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

Quantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation and long-distance quantum communication. 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 or long-lived but inefficient quantum memories 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 setup 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.Comment: 6 pages, 4 figure

Linewidth of collimated wavelength-converted emission in Rb vapour

We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power continuous-wave laser radiation at 780 and 776 nm and an internally generated mid-IR field at 5.23 μm in Rb vapour. Using a high-finesse Fabry–Perot interferometer, the spectral width of the CBL is found to be <1.3 MHz for a wide range of experimental conditions. We demonstrate using frequency-modulated laser light that the CBL linewidth is mainly limited by the temporal coherence of the applied laser fields rather than the atom–light interaction itself. The obtained result allows the same 1.3 MHz upper limit to be set for the linewidth of the collimated mid-IR radiation at 5.23 μm, which has not been directly detected.Alexander Akulshin, Christopher Perrella, Gar-Wing Truong, Andre Luiten, Dmitry Budker, Russell McLea