Vidul Joshi

Optimizing the pump coupling for a three-wave mixing Josephson parametric amplifier

  1. Wei Dai,
  2. Gangqiang Liu,
  3. Vidul Joshi,
  4. Alessandro Miano,
  5. Volodymyr Sivak,
  6. Shyam Shankar,
  7. and Michel H. Devoret
Josephson element-based parametric amplifiers (JPAs) typically require rf pump power that is several orders of magnitude stronger than the maximum signal power they can handle. The
low power efficiency and strong pump leakage towards signal circuitry could be critical concerns in application. In this work, we discuss how to optimize the pump coupling scheme for a three-wave mixing JPA by employing microwave filtering techniques, with the goal of maximizing the pump power efficiency and minimize pump leakage without sacrificing other properties of interest. We implement the corresponding filter design in a SNAIL-based JPA and demonstrate more than three orders of magnitude improvement in both power efficiency and pump leakage suppression compared to a similar device with regular capacitive coupling, while maintaining state-of-the-art dynamic range and near-quantum-limited noise performance. Furthermore, we show experimentally that the filter-coupled JPA is more robust against noise input from the pump port, exhibiting no significant change in added noise performance with up to 4 K of effective noise temperature at the pump port.
arxiv pdf

Fully Directional Quantum-limited Phase-Preserving Amplifier

  1. Gangqiang Liu,
  2. Andrew Lingenfelter,
  3. Vidul Joshi,
  4. Nicholas E. Frattini,
  5. Volodymyr V. Sivak,
  6. Shyam Shankar,
  7. and Michel H. Devoret
We present a way to achieve fully directional, quantum-limited phase-preserving amplification in a four-port, four-mode superconducting Josephson circuit by utilizing interference between
six parametric processes that couple all four modes. Full directionality, defined as the reverse isolation surpassing forward gain between the matched input and output ports of the amplifier, ensures its robustness against impedance mismatch that might be present at its output port during applications. Unlike existing directional phase-preserving amplifiers, both the minimal back-action and the quantum-limited added noise of this amplifier remains unaffected by noise incident on its output port. In addition, the matched input and output ports allow direct on-chip integration of these amplifiers with other circuit QED components, facilitating scaling up of superconducting quantum processors.
arxiv pdf