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Quantentechnologie

Dieter Meschedes Forschungsgruppe
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PhD theses

If you are looking for a master's thesis or a bachelor project, please follow the link to the respective page.

Research field:

Trapping single neutral atoms in high finesse optical cavities constitutes one of the foremost frontiers in quantum optics. The realization of strong coherent interactions between trapped atoms and single photons, i.e. atoms coupled to quantized cavity modes, opens new possibilities to explore the quantum realm. Furthermore, it provides novel exciting routes towards quantum communication and quantum information processing in which single atoms exchange quantum information with single photons, leading to the realization of entangled states of matter and light.

In another approach, engineering quantum transport in state-selective optical lattices, i.e. periodic arrays of micro optical traps which depend on the internal atomic state, makes possible to realize coherent interactions between single atoms in a scalable system. Coherent controlled collisions are employed to establish quantum correlations among a preselected group of neutral atoms, resulting in so-called entangled states which are an essential requisite for quantum information science. In addition, systems based on state-selective optical lattice are ideal candidates in which quantum walks—which itself constitutes a new emerging field—of interacting particles can be implemented.

What we offer:

We offer a challenging and international research environment at the forefront of modern physics. The students will be part of a strong team, where they will receive a hands-on experience on cutting-edge research techniques, such as laser cooling and trapping of single atoms, ultra-high vacuum, low-noise electronics, control and automatization systems, data analysis, computer-aided design of optics/electronics/mechanical components, and very importantly, development of independent scientific thinking. Student salaries are available and negotiable. Dissertations are usually completed after three years. The University of Bonn is an equal opportunities employer. Preference will be given to suitably qualified women or handicapped people, all other qualifications and requirements being equal.

What we expect:

We are looking for talented physicists who are highly motivated to acquire a deep knowledge in experimental Atomic Physics and Quantum Optics. We expect from students self-initiative and the ability of pursuing their own scientific ideas. Students should enjoy working in a strong team. Solid background in Solid State physics, Atomic Physics, and Quantum Optics are highly recommended. We also expect students to have received a hands-on experience on an experimental apparatus. Skilled students with either an experimental or theoretical background are welcome. A master’s degree or diploma in Physics is a prerequisite.

How to apply:

Send us a short curriculum vitae with a record of your achievements together together with a motivation letter to either Dr. A. Alberti at Diese E-Mail-Adresse ist gegen Spambots geschützt! JavaScript muss aktiviert werden, damit sie angezeigt werden kann. , or Dr. W. Alt at  Diese E-Mail-Adresse ist gegen Spambots geschützt! JavaScript muss aktiviert werden, damit sie angezeigt werden kann. , or Prof. D. Meschede at Diese E-Mail-Adresse ist gegen Spambots geschützt! JavaScript muss aktiviert werden, damit sie angezeigt werden kann. . We constantly look for talented and passioned students, who are eager to embark on a challenging project with us. You are also very welcome to bring your own ideas, which will be discussed together with the persons responsible. Note: because we continuously receive new applications, applications will be evaluated as they come in.

Proposed topics:

Studying two-atom interactions in state-dependent lattices

The project aims to realize two-atom entangled states through controlled coherent collisions. Atoms stored in a quantum register are selected pairwise and transported to the same sub-micrometer volume, where they interact through coherent cold collisions. Collisional phase shifts can be exploited to realize a universal two-qubit quantum logic gate operating with neutral cold atoms. Our unique approach relies on spin-dependent optical lattices, which promise to perform two-atom quantum gates much faster than other conventional atomic systems: (1) atoms can be transported into same lattice site on μs timescale rather than ms one, and (2) atoms are strongly confined by the deep optical lattice potential while interacting, which allows much higher collisional rates.

A necessary requirement for this experiment is the initialization of the two-atom register into the motional ground state of the optical lattice potential. The longitudinal motional degree of freedom of our one-dimensional state-dependent optical lattice is cooled to the ground state with microwave sideband cooling [1]. We instead use Raman sideband cooling to prepare atoms in the motional ground state in the direction perpendicular to the lattice. A hollow doughnut-shaped blue-detuned beam is employed to enhance the transverse confinement to enter the Lamb-Dicke regime needed for cooling. We will study collisional physics of two atoms, which are simultaneously tightly confined within a small volume (~ 20 x 30 x 30 nm3), and quantum inference effects among indistinguishable particles.  Precise control of the interaction strength will be achieved by means of Feshbach resonances and by precisely tailoring through optimal control theory the shape of transport ramps.

Image: Pictorial representation of a two-dimensional spin-dependent optical lattice. The green and red lattices are experienced by atoms in spin-up and spin-down states, respectively.
Field of research: Few-atom quantum systems