Extending Quantum Memory

Brian Julsgaard, Jacob Friis Sherson, Eugene Simon Polzik +2 more

The work reports on the experiments performed implementing quantum memory for light utilizing an atomic spin polarized gas of caesium atoms. The fidelity of the mapping up to 70%, significantly higher than the benchmark classical memory fidelity has been demonstrated. Future plans for extending the memory performance towards other quantum states of light and the memory readout protocols is described in the paper.

Wolfgang Tittel, Mikael Afzelius, Nicolas Gisin +2 more

Xi-Yu Luo, Chaoyang Wang, Ming-Yang Zheng +17 more

Long-distance entanglement is pivotal for quantum communication, distributed quantum computing and sensing. Significant progresses have been made in extending the distribution distance of entangled photons, either in free space or fiber. For future quantum network applications, matter-based entanglement is more favorable since the capability of storage is essential for advanced applications. Extending entanglement distance for memory qubits was partially hindered by the mismatch of its photonic emission wavelength with the low-loss transmission window of optical fiber. By incorporating quantum frequency conversion, memory-memory entanglement has been successfully extended to several tens of kilometers. Here, we make a significant step further by reporting the entanglement between two atomic ensemble quantum memories over 420 km. We convert photons emitted from the memories to telecom S-band, which enable us to exploit the significantly low transmission loss in fiber (0.17 dB/km). We employ the DLCZ scheme for remote entanglement generation, and delicately stabilize the relative phase between the two memories by using fulltime far-off-resonant locking to reduce high-frequency noise and intermittent dual-band locking to compensate low-frequency drift jointly. We demonstrate that the memory-memory entangling probability beats the repeaterless channel capacity for direct entanglement distribution. Our experiment provides a testbed of studying quantum network applications from metropolitan scale to intercity scale.

Nuala Timoney, Imam Usmani, Pierre Jobez +2 more

A necessary part of a quantum repeater is an on-demand quantum memory. In this paper we report on recent progress of achieving such a memory in a solid-state system. We show storage of a few photon optical pulse as a spin-wave in a crystal, preserving the states' coherence. We show how it is possible to extend the storage time and increase the process efficiency.

Ramón Alonso‐Sanz