Distinguishability and Many-Particle Interference

Abstract

Quantum interference of two independent particles in pure quantum states is fully described by the particles' distinguishability: the closer the particles are to being identical, the higher the degree of quantum interference. When more than two particles are involved, the situation becomes more complex and interference capability extends beyond pairwise distinguishability, taking on a surprisingly rich character. Here, we study many-particle interference using three photons. We show that the distinguishability between pairs of photons is not sufficient to fully describe the photons' behavior in a scattering process, but that a collective phase, the triad phase, plays a role. We are able to explore the full parameter space of threephoton interference by generating heralded single photons and interfering them in a fiber tritter. Using multiple degrees of freedom-temporal delays and polarization-we isolate three-photon interference from two-photon interference. Our experiment disproves the view that pairwise two-photon distinguishability uniquely determines the degree of nonclassical many-particle interference. DOI: 10.1103/PhysRevLett.118.153603 The famous Hong-Ou-Mandel (HOM) experiment in 1987 provided the first important example of nonclassical two-photon interference [1]. Two independent photons impinging on a beam splitter exhibit bunching behavior at the output ports that cannot be explained by a classical field model. The degree of bunching depends on how similar the two photons are in all degrees of freedom, for example, time, frequency, polarization, and spatial mode. Extending the study of interference to many particles is of interest from a fundamental as well as from a technological viewpoint [2][3][4][5][6][7]. The scattering of multiple photons in linear networks is related to solving problems in quantum information processing, metrology, and quantum state engineering [8][9][10][11][12][13][14][15][16]. Thus, understanding multiphoton interference is also of great relevance for practical applications.Here, we demonstrate how many-particle interference is fundamentally richer than two-particle interference [17]. Two situations with the same pairwise distinguishability can lead to a different output distribution. This is due to a phase, the triad phase, that occurs only when more than two photons interfere.We use independent photons and a tritter, a three-port symmetric beam splitter to investigate many-particle interference. We isolate the triad phase for the first time by interfering three photons in a tritter and exploiting multiple degrees of freedom, here time and polarization. We show that interfering three identical photons and varying time delays between them, as demonstrated in previous work [5,18,19], is not sufficient to study three-photon interference in full generality [20,21]. Our experiment allows us to isolate and tune the three-photon interference term as distinct from two-photon interference. In particular, manipulation of the triad phase goes beyond what is possible using temporal...

Characterizing multi-photon quantum interference with practical light sources and threshold single-photon detectors

“…We now estimate the three coincidence detection probability ( | ) P 1, 1, 1 1, 1, 1 for a tritter for two different scenarios. Both scenarios have been experimentally analysed very recently in [40], where the authors used heralded single-photon sources (based on spontaneous four-wave mixing in silica-on-silicon waveguides together with three threshold single-photon detectors for heralding) in combination with a measurement setup with five threshold single-photon detectors. If we denote by y y á ñ = f | r e j k jk i jk the inner product between the states of the single-photon signals at the jth and kth input ports of the tritter, quantum mechanics predicts that the probability ( | ) P 1, 1, 1 1, 1, 1 is given by [40,53] where f=f 12 +f 23 +f 31 is the so-called collective triad phase.…”

“…In the second scenario, the polarization states of the input light pulses are now chosen to compensate the temporal distinguishability between the arriving photons, and might be different for the signals at each input port. The motivation for this scenario is to observe the dependence that the three-photon coincidence probability ( | ) P 1, 1, 1 1, 1, 1 has on the triad phase f by keeping constant all those terms r jk that affect such probability but arise from two-photon distinguishability [40]. The results are shown in figure 3(b), where once again we can see that our method provides a tight estimation of the theoretical values, thus showing its practicality.…”

“…In both scenarios, we use our method to estimate the HOM dip by means of just two laser sources and two threshold single-photon detectors. In the second example, we estimate the three coincidence detection probability in a tritter [40] when there is just one single-photon pulse in each of its input ports-i.e. we estimate ( | ) P 1, 1, 1 1, 1, 1 .…”

Signatures of many-particle interference

“…All data are obtained from the bosonic random matrix approximations (215) and (216). much more intricate aspects of partial distinguishability, such as those discussed in [20,108].…”

Simultaneous sorting many quDits using different input ports

“…, [8], [9], [10], [11], quantum metrology [12], [13], [14], [15], entanglement between spatially separate multi-mode quantum systems [16], [17], [18], [19], [20]. In quantum information protocols, a key step for performing a task is the measurement of the states of the quantum system.…”