Quantum noise reduction using a cavity with a Bose Einstein condensate

We study an optomechanical system in which the collective density excitations (Bogoliubov modes) of a Bose Einstein condensate (BEC) is coupled to a cavity field. We show that the optical force changes the frequency and the damping constant of the collective density excitations of the BEC. We further analyze the occurrence of normal mode splitting (NMS) due to mixing of the fluctuations of the cavity field and the fluctuations of the condensate with finite atomic two-body interaction. The NMS is found to vanish for small values of the two-body interaction. We further show that the density excitations of the condensate can be used to squeeze the output quantum fluctuations of the light beam. This system may serve as an optomechanical control of quantum fluctuations using a Bose Einstein condensate.Comment: 8 figure

Fault-Tolerant Dissipative Preparation of Atomic Quantum Registers with Fermions

We propose a fault tolerant loading scheme to produce an array of fermions in an optical lattice of the high fidelity required for applications in quantum information processing and the modelling of strongly correlated systems. A cold reservoir of Fermions plays a dual role as a source of atoms to be loaded into the lattice via a Raman process and as a heat bath for sympathetic cooling of lattice atoms. Atoms are initially transferred into an excited motional state in each lattice site, and then decay to the motional ground state, creating particle-hole pairs in the reservoir. Atoms transferred into the ground motional level are no longer coupled back to the reservoir, and doubly occupied sites in the motional ground state are prevented by Pauli blocking. This scheme has strong conceptual connections with optical pumping, and can be extended to load high-fidelity patterns of atoms.Comment: 12 pages, 7 figures, RevTex

In situ measurement of the dynamic structure factor in ultracold quantum gases

We propose an experimental setup to efficiently measure the dynamic structure factor of ultracold quantum gases. Our method uses the interaction of the trapped atomic system with two different cavity modes, which are driven by external laser fields. By measuring the output fields of the cavity the dynamic structure factor of the atomic system can be determined. Contrary to previous approaches the atomic system is not destroyed during the measurement process.Comment: 5 pages, 3 figure

Journalistische Qualität von Musikkritiken

Ausgehend von der wahrzunehmenden Konkurrenzsituation zwischen Print- und Online-Medien vergleicht die Magisterarbeit Popmusikkritiken der drei Mediengattungen Tageszeitung, Musikmagazin und Online-Magazin. Es soll untersucht werden, ob aus journalistischer Sicht qualitative Unterschiede zwischen den einzelnen Ausprägungen zu attestieren sind und ob gerade die Online-Medien schon zu den Qualitätsmedien aufschließen konnten. Als zweiter Aspekt soll versucht werden, eine subkulturelle Funktion von Popjournalismus anhand der inhaltsanalytischen Betrachtung nachzuweisen. Als theoretische Basis dienen sowohl Ansätze der kritischen Medientheorie wie auch der Cultural Studies. Basierend auf bisherigen wissenschaftlichen Abhandlungen werden die Themenbereiche Musikkritik, Popjournalismus sowie Subkultur und Identitätsbildung eingegrenzt und ausführlich beschrieben, um eine fundierte Ausgangslage für die abschließende Analyse zu schaffen. Im Rahmen dieser sind 60 Artikel aus sechs unterschiedlichen Medien (pro Gattung ein österreichisches und ein deutsches Exemplar) anhand eines deduktiv wie induktiv gebildeten Kategoriensystems kodiert worden. Anhand der Beantwortung der eingangs aufgestellten Forschungsfragen kommt die Magisterarbeit zu dem Schluss, dass Popmusikkritiken in Tageszeitungen zwar sprachlich wie informationstechnisch tendenziell eine höhere Qualität aufweisen können, sich die Kritiken der drei Medienarten insgesamt aber recht ähnlich gestalten, was Metapherndichte oder vergleichbare Aspekte betrifft. Hervorzuheben sind die sehr positiven Merkmale von Online-Kritiken im Vergleich zu jenen in Printmagazinen. Somit lässt sich doch eine leichte Verschiebung popkultureller Berichterstattung in Richtung des World Wide Web artikulieren, auch was deren qualitative Eigenschaften anbelangt. Eine subkulturelle Funktion von Musikkritiken, ausgelöst etwa durch extrem positive Äußerungen der Kritiker zu einzelnen musikalischen wie gesellschaftlichen Phänomenen, kann bei keinem Medium in signifikantem Ausmaß nachgewiesen werden

