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Quantum technologies

Dieter Meschede's research group

Quantum technologies with single neutral atoms

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Ultra-low birefringence dodecagonal vacuum glass cell - patent pending

Modern experiments for the investigation of cold atom ensembles require an ultra-high vacuum apparatus with a very large optical access and an accurate preservation of the state of polarization of laser beams. Typical ultrahigh vacuum cells suffer from residual stress-induced birefringence, which deteriorates the polarisation's purity [1]. In addition, birefringence gradients prevent the full compensation of birefringence. This effect effectively limits the extinction ratio to typically η > 10-5. We recently developed an ultra-low birefringence ultra-high vacuum cell that exhibits a polarization extinction two orders of magnitude smaller than commercial vacuum cells at around η ≈ 10-7 [2]. Besides the ultra-low birefringence, the vacuum cell features a dodecagonal geometry with double-sided antireflection coated windows (see picture). The cell is currently utilized in one of our laboratories, where we manipulate ultracold Cs atoms in two-dimensional state-dependent optical lattices.

If you are interested in our invention for commercial applications, please see our patent abstract containing also the contact to our patent advisor, PROvendis [3].

[1]: S. Brakhane, and A. Alberti, "Technical note: Stress-Induced Birefringence in Vacuum Systems", download link (June, 2016)
[2]: S. Brakhane, W. Alt, D. Meschede, C. Robens, G. Moon, and A. Alberti, "Note: Ultra-low birefringence dodecagonal vacuum glass cell," Rev. Sci. Instrum. 86, 126108 (2015)
[3]: Patent abstract, PROvendis, Patent advisor of the University of Bonn, download link (March, 2016)

 

 
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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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Cavity QED with single atoms

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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. 

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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.

Our recent results include:

 
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