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Quantentechnologie

Dieter Meschedes Forschungsgruppe

Quantentechnologie mit einzelnen neutralen Atomen

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Intensive week: Introduction to topological insulators and their implementations in artificial matter setups

The intensive week consists of lectures introducing graduate students to the very active research field of topological insulators. Participants are required to have good knowledge of basic quantum mechanics and familiarity with basic concepts in condensed matter physics (Bloch theorem, energy bands, etc.). No prior knowledge of topology is assumed.

The main body of the intensive week is a course held by J. K. Asbóth, based on the lecture notes “A Short Course on Topological Insulators”, freely available at https://arxiv.org/abs/1509.02295. Through simple one- and two-dimensional model Hamiltonians, participants will acquire a good physical understanding of the core concepts of topological insulators. This is complemented by A. Alberti, presenting a selection of modern experiments demonstrating topological effects in ultracold atoms and nanophotonics setups. Additionally, guest speakers will give an introduction to “frontier” research topics in this field. The course will be accompanied by laboratory tours, exercise and interactive discussion sessions in the afternoon.

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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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Resonator-QED mit einzelnen Atomen

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Das Ziel der Resonator-Quantenelektrodynamik (Resonator-QED) ist es, die komplexe Licht-Materie-Wechselwirkung auf der grundlegensten Ebene zu verstehen, indem ein möglichst einfaches Modellsystem präpariert wird: ein einzelnes Atom gekoppelt an ein einzelnes Photon in einer kontrollterten Umgebung. Während sich einzelne Atome gut mittels Laserkühlung und optischen Dipolfallen kontrollieren lassen, müssen Photonen eingesperrt werden indem man sie zwischen zwei Spiegeln fortdauernd hin- und herreflektiert. Diese optischen Resonatoren bilden somit eine "Falle" für Licht.

In einem solchen System lässt sich die Physik hinter der spontanen und stimulierten Emission und Absorption von Photonen und den dazugehörigen Übergängen des Atoms zwischen verschiedenen Quantenzuständen in einzigartiger Klarheit untersuchen. Dies wird durch die starke Kopplung des Atoms mit dem Resonatorfeld ermöglicht, die es beispielsweise einem einzelnen Atom erlaubt, die optische Transmission durch die Cavity zu blockieren. Genauso kann ein einzelnes Photon den Zustand eines Atoms deterministisch ändern. In der Zukunft könnten solche stark gekoppelten Systeme aus Atom und Photon Anwendungen in der Quantenkommunikation besitzen.

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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: