5 research outputs found
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
Calibration of Drive Non-Linearity for Arbitrary-Angle Single-Qubit Gates Using Error Amplification
The ability to execute high-fidelity operations is crucial to scaling up
quantum devices to large numbers of qubits. However, signal distortions
originating from non-linear components in the control lines can limit the
performance of single-qubit gates. In this work, we use a measurement based on
error amplification to characterize and correct the small single-qubit rotation
errors originating from the non-linear scaling of the qubit drive rate with the
amplitude of the programmed pulse. With our hardware, and for a 15-ns pulse,
the rotation angles deviate by up to several degrees from a linear model. Using
purity benchmarking, we find that control errors reach , which
accounts for half of the total gate error. Using cross-entropy benchmarking, we
demonstrate arbitrary-angle single-qubit gates with coherence-limited errors of
and leakage below . While the exact
magnitude of these errors is specific to our setup, the presented method is
applicable to any source of non-linearity. Our work shows that the
non-linearity of qubit drive line components imposes a limit on the fidelity of
single-qubit gates, independent of improvements in coherence times, circuit
design, or leakage mitigation when not corrected for
Optimized graphene electrodes for contacting graphene nanoribbons
Atomically precise graphene nanoribbons (GNRs) are a promising emerging class of designer quantum materials with electronic properties that are tunable by chemical design. However, many challenges remain in the device integration of these materials, especially regarding contacting strategies. We report on the device integration of uniaxially aligned and non-aligned 9-atom wide armchair graphene nanoribbons (9-AGNRs) in a field-effect transistor geometry using electron beam lithography-defined graphene electrodes. This approach yields controlled electrode geometries and enables higher fabrication throughput compared to previous approaches using an electrical breakdown technique. Thermal annealing is found to be a crucial step for successful device operation resulting in electronic transport characteristics showing a strong gate dependence. Raman spectroscopy confirms the integrity of the graphene electrodes after patterning and of the GNRs after device integration. Our results demonstrate the importance of the GNR-graphene electrode interface and pave the way for GNR device integration with structurally well-defined electrodes.QN/van der Zant La
Calibration of Drive Nonlinearity for Arbitrary-Angle Single-Qubit Gates Using Error Amplification
The ability to execute high-fidelity operations is crucial to scaling up quantum devices to large numbers of qubits. However, signal distortions originating from nonlinear components in the control lines can limit the performance of single-qubit gates. In this work, we use a measurement based on error amplification to characterize and correct the small single-qubit rotation errors originating from the nonlinear scaling of the qubit drive rate with the amplitude of the programmed pulse. With our hardware, and for a 15-ns pulse, the rotation angles deviate by up to several degrees from a linear model. Using purity benchmarking, we find that control errors reach 2×10-4, which accounts for half of the total gate error. Using cross-entropy benchmarking, we demonstrate arbitrary-angle single-qubit gates with coherence-limited errors of 2×10-4 and leakage below 6×10-5. While the exact magnitude of these errors is specific to our setup, the presented method is applicable to most sources of nonlinearity. Our work shows that the nonlinearity of qubit drive line components imposes a limit on the fidelity of single-qubit gates, independent of improvements in coherence times, circuit design, or leakage mitigation when not corrected for.ISSN:2331-701
Optimized graphene electrodes for contacting graphene nanoribbons
Atomically precise graphene nanoribbons (GNRs) are a promising emerging class of designer quantum materials with electronic properties that are tunable by chemical design. However, many challenges remain in the device integration of these materials, especially regarding contacting strategies. We report on the device integration of uniaxially aligned and non-aligned 9-atom wide armchair graphene nanoribbons (9-AGNRs) in a field-effect transistor geometry using electron beam lithography-defined graphene electrodes. This approach yields controlled electrode geometries and enables higher fabrication throughput compared to previous approaches using an electrical breakdown technique. Thermal annealing is found to be a crucial step for successful device operation resulting in electronic transport characteristics showing a strong gate dependence. Raman spectroscopy confirms the integrity of the graphene electrodes after patterning and of the GNRs after device integration. Our results demonstrate the importance of the GNR-graphene electrode interface and pave the way for GNR device integration with structurally well-defined electrodes