Wednesday, June 19, 2013

1306.4262 (Zhongxiao Xu et al.)

Long lifetime and high-fidelity quantum memory of photonic polarization
qubit by lifting Zeeman degeneracy

Zhongxiao Xu, Yuelong Wu, Long Tian, Lirong Chen, Zhiying Zhang, Zhihui Yan, Shujing Li, Hai Wang, Changde Xie, Kunchi Peng
Receiving a photonic qubit, storing it with long lifetime and retrieving it with high fidelity are crucial for constructing quantum networks. Photonic polarization qubits (PPQs) are extensively used for encoding and transmitting quantum information since they are easily manipulated and analyzed. Dynamic Electromagnetically induced transparency (EIT) in atoms is an efficient process to store PPQs which has been studied. However, due to the decoherence induced by magnetic field fluctuations, the lifetime of the qubit memory is limited and the achieved longest lifetime in EIT based system is only about 470us, so far. Here we present an EIT based millisecond storage in which a moderate magnetic field is applied on a cold atom cloud to lift Zeeman degeneracy. PPQ states can be stored as two magnetic field insensitive spin waves and the influence of magnetic field sensitive spin waves on the storage is almost totally avoided. The measured average fidelity of polarization states is 0.986 at 200us and 0.784 at 4.5ms.
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