Demonstrating Noise-adapted Quantum Error Correction With Break-Even Performance

TL;DR

This paper demonstrates noise-adapted quantum error correction on IBM hardware, achieving break-even logical qubit lifetimes exceeding physical qubits by integrating variational circuits and dynamical decoupling.

Contribution

It introduces a noise-adapted 3-qubit QEC scheme with hardware-efficient circuits that surpasses physical qubit lifetimes on real quantum hardware.

Findings

Logical qubit lifetime exceeds physical qubits after multiple QEC rounds.

Incorporation of dynamical decoupling improves protection against crosstalk.

Performance limited mainly by measurement readout fidelity.

Abstract

The promise of quantum computing is closer to reality today than ever before, thanks to rapid progress in the development of quantum hardware. Even as qubit lifetimes and gate fidelities continue to improve, realizing robust, fault-tolerant quantum computers is contingent upon the successful implementation of quantum error correction (QEC). Conventional QEC schemes have rather high resource overheads and low threshold requirements, making them challenging to implement on present day hardware. Here, we use a recently developed noise-adapted 3-qubit QEC scheme to demonstrate break-even performance against native amplitude-damping (AD) noise on IBM quantum hardware. We use variational quantum circuits to construct hardware-efficient encoding and decoding circuits. This scheme is probabilistic due to the non-unitary nature of the recovery operators, which are implemented via the block-encoding technique. We demonstrate logical qubit lifetimes exceeding those of the physical qubits by performing multiple rounds of QEC. To further protect the qubits from dephasing due to crosstalk, we incorporate dynamical decoupling into our noise-adapted QEC scheme in a seamless fashion. To account for the post-selection overhead, we define a measure of gain, that allows for faithful performance benchmarking of the protocol. Our analysis suggests that the performance of our protocol is limited primarily by the measurement readout fidelity, and is bound to improve with successive generations of quantum processors.