Jinli Zhang

Low-noise on-chip coherent microwave source

  1. Chengyu Yan,
  2. Juha Hassel,
  3. Visa Vesterinen,
  4. Jinli Zhang,
  5. Joni Ikonen,
  6. Leif Grönberg,
  7. Jan Goetz,
  8. and Mikko Möttönen
The increasing need for scaling up quantum computers operating in the microwave domain calls for advanced approaches for control electronics. To this end, integration of components
at cryogenic temperatures hosting also the quantum devices seems tempting. However, this comes with the limitations of ultra-low power dissipation accompanied by stringent signal-quality requirements to implement quantum-coherent operations. Here, we present a device and a technique to provide coherent continuous-wave microwave emission. We experimentally verify that its operation characteristics accurately follow our introduced theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. From phase noise measurements, we evaluate that the infidelity of typical quantum gate operations owing to this cryogenic source is less than 0.1% up to 10-ms evolution times, which is well below the infidelity caused by dephasing of the state-of-the-art superconducting qubits. Our device provides a coherent tone of 25 pW, corresponding to the total power needed in simultaneous control of thousands of qubits. Thus, together with future cryogenic amplitude and phase modulation techniques, our results may open pathways for scalable cryogenic control systems for quantum processors.
arxiv pdf

Broadband Tunable Phase Shifter For Microwaves

  1. Jinli Zhang,
  2. Tianyi Li,
  3. Roope Kokkoniemi,
  4. Chengyu Yan,
  5. Wei Liu,
  6. Matti Partanen,
  7. Kuan Yen Tan,
  8. Ming He,
  9. Lu Ji,
  10. Leif Grönberg,
  11. and Mikko Möttönen
We implement a broadly tunable phase shifter for microwaves based on superconducting quantum interference devices (SQUIDs) and study it both experimentally and theoretically. At different
frequencies, a unit transmission coefficient, |S21|=1, can be theoretically achieved along a curve where the phase shift is controllable by magnetic flux. The fabricated device consists of three equidistant SQUIDs interrupting a transmission line. We model each SQUID embedded at different positions along the transmission line with two parameters, capacitance and inductance, the values of which we extract from the experiments. In our experiments, the tunability of the phase shift varies from from 0.07×π to 0.14×π radians along the full-transmission curve with the input frequency ranging from 6.00 to 6.28~GHz. The reported measurements are in good agreement with simulations, which is promising for future design work of phase shifters for different applications.
arxiv pdf