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Title:

ii Single-Atom Resolved Imaging and Manipulation in an Atomic Mott Insulator

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This thesis reports on new experimental techniques for the study of strongly correlated states of ultracold atoms in optical lattices. We used a high numerical aperture imaging system to probe 87 Rb atoms in a two-dimensional lattice with single-site resolution. Fluorescence imaging allows to detect single atoms with a large signal to noise rati...

This thesis reports on new experimental techniques for the study of strongly correlated states of ultracold atoms in optical lattices. We used a high numerical aperture imaging system to probe 87 Rb atoms in a two-dimensional lattice with single-site resolution. Fluorescence imaging allows to detect single atoms with a large signal to noise ratio and to reconstruct the atom distribution on the lattice. We applied this new technique to a two-dimensional Mott insulator and directly observed number squeezing and the emerging shell structure. A comparison of the radial density and variance distributions to theory provides a precise in situ temperature and entropy measurement from single images. We find entropies around the critical value for quantum magnetism. In a second series of experiments, we demonstrated two-dimensional single-site spin control in the optical lattice. The differential light shift of a tightly focused laser beam shifts selected atoms into resonance with a microwave field driving a spin flip. In this way, we reach sub-diffraction limited spatial resolution well below the lattice spacing. Starting from a Mott insulator with unity filling we were able to create Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2012-06-21

Source:

http://edoc.ub.uni-muenchen.de/13425/1/Weitenberg_Christof.pdf

http://edoc.ub.uni-muenchen.de/13425/1/Weitenberg_Christof.pdf Minimize

Document Type:

text

Language:

en

DDC:

530 Physics *(computed)*

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Title:

Single-Atom Resolved Imaging and Manipulation in an Atomic Mott Insulator

Description:

This thesis reports on new experimental techniques for the study of strongly correlated states of ultracold atoms in optical lattices. We used a high numerical aperture imaging system to probe 87Rb atoms in a two-dimensional lattice with single-site resolution. Fluorescence imaging allows to detect single atoms with a large signal to noise ratio...

