S. Hazra

Lumped-element broadband SNAIL parametric amplifier with on-chip pump filter for multiplexed readout

  1. V. R. Joshi,
  2. S. Hazra,
  3. A. Z. Ding,
  4. A. Miano,
  5. W. Dai,
  6. G. Umasankar,
  7. A. Kottandavida,
  8. G. Liu,
  9. L. Frunzio,
  10. and M. H. Devoret
We present a SNAIL-based parametric amplifier that integrates a lumped-element impedance matching network for increased bandwidth and an on-chip pump-port filter for efficient pump
delivery. The amplifier is fabricated using a single-layer optical lithography step, followed by a single-layer electron beam lithography step. We measure a flat 20 dB gain profile with less than 1 dB ripple across a bandwidth of up to 250 MHz on multiple devices, demonstrating robust performance against variations arising from fabrication and packaging. We characterize the amplifier’s linearity by analyzing gain compression and intermodulation distortion under simultaneous multi-tone excitation. We show that the intermodulation products remain suppressed by more than 23 dB relative to the signal tones, even at the 1 dB gain compression point. We further validate its utility by performing simultaneous high-fidelity readout of two transmon qubits, achieving state assignment fidelities of 99.51% and 98.55%. The combination of compact design, fabrication simplicity, and performance robustness makes this amplifier a practical device for quantum experiments with superconducting circuits.
arxiv pdf

Benchmarking the readout of a superconducting qubit for repeated measurements

  1. S. Hazra,
  2. W. Dai,
  3. T. Connolly,
  4. P. D. Kurilovich,
  5. Z. Wang,
  6. L. Frunzio,
  7. and M. H. Devoret
Readout of superconducting qubits faces a trade-off between measurement speed and unwanted back-action on the qubit caused by the readout drive, such as T1 degradation and leakage out
of the computational subspace. The readout is typically benchmarked by integrating the readout signal and choosing a binary threshold to extract the „readout fidelity“. We show that such a characterization may significantly overlook readout-induced leakage errors. We introduce a method to quantitatively assess this error by repeatedly executing a composite operation — a readout preceded by a randomized qubit-flip. We apply this technique to characterize the dispersive readout of an intrinsically Purcell-protected qubit. We report a binary readout fidelity of 99.63% and quantum non-demolition (QND) fidelity exceeding 99.00% which takes into account a leakage error rate of 0.12±0.03%, under a repetition rate of (380ns)−1 for the composite operation.
arxiv pdf