Superconducting Qubits as Quantum Sensors of Ionizing Radiation

We experimentally investigated superconducting transmon qubits as cryogenic quantum sensors of ionizing radiation.  We utilized a six-qubit chip with resonators inductively coupled on both sides of a central transmission line in a hanger geometry.  Measurements were performed without and with a source of ionizing radiation, external to the cryostat at room temperature, consisting of the isotope Cobalt 60 emitting gamma rays at energies of 1.17 MeV and 1.33 MeV from its radioactive decay.  Radiative flux was controlled by varying the height of the source relative to the bottom of the cryostat.  Without applied external radiation, we measured T1 relaxation times of 200 to 350 μs and Ramsey T2* coherence times of 100 to 150 μs for the six qubits.  Measurements performed without and with applied external radiation include power dependance of readout, state discrimination in the IQ plane, T1 traces, Ramsey traces, and single point in a T1 or Ramsey trace measurements with variable durations of applied radiation.  Based on the measured results, we describe prospective designs for qubits as detectors of ionizing radiation. 

 

This work was supported by the LDRD program at SNL, a multimission laboratory managed and operated by NTESS under DOE NNSA contract DE-NA0003525.  This work was performed in part at CINT, a U.S. DOE BES user facility.  The six-qubit chip was fabricated and provided by the SQUILL Foundry at MIT Lincoln Laboratory, with funding from the LPS Qubit Collaboratory.