Sami Rosenblatt

Dynamics of superconducting qubit relaxation times

  1. Malcolm Carroll,
  2. Sami Rosenblatt,
  3. Petar Jurcevic,
  4. Isaac Lauer,
  5. and Abhinav Kandala
Superconducting qubits are a leading candidate for quantum computing but display temporal fluctuations in their energy relaxation times T1. This introduces instabilities in multi-qubit
device performance. Furthermore, autocorrelation in these time fluctuations introduces challenges for obtaining representative measures of T1 for process optimization and device screening. These T1 fluctuations are often attributed to time varying coupling of the qubit to defects, putative two level systems (TLSs). In this work, we develop a technique to probe the spectral and temporal dynamics of T1 in single junction transmons by repeated T1 measurements in the frequency vicinity of the bare qubit transition, via the AC-Stark effect. Across 10 qubits, we observe strong correlations between the mean T1 averaged over approximately nine months and a snapshot of an equally weighted T1 average over the Stark shifted frequency range. These observations are suggestive of an ergodic-like spectral diffusion of TLSs dominating T1, and offer a promising path to more rapid T1 characterization for device screening and process optimization.
arxiv pdf

Laser-annealing Josephson junctions for yielding scaled-up superconducting quantum processors

  1. Jared B. Hertzberg,
  2. Eric J. Zhang,
  3. Sami Rosenblatt,
  4. Easwar Magesan,
  5. John A. Smolin,
  6. Jeng-Bang Yau,
  7. Vivek P. Adiga,
  8. Martin Sandberg,
  9. Markus Brink,
  10. Jerry M. Chow,
  11. and Jason S. Orcutt
As superconducting quantum circuits scale to larger sizes, the problem of frequency crowding proves a formidable task. Here we present a solution for this problem in fixed-frequency
qubit architectures. By systematically adjusting qubit frequencies post-fabrication, we show a nearly ten-fold improvement in the precision of setting qubit frequencies. To assess scalability, we identify the types of ‚frequency collisions‘ that will impair a transmon qubit and cross-resonance gate architecture. Using statistical modeling, we compute the probability of evading all such conditions, as a function of qubit frequency precision. We find that without post-fabrication tuning, the probability of finding a workable lattice quickly approaches 0. However with the demonstrated precisions it is possible to find collision-free lattices with favorable yield. These techniques and models are currently employed in available quantum systems and will be indispensable as systems continue to scale to larger sizes.
arxiv pdf