Ultrafast switching of photonic entanglement

TL;DR

This paper introduces a high-speed, low-noise photonic switch capable of routing entangled photons without degrading their quantum states, enabling advanced quantum network functionalities.

Contribution

The authors develop and characterize a novel ultrafast photonic switch that preserves entanglement and demonstrates multi-qubit encoding within a single photon.

Findings

Switch exhibits 200-ps window and 120:1 contrast ratio.

No measurable degradation in entangled-state fidelity (< 0.002).

Demonstrates multiplexing and controlled-bit-flip in entangled photon streams.

Abstract

To deploy and operate a quantum network which utilizes existing telecommunications infrastructure, it is necessary to be able to route entangled photons at high speeds, with minimal loss and signal-band noise, and---most importantly---without disturbing the photons' quantum state. Here we present a switch which fulfills these requirements and characterize its performance at the single photon level; it exhibits a 200-ps switching window, a 120:1 contrast ratio, 1.5 dB loss, and induces no measurable degradation in the switched photons' entangled-state fidelity (< 0.002). Furthermore, because this type of switch couples the temporal and spatial degrees of freedom, it provides an important new tool with which to encode multiple-qubit states in a single photon. As a proof-of-principle demonstration of this capability, we demultiplex a single quantum channel from a dual-channel, time-division-multiplexed entangled photon stream, effectively performing a controlled-bit-flip on a two-qubit subspace of a five-qubit, two-photon state.