Innovation and Development

New Design to Increase Fidelity of Quantum Memory

Recently, a group led by Prof. Li Chuanfeng from the Key Laboratory of Quantum Information under guidance of Prof. Guo Guangcan, member of CAS realized a high performance solid-state quantum memory for photonic polarizations. Two pieces of 1.4 mm Nd:YVO4 crystals (a kind of high performance laser crystals) are used to independently process the two orthogonal polarization states of light. A specially designed half-wave plate is inserted between the two crystals to exchange the two polarization states and ensure the symmetrical operations. The memory hardware just looks like a small piece of sandwiche which is compact, stable, scalable and easy to be integrated into other devices. The researchers abandoned the collinear configurations which are previously used in solid state quantum memory experiments. They designed a non-collinear configuration where the pump light and the probe light are spatially separated. These improvements in sample and setup designation greatly decreased the noise from pump light or the environment and improved the performance of fidelity. The memory process was analyzed with full quantum process tomography. They obtain up to 99.9% process fidelity for the storage and retrieval process of single-photon-level coherent pulse, which is much better than the highest fidelity (95%) obtained for storage of photonic polarization previously. This is also the best performance of fidelity obtained in all kinds of quantum memories. This noteworthy result was published on May 11th Physical Review Letters, and was also reported by Physics Synopsis (APS) and Physics world (IOP).