Thermal and Residual Excited-State Population in a 3D Transmon Qubit

Abstract

We present a systematic study of the first excited-state population in a 3D transmon qubit mounted in a dilution refrigerator with a variable temperature. Using a modified version of the protocol developed by Geerlings et al. [1], we observe the excited-state population to be consistent with a Maxwell-Boltzmann distribution, i.e., a qubit in thermal equilibrium with the refrigerator, over the temperature range 35-150 mK. Below 35 mK, the excited-state population saturates to 0.1%, near the resolution of our measurement. We verified this result using a flux qubit with ten-times stronger coupling to its readout resonator. We conclude that these qubits have effective temperature T_{eff} = 35 mK. Assuming T_{eff} is due solely to hot quasiparticles, the inferred qubit lifetime is 108 us and in plausible agreement with the measured 80 us.

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• Low-temperature environments for quantum computation and quantum simulation
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• Implementation of single-qubit gates via parametric modulation in the Majorana transmon
• A thermal-noise-resilient microwave quantum network traversing 4 K
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• Learning Fourier series with parametrized quantum circuits
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• Rapid on-demand generation of thermal states in superconducting quantum circuits
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• Mitigating errors in state preparation and measurement with noncomputational states
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• Protocol for temperature sensing using a three-level transmon circuit
• Dynamics of a dispersively coupled transmon qubit in the presence of a noise source embedded in the control line