# Deterministic entanglement swapping in a superconducting circuit

## TL;DR

This paper demonstrates a high-fidelity, deterministic entanglement swapping in a superconducting circuit, including delayed-choice experiments, advancing quantum communication and fundamental quantum mechanics understanding.

## Contribution

It reports the first deterministic entanglement swapping with delayed-choice in superconducting circuits, confirming entanglement transfer and duality.

## Key findings

- Concurrence above 0.75 confirms high-quality entanglement transfer.
- First demonstration of deterministic delayed-choice entanglement swapping.
- Shows entanglement-separability duality in a superconducting circuit.

## Abstract

Entanglement swapping, the process to entangle two particles without coupling them in any way, is one of the most striking manifestations of the quantum-mechanical nonlocal characteristic. Besides fundamental interest, this process has applications in complex entanglement manipulation and quantum communication. Here we report a high-fidelity, unconditional entanglement swapping experiment in a superconducting circuit. The measured concurrence characterizing the qubit-qubit entanglement produced by swapping is above 0.75, confirming most of the entanglement of one qubit with its partner is deterministically transferred to another qubit that has never interacted with it. We further realize delayed-choice entanglement swapping, showing whether two qubits previously behaved as in an entangled state or as in a separable state is determined by a later choice of the type of measurement on their partners. This is the first demonstration of entanglement-separability duality in a deterministic way.