In addition to the secret-key rate, several other performance metrics can be utilized to compare one-way and multiplexed two-way quantum repeater architectures. These include:
Fidelity of Entangled States: This metric assesses the quality of the entangled states produced by the repeaters. Higher fidelity indicates better performance in maintaining quantum coherence, which is crucial for applications like quantum teleportation and quantum cryptography. The relative performance may shift in favor of architectures that can maintain higher fidelity over longer distances, particularly in the presence of noise.
Latency: The time taken for quantum information to be transmitted from one point to another is critical in practical applications. One-way schemes may exhibit lower latency due to their reliance on deterministic operations, while two-way schemes might incur additional delays from classical communication and distillation processes. However, advancements in multiplexing could mitigate these delays in two-way architectures.
Resource Utilization: This includes the number of qubits, gates, and measurement operations required to achieve a certain level of performance. A lower resource requirement translates to reduced costs and complexity in implementation. The multiplexed two-way protocol may demonstrate superior resource efficiency, particularly in scenarios where high initial fidelity is achievable.
Scalability: The ability to expand the network without significant degradation in performance is vital for practical deployment. Metrics assessing how performance scales with the number of repeaters or distance can provide insights into the long-term viability of each architecture. Two-way schemes may offer better scalability due to their inherent design that allows for parallel operations.
Error Rates: Evaluating the operational and loss error rates associated with each architecture can provide a clearer picture of their robustness. One-way schemes, which rely on error correction, may perform better in environments with high error rates, while multiplexed two-way schemes could excel in low-error scenarios.
The relative performance of these metrics may vary based on the specific application and operational environment, highlighting the importance of a multi-faceted evaluation approach when comparing quantum repeater architectures.