Skip to content
Quantum Materials and Devices Lab

Qubits and high frequency measurements

Qubit Measurements

Schematic of our setup for performing measurements at GHz frequencies. This is used both for qubits and for generating Shapiro steps in junctions.
A chip with several qubit designs mounted to a custom PCB for RF measurements.
Ramsey fringes observed in qubits to the left.
Rabi oscillations observed with respect to varied pulse length (x-axis) and excitation power (y-axis).

The addition of our GHz measurement setup (schematic top left) gives us a more diverse approach towards characterization than classical transport alone. The primary goals of this project are twofold. First, we have spent some time measuring a series of transmons in an effort to familiarize ourselves with quantum computing techniques and benchmark our new setup. We hope to continue with qubit measurements, primarily as a means of characterizing novel materials and making steps toward a new generation of qubits with fewer losses due to material interfacial mismatch. This effort would then work in conjunction with our studies of quantum transport in complex oxides. The second goal of this project is a continuation of our work towards applying a microwave drive to Josephson junctions and observing the resulting Shapiro steps, as detailed below.

Shapiro Steps in Josephson Junctions

Bias-bias map where each step corresponds to an increase in applied RF power, leading to the emergence of Shapiro steps.
Power-bias map where many quantized voltage steps appear as power increases.
I-V curve where Shapiro steps are observed at either integer or half integer values, giving insight into the origin of this supercurrent.

As a part of our Josephson junction work, we use high frequency radiation to induce Shapiro steps. These quantized voltage steps form the basis of the “Josephson voltage standard”– a way of precisely defining the volt. In our research, these quantized steps enable probes of a supercurrent’s origin. We have applied this probe to reveal a more complete picture of a junction’s dependence on external parameters (Larson et al., 2020), demonstrate the multi-terminal inverse AC Josephson effect (Arnault at al., 2021), investigate unconventional switching behavior (Larson et al., 2022), and uncover the origin of dynamical supercurrents in a Josephson circuit (Arnault et al., 2025). We plan to continue these efforts in graphene junctions and apply these techniques to further inform our measurements of superconductivity in complex oxides.

Corresponding grad student: Johnny Chiles (john.chiles@duke.edu)

Related Publications

Multiplet Supercurrents in a Josephson Circuit.
E. G. Arnault, J. Chiles, T. F. Q. Larson,  C. Chen, L. Zhao, K. Watanabe, T. Taniguchi, F. Amet, and G. Finkelstein
Physical Review Letters (2025)

Noise-Induced Stabilization of Dynamical States With Broken Time-Reversal Symmetry.
T. F. Q. Larson, L. Zhao, E. G. Arnault, M. Wei, A. Seredinski, H. Li, K. Watanabe, T. Taniguchi, F. Amet, and G. Finkelstein
arXiv (2022)

Dynamical Stabilization of Multiplet Supercurrents in Multi-terminal Josephson Junctions.
E. G. Arnault, S. Idris, A. McConnell, L. Zhao, T. F. Q. Larson, K. Watanabe, T. Taniguchi, G. Finkelstein, and F. Amet
Nano Letters (2022)

The Multi-terminal Inverse AC Josephson Effect.
E. G. Arnault, T. F. Q. Larson, A. Seredinski, L. Zhao, H. Li, K. Watanabe, T. Taniguchi, I. V. Borzenets, F. Amet, and G. Finkelstein.
Nano Letters (2021)

Zero Crossing Steps and Anomalous Shapiro Maps in Graphene Josephson Junctions
T. F. Q. Larson, L. Zhao, E. G. Arnault, M. T. Wei, A. Seredinski, H. Li, K. Watanabe, T. Taniguchi, F. Amet, G. Finkelstein
Nano Letters (2020)

Sites@Duke Express is powered by WordPress. Read the Sites@Duke Express policies and FAQs, or request help.