Talks

coffee, tea, cookies at 16:15 in the main hall
Monday 16:30-17:30
Seminar room 1+2
- monthly seminars -
Seminar room 1+2
- weekly seminars -
Monday 11:00-12:00
Room 1D1
Wednesday 16:30 - 17:30
Seminar room 1D1
Thursday 14:00-15:00
Seminar room 4

 

 

 

Talks in chronological order

26 Feb 2018
04:30 PM

Colloquium: Chern numbers counted in a synthetic-dimension quantum Hall strip

Prof. Ian Spielman (University of Maryland, USA)

Ultra cold atoms are remarkable systems with a truly unprecedented level of experimental control and one application of this control is creating topological band structures. The most natural approach centers on creating suitable real-space lattice potentials that the atoms experience. Here we present our experimental work which uses the internal atomic states as an additional ``synthetic'' dimension. We engineered a two-dimensional magnetic lattice in an elongated strip geometry, with effective per-plaquette flux about 4/3 times the flux quanta. The long direction of this strip is formed from a 1D optical lattice while the short direction is built from the 5 mF states comprising the f=2 ground state hyperfine manifold of Rb-87. We imaged the localized edge and bulk states of atomic Bose-Einstein condensates in this strip, with single lattice-site resolution along the narrow direction. In this 5-site wide strip we are able to delineate between bulk behavior quantified by Chern numbers and edge behavior which is not.

Seminarroom 1+2+3 iCal Event
28 Feb 2018
04:30 PM

Anderson localization in the time domain

Uzy Smilansky (Weizmann Institute of Science, Rehovot)

A wave-packet is a solution of the wave equation, generated as a coherent superposition of free propagating waves, which describes a short pulse of localized wave-action that travels as a unit, at a constant speed. Recently, ultra – short wave packets of electromagnetic radiation became experimentally available, and they are used to explore the scattering of light by atomic and solid systems with high temporal resolution. In the present talk I shall discuss the modification of the wave packet by the scattering process, which causes a broadening of the wave-packet. This modified shape can be interpreted as the delay-time distribution due to the interaction. I shall illustrate the phenomenon by studying the scattering of wave-packets from a random potential on the real half-line - a paradigm one dimensional systems which displays Anderson Localization in the stationary case.

Room 1D1 iCal Event
05 Mar 2018
04:30 PM

Colloquium: The Quantum Way of Doing Computations

Prof. Dr. Rainer Blatt (Institute for Experimental Physics, University of Innsbruck and Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Austria)

Since the mid-nineties of the 20th century, it became apparent that one of the centuries’ most important technological inventions, computers in general and many of their applications could possibly be further enhanced by using operations based on quantum physics. This is timely since the classical roadmap for the development of computational devices, commonly known as Moore’s law, will cease to be applicable within the next decade. This is due to the ever-smaller sizes of the electronic components that will enter the realm of quantum physics. Computations, whether they happen in our heads or with any computational device, always rely on real physical devices and processes. Data input, data representation in a memory, data manipulation using algorithms and finally, data output require physical realizations with devices and practical procedures. Building a quantum computer then requires the implementation of quantum bits (qubits) as storage sites for quantum information, quantum registers and quantum gates for data handling and processing as well as the development of quantum algorithms. In this talk, the basic functional principle of a quantum computer will be reviewed. It will be shown how strings of trapped ions can be used to build a quantum information processor and how basic computations can be performed using quantum techniques. In particular, the quantum way of doing computations will be illustrated with analog and digital quantum simulations, which range from the simulation of quantum many-body spin systems over open quantum systems to the quantum simulation of a lattice gauge theory.

Seminarroom 1+2+3 iCal Event
14 Mar 2018
04:30 PM

tba

Heikki Huttunen (Technical University of Tampere)

Room 1D1 iCal Event
26 Mar 2018
04:30 PM

Colloquium: Lasing to Photon Bose-Einstein-Condensation Crossover: Open versus Closed System Dynamics

Prof. Dr. Martin Weitz (Universität Bonn)

Bose-Einstein condensation has been observed with cold atomic gases, exciton-polaritons, and more recently with photons in a dye-solution filled optical microcavity. I will here describe measurements of my Bonn group observing the transition between usual lasing dynamics and photon Bose-Einstein condensation. The photon Bose-Einstein condensate is generated in a wavelength-sized optical cavity, where the small mirror spacing imprints a low-frequency cutoff and photons confined in the resonator thermalize to room temperature by absorption re-emission processes on the dye molecules. This allows for a particle-number conserving thermalization, with photons showing a thermodynamic phase transition to a macroscopically occupied ground state, the Bose-Einstein condensate. When the thermalization by absorption and re-emission is faster than the photon loss rate in the cavity, the photons accumulate at lower energy states above the cavity cutoff, and the system finally thermalizes to a Bose-Einstein condensate of photons. On the other hand, for a small reabsorption with respect to the photon loss, the state remains laser-like. I will also report recent measurements of the heat capacity of the photon gas, which were performed under the conditions of the thermalization being much faster than both photon loss and pumping. At the Bose-Einstein phase transition, the observed specific heat shows a cusp-like singularity, as in the $\lambda$-transition of liquid helium, illustrating critical behavior of the photon gas. In my talk, I will begin with a general introduction and give an account of current work and future plans of the Bonn photon gas experiment.

Seminarroom 1+2+3 iCal Event
28 Mar 2018
11:00 AM

Glassy dynamics of active self-propelled particles and biological systems

Saroj Nandi (Weizmann Institute of Science)

Room 1D1 iCal Event
09 Apr 2018
04:30 PM

Colloquium: tba

Ali Yazdani (Princeton University, USA)

Seminarroom 1+2+3 iCal Event
16 Apr 2018
04:30 PM

Colloquium: tba

Jean-François Joanny (ESPCI Paris)

Seminarroom 1+2+3 iCal Event
23 Apr 2018
04:30 PM

Colloquium tba

Seminarroom 1+2+3 iCal Event
30 Apr 2018
04:30 PM

Colloquium: tba

Francoise Brochard (Curie Institute)

Seminarroom 1+2+3 iCal Event
07 May 2018
04:30 PM

Colloquium: tba

Udo Seifert (Universität Stuttgart)

Seminarroom 1+2+3 iCal Event
28 May 2018
04:30 PM

Colloquium: tba

Fred MacKintosch (Rice University, USA)

Seminarroom 1+2+3 iCal Event
04 Jun 2018
04:30 PM

Colloquium: tba

Sriram Ramaswamy (Indian Institute of Science, Bengaluru)

Seminarroom 1+2+3 iCal Event