Inline detection and reconstruction of multiphoton quantum states

Kai Wang,Andrey A Sukhorukov,James G Titchener,Alexander Szameit,Sergey V Suchkov

doi:10.1364/optica.6.000041

Kai Wang, Andrey A Sukhorukov + Show 3 more

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https://doi.org/10.1364/optica.6.000041

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Journal: Optica	Publication Date: Jan 7, 2019
Citations: 6	License type: cc-by

Affiliation: Australian National University, University of Rostock

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Integrated single-photon detectors open new possibilities for monitoring inside quantum photonic circuits. We present a concept for the in-line measurement of spatially-encoded multi-photon quantum states, while keeping the transmitted ones undisturbed. We theoretically establish that by recording photon correlations from optimally positioned detectors on top of coupled waveguides with detuned propagation constants, one can perform robust reconstruction of the density matrix describing the amplitude, phase, coherence and quantum entanglement. We report proof-of-principle experiments using classical light, which emulates single-photon regime. Our method opens a pathway towards practical and fast in-line quantum measurements for diverse applications in quantum photonics.

Highlights

Quantum properties of multiple entangled photons underpin a broad range of applications [1,2,3] encompassing enhanced sensing, imaging, secure communications, and information processing
Whereas entangled photon states were traditionally measured at the output of photonic circuits, the capability to measure the state within the circuits could enable direct monitoring of their operation and pinpointing possible issues in real-time
There remains an open question of how to perform inline measurements of the quantum features of multiphoton states encoded in their density matrices, while ideally keeping the transmitted states undisturbed apart from weak overall loss

Summary

Introduction

Quantum properties of multiple entangled photons underpin a broad range of applications [1,2,3] encompassing enhanced sensing, imaging, secure communications, and information processing. As we demonstrate in the following, the measurement of N -fold nonlocal correlations by averaging the coincidence events enables a full reconstruction of the density matrix ρN for N -photon states.

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