Controlling spontaneous emission from quantum dots by modified vacuum fluctuations

Contacts:

Henri Thyrrestrup Nielsen, DTU Fotonik, 4525 3772 (henri.nielsen@fotonik.dtu.dk)

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

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

Upper: Atomic force microscopy image of a layer of quantum dots grown on a semiconductor surface. Lower: Two decay curves measured for quantum dots located at two different distances to an interface showing a pronounced difference in the decay rates.

In this project, spontaneous emission of light from semiconductor quantum dots will be investigated. Quantum dots are nanometre-sized ‘artificial atoms’ located inside a semiconductor material that just like ordinary atoms can spontaneously emit photons once at a time (a single-photon source). Spontaneous emission is a quantum optics phenomenon and photon emission occurs due to the presence of vacuum fluctuations that stimulate the decay of the quantum dot. This has remarkable consequences. Thus spontaneous emission is not an immutable property of the quantum dot, but can be controlled by nano-structuring the material surrounding the quantum dot. The nano-structuring of the surrounding medium modifies locally the density of vacuum fluctuations, and thus provides a technique to control spontaneous emission.

In this experimental project, you will measure spontaneous emission from quantum dots embedded in nano-structured photonic media. By modifying the vacuum fluctuations, the decay rate of spontaneous emission will be altered. Various nanophotonic structures are used for controlling spontaneous emission in our group, including interfaces, photonic crystals, and nano-cavities and waveguides. The planer interface has the significant advantage that the density of vacuum fluctuations can be calculated exactly, and this means that it can be employed to obtain knowledge about the internal dynamics of the quantum dot. In this experiment, spontaneous emission decay curves (for examples of decay curves see the inserted figure) will be measured for a range of different distances to the interface. Depending on the distance to the interface, the quantum dot decay will be speeded up or slowed down. By comparing the measured decay rate versus distance to theory we can extract the fundamental light-matter coupling strength determining the interaction of quantum dots with nanophotonic structures.