Periodic Reporting for period 1 - QMET (Quantum Metrology Electrical Triangle)
Période du rapport: 2021-07-01 au 2023-06-30
Decades after the definition of quantum voltage and resistance standards, a quantum current standard is missing. This last one turned out to be more challenging than the previous two, and nowadays the current unit is basically given by extremely precise current sources. A standard definition of the Ampere can be obtained exploiting the dual counterpart of the Josephson effect, namely voltage Bloch Oscillations. A way to measure them consists in embedding a largely non-linear Josephson junction in a high impedance environment, irradiate it with a microwave pump to observe discrete DC current steps, the dual of Shapiro steps. The QMET action tackles this objective. Such result would provide a leap in quantum metrology and paves the way to the redefinition of the ampere using only fundamental constants.
We made the preliminary simulations which results were used to design and choose the circuit’s parameters, then developed the recipe and fabricated the actual devices. We designed and benchmarked the measurement circuitry in a dilution refrigerator, and programmed a dedicated data acquisition and analysis setup. We performed measurements and analysed the data comparing them with further simulations. In our device we observed dual Shapiro steps emerging from the synchronisation of an external microwave tone with the Cooper pair dynamics, which was the aim of this action. The results were discussed among the authors, and with expert colleagues like D. Haviland, T. Duty, and M. Devoret. We wrote a manuscript concerning the results. This was achieved in the timespan of one year. The scientific importance of the result was endorsed by several colleagues, and the paper received enthusiastic reviews, saying that this work “[...] represents a genuine breakthrough for the worldwide research in condensed matter physics”, and that “they do not rely only on transport measurements [...] but they use microwave spectroscopy using a circuit QED architecture. This represents a formidable and unique tool [...]”.
The following experiments were devoted to the study of the device, which shows a complicated but interesting physics, which are going to be published soon.
The following experiments were devoted to the study of the device, which shows a complicated but interesting physics, which are going to be published soon.
The experimental evidence of dual Shapiro steps, paves the way to the closure of the quantum metrology electrical triangle, it is the new state-of-the-art, and it unlocked a new field of study in superconducting circuits.