AtMol Research Seminar Archive
Index Current Seminars

Easter Term 2006

Date Speaker Home
Special Seminar: Bose-Einstein condensation in an optical trap
April 5th Dr Ajay Tripathi Albert-Ludwigs University of Freiburg

We employ a double-MOT system where atoms are firstly collected for their precooling in a 2D-geometry in a high pressure region. From this source region thereafter, the atoms are efficiently transferred into a conventional MOT inside a UHV chamber with capture rates exceeding 108 atoms/s. After a loading time of 1s and a loading phase (temporal dark MOT) of 60 ms about 1% of the atoms are trapped in a tight CO2 Laser focus region. Evaporative Cooling is optimized by lowering the dipole trap depth over a 7s period, leading to condensates of typically having 20000 atoms. In this talk detailed characterization of the system and its diagnostic tools will be presented.

Rochester Lecture: Time: From Harrison's clocks to the possibility of New Physics
May 3rd Prof Sir Arnold Wolfendale Durham University

3:00 pm in Scarborough lecture theatre

Three-body problem in cold Bose gases with resonance enhanced interactions
May 10th Dr Thorsten Köhler University of Oxford

I will discuss exact treatments of three-body collision phenomena associated with cold Bose gases subject to magnetically tunable pairwise interactions. This involves quantitative predictions of three-body recombination and atom-dimer collision rates in 87Rb Bose-Einstein condensates, as well as an interpretation of recent experiments on cold gases of 133Cs in the context of Efimov's effect. The approach explicitly includes the dependence of the interactions on the Zeeman levels of each atom. Both the weakly and strongly coupled Feshbach resonances of 87Rb and 133Cs, respectively, distort the diatomic energy spectra causing destructive and constructive interferences in both three-body recombination and collisions between atoms and Feshbach molecules. These interferences can be attributed to atom-dimer and three-body zero energy resonances associated, in part, with the series of metastable trimer states predicted by Efimov.

Special Seminar: Towards neutral atom logic gates by quantum control of ground state and Rydberg atoms in optical traps
May 11th Prof Mark Saffman University of Wisconsin, Madison

4:15 pm in Ph327

I present recent progress in loading and manipulation of neutral atoms in microscopic optical traps. Single Rb atoms are loaded into far off resonant optical traps from a background vapor of cold atoms. Tightly focused optical beams are used to perform two-photon stimulated Raman rotations between hyperfine qubit states. We demonstrate qubit rotations at a rate of 1.4 MHz, 1 ms coherence time, and individual site addressing with crosstalk at the level of 0.001. Strong interaction of atoms excited to Rydberg levels provides a mechanism for fast two-qubit gates. We discuss the physics of multiatom coupling due to Forster energy hopping, and demonstrate suppression of multiple excitation of Rydberg states in small atom clouds confined to a microscopic optical trap. These results are a significant step towards quantum computing using optically trapped neutral atoms.

Topological solitons in inhomogeneous media
May 17th Prof Wojtek Zakrzewski Durham University

We give a short introduction to the theory of topological solitons (in 1-3 dimensions) and then discuss their properties when they propagate in inhomogeneous media. In this discussion we concentrate our attention on solitons in (2+1) diemensions and on Sine-Gordon kinks in (1+1) dimensions.

Special seminar: Reflection of cold atoms from magnetic thin-film atom mirror: From atom optics to measurement of short range forces
May 24th Dr Ashok Mohapatra Tata Institute of Fundamental Research

12:00 noon in Ph327.

In this talk, first I will present a brief overview of the previous experiments performed in our group to measure the short range forces (Casimir and van der Waals forces). Then, I will focus on our recent experiment on the reflection of cold atoms from magnetic atom mirrors made of ferro-magnetic thin films. In the case of magnetic thin-film atom mirror, the closest approach of the atoms to the surface can be less than 100 nm. At this distance, the effect of the attractive atom-surface interaction can be comparable to the repulsive magnetic interaction potential. Hence, these kind of magnetic atom mirrors are very much suitable for the measurement of the atom-surface interaction. In our experiment, van der Waals interaction of a rubidium atom with a conducting surface is detremined with an uncertainty of 15%, by measuring the reflectivity of cold rubidium atoms from cobalt thin films of different thickness.

