K. Y. Tan

Initial experimental results on a superconducting-qubit reset based on photon-assisted quasiparticle tunneling

  1. V. A. Sevriuk,
  2. W. Liu,
  3. J. Rönkkö,
  4. H. Hsu,
  5. F. Marxer,
  6. T. F. Mörstedt,
  7. M. Partanen,
  8. J. Räbinä,
  9. M. Venkatesh,
  10. J. Hotari,
  11. L. Grönberg,
  12. J. Heinsoo,
  13. T. Li,
  14. J. Tuorila,
  15. K.W. Chan,
  16. J. Hassel,
  17. K. Y. Tan,
  18. and M. Möttönen
We present here our recent results on qubit reset scheme based on a quantum-circuit refrigerator (QCR). In particular, we use the photon-assisted quasiparticle tunneling through a superconductor–insulator–normal-metal–insulator–superconductor
junction to controllably decrease the energy relaxation time of the qubit during the QCR operation. In our experiment, we use a transmon qubit with dispersive readout. The QCR is capacitively coupled to the qubit through its normal-metal island. We employ rapid, square-shaped QCR control voltage pulses with durations in the range of 2–350 ns and a variety of amplitudes to optimize the reset time and fidelity. Consequently, we reach a qubit ground-state probability of roughly 97% with 80-ns pulses starting from the first excited state. The qubit state probability is extracted from averaged readout signal, where the calibration is based of the Rabi oscillations, thus not distinguishing the residual thermal population of the qubit.
arxiv pdf

Tunable electromagnetic environment for superconducting quantum bits

  1. P. J. Jones,
  2. J. A. M. Huhtamäki,
  3. K. Y. Tan,
  4. and M. Möttönen
We introduce a setup which realises a tunable engineered environment for experiments in circuit quantum electrodynamics. We illustrate this concept with the specific example of a quantum
bit, qubit, in a high-quality-factor cavity which is separated from a resistor in another cavity by a capacitor. The temperature of the resistor can be controlled in a well defined manner in order to provide a hot or cold environment for the qubit, as desired. Furthermore, introducing superconducting quantum interference devices (SQUIDs) into the resistor cavity provides control of the coupling strength between this artificial environment and the qubit. We demonstrate that our scheme allows us to couple strongly to the environment enabling rapid initialization of the system, and by subsequent tuning of the magnetic flux of the SQUIDs we may greatly reduce the resistor-qubit coupling, allowing the qubit to evolve unhindered.
arxiv pdf