Efficient and long-lived quantum memory with cold atoms inside a ring cavity

• Published in: Nature physics Vol. 8; no. 7; pp. 517 - 521
• Main Authors: Bao, Xiao-Hui, Reingruber, Andreas, Dietrich, Peter, Rui, Jun, Dück, Alexander, Strassel, Thorsten, Li, Li, Liu, Nai-Le, Zhao, Bo, Pan, Jian-Wei
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2012; Nature Publishing Group
• Subjects: 639/766/36/1125; 639/766/400/1100; 639/766/483/481; Atomic; Atoms & subatomic particles; Classical and Continuum Physics; Clocks; Cold atoms; Complex Systems; Condensed Matter Physics; Construction; Conversion; Holes; letter; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Photons; Physics; Physics and Astronomy; Quantum physics; Spin waves; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys2324

A quantum memory that combines high-efficiency and long lifetime is now demonstrated. Employing a collective excitation, or spin wave, in an ensemble of atoms in a trap improves memory lifetime, while incorporating the trap into an optical ring cavity simultaneously aids higher retrieval efficiency. Quantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation 1 and long-distance quantum communication 2 . A long-standing goal to realize scalable quantum information processing is to build a long-lived and efficient quantum memory. There have been significant efforts distributed towards this goal. However, either efficient but short-lived 3 , 4 or long-lived but inefficient quantum memories 5 , 6 , 7 have been demonstrated so far. Here we report a high-performance quantum memory in which long lifetime and high retrieval efficiency meet for the first time. By placing a ring cavity around an atomic ensemble, employing a pair of clock states, creating a long-wavelength spin wave and arranging the set-up in the gravitational direction, we realize a quantum memory with an intrinsic spin wave to photon conversion efficiency of 73(2)% together with a storage lifetime of 3.2(1) ms. This realization provides an essential tool towards scalable linear-optical quantum information processing.