Abstract
A primary requirement for a robust and unconditionally secure quantum network is the establishment of quantum nonlocal correlations over a realistic channel. While loophole-free tests of Bell nonlocality allow for entanglement certification in such a device-independent setting, they are extremely sensitive to loss and noise, which naturally arise in any practical communication scenario. Quantum steering relaxes the strict technological constraints of Bell nonlocality by reframing it in an asymmetric manner, with a trusted party only on one side. However, tests of quantum steering still require either extremely high-quality entanglement or very low loss. Here we introduce a test of quantum steering that harnesses the advantages of high-dimensional entanglement to be simultaneously noise robust and loss tolerant. Despite being constructed for qudits, our steering test is designed for single-detector measurements and is able to close the fair-sampling loophole in a time-efficient manner. We showcase the improvements over qubit-based systems by experimentally demonstrating quantum steering in up to 53 dimensions, free of the fair-sampling loophole, through simultaneous loss and noise conditions corresponding to 14.2-dB loss equivalent to 79 km of telecommunication fiber, and 36% of white noise. We go on to show how the use of high dimensions counterintuitively leads to a dramatic reduction in total measurement time, enabling a quantum steering violation almost 2 orders of magnitude faster obtained by simply doubling the Hilbert space dimension. Our work conclusively demonstrates the significant resource advantages that high-dimensional entanglement provides for quantum steering in terms of loss, noise, and measurement time, and opens the door toward practical quantum networks with the ultimate form of security.
- Received 26 April 2022
- Revised 29 September 2022
- Accepted 21 October 2022
DOI:https://doi.org/10.1103/PhysRevX.12.041023
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)
synopsis
Quantum Steering That’s Robust to Loss and Noise
Published 30 November 2022
Researchers demonstrate a loss-tolerant method for so-called quantum steering, a phenomenon that could give quantum communication networks complete security.
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Popular Summary
Quantum entanglement enables the most secure form of communication possible—one where the communication devices themselves can be in the hands of an adversary, and security is still guaranteed. However, distributing entanglement over long distances and through a noisy environment is not easy. Entangled photons can be lost while propagating through fibers, and detectors can be compromised by large amounts of noise. As a result, tests of quantum nonlocality—the most stringent form of entanglement—have been performed only under very controlled conditions. Quantum steering relaxes the strict requirements of nonlocality by assuming an untrusted device only on one side of an untrusted channel. In our work, we harness the advantages of high-dimensional entanglement to demonstrate quantum steering with the detection loophole closed under extreme conditions of noise and loss.
We develop a new test of quantum steering that requires only a single detector at each end, regardless of the dimension of the entanglement used. Using this test, we “steer” entanglement through loss equivalent to that encountered in 79 km of telecom fiber amidst white noise that makes up 36 percent of the signal probability. Remarkably, our technique also leads to a dramatic reduction in the total measurement time needed: By simply doubling the entanglement dimensionality, we reduce the measurement time by almost 2 orders of magnitude.
Our work demonstrates that the fundamental phenomenon of entanglement can indeed transcend the limits imposed by a realistic environment and opens a clear pathway toward quantum communication protocols with unconditional security.