Long Distance Entanglement Between Quantum Memories

Philip John Walther

W. Chang, Chang Li, Yukai Wu +5 more

Realization of long-distance quantum communication through the quantum repeater network requires a combination of some key elements, including a multiplexed quantum memory for storage of entanglement and a telecom photon for propagation of information through the fiber.Although impressive experimental advances have demonstrated the individual elements, combining these key capabilities together and realizing them in a single experimental system remains a significant challenge.Here, we report an experimental realization of long-distance entanglement between a multiplexed quantum memory with 49 individually accessible memory cells and a telecom photon after transmission in a 10-km optical fiber.Excitation of an atomic ensemble generates narrow-band polarization entanglement between a telecom photon of 1530-nm wavelength and another photon of 780-nm wavelength, which is then stored into a memory cell of a multiplexed atomic quantum memory and read out after a controllable delay.The entanglement is verified through quantum-state tomography after quantum storage in the atomic memory and fiber transmission of the telecom photon.This experiment demonstrates an important step towards realization of long-distance quantum communication networks.

Paul D. Kunz, Neal Solmeyer, Kevin C. Cox +1 more

A long-distance quantum network that could enable distributed quantum computing and unconditionally secure communication will require a quantum memory capable of supporting entanglement swapping over long distances. The memory qubit must preserve its entanglement to the communication qubit sent to a repeater for at least long enough to swap entanglement with an adjacent node. The most important figures-of-merit for a quantum memory are: fidelity, entanglement rate, and memory lifetime. Though many varieties of memories and repeaters are currently being researched (for a review see [1]) it remains an outstanding challenge to develop one that simultaneously meets all the necessary criteria to enable a practical long distance quantum network. We propose to use laser-cooled and trapped rubidium atoms, with Rydberg excitations, coupled to an optical cavity, to address these issues.

Zhen-Sheng Yuan, Yu-Ao Chen, Shuai Chen +2 more

Lin-Xiong Wang, Yi-Ping Ye, Can-Fu Zhang +2 more

Establishing quantum entanglement between pairs of distant quantum memories (QMs) is essential for numerous applications in quantum networks. In this paper, we propose some heralded schemes for entanglement generation between multiple pairs of QMs placed in long-distance separated nodes, where the qubits are encoded on QMs coupled to a one-dimensional waveguide. By distributing a pair of spatial-polarization hyperentangled photons to two distant nodes, where each photon scatters with QMs, we can generate entanglement between multiple pairs of distant QMs. In our schemes, the faulty scattering events can be filtered out and discarded via detecting the polarization states of scattered photon components within each module QM. Moreover, the responses from single-photon detectors placed at the end of each node enable us to obtain direct entangled states between QMs in a heralded manner. Eventually, we theoretically extend the proposed schemes by demonstrating specific regularities that arise when entangling more pairs of QMs. With recent advancements in hyperentanglement generation, our schemes become increasingly feasible for practical implementation.

Yong Yu, Fei Ma, Xi-Yu Luo +14 more