Universal quantum gates for photon-atom hybrid systems assisted by bad cavities

TL;DR

This paper proposes two deterministic, high-fidelity quantum gates for photon-atom hybrid systems using bad cavities, simplifying implementation and enabling fast, long-distance quantum communication.

Contribution

It introduces novel schemes for CNOT and Toffoli gates that operate in the intermediate coupling regime without auxiliary qubits or measurements.

Findings

High average fidelities achieved with current technology

Gates operate efficiently in the bad cavity regime

Simple setup especially for the Toffoli gate

Abstract

We present two deterministic schemes for constructing a CNOT gate and a Toffoli gate on photon-atom and photon-atom-atom hybrid quantum systems assisted by bad cavities, respectively. They are achieved by cavity-assisted photon scattering and work in the intermediate coupling region with bad cavities, which relaxes the difficulty of their implementation in experiment. Also, bad cavities are feasible for fast quantum operations and reading out information. Compared with previous works, our schemes do not need any auxiliary qubits and measurements. Moreover, the schematic setups for these gates are simple, especially that for our Toffoli gate as only a quarter wave packet is used to interact the photon with each of the atoms every time. These atom-cavity systems can be used as the quantum nodes in long-distance quantum communication as their relatively long coherence time is suitable for multi-time operations between the photon and the system. Our calculations show that the average fidelities and efficiencies of our two universal hybrid quantum gates are high with current experimental technology.