J. Heinsoo

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

Digital quantum simulation of spin models with circuit quantum electrodynamics

  1. Y. Salathé,
  2. M. Mondal,
  3. M. Oppliger,
  4. J. Heinsoo,
  5. P. Kurpiers,
  6. A. Potočnik,
  7. A. Mezzacapo,
  8. U. Las Heras,
  9. L. Lamata,
  10. E. Solano,
  11. S. Filipp,
  12. and A. Wallraff
Systems of interacting quantum spins show a rich spectrum of quantum phases and display interesting many-body dynamics. Computing characteristics of even small systems on conventional
computers poses significant challenges. A quantum simulator has the potential to outperform standard computers in calculating the evolution of complex quantum systems. Here, we perform a digital quantum simulation of the paradigmatic Heisenberg and Ising interacting spin models using a two transmon-qubit circuit quantum electrodynamics setup. We make use of the exchange interaction naturally present in the simulator to construct a digital decomposition of the model-specific evolution and extract its full dynamics. This approach is universal and efficient, employing only resources which are polynomial in the number of spins and indicates a path towards the controlled simulation of general spin dynamics in superconducting qubit platforms.
arxiv pdf