Demonstration of a passive photon-atom swap gate

TL;DR

This paper demonstrates a passive, deterministic photon-atom swap gate using single-photon Raman interaction in a nanofiber-coupled resonator, enabling automatic quantum state transfer without active control.

Contribution

It introduces a passive swap gate mechanism based on SPRINT, eliminating the need for feedback or control pulses in photon-atom quantum state transfer.

Findings

Achieved nonclassical fidelities in both directions of state transfer.

Demonstrated automatic operation at the atom's spontaneous emission timescale.

Applicable to waveguide-coupled {bcla} systems for scalable quantum information processing.

Abstract

Deterministic quantum interactions between single photons and single quantum emitters are a vital building block towards the distribution of quantum information between remote systems. Deterministic photon-atom state transfer has been demonstrated by using protocols that include active feedback or synchronized control pulses. Here we demonstrate a completely passive swap gate between the states of a single photon and a single atom. The underlying mechanism is single-photon Raman interaction (SPRINT) - an interference-based effect in which a photonic qubit deterministically controls the state of a material qubit encoded in the two ground states of a {\Lambda} system, and vice versa. Using a nanofiber-coupled microsphere resonator coupled to single Rb atoms we swap a photonic qubit into the atom and back, demonstrating nonclassical fidelities in both directions. Requiring no control fields or feedback protocol, the gate takes place automatically at the timescale of the atom's cavity- enhanced spontaneous emission time. Applicable to any waveguide-coupled {\Lambda} system, this scheme provides a versatile building block for the modular scaling up of quantum information processing systems.