This thesis reports on new experimental techniques for the study of strongly correlated states of ultracold atoms in optical lattices. We used a high numerical aperture imaging system to probe 87Rb atoms in a two-dimensional lattice with single-site resolution. Fluorescence imaging allows to detect single atoms with a large signal to noise ratio and to reconstruct the atom distribution on the lattice. We applied this new technique to a two-dimensional Mott insulator and directly observed number squeezing and the emerging shell structure. A comparison of the radial density and variance distributions to theory provides a precise in situ temperature and entropy measurement from single images. We find entropies around the critical value for quantum magnetism. In a second series of experiments, we demonstrated two-dimensional single-site spin control in the optical lattice. The differential light shift of a tightly focused laser beam shifts selected atoms into resonance with a microwave field driving a spin flip. In this way, we reach sub-diffraction limited spatial resolution well below the lattice spacing. Starting from a Mott insulator with unity filling we were able to create arbitrary spin patterns. We used this ability to prepare atom distributions to study one-dimensional single-particle tunneling dynamics in a lattice. By discriminating the dynamics of the ground state and of the first excited band, we find that our addressing scheme leaves most atoms in the vibrational ground state. Moreover, we studied coherent light scattering from the atoms in the optical lattice and found diffraction maxima in the far-field. We showed that an antiferromagnetic order leads to additional diffraction peaks which can be used to detect this order also when single-site resolution is not available. The new techniques described in this thesis open the path to a wide range of novel applications from quantum dynamics of spin impurities, entropy transport, implementation of novel cooling schemes, and engineering of quantum many-body phases to quantum information processing. ; In dieser Arbeit werden neue experimentelle Techniken für die Untersuchung von stark korrelierten Zuständen von ultrakalten Atomen in optischen Gittern vorgestellt. Wir untersuchen 87Rb Atome in einem zwei-dimensionalen Gitter und erreichen dabei eine Auflösung der einzelnen Gitterplätze mit Hilfe eines hochauflösenden Abbildungssystems. Fluoreszenzabbildung erlaubt es, einzelne Atome mit großem Signal-zu-Rausch-Verhältnis zu detektieren und die Verteilung der Atome auf dem Gitter zu rekonstruieren. Wir wenden diese neue Technik auf einen zwei-dimensionalen Mott-Isolator an and beobachten direkt das number squeezing und die Schalenstrukur. Ein Vergleich der radialen Dichte- und Varianzverteilung mit der Theorie ermöglicht eine präzise Temperatur- und Entropiemessung an einzelnen Bildern und wir finden Entropien um den kritischen Wert für Quantenmagnetismus. In einer zweiten Reihe von Experimenten zeigen wir, dass wir gezielt einzelne atomare Spinzustände im Gitter manipulieren können ohne die benachbarten Atome zu beeinflussen. Wir benutzen den differentiellen light shift eines stark fokussierten Laserstrahls, um einzelne Atome in Resonanz mit einem Mikrowellenfeld zu bringen, das den Spin umklappt. Auf diese Weise erreichen wir eine Ortsauflösung unter der Beugungsgrenze. Wir beginnen mit einem Mott-Isolator mit einem Atom pro Gitterplatz und können darin beliebige Spinmuster erzeugen. Diese neuen Möglichkeiten zur Präparation atomarer Verteilungen nutzen wir, um die eindimensionale Einteilchen-Tunneldynamik in einem Gitter zu untersuchen. Wir unterscheiden die Dynamik von Atomen im Grundzustand und im ersten angeregten Band und zeigen so, dass unser Adressierschema die meisten Atome im Grundzustand lässt. Darüber hinaus untersuchen wir kohärente Lichtstreuung an den Atomen im Gitter und finden Beugungsmaxima im Fernfeld. Wir zeigen, dass eine antiferromagnetische Ordnung der Atome zu zusätzlichen Beugungsmaxima führt, die man auch ohne unsere hohe Auflösung zum Nachweis dieser Ordnung nutzen könnte. Die neuen Techniken, die in dieser Arbeit vorgestellt werden, öffnen den Weg für viele neue Anwendungen von der Quantendynamik von Spin-Defekten, Entropietransport, der Umsetzung neuer Kühlschemata sowie der Realisierung von Quanten-Vielteilchenphasen bis hin zur Quanteninformationsverarbeitung. Minimize

Publisher:

Ludwig-Maximilians-Universität München

Year of Publication:

2011-05-26

Document Type:

Dissertation ; NonPeerReviewed

Subjects:

Fakultät für Physik

Fakultät für Physik Minimize

DDC:

530 Physics *(computed)*

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Title:

A quantum computation architecture using optical tweezers

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We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. W...

We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the non-adiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 us, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10^3. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing. ; Comment: 10 pages, 6 figures Minimize

Year of Publication:

2011-07-13

Document Type:

text

Subjects:

Quantum Physics ; Condensed Matter - Quantum Gases

Quantum Physics ; Condensed Matter - Quantum Gases Minimize

DDC:

535 Light & infrared & ultraviolet phenomena *(computed)*

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Title:

Emergence of coherence in a uniform quasi-two-dimensional Bose gas

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Phase transitions are ubiquitous in our three-dimensional world. By contrast most conventional transitions do not occur in infinite uniform two-dimensional systems because of the increased role of thermal fluctuations. Here we explore the dimensional crossover of Bose-Einstein condensation (BEC) for a weakly interacting atomic gas confined in a ...

Phase transitions are ubiquitous in our three-dimensional world. By contrast most conventional transitions do not occur in infinite uniform two-dimensional systems because of the increased role of thermal fluctuations. Here we explore the dimensional crossover of Bose-Einstein condensation (BEC) for a weakly interacting atomic gas confined in a novel quasi-two-dimensional geometry, with a flat in-plane trap bottom. We detect the onset of an extended phase coherence, using velocity distribution measurements and matter-wave interferometry. We relate this coherence to the transverse condensation phenomenon, in which a significant fraction of atoms accumulate in the ground state of the motion perpendicular to the atom plane. We also investigate the dynamical aspects of the transition through the detection of topological defects that are nucleated in a quench cooling of the gas, and we compare our results to the predictions of the Kibble-Zurek theory for the conventional BEC second-order phase transition. ; Comment: main text = 24 pages, 6 figures + supplementary material = 10 pages, 5 figures Minimize

