IAP logo UniBonn logo
  • Increase font size
  • Default font size
  • Decrease font size

Quantum technologies

Dieter Meschede's research group
Theses - FCQED


  • F. Hemmann
    Aufbau und Vorbereitungen für Cavity-Ring-Down-Spektroskopie mit monolithischen Faserresonatoren, (2020), Bachelor thesisBibTeX

    Zu Beginn der Arbeit werden in Abschnitt 2.1 Funktionsweise und Besonderheiten von Faser-Fabry-Perot-Resonatoren erläutert. Eine Einführung in Cavity-Ring-Down-Spektroskopie und eine erste Abschätzung der Genauigkeit, welche in einem miniaturisierten CRDS-Experiment mit Faserresonatoren erreicht werden sollte, folgen in Abschnitt 2.2. Die neu entwickelten Designs für monolithische FFPR werden in Kapitel 3 eingeführt. In den Abschnitten 3.1 und 3.2 wird erläutert, wie hier bei stabiler und kompakter Bauweise die Ausrichtungsgenauigkeit der Faserspiegel gewährleistet werden kann. Anschließend wird das Herstellungsverfahren der monolithischen FFPR beschrieben (Abschnitt 3.3). Kapitel 4 wendet sich schließlich dem Aufbau zu, mit welchem CRDS mit monolithischen FFPR erprobt werden soll. In diesem Aufbau wird das Licht eines durchstimmbaren Lasers (Abschnitt 4.1) in den Resonator gekoppelt, dessen Reflexionssignal auf einem Oszilloskop betrachtet werden kann (Abschnitt 4.2). Zur Durchführung von Spektroskopie-Messungen wird der Resonator in einer Kammer platziert, die mit einem Gasgemisch aus Sauerstoff und Stickstoff gefüllt wird (Abschnitt 4.3). Eine experimentelle Erprobung von CRDS mit diesem Aufbau steht zum Zeitpunkt der Abgabe dieser Arbeit noch aus.


  • T. Macha
    Storage of Short Light Pulses in a Fiber–Based Atom–Cavity System, (2018), PhD thesisBibTeXPDF

    In this work I theoretically investigate and experimentally realize the storage of short light-pulses in a fiber-based atom-cavity system. Our miniaturized optical resonator – with seven times the natural atomic linewidth and a small mode volume – simultaneously ensures a high bandwidth and operation in the strong-coupling regime. In particular, it enables the storage of light pulses with on average one photon and a temporal extent of less than 10 ns, which is more than a factor of two shorter than the atomic excited state lifetime of rubidium. We obtain a storage efficiency of 8%, consistent with both cavity losses and the employed level scheme.
     In order to improve the coupling and number of measurements for which a single atom can be recycled, we use dipole-trap assisted, degenerate Raman sideband cooling and a further development of our carrier-free Raman sideband cooling scheme, which permits a three-dimensional ground state population of 70%. The new techniques increase the measurement repetition rate by two orders of magnitude to ∼ 2 kHz. Moreover, for the first time we achieve a Zeeman state preparation fidelity above 95% in our experiment.
     On this basis, I present the deterministic generation of single photons in the near-adiabatic limit. By shaping the control laser pulse, we do not only show that we can control the temporal waveform of retrieved photons, but also reach a faster extraction from the cavity-coupled atom than possible in free-space. The quantum nature of the retrieved light is verified by measuring a second-order correlation function, which yields the expected antibunching. Moreover, the generation of photons in the cavity mode with an efficiency exceeding 66% is used as a fast hyperfine-state detection method, since our traditional, non-destructive state detection via a probe laser is no longer applicable in a Raman configuration due to the absence of a cycling transition. In order to realize Raman coupling between the two hyperfine ground states, we develop a scheme for shifting the cavity resonance frequency between two hyperfine transitions. During the scan, we are furthermore able to determine the atom-cavity coupling strength via the vacuum Rabi splitting in each individual measurement – a useful tool for post-selection of acquired data sets.
     By employing a numerical simulation based on a full quantum-mechanical master equation, I find the strategy to store a coherent laser pulse with the maximum possible efficiency for a given system. Although the cavity input field is treated classically, our simulation model is able to calculate efficiencies for a pure single-photon Fock-state input. Moreover, numerical optimal control methods enable us to find control pulses with storage efficiencies slightly above those achieved for temporally-scaled adiabatic control pulses. For our specific system, we finally demonstrate the non-adiabatic storage of a short, coherent light pulse.
     The ability to interact with pulses of high bandwidths encourages quantum hybrid experiments with quantum dots as single-photon sources. In this context, the stabilization of their emission frequency to an atomic transition is required. In collaboration with the IFW Dresden, I present a technique to counteract long-term frequency drifts by applying rate-based feedback to a strain-tunable quantum dot, which results in frequency deviations smaller than 1.5% of its emission linewidth. By simultaneously stabilizing the emission frequency of two quantum dots in separate cryostats, we enhance their two-photon interference visibility in a Hong-Ou-Mandel measurement from 31% to 41%, which corresponds to the maximum reachable visibility for the given emitters. Frequency-stable, efficient photon sources together with atom-cavity based quantum memories may facilitate the realization of quantum networks.


