Photon-Assisted Charge-Parity Jumps in a Superconducting Qubit

Area of Science:

• Quantum computing
• Superconducting circuits
• Quantum information science

Background:

• Superconducting qubits are sensitive to electromagnetic noise.
• Photon-induced relaxation is a critical factor in qubit decoherence.
• Understanding qubit-photon interactions is essential for improving quantum device performance.

Purpose of the Study:

• To evaluate energy and phase relaxation rates of superconducting qubits induced by high-energy stray photons.
• To identify and isolate photon-assisted relaxation channels based on charge parity changes.
• To provide a theoretical framework for characterizing the electromagnetic environment of superconducting devices.

Main Methods:

• Theoretical evaluation of relaxation rates.
• Analysis of photon-induced Cooper pair breaking mechanism.
• Separation of relaxation channels based on qubit charge parity.

Main Results:

• Identified a novel mechanism for superconducting qubit relaxation caused by stray photons.
• Demonstrated that all relaxation channels in this mechanism involve a change in qubit charge parity.
• Observed that qubit energy loss and gain transition rates are of the same order, matching experimental findings.

Conclusions:

• The proposed theory accurately describes photon-assisted relaxation in superconducting qubits.
• The charge parity signature allows for distinguishing this mechanism from other relaxation sources.
• This work enables single-photon level characterization of the electromagnetic environment for superconducting devices at frequencies above the superconducting gap.