(a) Fiber spools used for realizing a telescoping suite of fiber connections. (b) Entanglement throughput measurements and corresponding capacity estimates by light measurements on a Polatis all-optical switch and at the source and detector.
The Science
News — In quantum networks, the entangled quantum bits per second (ebps) indicates the network’s throughput. Scientists have developed theories to estimate the capacity of quantum connections and the maximum achievable ebps. In this study, researchers collected ebps measurements over a suite of fiber connections on a quantum network testbed. They then compared these measurements with capacity estimates for a conventional fiber-optic network at a range of distances.
The Impact
The study, based on physical measurements and analytical estimates, highlights the difference in throughput due to different underlying transport mechanisms in conventional and quantum networks. It also points to approaches for achieving higher ebps. Throughput is a critical performance metric for connections in both networks. For conventional networks, researchers have extensive analytical and experimental information on throughput. This information helps to design and optimize network infrastructures and protocols. For quantum connections, the new study shows that ebps throughput decays sharply with distance in ways that differ from conventional networks. Specifically, ebps drops faster than a linear decrease (compared to conventional networks). However, ebps drops slower than capacity estimates based on measurements of the intensity of the light traveling through the quantum network’s fiber optic cable.
Summary
The throughput of conventional and quantum network connections is an important performance metric, typically specified by bits per second (bps) and entangled quantum bits per second (ebps), respectively. It is measured over practical connections using specialized methods and estimated using analytical bounds developed by extensive theory. For practical connections, however, bps and ebps are difficult to correlate due to the lack of measurements and estimates derived under well-characterized common conditions. They both differ significantly from the conventional network throughput of Transmission Control Protocol (TCP), which employs buffers and loss recovery mechanisms.
In this study, researchers at Oak Ridge National Laboratory describe a conventional/quantum testbed that enables the comparison of these two quantities both qualitatively and quantitatively. The researchers measured bps and ebps throughput over fiber connections of distances between 0 and 75 kilometers. The measurements show that bps decreases significantly slower with distance than ebps in a qualitatively different way. The analytic capacity estimates of ebps are derived using transmissivity parameters, which in turn are derived from light intensity measurements, and they decrease more rapidly with distance than the measured ebps throughput. These results provide qualitative insights into the conventional transport mechanisms based on buffers, and the conditions used in deriving the analytical ebps capacity estimates.
Funding
This research was performed at Oak Ridge National Laboratory. The research was supported by the Department of Energy, Office of Science, Advanced Scientific Computing Research, under the Entanglement Management and Control in Transparent Optical Quantum Networks project.
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