Hybrid spatiotemporal architectures for universal linear optics

Abstract

We present two hybrid linear-optical architectures that simultaneously exploit spatial and temporal degrees of freedom of light to effect arbitrary discrete unitary transformations. Our architectures combine the benefits of spatial implementations of linear optics, namely low loss and parallel operation, with those of temporal implementations, namely modest resource requirements and access to transformations of potentially unbounded size. We arrive at our architectures by devising and employing decompositions of large discrete unitary transformations into smaller ones, decompositions we expect to have broad utility beyond spatio-temporal linear optics. We show that hybrid architectures promise important advantages over both spatial-only and temporal-only architectures. arXiv:1812.07939v2 [quant-ph]

Quantum receiver for phase-shift keying at the single photon level

“…An interesting experimental platform to test some of this work is the hybrid spatiotemporal architecture for universal linear optics [49]. This scheme would be useful to implement the optimized unitary receivers that we construct based on the design by Reck et al [42].…”

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“…In the actual situation, however, optical losses caused by long delay lines and optical switches can limit the performance of quantum computation. Therefore, several proposals to reduce the effect of losses while maintaining the scalability have been made, such as a chain-loop architecture composed of a chain of reconfigurable beam splitters and delay loops 107 and a hybrid architecture which simultaneously exploits spatial and temporal degrees of freedom 108 .…”

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“…Note that the interferometer operators respect the group structure of the unitary group. This last property makes it easy to decompose an arbitrary M -mode interferometer U(U ) into a product of interferometers acting on at most two modes by simply decomposing the associated matrix U into a product of unitary matrices where each unitary matrix couples at most two modes [48][49][50][51].…”