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arXiv:1605.00793 · Optics Express

Quantum optics of lossy asymmetric beam splitters

Ravitej Uppu, Tom A. W. Wolterink, Tristan Bernhard Horst Tentrup, Pepijn W. H. Pinkse

Published Jul 12, 2016• 48 citations
arXivHTMLPDF

Abstract

We theoretically investigate quantum interference of two single photons at a lossy asymmetric beam splitter, the most general passive 2×2 optical circuit. The losses in the circuit result in a non-unitary scattering matrix with a non-trivial set of constraints on the elements of the scattering matrix. Our analysis using the noise operator formalism shows that the loss allows tunability of quantum interference to an extent not possible with a lossless beam splitter. Our theoretical studies support the experimental demonstrations of programmable quantum interference in highly multimodal systems such as opaque scattering media and multimode fibers.

DOI
10.1364/oe.24.016440

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We theoretically investigate quantum interference of two single photons at a lossy asymmetric beam splitter, the most general passive 2×2 optical circuit. The losses in the circuit result in a non-unitary scattering matrix with a non-trivial set of constraints on the elements of the scattering matrix. Our analysis using the noise operator formalism shows that the loss allows tunability of quantum interference to an extent not possible with a lossless beam splitter. Our theoretical studies support the experimental demonstrations of programmable quantum interference in highly multimodal systems such as opaque scattering media and multimode fibers.
Light transport in opaque scattering media mixes the light across the large number of modes in the system. The mixing results in the scrambling of information encoded on the incident light, which is generally detrimental. However, the multimodal transport hints at the possibility of utilizing them as complex optical networks if the transport could be controlled. In recent years, wavefront shaping through adaptive phase control has been used to create multiport optical devices in opaque scattering media. We study the programmability of one such device created in opaque scattering medium, a two-port beam splitter which is a primitive for any complex linear optical network. Here, I will discuss our latest results on the quantum interference between single photons from an ultrabright quantum source at the two-port beam splitter. The novel feature of the realized beam splitter is the programmability of quantum interference between single photons, creating either bunched or anti-bunched light at the outputs. Our demonstration is a first step towards realizing complex optical networks with programmable quantum correlations using opaque scattering media.
We investigate two-photon quantum interference in an opaque scattering medium that intrinsically supports a large number of transmission channels. By adaptive spatial phase modulation of the incident wave fronts, the photons are directed at targeted speckle spots or output channels. From 103{10}^{3}103 experimentally available coupled channels, we select two channels and enhance their transmission to realize the equivalent of a fully programmable $2\ifmmode\times\else\texttimes\fi{}2$ beam splitter. By sending pairs of single photons from a parametric down-conversion source through the opaque scattering medium, we observe two-photon quantum interference. The programed beam splitter need not fulfill energy conservation over the two selected output channels and hence could be nonunitary. Consequently, we have the freedom to tune the quantum interference from bunching (Hong-Ou-Mandel-like) to antibunching. Our results establish opaque scattering media as a platform for high-dimensional quantum interference that is notably relevant for boson sampling and physical-key-based authentication.
The familiar input-output relations for an optical beam splitter are generalized to allow for linear absorption by the medium forming the mirror. Beam-splitter losses generally affect the noise levels detectable in experiments involving nonclassical light. When employed to investigate two-photon interference effects, a lossy beam splitter can lead to apparent nonlinear absorption, which, in the most extreme case, leads to either both or neither of the photons being absorbed. The degree of second-order coherence of antibunched light can be maintained on transmission through the beam splitter but any amplitude squeezing in the incident light is degraded.