Year of Publication:

2014-11-13

Document Type:

text

Subjects:

Condensed Matter - Quantum Gases ; Condensed Matter - Mesoscale and Nanoscale Physics ; Quantum Physics

Condensed Matter - Quantum Gases ; Condensed Matter - Mesoscale and Nanoscale Physics ; Quantum Physics Minimize

DDC:

535 Light & infrared & ultraviolet phenomena *(computed)*

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Title:

Coherent light scattering from a two-dimensional Mott insulator

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We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak pa...

We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak parameters by a simple analytic model. In contrast to Bragg scattering, scattering from a single plane yields diffraction peaks for any incidence angle. We demonstrate the feasibility of detecting spin correlations via light scattering by artificially creating a one-dimensional antiferromagnetic order as a density wave and observing the appearance of additional diffraction peaks. ; Comment: 4 pages, 4 figures Minimize

Year of Publication:

2011-02-18

Document Type:

text

Subjects:

Condensed Matter - Quantum Gases ; Quantum Physics

Condensed Matter - Quantum Gases ; Quantum Physics Minimize

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Title:

Fit-free determination of scale invariant equations of state: application to the 2D Bose gas across the Berezinksii-Kosterlitz-Thouless transition

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We present a general "fit-free" method for measuring the equation of state (EoS) of a scale-invariant gas. This method, which is inspired from the procedure introduced by Ku et al. [Science 335, 563 (2012)] for the unitary three-dimensional Fermi gas, provides a general formalism which can be readily applied to any quantum gas in a known trappin...

We present a general "fit-free" method for measuring the equation of state (EoS) of a scale-invariant gas. This method, which is inspired from the procedure introduced by Ku et al. [Science 335, 563 (2012)] for the unitary three-dimensional Fermi gas, provides a general formalism which can be readily applied to any quantum gas in a known trapping potential, in the frame of the local density approximation. We implement this method on a weakly-interacting two-dimensional Bose gas in the vicinity of the Berezinskii-Kosterlitz-Thouless transition, and determine its EoS with unprecedented accuracy in the critical region. Our measurements provide an important experimental benchmark for classical field approaches which are believed to accurately describe quantum systems in the weakly interacting but non-perturbative regime. ; Comment: 5 pages, 5 figures Minimize

Year of Publication:

2014-03-17

Document Type:

text

Subjects:

Condensed Matter - Quantum Gases

Condensed Matter - Quantum Gases Minimize

DDC:

541 Physical chemistry *(computed)*

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Title:

Single-Atom Resolved Fluorescence Imaging of an Atomic Mott Insulator

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The reliable detection of single quantum particles has revolutionized the field of quantum optics and quantum information processing. For several years, researchers have aspired to extend such detection possibilities to larger scale strongly correlated quantum systems, in order to record in-situ images of a quantum fluid in which each underlying...

The reliable detection of single quantum particles has revolutionized the field of quantum optics and quantum information processing. For several years, researchers have aspired to extend such detection possibilities to larger scale strongly correlated quantum systems, in order to record in-situ images of a quantum fluid in which each underlying quantum particle is detected. Here we report on fluorescence imaging of strongly interacting bosonic Mott insulators in an optical lattice with single-atom and single-site resolution. From our images, we fully reconstruct the atom distribution on the lattice and identify individual excitations with high fidelity. A comparison of the radial density and variance distributions with theory provides a precise in-situ temperature and entropy measurement from single images. We observe Mott-insulating plateaus with near zero entropy and clearly resolve the high entropy rings separating them although their width is of the order of only a single lattice site. Furthermore, we show how a Mott insulator melts for increasing temperatures due to a proliferation of local defects. Our experiments open a new avenue for the manipulation and analysis of strongly interacting quantum gases on a lattice, as well as for quantum information processing with ultracold atoms. Using the high spatial resolution, it is now possible to directly address individual lattice sites. One could, e.g., introduce local perturbations or access regions of high entropy, a crucial requirement for the implementation of novel cooling schemes for atoms on a lattice. Minimize

