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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Encoding and decoding non-separable states of polarization and spatial mode of single photons

Behzad Khajavi, Xiaxi Cheng, K. Kebede, Enrique J. Galvez

Published Mar 10, 2015• 1 citation
Publisher

Abstract

We prepare heralded single photons in a non-separable superposition of polarization and spatial modes using an in-beam polarization interferometer enabled by a spatial light modulator. We diagnose the quantum state using two techniques: quantum state tomography and imaging polarimetry. The results are in very good agreement with the expectations.

DOI
10.1117/12.2079038

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We prepare heralded single photons in a non-separable superposition of polarization and spatial modes using an in-beam polarization interferometer enabled by a spatial light modulator. We diagnose the quantum state using two techniques: quantum state tomography and imaging polarimetry. The results are in very good agreement with the expectations.
Non-separable superpositions of polarization and spatial mode of a single photon produce a state that has a polarization that depends on the transverse position, and contains all states of polarization represented on the Poincaré sphere. We have done measurements of the space-dependent state of polarization of single photons prepared in distinct 2×2 (qubit-qubit) and 2×3 (qubit-qutrit) non-separable superpositions of Laguerre-Gauss spatial and polarization states. Detection was done by polarimetry of the light projected at distinct locations in the transverse plane. The polarization patterns had a C-point polarization singularity (lemon, star or monstar) at the center of the transverse wavefunction.
We experimentally demonstrate a quantum state estimation and tomography for qubits encoded in a single photon's spatial degree of freedom. The experimental setup depicted in Fig. 1 consists of: 1) polarization entangled photon pairs source; 2) spatial encoder allowing to map a polarization state into spatial state; 3) polarization analyzer and 4) spatial state analyzer. The 28 element spatial quantum state measurement set was implemented using imaging optics and a linear array of 28 single photon avalanche diodes (SPAD). The timing information from all the detectors was acquired using custom made FPGA electronics.
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