Quantum optics and multiple scattering

Contacts:

Stephan Smolka, DTU Fotonik, 4525 6875 (stephan.smolka@fotonik.dtu.dk)

Peter Lodahl, DTU Fotonik, 4525 3807 (peter.lodahl@fotonik.dtu.dk)

Quantum Photonics Group: http://www.fotonik.dtu.dk/Quantumphotonics

(a) Intensity speckle pattern created from constructive and destructive interference of light propagating randomly through a multiple scattering medium. (b) Basic components in the experimental setup to investigate the transport of quantum noise through a multiple scattering random medium. The scattered light will be collected with a lens system and imaged onto a highly sensitive photodetector, and the quantum noise is recorded using a spectrum analyser.

Materials such as milk, clouds, and biological tissues owe their appearance to the way they interact with light; by multiple scattering of the incident light beam. Analogous to the Brownian motion of particles in a fluid, light performs a random walk through the material resulting in an intensity speckle pattern after exiting the medium (figure a). Surprisingly, the physical description for the light matter interaction is in all materials alike. It is the basis for applications like enhancing communication capacities or for acoustical and biomedical imaging. So far, researchers focused on a classical description of multiple scattered light, while quantum optics phenomena have not been treated.

In recent years, the research interest in the quantum nature of light has rapidly increased. The quantum properties of light-matter interaction are widely used in research on, e.g., quantum communication or quantum information. In quantum optics, a light source is described by its number of photons and its photon fluctuations, also called the quantum noise. By investigating the photon fluctuations, new phenomena are observed that cannot be explained with a classical description of light. Combining quantum optics and multiple scattering opens a new interdisciplinary research field where fundamentally new multiple scattering phenomena occur that are absent in a classical description.

The aim of this mainly experimental Physics Projects is to perform experiments that probe the quantum properties of multiple scattered light. This project offers a possibility to combine two fields of research, quantum optics and multiple scattering of light, with focus on understanding the underlying physics. In the first part of the project you will investigate the quantum noise of a laser source and learn how to distinguish between the classical and the quantum optical properties of light. The quantum noise will be measured using a sensitive photodetector and spectrum analyser. Furthermore the multiple scattering materials will be characterized, and a detailed study of the quantum noise transmitted through a multiple scattering medium is carried out. Figure b illustrates the main components in an experiment where the quantum noise of the total transmission through a multiple scattering medium is obtained. In addition to total transmission measurements, angular resolved experiments will be performed where quantum noise of the transmitted light is detected versus angle relative to the sample surface. Such measurements give detailed information about how quantum noise is transported through a multiple scattering medium. The experiments will be compared in detail to the quantum theory for multiple scattering.