Nonclassicality Criteria in Multiport Interferometry

Abstract

Interference lies at the heart of the behavior of classical and quantum light. It is thus crucial to understand the boundaries between which interference patterns can be explained by a classical electromagnetic description of light and which, on the other hand, can only be understood with a proper quantum mechanical approach. While the case of two-mode interference has received a lot of attention, the multimode case has not yet been fully explored. Here we study a general scenario of intensity interferometry: we derive a bound on the average correlations between pairs of output intensities for the classical wavelike model of light, and we show how it can be violated in a quantum framework. As a consequence, this violation acts as a nonclassicality witness, able to detect the presence of sources with sub-Poissonian photon-number statistics. We also develop a criterion that can certify the impossibility of dividing a given interferometer into two independent subblocks. DOI: 10.1103/PhysRevLett.117.213602 Hong, Ou, and Mandel (HOM) discovered that if two independent and indistinguishable photons, in pure quantum states, impinge on the two input ports of a balanced beam splitter, they always bunch together and exit the apparatus from the same output port [1]. This simple effect has many consequences, e.g., in distinguishability testing [2], linear-optical quantum computing [3], entanglement detection [4] or swapping [5], and metrology [6][7][8][9]. The nonclassicality of this phenomenon can be well understood by repeating the experiment many times, and by recording the intensities I 1 , I 2 at the two output ports: labeling the average over many runs by h·i, the correlation function,will be zero in the ideal case, because on each run the intensity at one of the two ports will vanish. G 12 has a well-defined classical limit, which makes it a suitable candidate to use in distinguishing quantum light beams from classical ones. We can either consider completely distinguishable photons, i.e., single excitations occupying orthogonal space-time modes, or pulses of classical light, described by electromagnetic fields. In both cases, if they are emitted by statistically independent sources and injected into the beam splitter, G 12 is constrained to be greater than or equal to 1=2 [10,11]. Therefore, the value G 12 ¼ 0 obtained in the ideal HOM effect represents a strong signature of nonclassicality.Several authors have investigated interference effects of noninteracting particles with the aim of reproducing or generalizing HOM's result to different situations (see Refs. [12,13]) not necessarily constrained to linear optics [14][15][16][17][18]. However, photonics remains the physical platform of choice for these studies, since it is now possible to prepare and manipulate several photons in ambient laboratory conditions, which can then be injected into multimode interferometers [19][20][21][22][23][24][25][26]. The recent investigations of many-particle interference effects have revealed a need for a deeper understanding ...

Criteria for single photon sources with variable nonclassicality threshold

“…However, the HBT test uses only single measurement layout among many where the nonclassicality of single photon states can manifest itself. Probably, many other linear optical (LO) schemes with single photon detectors can manifest single photon nonclassicality differently to that HBT test [17][18][19][20].…”

From many-particle interference to correlation spectroscopy

“…But how does partial distinguishability impact on statistical quantifiers [9,12,32,33] of the fine structure of many-particle interference, in cases where the complexity of the dynamics (measured by the number of many-particle amplitudes which are dynamically superimposed) prevents a deterministic description, as in principle given, e.g., by evaluation of the full counting statistics? And to which extent can also such statistical quantifiers then be employed as diagnostic tools?…”

Signatures of many-particle interference

“…For instance, a more profound extension of the method that considers three-point correlations was explored in [98]. Finally, the approach based on the C-dataset is closely related to those that use the g (2) and g (3) functions [99,100].…”