Three researchers from the Free University of Brussels, Belgium have discovered (Quantum computing: an anomaly discovered) a contradictory aspect of the physics of photonic interference.
In a paper published this month in Nature Photonics, they proposed a thought experiment that completely contradicts common knowledge about the so-called photon collection system.
Observing this unusual cluster effect shows that it will reach current photonics technology and, if it is recognized, it will have a great impact on our understanding of multiparticle quantum interference.
In an article published in Nature Photonics, the research team of the Center for Quantum Information and Communication – Brussels Polytechnic School of the Free University of Brussels, found an unexpected example for common knowledge of photon collection.
One of the cornerstones of quantum physics is Niels Bohr’s principle of complementarity, which is the fact that matter can behave like particles or like waves.
These two mutually exclusive interpretations are demonstrated in a two-symbol explosion experiment, where debris hits a plate with two slits.
If the trajectory of each particle is not checked, the part of the interference wave is seen during the collection of the particles after they pass through the slits.
On the contrary, if we look at the trajectories, then the fringes disappear and everything happens as if they were particles-like balls in a classical world.
According to the physicist Richard Feynman, interference arises from the lack of information in the path, so that the end will disappear as soon as experience allows us to learn that each part has been left and it is another thing to do. long burst.
Light does not escape these two things: it can be described as an electromagnetic wave, or understood as an infinite composition that moves at the speed of light, i.e. photons.
This is accompanied by another significant phenomenon: that of photon collection. Basically, if there is no way to separate the photons and know their path in a quantum interference experiment, then they collide.
This behavior can be observed by two photons each hitting one side of the transmission mirror, which splits the incoming light into two possible paths that are combined with the reflected and transmitted light.
In fact, the famous Hong-Ou-Mandel effect tells us here that two outgoing photons always appear on the same side of the mirror, which is due to the interruption of the waves in between their ways.
This cluster effect cannot be understood in the classical world view where we think of photons as classical balls, each taking a well-defined path.
Therefore, logically, one would expect the cluster to be smaller as it is called faster as one can distinguish between the photons and determine the paths they have taken.
This is exactly what is seen experimentally if the two photons incident on a semi-transparent mirror have, for example, different polarizations or different colors: they behave like these balls common and not the same.
It is generally accepted that this relationship between photon concentration and contrast reflects a general rule: concentration should be greatest for undetectable photons and gradually decrease as make the photon stronger.
Against all expectations, the team from the Center for Quantum Information and Communication (Brussels Polytechnic School, Free University of Brussels) recently refuted this claim led by Professor Nicolas Cerf, whose doctoral student, Benoît Seron helps, in his postdoc. Dr. Leonardo Novo, currently a researcher at the International Iberian Nanotechnology Laboratory, Portugal.
They considered a specific case where seven photons enter a large interferometer and investigated the case where all photons cluster at two interferometer exits.
The combination should be the most difficult when the seven photons agree to the same polarization since it makes them indistinguishable, which means that we do not get any information on their trajectories in the interferometer.
Surprisingly, the researchers discovered the existence of some cases where the collection of photons is greatly strengthened – instead of weakened – by making different photons different by a well-chosen polarization scheme.
The Belgian team took advantage of the connection between the physics of quantum interference and the mathematical theory of constants.
By taking advantage of the recently rejected concept of a permanent matrix, they were able to show that it is possible to enhance photon bunching by adjusting photon polarization.
Besides being interesting for the basic physics of photon interference, the phenomenon of negative aggregation should have implications for quantum photonic technologies, which have made rapid progress in recent years.
Attempts to build an optical quantum computer have reached an unprecedented level of control, where multiple photons can be generated, integrated into a complex optical circuit, and counted in a photon-counting detector.
Understanding the complexity of photon bunching, which is related to the quantum bosonic nature of photons, is important in this sense.
Source: Université libre de Bruxelles
