laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

Séminaire 3 septembre 2012

Jacek Kasprzak (Institut Néel, Grenoble, France)
Exploring coherence of individual emitters in a solid

Individual localized emitters embedded in a solid state matrix, like excitons confined in quantum dots, represent a model system for testing solid state quantum information processing schemes. A prerequisite of such activity is an accurate measurement, manipulation and modeling of coherent, nonlinear responses of single excitons.

The term “coherence” usually relates to the presence of a spatio-temporal phase relation within the physical field, which commonly is manifested by the appearance of an interference pattern. Conversely, quantum emitters are localized on sub-wavelength areas, and, as such, are not capable of producing spatially extended interferences. In the first part of this lecture I will present an intriguing and unique concept of retrieving coherence properties of individual emitters. This breakthrough was achieved with heterodyne spectral interferometry technique [1] allowing the retrieval of resonant nonlinear responses, like four-wave mixing (FWM).

In the second part I will highlight our recent advances in the FWM spectroscopy of a single, strongly-confined exciton-biexciton system [2]. I will discuss homogenous and inhomogeneous broadening and dephasing mechanisms of an exciton transition. I will report on observation of phonon-induced dephasing and polaron formation in a single quantum dot. I will present text-book examples of coherent dynamics, time-resolved
polarization state and polarization selection rules.
For the remaining part I will consider an individual exciton strongly-coupled with a photon mode of a pillar microcavity. By performing FWM spectroscopy I will demonstrate the Jaynes-Cummings nonlinearlity in this system [3]. Specifically, I will show that the polariton splitting increases as a square-root of number of photons present in the cavity.
As an outlook, I will discuss the prospects of quantum bus technology employing semiconductor nanostructures.

[1] W. Langbein and B. Patton Opt. Lett. 31, 1738 (2006)
[2] J. Kasprzak et al. to be published
[3] J. Kasprzak et al. Nature Mater. 9, 304 (2010).