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<p>We experimentally investigate macroscopic resonant tunneling (MRT) in a three-junction persistent-current flux qubit subject to a microwave driving field. The device is operated near half-flux quantum, where the double-well potential of the qubit supports two localized persistent-current states that form an effective two-level system. By sweeping the driving frequency at a fixed amplitude and, separately, the driving amplitude at a fixed frequency, we measure the tunneling probability from the ground to the excited energy eigenstate and its dependence on the microwave parameters. The oscillating magnetic field at the qubit loop is calibrated using the known mutual inductances and the attenuation of the experimental wiring, so that the driving amplitude used in the analysis is not a free fitting parameter. We numerically solve the time-dependent Schrödinger equation for the calibrated circuit Hamiltonian and obtain theoretical tunneling probabilities that quantitatively reproduce both the Lorentzian-shaped resonance line and the saturation behavior at large driving amplitudes. From the measured linewidth we extract the qubit dephasing time <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({T}_{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation>​ and find good agreement with the value required to fit the experimental data. Our results provide a consistent picture of MRT in a flux qubit driven by a microwave field and establish a parameter-free comparison between experiment and theory for this macroscopic quantum tunneling process.</p>

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Investigation of macroscopic resonant tunneling mechanism in superconducting flux qubit

  • 期刊论文

  • 发表日期：

    2026年5月8日

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  • Jianxin Shi

摘要

We experimentally investigate macroscopic resonant tunneling (MRT) in a three-junction persistent-current flux qubit subject to a microwave driving field. The device is operated near half-flux quantum, where the double-well potential of the qubit supports two localized persistent-current states that form an effective two-level system. By sweeping the driving frequency at a fixed amplitude and, separately, the driving amplitude at a fixed frequency, we measure the tunneling probability from the ground to the excited energy eigenstate and its dependence on the microwave parameters. The oscillating magnetic field at the qubit loop is calibrated using the known mutual inductances and the attenuation of the experimental wiring, so that the driving amplitude used in the analysis is not a free fitting parameter. We numerically solve the time-dependent Schrödinger equation for the calibrated circuit Hamiltonian and obtain theoretical tunneling probabilities that quantitatively reproduce both the Lorentzian-shaped resonance line and the saturation behavior at large driving amplitudes. From the measured linewidth we extract the qubit dephasing time \({T}_{2}\) T 2 ​ and find good agreement with the value required to fit the experimental data. Our results provide a consistent picture of MRT in a flux qubit driven by a microwave field and establish a parameter-free comparison between experiment and theory for this macroscopic quantum tunneling process.