Fidelity of quantum interferometers

Quantum cryptography with polarizing interferometers

In the Ekert cryptographic scheme (E91) [1] pairs of EPR particles were used to generate identical sequences of bits in remote places, while Bell’s theorem certified that the particles were not measured in transit by an eavesdropper. The modification of the Ekert scheme proposed by Bennett, Brassard and Mermin (BBM92) [2] did not use the Bell theorem and was based essentially on the fact that t...

Beating quantum limits in interferometers with quantum locking of mirrors

The sensitivity in interferometric measurements such as gravitationalwave detectors is ultimately limited by quantum noise of light. We discuss the use of feedback mechanisms to reduce the quantum effects of radiation pressure. Recent experiments have shown that it is possible to reduce the thermal motion of a mirror by cold damping. The mirror motion is measured with an optomechanical sensor b...

Quantum-enhanced multiparameter estimation in multiarm interferometers

Quantum metrology is the state-of-the-art measurement technology. It uses quantum resources to enhance the sensitivity of phase estimation over that achievable by classical physics. While single parameter estimation theory has been widely investigated, much less is known about the simultaneous estimation of multiple phases, which finds key applications in imaging and sensing. In this manuscript...

Superconducting Quantum Interferometers for Nondestructive Evaluation

We review stationary and mobile systems that are used for the nondestructive evaluation of room temperature objects and are based on superconducting quantum interference devices (SQUIDs). The systems are optimized for samples whose dimensions are between 10 micrometers and several meters. Stray magnetic fields from small samples (10 µm-10 cm) are studied using a SQUID microscope equipped with a...

Quantum Optical Noise in Advanced LIGO Interferometers