The team of Li Chengfeng, Zhou Zongquan and others from the CAS Key Lab of  Quantum Information developed a multi-degree-of-freedom (DOF) multiplexed  solid-state quantum memory, and demonstrated photon pulse operation functions  with time and frequency DOFs. The results were published in Nature  Communications recently.

The reliable storage and coherent manipulation of quantum states with  matter-systems enable the construction of large-scale quantum networks based on  a quantum repeater. To achieve useful communication rates, highly multi-mode  quantum memories will be required to construct a multiplexed quantum  repeater.

The team presented the first demonstration of 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 3-dimensional spatial DOF with 2-dimensional temporal and 2-dimensional  spectral DOFs, the team created a multiple-DOF memory with high multi-mode  capacity up to 3*2*2=12.

This device can also serve as a quantum mode converter with high fidelity,  which is the fundamental requirement for the construction of a multiplexed  quantum repeater.

The team further demonstrated that the device can perform arbitrary pulse  operations within time and frequency DOF. Representative operations include  pulse sequencer, multiplexer, selective spectral shifter and configurable beam  splitter. The experimental results showed that in all these operations, the  three-dimensional quantum states carried by photons maintained a fidelity of  about 89%.

This memory device can achieve all operations required for  Knill-Laflamme-Milburn type quantum computation, so it may be expected to find  application in the field of linear optical quantum computing.

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