Optical nonlinear dynamics with cold atoms in a cavity

This paper presents the nonlinear dynamics of laser cooled and trapped cesium atoms placed inside an optical cavity and interacting with a probe light beam slightly detuned from the 6S1/2(F=4) to 6P3/2(F=5) transition. The system exhibits very strong bistability and instabilities. The origin of the latter is found to be a competition between optical pumping and non-linearities due to saturation of the optical transition.Comment: 6 pages, 7 figures, LaTe

Exploring Interacting Quantum Many-Body Systems by Experimentally Creating Continuous Matrix Product States in Superconducting Circuits

Improving the understanding of strongly correlated quantum many body systems such as gases of interacting atoms or electrons is one of the most important challenges in modern condensed matter physics, materials research and chemistry. Enormous progress has been made in the past decades in developing both classical and quantum approaches to calculate, simulate and experimentally probe the properties of such systems. In this work we use a combination of classical and quantum methods to experimentally explore the properties of an interacting quantum gas by creating experimental realizations of continuous matrix product states - a class of states which has proven extremely powerful as a variational ansatz for numerical simulations. By systematically preparing and probing these states using a circuit quantum electrodynamics (cQED) system we experimentally determine a good approximation to the ground-state wave function of the Lieb-Liniger Hamiltonian, which describes an interacting Bose gas in one dimension. Since the simulated Hamiltonian is encoded in the measurement observable rather than the controlled quantum system, this approach has the potential to apply to exotic models involving multicomponent interacting fields. Our findings also hint at the possibility of experimentally exploring general properties of matrix product states and entanglement theory. The scheme presented here is applicable to a broad range of systems exploiting strong and tunable light-matter interactions.Comment: 11 pages, 9 figure

ATLAS monitored drift tube chambers for super-LHC

After the high-luminosity upgrade of the Large Hadron Collider (LHC) at CERN, the ATLAS muon spectrometer is expected to work at 10 times increased background rates of gammas and neutrons. This is challenging as the momentum resolution of the spectrometer is expected to be 10 %. This requires a single tube resolution of the muon drift tubes of 80 mum. At background rates around 1000 Hz/cm2 space charge effects will lead in the slow and non-linear AR:CO2 = 93:7 gas mixture to a degradation of the drift-tube spatial resolution. This was studied before experimentally for gammas and low energetic neutrons. Almost no information exists for fast neutrons. Therefore, we organized our studies under the following aspects: - We investigated the influence of 11 MeV neutrons on the position resolution of ATLAS MDT chambers. At flux densities between 4 and 16 kHz/cm2, almost no influence on the position resolution was found, it degrades by only 10 mum at a detection efficiency of only 4*10-4. - We investigated inert gas mixtures on fastness and linearity of their position-drifttime (r-t) relation. At a reduction of the maximum drift time by a factor of 2, the use of the present hardware and electronics might be possible. For our experimental studies we used our Munich cosmic ray facility. Two gas mixtures show almost identical position resolution as the standard gas. - For spectrometer regions of highest background rates we contributed to the investigation of newly developed 15 mm drift tubes. Position resolutions have been measured as a function of gamma background rates between 0 and 1400 Hz/cm2. - Garfield simulations have been performed to simulate space charge effects due to gamma irradiation. Results will be presented for the standard geometry as well as for the new 15 mm drift tubes.Comment: 3 pages, 7 figures, conferenc

Geometric Phase and Non-Adiabatic Effects in an Electronic Harmonic Oscillator

Steering a quantum harmonic oscillator state along cyclic trajectories leads to a path-dependent geometric phase. Here we describe an experiment observing this geometric phase in an electronic harmonic oscillator. We use a superconducting qubit as a non-linear probe of the phase, otherwise unobservable due to the linearity of the oscillator. Our results demonstrate that the geometric phase is, for a variety of cyclic trajectories, proportional to the area enclosed in the quadrature plane. At the transition to the non-adiabatic regime, we study corrections to the phase and dephasing of the qubit caused by qubit-resonator entanglement. The demonstrated controllability makes our system a versatile tool to study adiabatic and non-adiabatic geometric phases in open quantum systems and to investigate the potential of geometric gates for quantum information processing

Information/disturbance trade-off in continuous variable Gaussian systems

We address the information/disturbance trade-off for state-measurements on continuous variable Gaussian systems and suggest minimal schemes for implementations. In our schemes, the symbols from a given alphabet are encoded in a set of Gaussian signals which are coupled to a probe excited in a known state. After the interaction the probe is measured, in order to infer the transmitted state, while the conditional state of the signal is left for the subsequent user. The schemes are minimal, {\em i.e.} involve a single additional probe, and allow for the nondemolitive transmission of a continuous real alphabet over a quantum channel. The trade-off between information gain and state disturbance is quantified by fidelities and, after optimization with respect to the measurement, analyzed in terms of the energy carried by the signal and the probe. We found that transmission fidelity only depends on the energy of the signal and the probe, whereas estimation fidelity also depends on the alphabet size and the measurement gain. Increasing the probe energy does not necessarily lead to a better trade-off, the most relevant parameter being the ratio between the alphabet size and the signal width, which in turn determine the allocation of the signal energy.Comment: 9 pages, 6 figures, revised version, title changed, accepted PR

ATLAS Monitored Drift Tube Chambers in E = 11 MeV Neutron Background

The influence of fast neutrons on the occupancy and the single tube resolution of ATLAS muon drift detectors was investigated by exposing a chamber built out of 3 layers of 3 short standard drift tubes to neutron flux-densities of up to 16 kHz/cm2 at a neutron energy of E=11 MeV. Pulse shape capable NE213 scintillaton detectors and a calibrated BF3 neutron detector provided monitoring of the neutron flux-density and energy. The sensitivity of the drift chamber to the neutrons was measured to be 4*10-4 by comparing data sets with and without neutron background. For the investigation of tracks of cosmic muons two silicon-strip detectors above and underneath the chamber allow to compare measured drift-radii with reference tracks. Alternatively, the single tube resolution was determined using the triple-sum method. The comparison between data with and without neutron irradiation shows only a marginal effect on the resolution and little influence on the muon track reconstruction.Comment: 4 pages, 11 figures, conferenc