B. M. Tarasinski

Leakage detection for a transmon-based surface code

  1. B. M. Varbanov,
  2. F. Battistel,
  3. B. M. Tarasinski,
  4. V.P. Ostroukh,
  5. T. E. O'Brien,
  6. L. DiCarlo,
  7. and B. M. Terhal
Leakage outside of the qubit computational subspace, present in many leading experimental platforms, constitutes a threatening error for quantum error correction (QEC) for qubits. We
develop a leakage-detection scheme via Hidden Markov models (HMMs) for transmon-based implementations of the surface code. By performing realistic density-matrix simulations of the distance-3 surface code (Surface-17), we observe that leakage is sharply projected and leads to an increase in the surface-code defect probability of neighboring stabilizers. Together with the analog readout of the ancilla qubits, this increase enables the accurate detection of the time and location of leakage. We restore the logical error rate below the memory break-even point by post-selecting out leakage, discarding about 47% of the data. Leakage detection via HMMs opens the prospect for near-term QEC demonstrations, targeted leakage reduction and leakage-aware decoding and is applicable to other experimental platforms.
arxiv pdf

Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor

  1. M. A. Rol,
  2. L. Ciorciaro,
  3. F. K. Malinowski,
  4. B. M. Tarasinski,
  5. R. E. Sagastizabal,
  6. C. C. Bultink,
  7. Y. Salathe,
  8. N. Haandbaek,
  9. J. Sedivy,
  10. and L. DiCarlo
We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the
step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature arbitrary waveform generator producing the control pulses. As a first application, we iteratively improve this step response using optimized real-time digital filters to counter the linear-dynamical distortion in the control line, as needed for high-fidelity, repeatable one- and two-qubit gates based on dynamical control of qubit frequency.
arxiv pdf