We study a class of receiver-device-independent quantum key distribution protocols based on a prepare-and-measure setup which aims to simplify their implementation. The security of the presented protocols relies on the assumption that the sender, Alice, prepares states that have limited inner-products. Hence, Alice’s device is partially characterized. There is no explicit bound on the Hilbert space dimension required. The receiver’s, Bob’s, device demands no characterization and can be represented as a black-box. The protocols are therefore immune to attacks on Bob’s device, such as blinding attacks. The users can generate a secret key while monitoring the correct functioning of their devices through observed statistics. We report a proof-of-principle demonstration, involving mostly off-the-shelf equipment, as well as a high-efficiency superconducting nanowire detector. A positive key rate is demonstrated over a 4.8 km low-loss optical fiber with finite-key analysis.
We derive an explicit condition that determines whether in a noisy quantum frequency estimation problem
the estimation precision of the most general adaptive quantum metrological protocol cannot reach the
Heisenberg-like scaling. The condition is a simple algebraic statement on a relation between the Hamiltonian operator representing the unitary part of the dynamics and the noise operators appearing in the quantum Master equation, and does not require any finite-time integration of the dynamics. In particular these results allow us to understand when application of quantum error correction protocols in order to recover the Heisenberg scaling in quantum metrology is not possible. Additionally, we provide methods to obtain quantitative bounds on achievable precision in the most general adaptive quantum metrological models. Finally, we apply the newly developed tools to prove fundamental bounds in atomic interferometry with many-body effects such as many body losses as well as models involving many-body terms in the Hamiltonian part of the dynamics commonly referred to as non-linear quantum metrology.
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