Search

Axel Kuhn: Christian Wagner: ein erfolgreiches Dichterleben (Warmbronner Schriften, 31) Christian- Wagner-Gesellschaft Leonberg 2021. 201 Seiten mit 20 Abbildungen. Paperback 15,– €. ISBN 978-3-9819137-2-9

We report the realisation of a high-finesse open-access cavity array, tailored towards the creation of multiple coherent light-matter interfaces within a compact environment. We describe the key technical developments put in place to fabricate such a system, comprising the creation of tapered pyramidal substrates and an in-house laser machining setup. Cavities made from these mirrors are characterised, by laser spectroscopy, to possess similar optical properties to state-of-the-art fibre-tip cavities, but offer a compelling route towards improved performance, even when used to support only a single mode. The implementation of a 2×2 cavity array and the independent frequency tuning between three neighbouring sites are demonstrated.

We propose a scheme to generate single photons from 87Rb atoms. The com-bination of coherent STIRAP re-preparation and optical pumping allows for the efficient generation of streams of indistinguishable photons with promising use-cases.

In his 1935 Gedankenexperiment, Erwin Schrödinger imagined a box with a cat and a poisonous substance which has a 50% probability of being released, based on the decay of a radioactive atom. As such, the life of the cat and the state of the poison become entangled, and the fate of the cat is determined upon opening the box. We present an experimental technique that keeps the cat alive on any account. This method relies on the time-resolved Hong–Ou–Mandel effect: two long, identical photons impinging on a beam splitter always bunch in either of the outputs. Interpreting the first photon detection as the state of the poison, the second photon is identified as the state of the cat. Even after the collapse of the first photon’s state, we show their fates are intertwined through quantum interference. We demonstrate this by a sudden phase change between the inputs, administered conditionally on the outcome of the first detection, which steers the second photon to a pre-defined output and ensures that the cat is always observed alive.

The enhanced interaction of quantum states of light and matter within an optical resonator is a powerful tool for both addressing fundamental questions of nature and pursuing quantum technologies. Here, we discuss the impact of cavity birefringence — a lifting of the degeneracy of polarisation modes within the resonator — on both of these challenges. A novel model for such systems is experimentally verified by the cavity emission of single photons with time-dependent polarisation states that evolve along their wavepacket [1]. This model is then used to demonstrate how a tailored birefringence allows for enhanced photon emission beyond previous limitations [2].

STIRAP (stimulated Raman adiabatic passage) is a powerful laser-based method, usually involving two photons, for efficient and selective transfer of populations between quantum states. A particularly interesting feature is the fact that the coupling between the initial and the final quantum states is via an intermediate state, even though the lifetime of the latter can be much shorter than the interaction time with the laser radiation. Nevertheless, spontaneous emission from the intermediate state is prevented by quantum interference. Maintaining the coherence between the initial and final state throughout the transfer process is crucial. STIRAP was initially developed with applications in chemical dynamics in mind. That is why the original paper of 1990 was published in The Journal of Chemical Physics. However, from about the year 2000, the unique capabilities of STIRAP and its robustness with respect to small variations in some experimental parameters stimulated many researchers to apply the scheme to a variety of other fields of physics. The successes of these efforts are documented in this collection of articles. In Part A the experimental success of STIRAP in manipulating or controlling molecules, photons, ions or even quantum systems in a solid-state environment is documented. After a brief introduction to the basic physics of STIRAP, the central role of the method in the formation of ultracold molecules is discussed, followed by a presentation of how precision experiments (measurement of the upper limit of the electric dipole moment of the electron or detecting the consequences of parity violation in chiral molecules) or chemical dynamics studies at ultralow temperatures benefit from STIRAP. Next comes the STIRAP-based control of photons in cavities followed by a group of three contributions which highlight the potential of the STIRAP concept in classical physics by presenting data on the transfer of waves (photonic, magnonic and phononic) between respective waveguides. The works on ions or ion strings discuss options for applications, e.g. in quantum information. Finally, the success of STIRAP in the controlled manipulation of quantum states in solid-state systems, which are usually hostile towards coherent processes, is presented, dealing with data storage in rare-earth ion doped crystals and in nitrogen vacancy (NV) centers or even in superconducting quantum circuits. The works on ions and those involving solid-state systems emphasize the relevance of the results for quantum information protocols. Part B deals with theoretical work, including further concepts relevant to quantum information or invoking STIRAP for the manipulation of matter waves. The subsequent articles discuss the experiments underway to demonstrate the potential of STIRAP for populating otherwise inaccessible high-lying Rydberg states of molecules, or controlling and cooling the translational motion of particles in a molecular beam or the polarization of angular-momentum states. The series of articles concludes with a more speculative application of STIRAP in nuclear physics, which, if suitable radiation fields become available, could lead to spectacular results., Journal of Physics B: Atomic, Molecular and Optical Physics, 52 (20), ISSN:1361-6455, ISSN:0368-3508, ISSN:0953-4075, ISSN:0022-3700

We present the effects of resonator birefringence on the cavity-enhanced interfacing of quantum states of light and matter, including the first observation of single photons with a time-dependent polarization state that evolves within their coherence time. A theoretical model is introduced and experimentally verified by the modified polarization of temporally long single photons emitted from a ^{87}Rb atom coupled to a high-finesse optical cavity by a vacuum-stimulated Raman adiabatic passage process. Further theoretical investigation shows how a change in cavity birefringence can both impact the atom-cavity coupling and engender starkly different polarization behavior in the emitted photons. With polarization a key resource for encoding quantum states of light and modern micron-scale cavities particularly prone to birefringence, the consideration of these effects is vital to the faithful realization of efficient and coherent emitter-photon interfaces for distributed quantum networking and communications.

In einem aktuellen Forschungsuberblick zur historischen Presseforschung stellt Daniel Bellingradt die These auf, dass es sich lohnen wurde, mit theoretischen Modellen als historiographischer Methode zu experimentieren, denn »Theorieangebote, die aus der Pressehistoriographie heraus entwickelt worden sind, stellen wie haufig in interdisziplinar gepragten Forschungsfeldern ein grundlegendes Desiderat dar.« Im Rahmen der skizzierten systemfunktionalistischen Perspektive soll die soziale Funktionalitat der Zeitschrift daher im Folgenden nicht aus der Gegenwart heraus, sondern im Hinblick auf ihre Evolution theoretisch rekonstruiert werden. Zeitschriften werden deshalb ursachlich und folglich zur Evolution der Gesellschaft und des Mediensystems bestimmt.

Systemtheoretische Ansatze existieren in der Buchforschung bereits seit dem 18. Jahrhundert. In ihrer systemfunktionalen Form wurden sie allerdings bisher kaum in buchwissenschaftliche Forschung integriert, weil sie in der oft noch zu praktisch orientierten Forschung als schwierig umzusetzen, sprachlich zu abstrakt und wenig erkenntnisgenerierend gelten. Die interdisziplinare Zusammensetzung der in der Buchwissenschaft arbeitenden Forscher tragt zusatzlich dazu bei, dass es keine grundlegende Wissensbasis ihrer Anwendung gibt und systemfunktionale Analysen somit bisher Einzelfalle geblieben sind.

Die systemfunktionale Rekonstruktion der Zeitschriftengeschichte als Medienevolution hat gezeigt, dass Zeitschriften als Formdifferenzierungen Ausdruck veranderter Medienfunktionalitat sind. Alle evolutionaren Prozesse in Folge des Buchdrucks lassen sich uber Variationen, Selektionen und temporare Stabilisierungen erklaren, wobei Zeitschriften als Formen auf mehreren Ebenen funktionaler Differenzierung eine Rolle spielen. Ihre Entstehung, Deund Restabilisierungen erlauben tiefe Einblicke in die funktionale und strukturelle Evolution des Mediensystems in der Gesellschaft.

Zeitschriften wurden als funktionale Formen des medialen und sozialen Wandels bestimmt, die in ihren evolutionaren Differenzierungen unterschiedliche Beitrage in Form von Effizienz- und Effektivitatssteigerungen kommunikativer Operationen und sozialer Wirklichkeitskonstruktionen geleistet haben und noch immer leisten. Insbesondere populare Zeitschriften werden in ihrer historischen Entstehung gleichzeitig als Unterhaltungsmedien beschrieben, also mit einer spezifischen medialen Funktion fur Bewusstsein und Gesellschaft verknupft, die wechselseitig zu kultureller Differenzierung als Eigenschaft der Moderne bestimmt wird. Damit stellen sich Fragen, wie Unterhaltung als Teilbereich medialer und sozialer Evolution bestimmt werden kann.

