Qubit teleportation between non-neighboring nodes in a quantum network (2110.11373v1)

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.

• The paper introduces a protocol for remote qubit teleportation using entanglement swapping at an intermediary node, achieving fidelities exceeding 0.7.
• It employs an enhanced readout technique and decoupling pulses to improve memory coherence and ensure robust qubit measurements.
• The results pave the way for scalable quantum networks by extending teleportation beyond directly connected nodes with practical error mitigation.

Qubit Teleportation Between Non-Neighboring Nodes in a Quantum Network

This paper presents a significant paper in quantum networks, demonstrating the successful implementation of qubit teleportation between non-neighboring nodes. The network consists of three optically connected nodes with solid-state spin qubits, specifically using nitrogen-vacancy (NV) centers in diamond. This research addresses the challenge of extending quantum teleportation beyond directly connected nodes, which has been a critical hurdle due to the complex requirements for entanglement, coherence, and readout.

The methodology employed involves setting up remote entanglement across two links, followed by entanglement swapping at an intermediary node, Bob, with the states stored in a memory qubit. Subsequently, arbitrary qubit states can be teleported between these non-neighboring nodes, achieving fidelities that surpass classical limitations even under unit efficiency conditions.

Innovations and Results

Key innovations support the discussed teleportation protocol:

1. Enhanced Qubit Readout: A basis-alternating repetitive readout method was developed, allowing for near-deterministic memory qubit measurement by alternating between computational basis states. This notably improved readout fidelity and reduced asymmetry, a critical enhancement for scaling protocols with multiple readout operations.
2. Memory Qubit Coherence: The application of decoupling pulses and real-time error correction during entanglement attempts significantly improved memory coherence times. This facilitated longer preservation of quantum states amidst noise, enabling a notably larger number of entanglement attempts before state fidelity decoheres below a viable threshold.
3. Error Mitigation in Entanglement Generation: The experimental setup monitors phonon-side band photons for real-time rejection of false heralding signals. This process successfully mitigated double-occupancy and optical excitation errors, increasing the fidelity of the entangled state preparation.

The results achieved include a demonstrated teleportation fidelity of approximately 0.702, surpassing the classical bound of 2/3 by a statistically significant margin. Moreover, the paper claims an unconditional teleportation that exceeds this bound with an average fidelity of around 0.688 for reduced detection windows, indicating robustness for practical implementations.

Implications and Future Directions

The research provides critical foundations for quantum communication, distributed quantum computing, and complex networking protocols. The demonstration of teleportation across non-neighbor nodes underscores the viability of larger-scale quantum networks, crucial for future quantum internet applications.

Future research can focus on refining the optical interface to further increase rates and fidelity, exploring deterministic teleportation protocols, and adapting the demonstrated methods to different quantum hardware platforms such as group-IV color centers or rare-earth ion systems. Implementing scalable and fault-tolerant quantum network nodes with robust qubit interconnectivity remains a key challenge, with implications for developing node architectures that seamlessly integrate with current technological infrastructures.

Overall, this work represents an essential step towards realizing operational quantum networks, offering a framework for ongoing experiments and theoretical advancements in the quantum network domain.