Restless Tuneup of High-Fidelity Qubit Gates
M. A. Rol (Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab, TU Delft - QuTech Advanced Research Centre)
C.C. Bultink (TU Delft - QCD/DiCarlo Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
T.E. O'Brien (Universiteit Leiden)
S. R. De Jong (Student TU Delft, Kavli institute of nanoscience Delft)
L. S. Theis (Saarland University)
Xiang Fu (TU Delft - Computer Engineering)
F. Luthi (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/DiCarlo Lab)
R.F.L. Vermeulen (TU Delft - ALG/General, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
J.C. Sterk (TU Delft - QCD/DiCarlo Lab, TU Delft - QuTech Advanced Research Centre, Topic Embedded Systems B.V.)
A Bruno (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab)
D. Deurloo (TU Delft - BUS/General, TNO, TU Delft - QuTech Advanced Research Centre)
RN Schouten (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - ALG/General)
F. K. Wilhelm (Saarland University)
L di Carlo (TU Delft - QN/DiCarlo Lab, TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/DiCarlo Lab, Kavli institute of nanoscience Delft)
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Abstract
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 nondemolition 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 the detection of fractional changes in the gate error with a nearly constant signal-to-noise ratio. The restless concept demonstrated can be readily extended to the tuneup of two-qubit gates and measurement operations.