Abstract
Information exchange requires a measurement of physical states. Because quantum measurements enable accuracy beyond the classical shot-noise limit, they are successfully used to develop measurement tools and applications. In particular, quantum-measurement-enhanced strategies are used for the discrimination of nonorthogonal coherent states. The efficient discrimination of these states is crucial for optical communication networks, that are now approaching the classical limits of the underlying physical systems. However, quantum-enhanced discrimination strategies demonstrated to date are based on legacy communication protocols designed for classical measurements and thus provide only a limited advantage. In our work, we use photon detection times readily available in quantum measurement, but not accessible by classical means. We measure and use these times to maximize our knowledge about faint nonorthogonal coherent states. We employ communication strategies designed to benefit most from this knowledge. This holistic approach in our experiment has resulted in the record low error rates in discrimination of multiple faint nonorthogonal coherent states carrying energy corresponding to just one photon per bit of transmitted information. We demonstrate successful discrimination of large alphabets of optical states () beyond the ideal classical shot-noise limit, showing the scalability of quantum-measurement-enabled communication. This experimental work explores unforeseen advantages of quantum measurement on one hand, and may help address the capacity crunch in modern optical networks caused by the exponential growth of data exchange on the other.
- Received 27 November 2019
- Accepted 28 August 2020
DOI:https://doi.org/10.1103/PRXQuantum.1.010308
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The connection between information and physics is now well-established. To communicate, one must measure and distinguish different states of a physical system used to store and/or transmit information. Exabytes of information are sent through the Internet monthly, and the demand grows exponentially. The need for energy-efficient communication is universally recognized, driving research efforts for more efficient networks. However, networks are reaching their limits caused by inherent limitations of classical measurements, and only incremental progress is currently possible. Quantum measurements offer many advantages over classical measurements and could help alleviate these limitations. Particularly, quantum measurement-enabled receivers allow energy efficiency beyond the classical limits. Until now, quantum receivers used communication schemes that were originally developed for classical measurement methods.
In our work, we identified information readily available in quantum measurement, but not accessible by classical means. We found a way to harness this additional information about quantum states. The result is the first experimental demonstration of a holistic quantum-enabled communications scheme with record energy efficiency. We report the lowest error rates in discrimination of multiple optical states carrying energy corresponding to just one photon per bit of transmitted information. We demonstrate discrimination of a large number of optical states beyond ideal classical limits, showing the scalability of quantum measurement-enabled communication for the first time. Our holistic approach may be of interest to a wide range of research that employs quantum measurement: from communications and astronomy to biophotonics and microscopy.