Demonstration of dual Shapiro steps in small Josephson junctions
Fabian Kaap, Christoph Kissling, Victor Gaydamachenko, Lukas Grünhaupt, S. V. Lotkhov
Abstract
Abstract Bloch oscillations in small Josephson junctions were predicted theoretically as the quantum dual to Josephson oscillations. A significant consequence of this prediction is the emergence of quantized current steps, so-called dual Shapiro steps, when synchronizing Bloch oscillations to an external microwave signal. These steps potentially enable a fundamental standard of current I , defined via the frequency f of the external signal and the elementary charge e , I = ± n × 2 e f , where n is a natural number. Here, we realize this fundamental relation by synchronizing the Bloch oscillations in small Al/AlO x /Al Josephson junctions to sinusoidal drives with frequencies from 1 to 6 GHz and observe dual Shapiro steps up to I ≈ 3 nA. Inspired by today’s voltage standards and to further confirm the duality relation, we investigate a pulsed drive regime and observe an asymmetric pattern of dual Shapiro steps. This work confirms quantum duality effects in Josephson junctions and paves the way towards a range of applications in quantum metrology based on well-established fabrication techniques and straightforward circuit design.