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High-frequency readout free from transmon multi-excitation resonances
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Quantum computation will rely on quantum error correction to counteract decoherence. Successfully implementing an error correction protocol requires the fidelity of qubit operations to be well-above error correction thresholds. In superconducting quantum computers, measurement of the qubit state remains the lowest-fidelity operation. For the transmon, a prototypical superconducting qubit, measurement is carried out by scattering a microwave tone off the qubit. Conventionally, the frequency of this tone is of the same order as the transmon frequency. The measurement fidelity in this approach is limited by multi-excitation resonances in the transmon spectrum which are activated at high readout power. These resonances excite the qubit outside of the computational basis, violating the desired quantum non-demolition character of the measurement. Here, we find that strongly detuning the readout frequency from that of the transmon exponentially suppresses the strength of spurious multi-excitation resonances. By increasing the readout frequency up to twelve times the transmon frequency, we achieve a quantum non-demolition measurement fidelity of 99.93% with a residual probability of leakage to non-computational states of only 0.02%.
Forward citations
Cited by 10 Pith papers
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Full characterization of measurement-induced transitions of a superconducting qubit
Readout-induced leakage in high-frequency transmon readout is dominated by inelastic single-photon Raman scattering, with rate proportional to drive power and to the dissipative impedance at the emitted-photon frequency.
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Collapse and Inversion of the Josephson Potential in a Strongly Driven Superconducting Circuit
The Josephson potential of a transmon collapses and inverts under a strong fast flux drive, dynamically stabilizing the qubit at φ=π, as shown by spectroscopy and readout.
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Analytic gradients for low-rank quantum optimal control
A new gradient-based quantum control algorithm propagates only a low-rank factorization of the density matrix, giving analytic gradients and quadratic speedups over full master-equation simulations for high-purity protocols.
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Readout-Induced Leakage in Superconducting Circuits with Nonlinear Couplings
Native nonlinear qubit-readout couplings alone neither eliminate nor reliably suppress readout-induced leakage; auxiliary modes reintroduce multiphoton channels whose rates vary by orders of magnitude over <7% frequen...
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The Pound-Drever-Hall Method for Superconducting-Qubit Readout
Three-tone Pound-Drever-Hall readout cancels microwave phase drift in a transmon and tolerates strong detuned sidebands, pointing to a 14 dB readout-gain path.
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Cross-Resonant Gates in Hybrid Fluxonium-Transmon Systems
A simulation study shows that cross-resonance CNOT gates between fluxoniums and a central transmon support high-fidelity parity checks and logical gates in a scalable dual-species architecture.
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Suppression of measurement-induced state transitions in cos{\phi}-coupling transmon readout
A cos-phi-coupled transmon readout is experimentally free of measurement-induced state transitions up to roughly 300 photons, with flux-controlled activation of specific transitions.
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Mitigating state transition errors during readout with a synchronized flux pulse
A synchronized flux pulse that compensates the readout-induced frequency shift avoids two-level-system resonances and achieves 99% (98.4%) fluxonium readout fidelity in 1 microsecond (0.5 microsecond).
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High-power readout of a transmon qubit using a nonlinear coupling
A transmon molecule with nonlinear cosφ coupling achieves 99.21% readout fidelity at 89 photons and remains QND with less than 4% errors up to 300 photons, with a theoretical critical photon number of 377.
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Mitigation of Measurement-Induced State Transitions via a Fast-Load and Fast-Clear Readout
State-independent fast-load/fast-clear three-step pulses suppress ng-dependent measurement-induced state transitions in transmons and minimize ng-averaged readout and post-readout errors.
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