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Quantum technologies

Dieter Meschede's research group

Quantum technologies with single neutral atoms

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Low-entropy states: Persuading Maxwell’s Demon to order atoms

A new technique allows sorting atoms one by one to form ordered patterns in a periodic lattice with angstrom precision
For German speakers, you can hear the interview with Forschung aktuell of Deutschlandfunk – Sortiergerät für Atome: Forscher präparieren Quantenregister im Rekordtempo (broadcast on March 9th)
Creating low-entropy states of neutral matter is one of the outstanding problems in the field of quantum optics. These states are an indispensable cornerstone of future applications in quantum information science, ranging from quantum simulations to quantum information processing. In Robens et al. Phys. Rev. Lett. 118, 065302 (2017), we demonstrate a new technique using two periodic optical potentials—the storage and shift register—to sort neutral atoms one by one into predefined patterns. Hence, our original experimental scheme acts akin to a Maxwell daemon preparing states with virtually zero entropy. Behind this scheme stands a novel idea for the fast, high-precision synthesis of polarization states of light—hence the name of polarization-synthesized optical lattices. Using the storage and shift register enables a novel sorting algorithm of logarithmic complexity, which holds promise to sort even a thousand atoms into a predefined target pattern with angstrom precision in a second. In our manuscript, we give a proof-of-concept demonstration by generating low entropy states with four atoms (see figure).
Original publication: C. Robens, J. Zopes, W. Alt, S. Brakhane, D. Meschede, and A. Alberti, "Low-Entropy States of Neutral Atoms in Polarization-Synthesized Optical Lattices", Phys. Rev. Lett. 118, 065302 (2017).
 
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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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