  • L. Ahlheit
    Frequenzvariable Phasenstabilisierung eines Diodenlasers auf einen optischen Frequenzkamm, (2017), Bachelor thesisBibTeXPDF
  • J. C. Gallego







  • M. Ammenwerth


  • M. M. Dorantes
    Fast non-destructive internal state detection of neutral atoms in optical potentials, (2016), PhD thesisBibTeXPDF

    Neutral atoms trapped in optical lattices are promising candidates for quantum information processing and quantum simulation. Over the last decades, elegant tools for the manipulation of the internal and external states of optically trapped atoms have been developed. The crucial capability of scalable internal state readout in these systems, however, still relies on destructive methods. In spite of the important role of near-resonant illumination for the manipulation and detection of atoms in the lattice, there also exists a significant lack of studies on the heating and cooling dynamics of optically trapped atoms interacting with near-resonant light. An in-depth understanding of the heating and cooling processes is essential to finding the conditions of illumination that enable the non-destructive internal state readout of multiple atoms.

    This work presents an experimental system to cool, trap, manipulate, and detect the internal and external states of a small ensemble of 87Rb neutral atoms trapped in a one-dimensional optical lattice. A high photon detection efficiency in our experimental system allows for fast fluorescence imaging with acquisition times of 20 ms and fast position determination of atoms in the optical lattice with an accuracy of ∼40 nm.

    Using this experimental system, we investigate the heating dynamics of a neutral atom trapped in a standing wave dipole trap illuminated by a single near-resonant laser beam. A theoretical description to describe our measurements is provided in two experimentally relevant regimes. First, we consider the case of a weak near-resonant beam and later the case of off-resonant illumination. From this analysis, we find settings for the illumination light which allows an atom to scatter many photons before it is expelled from the trap.

    Building on these results we demonstrate simultaneous, non-destructive determination of the internal state of spatially resolved atoms trapped in a one-dimensional optical lattice with a fidelity of 98.6 ± 0.2% and a survival probability of 99.0 ± 0.2%. During the readout process, less than 2% of the atoms change their initial ground state.

    In order to determine the state of atoms that are not spatially resolved, a novel image analysis technique is presented. The technique uses Bayesian methods, which include the statistics of the detected photons as well as the response from the EMCCD camera. The Bayesian method is implemented on experimental data for atoms trapped in a one-dimensional optical lattice and its accuracy is tested by numerical simulations. In addition, an extension of this algorithm for atoms trapped in two-dimensional lattices is provided.

    Finally, the non-destructive state detection method is utilized as a tool for the state determination following the coherent control of the internal and external states of atoms in the optical trap. Here Raman sideband cooling is implemented and utilized in an atomic compression sequence for the creation of a small and dense atomic ensemble. These techniques will play an important role in experiments studying the collective light interaction of the atomic ensemble in a recently added optical fiber cavity.


  • S. Urban
    Optimization of an optical fiber endfacet machine, (2013), Bachelor thesisBibTeX


  • F. Seidler
    Aufbau einer Maschine zur Bearbeitung von Glasfaser-Endflächen, (2012), Bachelor thesisBibTeX
    Der einfachste Optische Resonator besteht aus zwei einander gegenüber positionierten Spiegeln (ein sogenannter Fabry-Pérot-Resonator). Die Eigenschaften dieser Resonatoren hängen stark von Form, Oberfläche und Positionierung der verwendeten Spiegel ab. Um einen besonders vorteilhafte Satz an Parametern für Experimente auf dem Gebiet der CQED (Cavity Qantum Electro Dynamics) zu erhalten, möchte man die Endflächen von Glasfasern als Spiegel verwenden. Dies setzt insbesondere eine Möglichkeit zur Bearbeitung der Faserendflächen voraus.Grundlegende Zusammenhänge und Eigenschaften dieser Faser-Fabry-Pérot Resonatoren, wie auch theoretische Betrachtungen zur gewählten Bearbeitungsmethode für die Faserendflächen folgen in Kapitel 2. Anschließend wird der Aufbau einer Maschine zur Bearbeitung von Faserendflächen geschildert (Kapitel 3). Erste Tests werden in Kapitel 4 dargelegt. Abschließend wird ein Ausblick auf noch ausstehende Arbeiten gegeben, die schließlich die Herstellung von Faserresonatoren im gewünschten Rahmen ermöglichen sollen (Kapitel 5).

Open projects