[Paper Review] Qubit teleportation between non-neighboring nodes in a quantum network

Sophie Hermans, Matteo Pompili+4 more|arXiv (Cornell University)|Oct 21, 2021

Quantum Information and Cryptography4 citations

TL;DR

This paper demonstrates deterministic quantum teleportation between non-neighboring nodes in a solid-state quantum network using three nitrogen-vacancy (NV) centers in diamond. By entanglement swapping via a middle node and employing tailored heralding, basis-alternating repetitive readout, and active memory protection, the authors achieve teleportation fidelity above the classical limit (0.702 ± 0.011) with unit efficiency, marking a key step toward scalable quantum networks.

ABSTRACT

Future quantum internet applications will derive their power from the ability to share quantum information across the network. Quantum teleportation allows for the reliable transfer of quantum information between distant nodes, even in the presence of highly lossy network connections. While many experimental demonstrations have been performed on different quantum network platforms, moving beyond directly connected nodes has so far been hindered by the demanding requirements on the pre-shared remote entanglement, joint qubit readout and coherence times. Here we realize quantum teleportation between remote, non-neighboring nodes in a quantum network. The network employs three optically connected nodes based on solid-state spin qubits. The teleporter is prepared by establishing remote entanglement on the two links, followed by entanglement swapping on the middle node and storage in a memory qubit. We demonstrate that once successful preparation of the teleporter is heralded, arbitrary qubit states can be teleported with fidelity above the classical bound, even with unit efficiency. These results are enabled by key innovations in the qubit readout procedure, active memory qubit protection during entanglement generation and tailored heralding that reduces remote entanglement infidelities. Our work demonstrates a prime building block for future quantum networks and opens the door to exploring teleportation-based multi-node protocols and applications.

Motivation & Objective

• To enable reliable long-distance quantum information transfer across lossy quantum networks by extending teleportation beyond directly connected nodes.
• To overcome the challenges of pre-shared entanglement fidelity, joint qubit measurement, and coherence time limitations in multi-node quantum networks.
• To implement a scalable, heralded teleportation protocol using solid-state spin qubits with integrated memory and optical links.

Proposed method

• Entanglement is generated between neighboring nodes (Alice-Bob and Bob-Charlie) using a single-photon protocol with phase-stabilized optical links.
• Entanglement swapping is performed on Bob’s node to create remote entanglement between Alice and Charlie, forming the teleporter.
• Basis-alternating repetitive (BAR) readout is used to improve memory qubit fidelity and reduce readout errors.
• Tailored heralding protocols are implemented to minimize false positives from double excitation and $\\\ket{0}$ state occupancy.
• Active memory protection during entanglement generation suppresses decoherence and improves fidelity.
• Conditional Bell-state measurement is performed on Charlie’s communication and memory qubits, followed by feed-forward operations on Alice to complete teleportation.

Experimental results

Research questions

• RQ1 Can quantum teleportation be achieved between non-neighboring nodes in a solid-state quantum network with high fidelity and unit efficiency?
• RQ2 How can remote entanglement fidelity be preserved and enhanced in the presence of double excitation and $\\\ket{0}$ state occupancy errors?
• RQ3 To what extent do tailored heralding and BAR readout improve teleportation fidelity and experimental rate in multi-node networks?
• RQ4 What is the impact of memory qubit coherence and joint qubit measurement on teleportation performance?
• RQ5 Can deterministic teleportation be achieved with real-time feed-forward in a network with lossy photonic channels?

Key findings

• The average teleportation fidelity for arbitrary input states reached 0.702 ± 0.011, exceeding the classical bound of 2/3.
• Teleportation fidelity for specific Pauli eigenstates ranged from 0.651 ± 0.027 (−Y) to 0.760 ± 0.024 (X), with superposition states achieving 0.4936 ± 0.0019 fidelity.
• The use of basis-alternating repetitive (BAR) readout increased memory qubit readout fidelity, reducing inconsistent patterns to below 1% with 10 repetitions.
• Tailored heralding reduced remote entanglement infidelity, contributing to a combined two-node link fidelity of 0.808 ± 0.017.
• The experimental rate was improved to 1 teleportation per 74 seconds with all innovations, compared to 1 per 53 seconds in the baseline.
• Simulations show that combining all error sources leads to a total infidelity of 0.305, but experimental fidelity remains above classical limits due to error mitigation.