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Quantum technologies

Dieter Meschede's research group

Quantum technologies with single neutral atoms

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Talented students wanted

Scientists at workScientists at work

We are constantly seeking young talented scientists, who are willing to play a key role in one of our quantum experiments. If you believe that you are one of these students, please get in contact with us. We will be very happy to show you around in our laboratories and to discuss with you some exciting physics project.

Why with us? Because here your ideas and your skills make a significant difference and because "taming" single atoms at the most fundamental quantum level is indeed an exciting job! That is what we experience everyday. You also will get thorough supervision by experienced senior scientists, but more importantly you will be given much freedom to express yourself.

 
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VIsiting scientist from Laboratoire Kastler-Brossel

We are very glad to host Jean-Michel Raimond in our group for about 10 weeks. Jean-Michel Raimond is Professor of the Université Pierre et Marie Curie and former director of the Physics departement at the Ecole Normale Supérieure. He devoted is research to the exploration of interaction of light and matter at the most fundamental quantum level at the Laboratoire Kastler-Brossel, where he is a very close collaborator of the recent nobel laureate Serge Haroche. His stay in Bonn is supported by the Alexander von Humboldt foundation, from which he has been recently awarded the Humboldt Prize. We are enjoying a fruitful scientific collaboration! 
 
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Realizing a digital single-atom interferometer

Split single atom
Coherent splitting a single atom. (a) A spin-dependent optical lattice (red wave) transports the atom depending on its spin state (color) in opposite directions. After merging the two paths again, the accumulated quantum phase is measured. (b) Fluorescence images of single atoms (coloured) illustrate the mesoscopic spatial splitting achieved in the experiment.

We have recently shown that the wave function of a single atom can be manipulated to form the atom-analogue of a Mach-Zehnder interferometer: a single atom is split over a mesoscopic distance and coherently recombined to read out the quantum phase information. By using trapped atoms in a spin-dependent optical lattice, the interfering quantum paths can be steered with very high precision, while the atomic wavepackets remain tightly localized. The coherent splitting over up to 10 µm demonstrad here is implemented from of a sequence of about 100 discrete elementary quantum operations, which can be used to "program" complex interferometer geometries from basic building blocks. In this way, control over neutral particles is pushed to a new level. Our results have recently appeared in PNAS, see also the corresponding press release.

 
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Cavity QED

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The goal of cavity quantum electrodynamics (cavity-QED) is to investigate and understand light-matter interaction at the most fundamental level by preparing a basic model system: a single atom strongly coupled to a single photon in a well-controlled environment. While individual atoms can be controlled well by laser-cooling and trapping techniques, photons have to be confined by reflecting them back and forth in cavities, which thus act as a "trap" for light.

In such a system the physics behind spontaneous and stimulated emission of light and the associated transitions of the atom between different quantum states can be investigated and illustrated in a unique way. This becomes possible due to the strong coupling between the atom and the cavity field, enabling a single atom to control the transmission of light through the cavity, and allowing a single photon to deterministically change the state of the atom. Quantum communication could be a future application of these controlled interaction between individual photons and atoms. 

In our experiment we couple single neutral cesium atoms to the field of a high finesse optical resonator. Single photons can be stored for a long time between the mirrors of our resonator: A single photon is reflected 300,000 times on average before it gets lost! Moreover, the confinement of the electric field to a small volume results in a high atom-cavity coupling strength, i.e. the rate of coherent energy exchange between atoms and the cavity field. A possible goal is to couple several atoms via the cavity field and to create correlated (e.g. entangled) atomic states. If you are interested in a master or diploma project download our flyer. For open PhD positions have a look at the right side of this page.

 
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Few-atom quantum systems

Fig. 1: The vacuum cell with lattice and imaging system: Individual cesium atoms can be trapped and observed.

Our team is working on quantum information processing using a small number of Cesium atoms. We load the atoms into a 1D optical lattice and use the spin of each atom as a quantum bit, with the ability to set and read out each atom individually - a quantum register. Our lattice uses a special wavelength which makes the optical potential state-depedent, giving us the ability to shift atoms in the lattice depending on their internal state. We are currently researching the phenomena exhibited by a single atom when it is coherently separated over several sites. Ultimately, our goal is the controlled interaction of two atoms, creating entanglement that can be used in a quantum computation.

Read more about our recent results:

 
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