Petar Jurcevic

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

Reducing unitary and spectator errors in cross resonance with optimized rotary echoes

  1. Neereja Sundaresan,
  2. Isaac Lauer,
  3. Emily Pritchett,
  4. Easwar Magesan,
  5. Petar Jurcevic,
  6. and Jay M. Gambetta
We present an improvement to the cross resonance gate realized with the addition of resonant, target rotary pulses. These pulses, applied directly to the target qubit, are simultaneous
to and in phase with the echoed cross resonance pulses. Using specialized Hamiltonian error amplifying tomography, we confirm a reduction of error terms with target rotary — directly translating to improved two-qubit gate fidelity. Beyond improvement in the control-target subspace, the target rotary reduces entanglement between target and target spectators caused by residual quantum interactions. We further characterize multi-qubit performance improvement enabled by target rotary pulsing using unitarity benchmarking and quantum volume measurements, achieving a new record quantum volume for a superconducting qubit system.
arxiv pdf