Mainz 2017 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 17: Quantum Repeater and Quantum Communication

Q 17.4: Talk

Tuesday, March 7, 2017, 11:45–12:00, P 3

Memory for photonic polarization qubits with long coherence time — •Matthias Körber, Olivier Morin, Stefan Langenfeld, Andreas Neuzner, Stephan Ritter, and Gerhard Rempe — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching, Germany

The ability to faithfully store quantum information is one of the key requirements for many quantum technologies. Here, we present a quantum memory based on a single ⁸⁷Rb atom in a high-finesse optical resonator, capable of storing and retrieving single-photon polarizaion qubits with an overall efficiency of 18% when probed with highly attenuated coherent laser pulses containing one photon on average. Based on seminal work, the polarization of the photon is mapped onto the atom via a stimulated Raman adiabatic passage (STIRAP). The two atomic levels used to encode the qubit shift in opposite directions in the presence of a magnetic field due to the Zeeman effect. The memory is therefore susceptible to magnetic field fluctuations limiting the coherence time of the memory to a few hundred microseconds. Using an optical Raman transfer we temporarily map the qubit to a protected subspace, thereby extending the coherence time to tens of milliseconds. The coherence time can be further increased to more than 100 milliseconds by means of a spin-echo technique. Our results are an important milestones towards the implementation of a quantum repeater allowing for long distance quantum communication.