Entanglement purification and protection in a superconducting quantum network

TL;DR

This paper demonstrates entanglement purification and protection techniques in a superconducting quantum network, significantly improving entanglement fidelity and coherence times between remote nodes over a short communication cable.

Contribution

It introduces a practical entanglement purification protocol for superconducting qubits over a 1-meter cable, enhancing fidelity by up to 25% and employing noise protection methods to extend qubit coherence.

Findings

Fidelity increased by up to 25% after purification.

Achieved a maximum fidelity of approximately 94%.

Extended qubit dephasing time fourfold using dynamical decoupling and Rabi driving.

Abstract

High-fidelity quantum entanglement is a key resource for quantum communication and distributed quantum computing, enabling quantum state teleportation, dense coding, and quantum encryption. Any sources of decoherence in the communication channel however degrade entanglement fidelity, thereby increasing the error rates of entangled state protocols. Entanglement purification provides a method to alleviate these non-idealities, by distilling impure states into higher-fidelity entangled states. Here we demonstrate the entanglement purification of Bell pairs shared between two remote superconducting quantum nodes connected by a moderately lossy, 1-meter long superconducting communication cable. We use a purification process to correct the dominant amplitude damping errors caused by transmission through the cable, with fractional increases in fidelity as large as $25\%$, achieved for higher damping errors. The best final fidelity the purification achieves is $94.09\pm 0.98\%$. In addition, we use both dynamical decoupling and Rabi driving to protect the entangled states from local noise, increasing the effective qubit dephasing time by a factor of 4, from $3~\rm \mu s$ to $12~\rm\mu s$. These methods demonstrate the potential for the generation and preservation of very high-fidelity entanglement in a superconducting quantum communication network.