In principle, quantum key distribution (QKD) offers information-theoretic security based on
the laws of physics. In practice, however, the imperfections of realistic devices might …

Bell's 1964 theorem, which states that the predictions of quantum theory cannot be
accounted for by any local theory, represents one of the most profound developments in the …

Abstract Quantum key distribution (QKD),–is a theoretically secure way of sharing secret
keys between remote users. It has been demonstrated in a laboratory over a coiled optical …

More than 50 years ago, John Bell proved that no theory of nature that obeys locality and
realism can reproduce all the predictions of quantum theory: in any local-realist theory, the …

Quantum cryptography promises levels of security that are impossible to attain in a classical
world. Can this security be guaranteed to classical users of a quantum protocol, who may …

We present a source of entangled photons that violates a Bell inequality free of the “fair-
sampling” assumption, by over 7 standard deviations. This violation is the first reported …

The violation of a Bell inequality is an experimental observation that forces the
abandonment of a local realistic viewpoint—namely, one in which physical properties are …

These lecture notes grew out of a course on quantum key distribution taught at Leibniz
Universität Hannover during the summer term of 2020 as part of the physics master's …

Bell inequalities are intended to show that local realist theories cannot describe the world. A
local realist theory is one where physical properties are defined prior to and independent of …

Nonlocality was discovered by John Bell in 1964, in the context of the debates about
quantum theory, but is a phenomenon that can be studied in its own right. Its observation …