Photons and Interference

Yanhua H. Shih, Dmitry Strekalov, T. D. Pittman +1 more

In his famous book, The Principles of Quantum Mechanics, Dirac stated that “... photon ... interferes only with itself. Interference between two different photons never occurs.” However, two-photon interference has been demonstrated experimentally. Was Dirac wrong? We report an new experiment in this paper. It demonstrated that two-photon interference can not be considered the interference of two photons. “Two-photon” is not two photons. Two-photon is a single entity, which is just like a photon. We may call it biphoton. Dirac was correct. Biphoton interferes only with itself.

Pieter Kok

John Gordon King, Malcolm Correll

Sascha Agne, Thomas Kauten, Jeongwan Jin +6 more

Three photons can display qualitatively new interference phenomena such as genuine three-photon interference. Here we show how to isolate three-photon interference with more than 90 % visibility, completely suppressing two-photon and single-photon interference.

Adrian J. Menssen

In this work I demonstrate the interference of three photons, a generalisation of the famous Hong Ou Mandel (HOM) interference. I show that three-photon interference is governed by four parameters and measure three-photon interference independent of two-photon interference. I demonstrate that even when the states of the photons are highly distinguishable they can still exhibit strong quantum interference, challenging our intuition formed by the double slit and HOM interference. This is followed by a demonstration of four-photon interference, where surprisingly we can still observe a "fringe" when the involved particles are pairwise orthogonal. To explain these effects, I present a new framework to describe multi-photon interference in terms of a graph-theoretical approach, which illustrates the origin of different orders of multi-photon interference. My work leads to a more general definition of what we regard as an interference fringe in multi-photon scattering. This study of multi-photon interference is followed by an interdisciplinary work between photonics and solid state physics in the newly developing field of topological photonics. I realise a simulation of the Jackiw-Rossi model as a localised topological mode in a photonic-crystal analogue of the 2D graphene lattice. I succeed in the experimental demonstration of a single such excitation and I am able to study the detailed mode structure for the first time. The mode is a result of a topological defect and is, as such, protected against errors that do not change the topology of the system.

Jan Peřina, Z. Hradil, Branislav Jurčo