Characterizing Coherent Errors using Matrix-Element Amplification

Abstract

Repeating a gate sequence multiple times amplifies systematic errors coherently, making it a useful tool for characterizing quantum gates. However, the precision of such an approach is limited by low-frequency noises, while its efficiency hindered by time-consuming scans required to match up the phases of the off-diagonal matrix elements being amplified. Here, we overcome both challenges by interleaving the gate of interest with dynamical decoupling sequences in a protocol we call Matrix-Element Amplification using Dynamical Decoupling (MEADD). Using frequency-tunable superconducting qubits from a Google Sycamore quantum processor, we experimentally demonstrate that MEADD surpasses the accuracy and precision of existing characterization protocols for estimating systematic errors in single- and two-qubit gates. In particular, MEADD yields factors of 5 to 10 improvements in estimating coherent parameters of the $\mathrm{CZ}$ gates compared to existing methods, reaching a precision below one milliradian. We also use it to characterize coherent crosstalk in the processor which was previously too small to detect reliably.

References in corpus (26)

• Supplementary information for "Quantum supremacy using a programmable superconducting processor"
• Circuit Quantum Electrodynamics
• A Quantum Engineer's Guide to Superconducting Qubits
• Coherent Quantum Dynamics of a Superconducting Flux Qubit
• Characterizing Quantum Supremacy in Near-Term Devices
• Suppressing quantum errors by scaling a surface code logical qubit
• Randomized Benchmarking of Quantum Gates
• Simple pulses for elimination of leakage in weakly nonlinear qubits
• Keeping a Quantum Bit Alive by Optimized $\pi$-Pulse Sequences
• Fault-Tolerant Quantum Dynamical Decoupling
• Direct Fidelity Estimation from Few Pauli Measurements
• Introduction to Quantum Electromagnetic Circuits
• Demonstrating a Continuous Set of Two-qubit Gates for Near-term Quantum Algorithms
• Gate Set Tomography
• A fast, low-leakage, high-fidelity two-qubit gate for a programmable superconducting quantum computer
• Reducing unitary and spectator errors in cross resonance with optimized rotary echoes
• Observation of classical-quantum crossover of 1/f flux noise and its paramagnetic temperature dependence
• Diabatic gates for frequency-tunable superconducting qubits
• High-fidelity controlled-Z gate with maximal intermediate leakage operating at the speed limit in a superconducting quantum processor
• Observation of separated dynamics of charge and spin in the Fermi-Hubbard model
• Accurately computing electronic properties of a quantum ring
• Hamiltonian tomography for quantum many-body systems with arbitrary couplings
• Experimental demonstration of cheap and accurate phase estimation
• Constructive Quantum Shannon Decomposition from Cartan Involutions
• Characterizing non-Markovian Off-Resonant Errors in Quantum Gates
• Context Aware Fidelity Estimation

Cited by in corpus (7)

• Benchmarking quantum gates and circuits
• Efficient Chromatic-Number-Based Multi-Qubit Decoherence and Crosstalk Suppression
• Optimal Low-Depth Quantum Signal-Processing Phase Estimation
• Virtual Z gates and symmetric gate compilation
• Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device
• The surface code beyond Pauli channels: Logical noise coherence, information-theoretic measures, and errorfield-double phenomenology
• Sparse Non-Markovian Noise Modeling of Transmon-Based Multi-Qubit Operations