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arXiv:1201.4149 · Physical Review Letters

Quantum Storage of a Photonic Polarization Qubit in a Solid

Mustafa Gündoğan, Patrick M. Ledingham, Attaallah Almasi, Matteo Cristiani, Hugues de Riedmatten

Published May 10, 2012• 148 citations
arXivHTMLPDF

Abstract

We report on the quantum storage and retrieval of photonic polarization quantum bits onto and out of a solid state storage device. The qubits are implemented with weak coherent states at the single photon level, and are stored for a predetermined time of 500 ns in a praseodymium doped crystal with a storage and retrieval efficiency of 10%, using the atomic frequency comb scheme. We characterize the storage by using quantum state tomography, and find that the average conditional fidelity of the retrieved qubits exceeds 95% for a mean photon number μ=0.4. This is significantly higher than a classical benchmark, taking into account the poissonian statistics and finite memory efficiency, which proves that our crystal functions as a quantum storage device for polarization qubits. These results extend the storage capabilities of solid state quantum light matter interfaces to polarization encoding, which is widely used in quantum information science.

DOI
10.1103/physrevlett.108.190504

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Faithfully storing an unknown quantum light state is essential to advanced quantum communication and distributed quantum computation applications. The required quantum memory must have high fidelity to improve the performance of a quantum network. Here we report the reversible transfer of photonic polarization states into collective atomic excitation in a compact solid-state device. The quantum memory is based on an atomic frequency comb (AFC) in rare-earth ion-doped crystals. We obtain up to 0.999 process fidelity for the storage and retrieval process of single-photon-level coherent pulse. This reliable quantum memory is a crucial step toward quantum networks based on solid-state devices.
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An optical quantum memory is a stationary device that is capable of storing and recreating photonic qubits with a higher fidelity than any classical device. Thus far, these two requirements have been fulfilled for polarization qubits in systems based on cold atoms and cryogenically cooled crystals. Here, we report a room-temperature memory capable of storing arbitrary polarization qubits with a signal-to-background ratio higher than 1 and an average fidelity surpassing the classical benchmark for weak laser pulses containing 1.6 photons on average, without taking into account non-unitary operation. Our results demonstrate that a common vapor cell can reach the low background noise levels necessary for polarization qubit storage using single-photon level light, and propels atomic-vapor systems towards a level of functionality akin to other quantum information processing architectures.
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