Adversaries perturbing shared entanglement in distributed VQAs can manipulate a new Kraus expressibility metric to keep gradients large but steer training to incorrect solutions.
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2508.16437 (2025)
13 Pith papers cite this work. Polarity classification is still indexing.
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Pith papers citing it
abstract
Achieving high-fidelity single-qubit gates, two-qubit gates, and qubit readout is critical for building scalable, error-corrected quantum computers. However, device parameters that enhance one operation often degrade the others, making simultaneous optimization challenging. Here, we demonstrate that careful tuning of qubit-coupler coupling strengths in a superconducting circuit with two transmon qubits coupled via a tunable coupler enables high-fidelity single- and two-qubit gates, without compromising readout performance. As a result, we achieve a 40h-averaged CZ gate fidelity of 99.93%, simultaneous single-qubit gate fidelities of 99.98%, and readout fidelities over 99.94% in a single device. These results are enabled by optimized coupling parameters, an efficient CZ gate calibration experiment based on our new Phased-Averaged Leakage Error Amplification (PALEA) protocol, and a readout configuration compatible with high coherence qubits. Our results demonstrate a viable path toward scaling up superconducting quantum processors while maintaining consistently high fidelities across all core operations.
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A capacitively shunted double-transmon coupler enables a 99.92% fidelity parametrically driven iSWAP gate at zero flux between detuned transmons with minimal residual ZZ interaction.
A calibration workflow using ELEA and CAFE circuits achieves CZ gate fidelity above 99.9% on an 84-qubit superconducting processor with 0.007% coherent error and median 99.25% across 72 gates.
Cyclic control via parameter-space expansion restores controllability in fast CZ gates despite short-timescale distortions, cutting average coherent error from 0.27% to 0.12% in superconducting qubit experiments without extending gate duration.
Generalizes fidelity-reduction formulas from static to time-dependent Markovian dissipation and applies the result to bound adiabatic CZ gate fidelity in tunable superconducting qubits.
Proof-of-principle measurement-based blind quantum computation on a modular superconducting processor executing a 3-qubit Deutsch-Jozsa algorithm with verified information privacy.
Far-detuned cross-resonance designs cut frequency collisions in transmon processors, achieving 10% collision-free yield for 1024 qubits with qubit-frequency spread reduced to 6.8 MHz.
Constraint-aware initialization and hybrid XY-X mixer in QAOA for VRP yield lower average energies and higher feasible-solution ratios than standard QAOA across ideal, finite-shot, and noisy simulations.
A floating tunable coupler allows 24 ns adiabatic CZ gates above 99.9% fidelity with exact ZZ=0 at idle for fixed-frequency transmons.
A compilation scheme called Parity Twine achieved a 50-qubit unitary QFT with process fidelity ≈1e-2 on IBM Heron r3, and up to 52 qubits with plurality voting, surpassing prior unitary QFT demonstrations.
Simulations show that optimal control pulses designed with the non-adiabatic master equation can mitigate thermal noise in quantum gates by up to two orders of magnitude in specific parameter windows, with direct qubit control outperforming ancilla-only schemes.
Offset-charge-tunable transmon qubit achieves 99.37% fidelity in charge-parity mapping and over 93.4% in continuous monitoring at 4 μs intervals via randomized benchmarking.
Using DMET to fragment molecules and SQD to solve the fragments on IBM hardware, the authors report ground-state energies for eight ligand-like molecules that agree with DMET-FCI to within about 10⁻⁶ Hartree.
citing papers explorer
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Adversarial Effects on Expressibility and Trainability in Distributed Variational Quantum Algorithms
Adversaries perturbing shared entanglement in distributed VQAs can manipulate a new Kraus expressibility metric to keep gradients large but steer training to incorrect solutions.
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Parametrically Driven iSWAP Gate Using a Capacitively Shunted Double-Transmon Coupler at the Zero-Flux Sweet Spot
A capacitively shunted double-transmon coupler enables a 99.92% fidelity parametrically driven iSWAP gate at zero flux between detuned transmons with minimal residual ZZ interaction.
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High-Precision Calibration Workflow Achieves Above $99.9\%$ CZ Gate Fidelity on a Scalable Superconducting Processor
A calibration workflow using ELEA and CAFE circuits achieves CZ gate fidelity above 99.9% on an 84-qubit superconducting processor with 0.007% coherent error and median 99.25% across 72 gates.
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Overcoming the Speed-Fidelity Trade-off in Fast CZ Gates via Cyclic Control
Cyclic control via parameter-space expansion restores controllability in fast CZ gates despite short-timescale distortions, cutting average coherent error from 0.27% to 0.12% in superconducting qubit experiments without extending gate duration.
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Fidelity bounds for adiabatic gates and other quantum operations with time-dependent dissipation
Generalizes fidelity-reduction formulas from static to time-dependent Markovian dissipation and applies the result to bound adiabatic CZ gate fidelity in tunable superconducting qubits.
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Blind Quantum Computation on a Modular Superconducting Processor
Proof-of-principle measurement-based blind quantum computation on a modular superconducting processor executing a 3-qubit Deutsch-Jozsa algorithm with verified information privacy.
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Systematic frequency-collision analysis of the cross-resonance gate outside the straddling regime
Far-detuned cross-resonance designs cut frequency collisions in transmon processors, achieving 10% collision-free yield for 1024 qubits with qubit-frequency spread reduced to 6.8 MHz.
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Improving Feasibility in Quantum Approximate Optimization Algorithm for Vehicle Routing via Constraint-Aware Initialization and Hybrid XY-X Mixing
Constraint-aware initialization and hybrid XY-X mixer in QAOA for VRP yield lower average energies and higher feasible-solution ratios than standard QAOA across ideal, finite-shot, and noisy simulations.
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Unlocking a fast adiabatic CZ gate and exact residual $ZZ$ cancellation between fixed-frequency transmons using a floating tunable coupler
A floating tunable coupler allows 24 ns adiabatic CZ gates above 99.9% fidelity with exact ZZ=0 at idle for fixed-frequency transmons.
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Demonstrating Record Fidelity for the Quantum Fourier Transform
A compilation scheme called Parity Twine achieved a 50-qubit unitary QFT with process fidelity ≈1e-2 on IBM Heron r3, and up to 52 qubits with plurality voting, surpassing prior unitary QFT demonstrations.
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Optimal Control of thermally noisy quantum gates in a multilevel system
Simulations show that optimal control pulses designed with the non-adiabatic master equation can mitigate thermal noise in quantum gates by up to two orders of magnitude in specific parameter windows, with direct qubit control outperforming ancilla-only schemes.
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Characterizing charge-parity detection based on an offset-charge-tunable transmon qubit via randomized benchmarking
Offset-charge-tunable transmon qubit achieves 99.37% fidelity in charge-parity mapping and over 93.4% in continuous monitoring at 4 μs intervals via randomized benchmarking.
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Quantum Simulation of Ligand-like Molecules through Sample-based Quantum Diagonalization in Density Matrix Embedding Framework
Using DMET to fragment molecules and SQD to solve the fragments on IBM hardware, the authors report ground-state energies for eight ligand-like molecules that agree with DMET-FCI to within about 10⁻⁶ Hartree.