A Reconfigurable Quantum Local Area Network Over Deployed Fiber (2102.13596v1)

Abstract: Practical quantum networking architectures are crucial for scaling the connection of quantum resources. Yet quantum network testbeds have thus far underutilized the full capabilities of modern lightwave communications, such as flexible-grid bandwidth allocation. In this work, we implement flex-grid entanglement distribution in a deployed network for the first time, connecting nodes in three distinct campus buildings time-synchronized via the Global Positioning System (GPS). We quantify the quality of the distributed polarization entanglement via log-negativity, which offers a generic metric of link performance in entangled bits per second. After demonstrating successful entanglement distribution for two allocations of our eight dynamically reconfigurable channels, we demonstrate remote state preparation -- the first realization on deployed fiber -- showcasing one possible quantum protocol enabled by the distributed entanglement network. Our results realize an advanced paradigm for managing entanglement resources in quantum networks of ever-increasing complexity and service demands.

• The paper presents a reconfigurable quantum network that dynamically allocates entanglement using an eight-channel photon source and wavelength-selective switches.
• The paper showcases performance metrics of up to 56 ± 6 ebits/s and over 92% fidelity, highlighting efficient and robust bandwidth provisioning.
• The paper implements remote state preparation across spatially separated nodes, paving the way for scalable quantum communications and future quantum internet infrastructures.

A Reconfigurable Quantum Local Area Network Over Deployed Fiber

The paper presented here discusses the development and experimental implementation of a reconfigurable quantum local area network (QLAN) utilizing deployed optical fibers. In the context of quantum networks, the capacity to dynamically allocate and manage quantum resources is imperative for the scalable and effective distribution of quantum information. The paper advances the domain by integrating flex-grid lightwave technology—commonly used in conventional optical communications—into quantum network testbeds for the first time, enhancing the dynamic allocation of resources across the network.

Highlights and Methodology

The research harnesses an eight-channel polarization-entangled photon source. This source facilitates multiple configurations of channel allocations across three spatially separated nodes, set across buildings on a campus and interconnected through fiber optics. The network leverages the capabilities of a wavelength-selective switch (WSS) for dynamic bandwidth provisioning, which allows the reallocation of entanglement resources without physical reconfiguration of the network. The nodes, synchronized using GPS time signals, are capable of background-free detections, thereby enhancing the fidelity of distributed entanglement.

The efficacy of entanglement distribution is quantified using log-negativity, which allows researchers to gauge the link performance in terms of entangled bits per second (ebits/s). The paper demonstrates successful entanglement distribution over various network configurations with up to eight channel pairs, highlighting the significant spectral differentiation enabled by flex-grid entanglement distribution.

Furthermore, the paper accomplished remote state preparation (RSP) across the deployed network. RSP simplifies the conventional quantum teleportation protocol, capitalizing on the non-classical correlations of the entangled pairs to prepare a quantum state remotely at another node. This achievement underscores one potential quantum communication protocol enabled by the developed QLAN, marking the first such demonstration over a deployed fiber setup.

Key Results

1. Dynamic Bandwidth Allocation: The network supports on-demand reconfiguration of entanglement resources, adapting to user requirements without added operational complexity. The dynamic allocation fosters the ability to balance the entanglement distribution among varied links actively.
2. Performance Metrics: The paper introduces a combined measurement of both the fidelity of quantum states and the quantity of entanglement available—expressed in entangled bits per second. For instance, the A–B link achieves an entanglement rate of 56 ± 6 ebits/s under one configuration, proving the system's effectiveness for practical deployments.
3. Robustness and Stability: The results indicate that even modest adjustments to the network configuration—such as altering the bandwidth allocation—result in quantifiable differences in network performance. The accidentals-subtracted fidelity reaches over 92% across configurations, indicating that reducing background noise remains an area for potential optimization.

Implications and Future Outlook

This paper's contributions have practical and theoretical implications for the development of broader quantum networks and future quantum internet infrastructures. The integration of flex-grid technology into quantum network setups denotes a significant step towards handling the growing complexity and service demands of quantum networks. It offers an adaptable framework to equip resilient quantum networks capable of interconnecting nodes over varying distances and configurations.

Unique to this approach is the scalability implied by potentially nesting multiple WSS units to create expansive networks, which would further optimize the management of entanglement distribution over broad and diverse quantum resources. The architecture resonates with the layered model of classical networks, providing a strategic blueprint for inter-network communications and, ultimately, a genuine quantum internet.

From a broader perspective, this research raises intriguing questions about the optimal metrics for evaluating quantum networks' performance. The adoption of concepts paralleling quantum volume from quantum computing to quantum networking could help unify performance characteristics into a singular determinant, aiding in the objective assessment and comparison of future quantum communication infrastructures.