Year of Publication:

2010-06-18

Document Type:

text

Subjects:

Condensed Matter - Quantum Gases ; Quantum Physics

Condensed Matter - Quantum Gases ; Quantum Physics Minimize

DDC:

530 Physics *(computed)*

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Title:

Superfluid behaviour of a two-dimensional Bose gas

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Two-dimensional (2D) systems play a special role in many-body physics. Because of thermal fluctuations, they cannot undergo a conventional phase transition associated to the breaking of a continuous symmetry. Nevertheless they may exhibit a phase transition to a state with quasi-long range order via the Berezinskii-Kosterlitz-Thouless (BKT) mech...

Two-dimensional (2D) systems play a special role in many-body physics. Because of thermal fluctuations, they cannot undergo a conventional phase transition associated to the breaking of a continuous symmetry. Nevertheless they may exhibit a phase transition to a state with quasi-long range order via the Berezinskii-Kosterlitz-Thouless (BKT) mechanism. A paradigm example is the 2D Bose fluid, such as a liquid helium film, which cannot Bose-condense at non-zero temperature although it becomes superfluid above a critical phase space density. Ultracold atomic gases constitute versatile systems in which the 2D quasi-long range coherence and the microscopic nature of the BKT transition were recently explored. However, a direct observation of superfluidity in terms of frictionless flow is still missing for these systems. Here we probe the superfluidity of a 2D trapped Bose gas with a moving obstacle formed by a micron-sized laser beam. We find a dramatic variation of the response of the fluid, depending on its degree of degeneracy at the obstacle location. In particular we do not observe any significant heating in the central, highly degenerate region if the velocity of the obstacle is below a critical value. ; Comment: 5 pages, 3 figures Minimize

Year of Publication:

2012-05-21

Document Type:

text

Subjects:

Condensed Matter - Quantum Gases ; Quantum Physics

Condensed Matter - Quantum Gases ; Quantum Physics Minimize

DDC:

535 Light & infrared & ultraviolet phenomena *(computed)*

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Title:

Quench-induced supercurrents in an annular Bose gas

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We create supercurrents in annular two-dimensional Bose gases through a temperature quench of the normal-to-superfluid phase transition. We detect the amplitude and the chirality of these supercurrents by measuring spiral patterns resulting from the interference of the cloud with a central reference disk. These measurements demonstrate the stoch...

We create supercurrents in annular two-dimensional Bose gases through a temperature quench of the normal-to-superfluid phase transition. We detect the amplitude and the chirality of these supercurrents by measuring spiral patterns resulting from the interference of the cloud with a central reference disk. These measurements demonstrate the stochastic nature of the supercurrents. We further measure their distribution for different quench times and compare it with the predictions based on the Kibble-Zurek mechanism. Minimize

Year of Publication:

2014-06-16

Document Type:

text

Subjects:

Condensed Matter - Quantum Gases

Condensed Matter - Quantum Gases Minimize

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Title:

Quantum computation architecture using optical tweezers

Author:

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We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. W...

We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 μs, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10−3. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing. Minimize

Publisher:

American Physical Society

Year of Publication:

2011-09-16

Source:

Weitenberg , C , Kuhr , S , Mølmer , K & Sherson , J 2011 , ' Quantum computation architecture using optical tweezers ' Physical Review A (Atomic, Molecular and Optical Physics) , vol 84 , no. 3 , pp. 032322 . , 10.1103/PhysRevA.84.032322

Weitenberg , C , Kuhr , S , Mølmer , K & Sherson , J 2011 , ' Quantum computation architecture using optical tweezers ' Physical Review A (Atomic, Molecular and Optical Physics) , vol 84 , no. 3 , pp. 032322 . , 10.1103/PhysRevA.84.032322 Minimize

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article

Language:

eng

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