抗磁场三维transmon中的准粒子效应
Quasiparticle effects in magnetic-field-resilient 3D transmons
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中文总结 AI 辅助
该研究测量了抗磁场三维transmon的宇称切换时间随面内磁场的非单调演化，揭示了超导能隙不对称性对宇称寿命的调控机制，并证实Al-AlOₓ-Al约瑟夫森结可用于拓扑量子比特的宇称操控架构。
中文摘要 AI 辅助
近期研究表明，超导量子比特的准粒子诱导退相干取决于Al/AlOₓ/Al结中上下薄膜厚度不同所导致的超导能隙不对称性。磁场是研究这种依赖关系的关键调控手段，因为它可以原位改变超导能隙。我们对一个面内磁场最高达0.41T的抗磁场三维transmon的宇称切换时间进行了测量。在低场下，较小的宇称劈裂需要采用qutrit脉冲序列来完成宇称测量。我们测得宇称寿命随面内磁场呈非单调演化：在磁场升至0.2T前寿命增加，在更高磁场下则下降。我们证明超导能隙不对称性在观测到的行为中起到关键作用。零场下，量子比特频率与超导能隙差近乎共振，有利于与准粒子发生能量交换，从而提高了宇称切换速率。随着磁场升高，量子比特频率降低并与能隙差失谐，导致宇称寿命初始上升；而光子辅助的量子比特跃迁增多，造成了高场下寿命随后下降的现象。本研究除了深入揭示了常规transmon量子比特中的宇称切换机制，还证实Al-AlOₓ-Al约瑟夫森结（JJs）可用于基于马约拉纳零模的拓扑量子比特的宇称读取与操控架构。
英文摘要
Recent research shows that quasiparticle-induced decoherence of superconducting qubits depends on the superconducting-gap asymmetry originating from the different thicknesses of the top and bottom films in Al/AlO$_x$/Al junctions. Magnetic field is a key tuning knob to investigate this dependence as it can change the superconducting gaps in situ. We present measurements of the parity-switching time of a field-resilient 3D transmon with in-plane field up to 0.41T. At low fields, small parity splitting requires qutrit pulse sequences for parity measurements. We measure a non-monotonic evolution of the parity lifetime with in-plane magnetic field, increasing up to 0.2T, followed by a decrease at higher fields. We demonstrate that the superconducting-gap asymmetry plays a crucial role in the observed behavior. At zero field, the qubit frequency is nearly resonant with the superconducting-gap difference, favoring the energy exchange with the quasiparticles and so enhancing the parity-switching rate. With a higher magnetic field, the qubit frequency decreases and gets detuned from the gap difference, causing the initial increase of the parity lifetime, while photon-assisted qubit transitions increase, producing the subsequent decrease at higher fields. Besides giving a deeper insight into the parity-switching mechanism in conventional transmon qubits, we establish that Al-AlO$_x$-Al JJs could be used in architectures for the parity-readout and manipulation of topological qubits based on Majorana zero modes.
