefore, realistically, it is expected that bunching becomes less pronounced as soon as we have the ability to distinguish the photons and trace back which courses they have taken.
This is exactly what one observes experimentally if the two event photons on the half-transparent mirror have, for example, distinct polarization or various colors: they act as classical balls and do not lot anymore. This interplay in between photon bunching and distinguishability is typically confessed to reflect a general guideline: bunching should be optimal for completely equivalent photons and gradually decline when photons are made increasingly appreciable.
Versus all odds, this common assumption has just recently been proven wrong by a group from the Center for Quantum Information and Communication (Brussels Polytechnic School of the Free University of Brussels) led by Professor Nicolas Cerf, helped by his Ph.D. student, Benoît Seron, and his postdoc, Dr. Leonardo Novo, now a staff scientist at the International Iberian Nanotechnology Laboratory, Portugal.
They have considered a specific theoretical circumstance where seven photons impinge on a big interferometer and probed the instances where all photons bunch into 2 output paths of the interferometer. Bunching need to rationally be the greatest when all 7 photons admit the same polarization given that it makes them totally identical, implying that we get no info on their courses in the interferometer. Quite remarkably, the researchers have actually discovered the presence of some circumstances where photon bunching is considerably strengthened– rather of deteriorated– by making photons partly appreciable via a well-chosen polarization pattern.
The Belgian team made the most of a connection between the physics of quantum disturbances and the mathematical theory of permanents. By leveraging a recently disproved opinion on matrix permanents, they might prove that it is possible to even more boost photon bunching by fine-tuning the polarization of the photons.
Aside from being appealing for the fundamental physics of photon disturbance, this anomalous bunching phenomenon ought to have ramifications for quantum photonic innovations, which have actually shown quick development over recent years.
Experiments focused on building an optical quantum computer system have reached an unprecedented level of control, where lots of photons can be produced, interfered by means of complex optical circuits, and counted with photon-number solving detectors. Understanding the subtleties of photon bunching, which is connected to the quantum bosonic nature of photons, is therefore a substantial step in this point of view.
Referral: “Boson bunching is not made the most of by identical particles” by Benoit Seron, Leonardo Novo and Nicolas J. Cerf, 15 June 2023, Nature Photonics.DOI: 10.1038/ s41566-023-01213-0.
Light does not leave this duality: it can either be described as an electromagnetic wave or it can be understood as consisting of massless particles taking a trip at the speed of light, specifically photons. Loosely speaking, if there is no method to identify photons and understand which course they follow in a quantum disturbance experiment, then they tend to stick together.
They have actually considered a particular theoretical situation where seven photons impinge on a big interferometer and penetrated the circumstances where all photons bunch into two output paths of the interferometer. Bunching must realistically be the strongest when all 7 photons confess the very same polarization considering that it makes them totally equivalent, implying that we get no info on their paths in the interferometer. Rather surprisingly, the scientists have discovered the presence of some instances where photon bunching is significantly enhanced– instead of compromised– by making photons partly distinguishable through a well-chosen polarization pattern.
