Robust atom-photon gate for quantum information processing

For scalable quantum networking, distributed quantum computing, and quantum sensing, an interaction mechanism between remote atomic qubits is crucial. Two-qubit gates between atomic qubits in cavities and flying photons realize such an interaction. Previously proposed atom-photon gates are sensitive to many experimental imperfections affecting the gate operation, with fidelities typically limited to the range of 75-80%. We propose an atom-photon CZ gate with doubly degenerate ground and excited state energy levels mediating the atom-light interaction. The setup consists of a cavity and a Mach-Zehnder interferometer. The gate works by converting the error-inducing photons into losses, making the scheme less sensitive to errors. Error analysis of the gate shows that the present scheme is more robust against various errors (e.g., spatial mode mismatch between the photon and the cavity, spontaneous emission, cavity losses, detunings, and random fluctuations of the cavity parameters and frequencies) and achieves higher fidelity than previous schemes.