Zeitschriften und ihre wissenschaftliche Betrachtung verhalten sich zueinander seltsam ambivalent: Als meinungsbildende Medien anerkannt, waren sie schon fruh in der Medienforschung Gegenstand der Reflektion, die aber vor allem in Form wertender Diskurse uber ihren funktionalen Nutzen und ihre dysfunktionalen Folgen fur bestimmte Bevolkerungsgruppen wie Frauen, Arbeiter und Jugendliche erfolgte. Ihre bibliographische Erfassung fand fruh statt und fuhrte zu umfassenden historischen Uberblickswerken, wobei deren teilweise vorhandene Eingrenzung auf bestimmte ›literarisch wertvolle‹ Zeitschriften, ›bedeutende‹ Autoren, Verleger und Verlage problematisch ist. Wahrend Zeitschriften vor allem als Materialobjekte in ihrer Bereitstellungsqualitat umfassend beschrieben werden, wurde ihr Formalobjekt aufgrund der sehr heterogenen Strukturen bisher nicht eindeutig erfasst.

In Diskursen um Medienunterhaltung wird deren stetige Zunahme in Form unterhaltsamer Medienangebote und unterhaltender Praktiken festgestellt und kausallogisch auf die Zunahme freier Zeit fur die Mediennutzung, die leichtere Zuganglichkeit von Medien oder zunehmende eskapistische Bedurfnisse der Mediennutzer reduziert. Das ist auch auf die bisherigen Medienhistoriographien zuruckzufuhren, welche die Entstehung der Moderne, die kulturgeschichtlich mit der Industrialisierung und der Bildung der Nationalstaaten einhergeht, fokussieren. Das 18. und 19. Jahrhundert werden dabei als Schwellenzeit identifiziert, in der Unterhaltung als ubiquitares Element in den Lebenswelten der Menschen wirksam und auch reflexiv wahrgenommen wird.

Der Diskurs zur Erforschung von Unterhaltung entfaltet sich zwischen kommunikations- und kulturwissenschaftlichen Perspektiven uber grundsatzlich andere Vorstellungen des Gegenstands.

Die Metaebene wissenschaftstheoretischer Uberlegungen zur systemfunktionalen Erweiterung buchwissenschaftlicher Forschung wird in dieser Arbeit exemplarisch anhand der Themenbereiche ›Zeitschrift‹ und ›Medienunterhaltung‹ entwickelt.

We demonstrate the trapping and manipulation of single neutral atoms in reconfigurable arrays of optical tweezers. Our approach offers unparalleled speed by using a Texas Instruments Digital Micro-mirror Device (DMD) as a holographic amplitude modulator with a frame rate of 20,000 per second. We show the trapping of static arrays of up to 20 atoms, as well as transport of individually selected atoms over a distance of 25{\mu}m with laser cooling and 4{\mu}m without. We discuss the limitations of the technique and the scope for technical improvements.

We describe the preparation of Fock states of motion of cesium atoms trapped in potential wells of a far detuned optical lattice. Direct observation of the velocity distribution of the |n = 0〉 and |n= 1〉 Fock states is obtained by an absorption imaging technique. © 1999 The American Physical Society.

The free expansion of a Bose-Einstein condensate of about 105 rubidium-87 atoms released from an Ioffe-Pritchard magnetic trap is investigated experimentally. The expansion dynamics depend only on the trap frequencies, which are determined independently. The data are in good agreement with the expected expansion of a condensate, and are clearly distinct from the behaviour of a classical gas in the hydrodynamic regime. © Springer-Verlag 1998.

Single-photons of well-defined polarisation that are deterministically generated in a single spatio-temporal field mode are the key to the creation of multi-partite entangled states in photonic networks. Here, we present a novel scheme to produce such photons from a single atom in an optical cavity, by means of vacuum-stimulated Raman transitions between the Zeeman substates of a single hyperfine state. Upon each transition, a photon is emitted into the cavity, with a polarisation that depends on the direction of the Raman process., Comment: 7 pages, 4 figures

The photon statistics of the light emitted from an atomic ensemble into a single field mode of an optical cavity is investigated as a function of the number of atoms. The light is produced in a Raman transition driven by a pump laser and the cavity vacuum [M.Hennrich et al., Phys. Rev. Lett. 85, 4672 (2000)], and a recycling laser is employed to repeat this process continuously. For weak driving, a smooth transition from antibunching to bunching is found for about one intra-cavity atom. Remarkably, the bunching peak develops within the antibunching dip. For saturated driving and a growing number of atoms, the bunching amplitude decreases and the bunching duration increases, indicating the onset of Raman lasing., 4 pages, 4 figures

