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Frontiers in Optics

Realizing a Variable Isotropic Depolarizer

Assaf Shaham, H. S. Eisenberg

Published Jan 1, 2012• 0 citations
Publisher

Abstract

We demonstrate an isotropic depolarizing channel with controlled degree of depolarization. The depolarizer is composed of four birefringent crystals. Quantum process tomography of the depolarizing channel agrees well with the theoretical prediction.
DOI
10.1364/fio.2012.fth4b.5

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Controlling the depolarization of light is a long-standing open problem. In recent years, many demonstrations have used the polarization of single photons to encode quantum information. The depolarization of these photons is equivalent to the decoherence of the quantum information they encode. We present schemes for building various depolarizing channels with controlled properties using birefringent crystals. Three such schemes are demonstrated, and their effects on single photons are shown by quantum process tomography to be in good agreement with a theoretical model.
We show that a configuration of four birefringent crystals and wave-plates can emulate almost any arbitrary unital channel for polarization qubits encoded in single photons, where the channel settings are controlled by the wave-plate angles. The scheme is applied to a single spatial mode and its operation is independent of the wavelength and the fine temporal properties of the input light. We implemented the scheme and demonstrated its operation by applying a dephasing environment to classical and quantum single-photon states with different temporal properties. The applied process was characterized by a quantum process tomography procedure, and a high fidelity to the theory was observed.