Kurilovich Vladislav D, Remez Benjamin, Glazman Leonid I
Department of Physics, Yale University, New Haven, CT, 06520, USA.
Google Research, Mountain View, CA, USA.
Nat Commun. 2025 Feb 5;16(1):1384. doi: 10.1038/s41467-025-56411-x.
A transmon qubit embedded in a high-impedance environment acts in a way dual to a conventional Josephson junction. In analogy to the AC Josephson effect, biasing of the transmon by a direct current leads to the oscillations of voltage across it. These oscillations are known as the Bloch oscillations. We find the Bloch oscillations spectrum, and show that the zero-point fluctuations of charge make it broadband. Despite having a broad-band spectrum, Bloch oscillations can be brought in resonance with an external microwave radiation. The resonances lead to steps in the voltage-current relation, which are dual to the conventional Shapiro steps. We find how the shape of the steps depends on the environment impedance R, parameters of the transmon, and the microwave amplitude. The Bloch oscillations rely on the insulating state of the transmon which is realized at impedances exceeding the Schmid transition point, R > R = h/(2e).
嵌入高阻抗环境中的跨导量子比特的行为方式与传统约瑟夫森结相反。类似于交流约瑟夫森效应，通过直流对跨导进行偏置会导致其两端电压振荡。这些振荡被称为布洛赫振荡。我们找到了布洛赫振荡频谱，并表明电荷的零点涨落使其具有宽带特性。尽管具有宽带频谱，但布洛赫振荡可与外部微波辐射发生共振。这些共振导致电压 - 电流关系中出现台阶，这与传统的夏皮罗台阶相反。我们发现台阶的形状如何取决于环境阻抗R、跨导的参数以及微波幅度。布洛赫振荡依赖于跨导的绝缘态，该绝缘态在阻抗超过施密德转变点R > R = h/(2e)时实现。
