Quantum CNOT Gate with Actively Synchronized Photon Pairs

TL;DR

This paper demonstrates a probabilistic quantum CNOT gate using actively synchronized photon pairs stored in warm atomic vapor, achieving high fidelity and Bell-inequality violation, advancing quantum information processing.

Contribution

It introduces a quantum CNOT gate with active synchronization and storage, providing a quantitative relation between HOM visibility and gate fidelity.

Findings

Achieved >85% truth-table fidelity

Demonstrated Bell-inequality violation for all four Bell states

Identified HOM interference visibility as a key fidelity limit

Abstract

Controlling the synchronization of photons from probabilistic quantum sources plays a pivotal role in advancing efficient quantum information processing. We report the realization of a probabilistic entangling gate operating on actively synchronized photon pairs, using a quantum memory based on warm atomic vapor. We achieve a truth-table fidelity exceeding 85% and demonstrate Bell-inequality violation for all four Bell states. The reduction in visibility of the Hong-Ou-Mandel (HOM) interference introduced by the storage process is identified as a primary factor limiting the gate fidelity. We derive an exact quantitative relation between HOM visibility and gate fidelity for pure single photons, which applies to all photonic gates relying on interference, regardless of the physical platform.