Randomness Extraction from Bell Violation with Continuous Parametric Down-Conversion.

We present a violation of the Clauser-Horne-Shimony-Holt inequality without the fair sampling assumption with a continuously pumped photon pair source combined with two high efficiency superconducting detectors. Because of the continuous nature of the source, the choice of the duration of each measurement round effectively controls the average number of photon pairs participating in the Bell test. We observe a maximum violation of S=2.

A universal setup for active control of a single-photon detector.

The influence of bright light on a single-photon detector has been described in a number of recent publications. The impact on quantum key distribution (QKD) is important, and several hacking experiments have been tailored to fully control single-photon detectors. Special attention has been given to avoid introducing further errors into a QKD system.

High quantum-efficiency photon-number-resolving detector for photonic on-chip information processing.

The integrated optical circuit is a promising architecture for the realization of complex quantum optical states and information networks. One element that is required for many of these applications is a high-efficiency photon detector capable of photon-number discrimination. We present an integrated photonic system in the telecom band at 1550 nm based on UV-written silica-on-silicon waveguides and modified transition-edge sensors capable of number resolution and over 40 % efficiency.

Detection of single molecules illuminated by a light-emitting diode.

Optical detection and spectroscopy of single molecules has become an indispensable tool in biological imaging and sensing. Its success is based on fluorescence of organic dye molecules under carefully engineered laser illumination. In this paper we demonstrate optical detection of single molecules on a wide-field microscope with an illumination based on a commercially available, green light-emitting diode.

Experimentally faking the violation of Bell's inequalities.

Entanglement witnesses such as Bell inequalities are frequently used to prove the nonclassicality of a light source and its suitability for further tasks. By demonstrating Bell inequality violations using classical light in common experimental arrangements, we highlight why strict locality and efficiency conditions are not optional, particularly in security-related scenarios.

Full-field implementation of a perfect eavesdropper on a quantum cryptography system.

Quantum key distribution (QKD) allows two remote parties to grow a shared secret key. Its security is founded on the principles of quantum mechanics, but in reality it significantly relies on the physical implementation. Technological imperfections of QKD systems have been previously explored, but no attack on an established QKD connection has been realized so far.

Sagnac-loop phase shifter with polarization-independent operation.

A bulk-optics, polarization-independent phase shifter for photonic quantum information applications is demonstrated. The device is based on a transverse electro-optic modulator in a Sagnac-type loop containing Faraday rotators. This direction-dependent polarization rotation in the loop is combined with a Mach-Zehnder interferometer to form an optical switch with an on/off contrast of 96% and a switching time of 1.

Experimental falsification of Leggett's nonlocal variable model.

Bell's theorem guarantees that no model based on local variables can reproduce quantum correlations. Also, some models based on nonlocal variables, if subject to apparently "reasonable" constraints, may fail to reproduce quantum physics. In this Letter, we introduce a family of inequalities, which use a finite number of measurement settings, and which therefore allow testing Leggett's nonlocal model versus quantum physics.

Breaking a quantum key distribution system through a timing side channel.

The security of quantum key distribution relies on the validity of quantum mechanics as a description of nature and on the non-existence of leaky degrees of freedom in the practical implementations. We experimentally demonstrate how, in some implementations, timing information revealed during public discussion between the communicating parties can be used by an eavesdropper to undetectably access a significant portion of the "secret" key.

Experimental quantum cloning of single photons.

Although perfect copying of unknown quantum systems is forbidden by the laws of quantum mechanics, approximate cloning is possible. A natural way of realizing quantum cloning of photons is by stimulated emission. In this context, the fundamental quantum limit to the quality of the clones is imposed by the unavoidable presence of spontaneous emission.

Experimental violation of a spin-1 bell inequality using maximally entangled four-photon states.

We demonstrate the experimental violation of a spin-1 Bell inequality. The spin-1 inequality is based on the Clauser, Horne, Shimony, and Holt formalism. For entangled spin-1 particles, the maximum quantum-mechanical prediction is 2.