Faithfully storing an unknown quantum light state is essential to advanced quantum communication and distributed quantum computation applications, currently that role is well played by quantum memory, one of the core devices in quantum information, which is also indispensable in the processes of quantum teleportation, quantum encoding, and reducing information loss, to name a few.
Despite there are some remarkable efforts based on cold atoms single atom in a cavity Bose-Einstein condensate, atomic vapors and trapped ions,they are suffering from several practical drawbacks, such as extra step of spatially splitting the input state, imperfect spatial mode matching and strong control or read light pulse during the memory sequence required.
This quantum memory is based on an atomic frequency comb(AFC) in rare-earth ion-doped crystals, for the crystals have shown several seldom equaled advantages, such as excellent capability to store light for extended periods with high efficiency and a large bandwidth. However, due to the strongly polarization dependent absorption of ions in crystal, all previous experiments have been conducted with a single predefined polarization. To get rid of that limitation,LI’s group uses an alternative approachto realize AFC quantum memory for polarizationencodedsingle photons.
The hardware of this quantum memory is composed of two pieces of Nd3t:YVO4 crystals (a kind of high performance laser crystal) sandwiching a half-wave plate, and this structure helps prevent a single piece of Nd3t:YVO4 crystal from functioning as a polarization-qubit memory. Moreover,the experimental setup has been improved to achieve an optimum polarization storage performance. The group measured the process fidelity for a 200 ns storage time with single-photon-level input pulses at 99.9%±0.2%, which should make the quantum memory suitable for quantum error-correction applications in large-scale quantum computation. Additionally, the results shows bright prospect in producing solid-state devices that are capable of functioning as a quantum memory for light’s polarization, temporal, and spatial information.
This research was supported by the National Basic Research Program and National Natural Science Foundation of China. Key Laboratory of Quantum Information is a laboratory under the guidance of CAS academician GUO Guangcan.
(XU Chenguang)