Excess Quasiparticles in Superconducting Qubits

Felix Wagner

PostDoc at the Quantum Device Lab

Abstract

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Recent advances in superconducting qubits make them one of the most promising candidates for practical, error-corrected quantum computing. However, these devices are sensitive to their environment because of the low energy of the captured photon used to operate a quantum state and the fragility of the Cooper pair binding in the superconductor. Ambient photon backgrounds, such as microwave fields, infrared radiation, and cosmic rays, can disrupt this binding and generate Bogoliubov quasiparticles—unbound electrons in the superconductor. These quasiparticles are detrimental to qubit performance because they can interact with the trapped photon state, causing relaxation and dephasing. Conversely, the ability of superconducting qubits to interact with single quasiparticles renders them promising for quantum sensing applications. In this talk, we discuss the challenge of quasiparticle poisoning in superconducting qubits and present our use of charge-sensitive superconducting qubits as quasiparticle sensors to investigate infrared backgrounds in quantum computing setups.