RESUMO
The storage and retrieval efficiency (SRE) and lifetime of optical quantum memories are two key performance indicators for scaling up quantum information processing. Here, we experimentally demonstrate a cavity-enhanced long-lived optical memory for two polarizations in a cold atomic ensemble. Using electromagnetically induced-transparency (EIT) dynamics, we demonstrate the storages of left-circularly and right-circularly polarized signal light pulses in the atoms, respectively. By making the signal and control beams collinearly pass through the atoms and storing the two polarizations of the signal light as two magnetic-field-insensitive spin waves, we achieve a long-lived (3.5 ms) memory. By placing a low-finesse optical ring cavity around the cold atoms, the coupling between the signal light and the atoms is enhanced, which leads to an increase in SRE. The presented cavity-enhanced storage shows that the SRE is â¼30%, corresponding to an intrinsic SRE of â¼45%.
RESUMO
In this paper, we report a generation of a spin-wave excitation (SWE) with a near-unity (0.996±0.003) probability in a given time (~730 µ s). Such deterministic generation relies on a feedback scheme with a millisecond quantum memory. The millisecond memory is achieved by maximizing the wavelength of the spin wave and storing the SWE as the magnetic-field-insensitive transition. We then demonstrate partial retrievals of the spin wave by applying a first read pulse whose area is smaller than the value of π. The remained SWE is fully retrieved by a second pulse. Anti-correlation function between the detections in the first and second readouts has been measured, which shows that the partial-retrieval operation on the SWE is in the quantum regime. The presented experiment represents an important step towards the realization of the improved DLCZ quantum repeater protocol proposed in Phys. Rev. A 77, 062301 (2008).