Dissipative dynamics of atomic Hubbard models coupled to a phonon bath:Dark state cooling of atoms within a Bloch band of an optical lattice

We analyse a laser assisted sympathetic cooling scheme for atoms within the lowest Bloch band of an optical lattice. This scheme borrows ideas from sub-recoil laser cooling, implementing them in a new context in which the atoms in the lattice are coupled to a BEC reservoir. In this scheme, excitation of atoms between Bloch bands replaces the internal structure of atoms in normal laser cooling, and spontaneous emission of photons is replaced by creation of excitations in the BEC reservoir. We analyse the cooling process for many bosons and fermions, and obtain possible temperatures corresponding to a small fraction of the Bloch band width within our model. This system can be seen as a novel realisation of a many-body open quantum system

Entangling two Bose Einstein condensates in a double cavity system

We propose a scheme to transfer the quantum state of light fields to the collective density excitations of a Bose Einstein condensate (BEC) in a cavity. This scheme allows to entangle two BECs in a double cavity setup by transferring the quantum entanglement of two light fields produced from a nondegenerate parametric amplifier (NOPA) to the collective density excitations of the two BECs. An EPR state of the collective density excitations can be created by a judicious choice of the system parameters.Comment: 3 figure

Collective decoherence of cold atoms coupled to a Bose-Einstein condensate

We examine the time evolution of cold atoms (impurities) interacting with an environment consisting of a degenerate bosonic quantum gas. The impurity atoms differ from the environment atoms, being of a different species. This allows one to superimpose two independent trapping potentials, each being effective only on one atomic kind, while transparent to the other. When the environment is homogeneous and the impurities are confined in a potential consisting of a set of double wells, the system can be described in terms of an effective spin-boson model, where the occupation of the left or right well of each site represents the two (pseudo)-spin states. The irreversible dynamics of such system is here studied exactly, i.e., not in terms of a Markovian master equation. The dynamics of one and two impurities is remarkably different in respect of the standard decoherence of the spin - boson system. In particular we show: i) the appearance of coherence oscillations, i) the presence of super and sub decoherent states which differ from the standard ones of the spin boson model, and iii) the persistence of coherence in the system at long times. We show that this behaviour is due to the fact that the pseudospins have an internal spatial structure. We argue that collective decoherence also prompts information about the correlation length of the environment. In a one dimensional configuration one can change even stronger the qualitative behaviour of the dephasing just by tuning the interaction of the bath.Comment: 18 pages, 6 figures, two references adde

Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits

We analyze two configurations for laser cooling of neutral atoms whose internal states store qubits. The atoms are trapped in an optical lattice which is placed inside a cavity. We show that the coupling of the atoms to the damped cavity mode can provide a mechanism which leads to cooling of the motion without destroying the quantum information.Comment: 12 page

Phonon-induced artificial magnetic fields

We investigate the effect of a rotating Bose-Einstein condensate on a system of immersed impurity atoms trapped by an optical lattice. We analytically show that for a one-dimensional, ring-shaped setup the coupling of the impurities to the Bogoliubov phonons of the condensate leads to a non-trivial phase in the impurity hopping. The presence of this phase can be tested by observing a drift in the transport properties of the impurities. These results are quantitatively confirmed by a numerically exact simulation of a two-mode Bose-Hubbard model. We also give analytical expressions for the occurring phase terms for a two-dimensional setup. The phase realises an artificial magnetic field and can for instance be used for the simulation of the quantum Hall effect using atoms in an optical lattice.Comment: 6 pages, 4 figure