We examine similarities and differences in three schemes that are capable of producing complete population transfer in multistate systems: generalized \ensuremath{\pi} pulses, adiabatic passage by pulse chirping, and counterintuitive pulses or stimulated Raman adiabatic passage. We use the picture of adiabatic following through avoided crossings of instantaneous eigenvalues to exhibit the essential differences between the latter two procedures.

A robust scheme for trapping and cooling atoms is described. It combines a deep dipole-trap which localizes the atom in the center of a cavity with a laser directly exciting the atom. In that way one obtains three-dimensional cooling while the atom is dipole-trapped. In particular, we identify a cooling force along the large spatial modulations of the trap. A feature of this setup, with respect to a dipole trap alone, is that all cooling forces keep a constant amplitude if the trap depth is increased simultaneously with the intensity of the probe laser. No strong coupling is required, which makes such a technique experimentally attractive. Several analytical expressions for the cooling forces and heating rates are derived and interpreted by analogy to ordinary laser cooling.

Vacuum-stimulated Raman scattering in strongly coupled atom-cavity systems allows one to generate free-running single photon pulses on demand. Most properties of the emitted photons are well defined, provided spontaneous emission processes do not contribute. Therefore, electronic excitation of the atom must not occur, which is assured for a system adiabatically following a dark state during the photon-generation process. We experimentally investigate the conditions that must be met for adiabatic following in a time-of-flight driven system, with atoms passing through a cavity and a pump beam oriented transverse to the cavity axis. From our results, we infer the optimal intensity and relative pump-beam position with respect to the cavity axis., 4 pages, 4 figures

The scattering of high vibrationally excited sodium molecules Na2(v=31) with Ne atoms at 180 meV collision energy is investigated in a crossed molecular beam arrangement using laser optical methods. Angularly resolved rotationally inelastic and vibrationally elastic cross sections ji→jf are measured for ji =5, 7, and 9≤jf ≤25. Pronounced rotational rainbow maxima are observed, the angular position of which indicates a significantly larger anisotropy of the interaction potential compared to that of Na2(v=0)–Ne. Except for the increase of the anisotropy the vibrational excitation has little effect on the dynamics of rotational energy transfer. Good agreement with a new semiempirical Na2–Ne potential surface V(r,R,γ) is found.

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a rubidium-87 atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatio-temporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference., Comment: 4 pages, 3 figures

We propose a new method for the generation of single photons. Our scheme will lead to the emission of one photon into a single mode of the radiation field in response to a trigger event. This photon is emitted from an atom strongly coupled to a high-finesse optical cavity, and the trigger is a classical light pulse. The device combines cavity-QED with an adiabatic transfer technique. We simulate this process numerically and show that it is possible to control the temporal behaviour of the photon emission probability by the shape and the detuning of the trigger pulse. An extension of the scheme with a reloading mechanism will allow one to emit a bit-stream of photons at a given rate.

We investigate the efficiency of atom-cavity based photon-generation schemes to deliver single photons of arbitrary temporal shape. Our model applies to Raman transitions in three-level atoms with one branch of the transition driven by a laser pulse, and the other coupled to a cavity mode. For any possible shape of the single-photon wavepacket, we derive an unambiguous analytic expression for the shape of the required driving laser pulse. We furthermore discuss the constraints limiting the maximum probability for emitting any desired photon, and use these to estimate upper bounds for the efficiency of the process. The model is not only valid for Vacuum-Stimulated Raman Adiabatic Passages (V-STIRAP) in the strong-coupling and bad-cavity regime, but it generally allows controlling the coherence and population flow in any Raman process., Comment: 4 pages, 3 figures

We report on the detection of single, slowly moving Rubidium atoms using laser-induced fluorescence. The atoms move at 3 m/s while they are detected with a time resolution of 60 microseconds. The detection scheme employs a near-resonant laser beam that drives a cycling atomic transition, and a highly efficient mirror setup to focus a large fraction of the fluorescence photons to a photomultiplier tube. It counts on average 20 photons per atom., Comment: 6 pages, 7 figures