# Entanglement Stabilization using Parity Detection and Real-Time Feedback in Superconducting Circuits

## TL;DR

This paper demonstrates real-time stabilization of entangled states in superconducting circuits by using parity detection and feedback, advancing quantum error correction capabilities.

## Contribution

It introduces an experimental method for stabilizing Bell states through repeated parity measurements and feedback in superconducting qubits, showing improved state fidelity.

## Key findings

- Achieved Bell state stabilization with 74% fidelity over 12 cycles
- Demonstrated real-time feedback effectively maintains entanglement
- Compared real-time stabilization with Pauli frame updating, showing advantages in fidelity retention

## Abstract

Fault tolerant quantum computing relies on the ability to detect and correct errors, which in quantum error correction codes is typically achieved by projectively measuring multi-qubit parity operators and by conditioning operations on the observed error syndromes. Here, we experimentally demonstrate the use of an ancillary qubit to repeatedly measure the $ZZ$ and $XX$ parity operators of two data qubits and to thereby project their joint state into the respective parity subspaces. By applying feedback operations conditioned on the outcomes of individual parity measurements, we demonstrate the real-time stabilization of a Bell state with a fidelity of $F\approx 74\%$ in up to 12 cycles of the feedback loop. We also perform the protocol using Pauli frame updating and, in contrast to the case of real-time stabilization, observe a steady decrease in fidelity from cycle to cycle. The ability to stabilize parity over multiple feedback rounds with no reduction in fidelity provides strong evidence for the feasibility of executing stabilizer codes on timescales much longer than the intrinsic coherence times of the constituent qubits.