deviceindependent

Device-independent refers to a class of methods and protocols whose security, correctness, or reliability does not depend on trusting the internal workings of the devices involved. Instead, conclusions are drawn from externally observable statistics and general physical principles, such as the no-signaling condition. In quantum information, this approach builds on the idea that certain correlations between distant measurements cannot be explained by local hidden-variable theories, as witnessed by violations of Bell inequalities.

In a device-independent setting, the devices used to prepare, measure, or process quantum systems are treated as black boxes. The main idea is that one can certify desired properties, such as secure key material or genuine randomness, solely from the observed input-output behavior, without assuming a specific implementation. Self-testing is a related concept that aims to infer, from the statistics, that the devices are effectively performing particular quantum states and measurements.

Prominent examples include device-independent quantum key distribution (DI-QKD) and device-independent randomness generation or expansion. The CHSH inequality is a commonly used benchmark: a violation indicates nonlocal correlations and allows parties to bound an eavesdropper’s information under suitable assumptions, typically including no-signaling and the validity of quantum mechanics.

Practical implementation faces significant challenges, including the need to close detection and locality loopholes, achieve high detection efficiencies, and manage noise and finite-key effects. As a result, DI protocols remain predominantly in experimental research with limited key rates, though progress continues toward more robust demonstrations. DI is notably more stringent than measurement-device-independent approaches, which relax some assumptions but retain trust in certain components.