Quantum storage of polarization qubits in birefringent and anisotropically absorbing materials

TL;DR

This paper demonstrates a simple scheme for storing polarization qubits in birefringent and absorbing materials, achieving high fidelity in a solid-state quantum memory using rare-earth ions in a biaxial crystal.

Contribution

The authors introduce a novel compensation scheme for polarization effects in quantum memories, enabling high-fidelity storage of polarization qubits in birefringent, absorbing materials.

Findings

Achieved 97.5% average fidelity in storing polarization qubits.

Demonstrated the scheme with a solid-state quantum memory using rare-earth doped crystal.

Significantly improved over measure-and-prepare strategies.

Abstract

Storage of quantum information encoded into true single photons is an essential constituent of long-distance quantum communication based on quantum repeaters and of optical quantum information processing. The storage of photonic polarization qubits is, however, complicated by the fact that many materials are birefringent and have polarization-dependent absorption. Here we present and demonstrate a simple scheme that allows compensating for these polarization effects. The scheme is demonstrated using a solid-state quantum memory implemented with an ensemble of rare-earth ions doped into a biaxial yttrium orthosilicate ($Y_2SiO_5$) crystal. Heralded single photons generated from a filtered spontaneous parametric downconversion source are stored, and quantum state tomography of the retrieved polarization state reveals an average fidelity of $97.5 \pm 0.4%$, which is significantly higher than what is achievable with a measure-and-prepare strategy.