Experimental Investigation of Transmon Charge Sensitivity for Quantum Sensing

Quantum sensing is the use of a quantum system, quantum properties, or quantum phenomena to perform a measurement of a physical quantity. We present experimental results directed toward developing a superconducting transmon qubit as a quantum sensor for the detection of ionizing radiation. A parameter characterizing a transmon is the ratio of the Josephson energy to the charging energy, (EJ/EC). Lower values of (EJ/EC) have increased charge sensitivity due to increased charge dispersion. While this is detrimental for quantum computation, increased charge sensitivity can be beneficial for quantum sensing. The lower limit of usable (EJ/EC) is not well characterized for quantum sensing. We present experimental data from a multi-qubit device with a lower (EJ/EC) = 10 ± 1 qubit, a higher (EJ/EC) = 37 ± 4 qubit, and a tunable qubit bridging the stated (EJ/EC) range. This enables exploration of a wide range of sensitivity for the detection of ionizing radiation while simultaneously allowing us to characterize experimental limits in measuring lower (EJ/EC) qubits. We present experimental data without and with a source of ionizing radiation.

This work was performed in part at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by NTESS under DOE NNSA contract DE-NA0003525.