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3. Physikalisches Institut

Open positions

Opportunity to participate and contribute to research on applicative quantum science

Master/Bachelor Thesis

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Solid state lasers are the working horses of todays science. Current trends in minituarizing lasers as well as scaling the number of laser sources up to very high numbers led to the idea of multiple microscale photonic sources on the same chip. Current project is devoted to creation of on-chip Ti: Sapphire microlaser and assessing its performance. The flow of the project is as follows:

  • titanium ions are implanted into sapphire,
  • titanium dioxide thin film is deposited on the surface of the surface of the latter and
  • shaped by a combination of lithography and plasma etching to form the optical resonator (the implanted Ti ions are coupled to the resonator evanascently),
  • finally, the performance of the produced device is tested in one of our confocal microscopes.

This project is the first step towards on-chip single photon sources for quantum telecommunication.

 Contact
Dr. Roman Kolesov

The highly sensitive determination of localized magnetic fields has a counterpart in microscopy. With defined magnetic fields, such as nanoscopic magnetic beads, we are able to determine the location of a single sensing counterpart, e.g. an NV- center in diamond. Here, a magnetic bead is scanned above the sample under study and when a resonance condition is fulfilled, concentric rings around the emitter can be detected [1,2,3]. At present, it is not entirely clear how the best localization accuracy can be achieved. Parameters such as pixel size, orientation, scanning speed, etc. have to be determined.

For this we will perform Monte-Carlo simulations, i.e. we simulate artificial images and determine the localization accuracy in respect to a variety of parameters.

 Tasks: Calculations in Mathematica, utilizing a pre-written Monte-Carlo tool-kit, earlier utilized in [2].

If you like this project: Ilja Gerhardt

[1] G. Balasubramanian et al., Nature, 455, 648, 2008
[2] I. Gerhardt et al., Physical Review A, 82, 063823, 2010
[3] M. S. Grinolds et al., Nature Physics, 7, 687, 2011

Single molecules and other nanoscopic quantum emitters often emit as a single dipole [1]. The emission pattern can be highly modified, when the emitter is embedded in a dielectric medium and the dielectric environment is not entirely homogeneous [2]. Therefore, it is also possible to determine the location and the orientation of a single emitter, when the emitted light is thoroughly analyzed [3]. Since the math is described in literature, we like to determine the possibility of orientational imaging a single NV- center, which has instead of a single transition dipole two emitting orientations.

Furthermore, an exact determination of the emission pattern can allow for a highly efficient collection efficiency in single emitter experiments [4].

Tasks: Calculations in Mathematica, calculating the emission pattern in and above thin dielectric slabs. Ideally to a) determine the exact orientation of a dipolar emitter and b) allowing an estimation on the exact collection efficiency.

If you like this project: Ilja Gerhardt

[1] L. Novotny and B. Hecht, Principles of Nano-optics, Chapter 10, Cambridge Uni. Press, 2008
[2] W. Lukosz and R. E. Kunz, JOSA, 67, 1615, 1977
[3] M. A. Lieb et al., JOSA B, 21, 6, 1210, 2004
[4] K. G. Lee et al., Nature Photonic, 5, 166, 2011

The usual scheme of detecting a single molecule is the detection of the Stokes shifted emission [1]. Commonly, optical long-pass filters are used for this task. Since a single molecule might also act as a single dipolar emitter, it also might be possible to detect a single molecule with two crossed polarizers and with an orientation with 45 degree out of the excitation wave. Experimentally, this has been performed at cryogenic conditions, where the optical properties of a single emitter are very good [2]. Here, a single molecule acts as a mode converter from the incident light towards the detected light. Earlier attempts at ambient conditions seem to have failed, since no high-NA objectives have been used [3].

We like to estimate the required extinction ratio and setup a simple single molecule experiment (basically a confocal microscope), which aims to detect single molecules without the need of any spectral filtering.

Tasks: Estimations to understand the requirements for this detection scheme. Setup and modification of an existing single molecule setup.

If you like this project: Ilja Gerhardt

[1] S. Weiss, Science, 283, 1676, 1999
[2] G. Wrigge, Nature Physics, 4, 60, 2008
[3] J. Hwang, Physical Review A, 73, 021802®, 2006

In extinction type experiments, the coherent scattering of a single emitter and the incident light are interfering destructively, such that the light is `swallowed' by the emitter. When the Poynting vector is plotted [1] (see also Fig. 1), one gets an intuitive insight in the path-way of light traveling towards the emitter and also one gets a `shadow' in the far-field [2]. Careful calculations [3,4] allow the estimation, that e.g. a single atom or molecule might perfectly reflect the light back to the source. These calculations were performed with a number of simplifications.

Since a couple of years, this kind of physics is also accessible in experiments [5,6]. We like to gain insight in the influencing parameters how to optimize the light-matter interaction on a nanoscopic scale.

Motivated students who are interested to join the Volkmer Lab in order to conduct scientific research for their thesis project are strongly encouraged to apply. Applicants should have a basic knowledge of ultrafast laser physics, nonlinear spectroscopy or quantum optics. A vital interest in macromolecular Biophysics is very helpful.
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Contact:
Dr. A. Volkmer