2 research outputs found
Toolbox for nonreciprocal dispersive models in circuit QED
We provide a systematic method for constructing effective dispersive Lindblad
master equations to describe weakly-anharmonic superconducting circuits coupled
by a generic dissipationless nonreciprocal linear system, with effective
coupling parameters and decay rates written in terms of the immittance
parameters characterizing the coupler. This article extends the foundational
work of Solgun et al. (2019) for linear reciprocal couplers described by an
impedance response. Here, we expand the existing toolbox to incorporate
nonreciprocal elements, account for direct stray coupling between immittance
ports, circumvent potential singularities, and include dissipative interactions
arising from interaction with a common bath. We illustrate the use of our
results with a circuit of weakly-anharmonic Josephson junctions coupled to a
multiport nonreciprocal environment and a dissipative port. The results
obtained here can be used for the design of complex superconducting quantum
processors with non-trivial routing of quantum information, as well as analog
quantum simulators of condensed matter systems.Comment: 41 pages, 12 figures. Comments are welcom
Fast Flux-Activated Leakage Reduction for Superconducting Quantum Circuits
Quantum computers will require quantum error correction to reach the low
error rates necessary for solving problems that surpass the capabilities of
conventional computers. One of the dominant errors limiting the performance of
quantum error correction codes across multiple technology platforms is leakage
out of the computational subspace arising from the multi-level structure of
qubit implementations. Here, we present a resource-efficient universal leakage
reduction unit for superconducting qubits using parametric flux modulation.
This operation removes leakage down to our measurement accuracy of in approximately with a low error of on the computational subspace, thereby reaching durations and
fidelities comparable to those of single-qubit gates. We demonstrate that using
the leakage reduction unit in repeated weight-two stabilizer measurements
reduces the total number of detected errors in a scalable fashion to close to
what can be achieved using leakage-rejection methods which do not scale. Our
approach does neither require additional control electronics nor on-chip
components and is applicable to both auxiliary and data qubits. These benefits
make our method particularly attractive for mitigating leakage in large-scale
quantum error correction circuits, a crucial requirement for the practical
implementation of fault-tolerant quantum computation