Detecting bit-flip errors in a logical qubit using stabilizer measurements

TLDR

Quantum data are vulnerable to decoherence and hardware errors, and fault‑tolerant quantum computers will use quantum error correction to protect against them; in the smallest codes a logical qubit is encoded in a subspace of multiple physical qubits, and stabilizers—non‑demolition multi‑qubit measurements—discretize and signal physical qubit errors without collapsing the encoded information. The study aims to realize the two parity stabilizer measurements of the three‑qubit repetition code that protects a logical qubit from physical bit‑flip errors on a five‑qubit superconducting processor. This is achieved by performing the two parity measurements on the five‑qubit device, thereby demonstrating the stabilizer operations required for the repetition code. The demonstration, though limited by current coherence times and block lengths, marks a critical step toward larger codes based on multiple parity measurements.

Abstract

Abstract Quantum data are susceptible to decoherence induced by the environment and to errors in the hardware processing it. A future fault-tolerant quantum computer will use quantum error correction to actively protect against both. In the smallest error correction codes, the information in one logical qubit is encoded in a two-dimensional subspace of a larger Hilbert space of multiple physical qubits. For each code, a set of non-demolition multi-qubit measurements, termed stabilizers, can discretize and signal physical qubit errors without collapsing the encoded information. Here using a five-qubit superconducting processor, we realize the two parity measurements comprising the stabilizers of the three-qubit repetition code protecting one logical qubit from physical bit-flip errors. While increased physical qubit coherence times and shorter quantum error correction blocks are required to actively safeguard the quantum information, this demonstration is a critical step towards larger codes based on multiple parity measurements.