Hybrid Quantum Repeater Using Bright Coherent Light

We describe a quantum repeater protocol for long-distance quantum communication. In this scheme, entanglement is created between qubits at intermediate stations of the channel by using a weak dispersive light-matter interaction and distributing the outgoing bright coherent-light pulses among the stations. Noisy entangled pairs of electronic spin are then prepared with high success probability via homodyne detection and postselection. The local gates for entanglement purification and swapping are deterministic and measurement-free, based upon the same coherent-light resources and weak interactions as for the initial entanglement distribution. Finally, the entanglement is stored in a nuclear-spin-based quantum memory. With our system, qubit-communication rates approaching 100 Hz over 1280 km with fidelities near 99% are possible for reasonable local gate errors.

Figure 1

Schematic for the generation of spin entanglement between two qubits at neighboring stations via homodyne detection discriminating between conditionally phase-rotated coherent probe beams; the LO pulse is a sufficiently strong local oscillator used for the homodyne detection.

Figure 2

(a) The maximum fidelity $F_{\max }$ and success probability $P_s$ as a function of the postselection window $p_c$ for ${\eta }^2=2/3$. (b) Achievable qubit rates for different target fidelities vs local optical losses $ϵ$. Each point corresponds to a single Monte Carlo simulation of the nested purification protocol over 9 complete qubit teleportations; each point is the average difference in time between teleported qubit arrival times, and the error bar is the standard deviation.