A team from the University of Science and Technology of China has developed multi-degree-of-freedom (DOF) multiplexed solid-state quantum memory and has demonstrated photon pulse operation functions with time and frequency DOFs. The researchers demonstrated the on-demand storage of orbital-angular-momentum states with weak coherent pulses at the single-photon level in a rare-earth-ion-doped crystal. Through the combination of this 3D spatial DOF with 2D temporal and 2D spectral DOFs, the team created a multiple-DOF memory with high multimode capacity. According to the researchers, this device could serve as a quantum mode converter with high fidelity — a fundamental requirement for the construction of a multiplexed quantum repeater. The team further demonstrated that the device could perform arbitrary pulse operations within time and frequency DOF. Representative operations included pulses sequencer, multiplexer, selective spectral shifter, and configurable beamsplitter. The experimental results showed that in all of these operations, the 3D quantum states carried by photons maintained a fidelity of about 89 percent. The researchers believe that the developed quantum memory could serve as a building block for scalable photonic quantum information processing architectures. The memory device can realize all the operations required for Knill-Laflamme-Milburn-type quantum computation. It could also find application in the field of linear optical quantum computing. A multi-degree-of-freedom (DOF) multiplexing quantum storage experimental device. Courtesy of Tianshu Yang. The research was published in Nature Communications (doi: 10.1038/s41467-018-05669-5).