High Bandwidth Squeezed States of Light

Two-mode squeezed states of light can be utilized to distribute a quantum key that allows for arbitrary secure communication, regardless of the level of even future technology. High transmission rates for the secret quantum key are achieved via large squeezing factors as well as a high squeezing bandwidth. While the first improves the measured bits per sample, the latter allows for a higher sample measuring rate per second. The generation of high bandwidth squeezed light with a strong non-classical noise suppression is implemented to address both topics.


Quantum Up-Conversion

Quantum up-conversion is a versatile tool in today’s quantum optics experiments. It has the potential to overcome frequency differences between disparate subsystems within a quantum information network. Today, the generation and fibre-based transmission of nonclassical states of light are most efficient at near infra-red wavelengths, for instance at the telecommunication wavelength of 1550 nm. Future quantum memories based on trapped atoms, ions or atomic ensembles will potentially use shorter wavelengths, up to the visible spectrum. Furthermore, the up-conversion into the visible regime enables the efficient detection of infrared single photons with commercially available, low-noise and easy-to-handle silicon avalanche photodetectors.


Entanglement Distribution with Separable States

Entanglement is a fundamental resource for quantum information processing. Usually, the distribution of bipartite entanglement is performed by generating the entangled modes at one place and sending one of the modes to a distant party. Thereby, the mode sent from A to B is obviously entangled with the mode kept by A. It was theoretically shown that if more than two modes are involved, bipartite entanglement can also be distributed by sending fully separable states. This remarkable and seemingly paradoxical protocol is made possible by a specific structure of quantum correlations within an underlying state of three modes A, B, and C.


Squeezed Light for GEO600

Since 2007, the Quantum Interferometry Group has been tackling the task of designing and fabricating the first squeezed light laser for gravitational wave (GW) detectors, and bringing it into application in GEO600.

Laser Interferometry and Nonclassical Light

The sensitivity of laser interferometers is limited by the quantum noise of light. The quantum noise can be reduced and laser interferometers be improved by using squeezed light.

Quantum Information

Nonclassical states of light cannot be described by a (classical) probability distribution of coherent states. In other words: in nonclassical states of light the photons are not independent from each other but rather show quantum correlations. This property can be used in quantum information protocols in order to outperform any classical protocol.

Laser Interferometry and Nano-Structured Optics

Mirrors and beam splitters with nano-structured surfaces have applications in high-precision interferometry. A reflection grating can be used to couple a laser beam into a high-finesse resonator without transmitting the light through an optical material. Nano-structured surfaces can also replace multilayer dielectric anti- or high-reflectivity coatings.


A light field can couple to the motion of a mechanical oscillator through its radiation pressure. Recent research has shown that this coupling can be used to generate and observe quantum mechanical properties of mechanical devices being visible to the naked eye.

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