Yash J. Joshi

Broadband Bandpass Purcell Filter for Circuit Quantum Electrodynamics

  1. Haoxiong Yan,
  2. Xuntao Wu,
  3. Andrew Lingenfelter,
  4. Yash J. Joshi,
  5. Gustav Andersson,
  6. Christopher R. Conner,
  7. Ming-Han Chou,
  8. Joel Grebel,
  9. Jacob M. Miller,
  10. Rhys G. Povey,
  11. Hong Qiao,
  12. Aashish A. Clerk,
  13. and Andrew N. Cleland
In circuit quantum electrodynamics (QED), qubits are typically measured using dispersively-coupled readout resonators. Coupling between each readout resonator and its electrical environment
however reduces the qubit lifetime via the Purcell effect. Inserting a Purcell filter counters this effect while maintaining high readout fidelity, but reduces measurement bandwidth and thus limits multiplexing readout capacity. In this letter, we develop and implement a multi-stage bandpass Purcell filter that yields better qubit protection while simultaneously increasing measurement bandwidth and multiplexed capacity. We report on the experimental performance of our transmission-line–based implementation of this approach, a flexible design that can easily be integrated with current scaled-up, long coherence time superconducting quantum processors.
arxiv pdf

Cryogenic electro-optic interconnect for superconducting devices

  1. Amir Youssefi,
  2. Itay Shomroni,
  3. Yash J. Joshi,
  4. Nathan Bernier,
  5. Anton Lukashchuk,
  6. Philipp Uhrich,
  7. Liu Qiu,
  8. and Tobias J. Kippenberg
Encoding information onto optical fields is the backbone of modern telecommunication networks. Optical fibers offer low loss transport and vast bandwidth compared to electrical cables,
and are currently also replacing copper cables for short-range communications. Optical fibers also exhibit significantly lower thermal conductivity, making optical interconnects attractive for interfacing with superconducting circuits and devices. Yet little is known about modulation at cryogenic temperatures. Here we demonstrate a proof-of-principle experiment, showing that currently employed Ti-doped LiNbO modulators maintain the Pockels coefficient at 3K—a base temperature for classical microwave amplifier circuitry. We realize electro-optical read-out of a superconducting electromechanical circuit to perform both coherent spectroscopy, measuring optomechanically-induced transparency, and incoherent thermometry, encoding the thermomechanical sidebands in an optical signal. Although the achieved noise figures are high, approaches that match the lower-bandwidth microwave signals, use integrated devices or materials with higher EO coefficient, should achieve added noise similar to current HEMT amplifiers, providing a route to parallel readout for emerging quantum or classical computing platforms.
arxiv pdf