D. Deurloo

Restless Tuneup of High-Fidelity Qubit Gates

  1. M. A. Rol,
  2. C. C. Bultink,
  3. T. E. O'Brien,
  4. S.R. de Jong,
  5. L.S. Theis,
  6. X. Fu,
  7. F. Luthi,
  8. R.F.L. Vermeulen,
  9. J. C. de Sterke,
  10. A. Bruno,
  11. D. Deurloo,
  12. R. N. Schouten,
  13. F.K. Wilhelm,
  14. and L. DiCarlo
We present a tuneup protocol for qubit gates with tenfold speedup over traditional methods reliant on qubit initialization by energy relaxation. This speedup is achieved by constructing
a cost function for Nelder-Mead optimization from real-time correlation of non-demolition measurements interleaving gate operations without pause. Applying the protocol on a transmon qubit achieves 0.999 average Clifford fidelity in one minute, as independently verified using randomized benchmarking and gate set tomography. The adjustable sensitivity of the cost function allows detecting fractional changes in gate error with nearly constant signal-to-noise ratio. The restless concept demonstrated can be readily extended to the tuneup of two-qubit gates and measurement operations.
arxiv pdf

Independent, extensible control of same-frequency superconducting qubits by selective broadcasting

  1. S. Asaad,
  2. C. Dickel,
  3. S. Poletto,
  4. A. Bruno,
  5. N. K. Langford,
  6. M. A. Rol,
  7. D. Deurloo,
  8. and L. DiCarlo
A critical ingredient for realizing large-scale quantum information processors will be the ability to make economical use of qubit control hardware. We demonstrate an extensible strategy
for reusing control hardware on same-frequency transmon qubits in a circuit QED chip with surface-code-compatible connectivity. A vector switch matrix enables selective broadcasting of input pulses to multiple transmons with individual tailoring of pulse quadratures for each, as required to minimize the effects of leakage on weakly anharmonic qubits. Using randomized benchmarking, we compare multiple broadcasting strategies that each pass the surface-code error threshold for single-qubit gates. In particular, we introduce a selective-broadcasting control strategy using five pulse primitives, which allows independent, simultaneous Clifford gates on arbitrary numbers of qubits.
arxiv pdf