High-Bandwidth Hybrid Quantum Repeater

We present a physical- and link-level design for the creation of entangled pairs to be used in quantum repeater applications where one can control the noise level of the initially distributed pairs. The system can tune dynamically, trading initial fidelity for success probability, from high fidelity pairs ($F=0.98$ or above) to moderate fidelity pairs. The same physical resources that create the long-distance entanglement are used to implement the local gates required for entanglement purification and swapping, creating a homogeneous repeater architecture. Optimizing the noise properties of the initially distributed pairs significantly improves the rate of generating long-distance Bell pairs. Finally, we discuss the performance trade-off between spatial and temporal resources.

Figure 1

Schematic of an entanglement distribution scheme based on two qubits in individual cavities interacting indirectly via a shared probe beam and controlled displacement operations. An optical circulator before the second qubit routes the probe field into the cavity and the resulting beam leaking out to the detector. A phase reference is sent along the same lossy channel.

Figure 2

Plot of the probability $P[F]$ of successfully establishing an entangled pair at an attenuation length of $l/l_0=0.8$ (20 km in commercial fiber) versus fidelity for the different measurement strategies: (a) odd state cat projector CSP, (b) ideal SPD, and ($c$) SPD with ${\eta }^2=0.9$.