The details of the measurement of the van der Waals force using cobalt thin-film atom mirrors will be presented.

Optical quantum information processing
May 24th Dr Bill Munro Hewlett-Packard Laboratories

Quantum information processing (QIP) offers the promise of being able to do things that we cannot do with conventional technology. Here we present a new route for distributed optical QIP, based on generalized quantum non-demolition measurements, providing a unified approach for quantum communication and computing. Interactions between photons are generated using weak non-linearities and intense laser fields---the use of such fields provides for robust distribution of quantum information. Our approach requires only a practical set of resources, and it uses these very efficiently. Thus it promises to be extremely useful for the first quantum technologies, based on scarce resources. Furthermore, in the longer term this approach provides both options and scalability for efficient many-qubit QIP.

Inaugural Lecture: Entangled in a quantum web
May 31st Prof Charles Adams Durham University

5:15 pm in Ph8

The quantum world is a strange exotic place where things behave in ways that seem to contradict our human reasoning. The first quantum revolution began one hundred years ago when physicists such as Einstein, Heisenberg and Schrödinger established the laws of quantum mechanics. These laws have enabled us to exploit quantum phenomena and enabled new technologies such as electronics and computing. The second quantum revolution is ongoing, and is about gaining complete control of the quantum world. This talk will discuss where to find the quantum world in its purest unpolluted forms, and what we are going to try to control it.

Optical Matter
June 7th Prof Colin Bain Durham University

2:15 pm in OC218

It is well-known that focussed light beams can be used to manipulate small colloidal particles (optical tweezers). What is less well-known is that colloidal particles can spontaneously organise due to scattering of light in a laser beam (optical binding). This talk will describe some of our recent work assembling arrays of polystyrene particles in an evanescent field at a silica-water interface.1,2 The effect of particle size and the polarisation of the light on the symmetry of the arrays is explored. Interesting dynamical effects can also be observed. Other work in which laser beams are used to shape emulsion droplets (optical sculpting) will be briefly described.

  1. Array Formation in Evanescent Waves, CD Mellor, CD Bain, ChemPhysChem 7, 329 (2006)
  2. Stuff of Beams, J Mullins, New Scientist 2551, 44 (13 May 2006)
Adaptive Optics & Optical Trapping: from Astro to Nano
June 14th Dr Gordon Love Durham University

Adaptive optics is normally connected with controlling light in large astronomical telescopes. However the ability to spatially control the amplitude, phase, and polarization of light opens up many opportunities in other fields, including control at the microscopic scale. In this talk I will describe the work of the Centre for Advanced Instrumentation in optical tweezing and trapping.

First-year talk:
June 21st Mr Mark Bason Durham University
First-year talk: Shocks In Regions of Stellar Formation
June 28th Mr Antoine Gusdorf Durham University

Recent observations show that young stellar objects eject matter at a velocity of about ten kilometer per second, in the form of jets that impact the collapsing matter at the origin of the formation of the star. This supersonic impact gives birth to a shock front, propagating in the interstellar cloud. The structure of these shocks depends on their speed and on the physical properties of the matter in which they propagate, and these properties themselves allow us to deduce informations on the star formation scenario. In this talk I will show how it is possible to use molecular emission diagnoses in this kind of regions to constraint their physical properties and thus maybe discriminate among the existing star formation scenarios.

First-year talk: Manipulation of trapped particles
July 5th Mr Johnny Taylor Durham University

Our group has been building and using liquid crystal devices to trap and manipulate micro-particles in optical tweezers and traps. In this talk I will describe some of the devices I'm intending to integrate into cold atom trapping experiments to provide more precise control over the trapped atoms. I will also show some of the unexpected effects we have been observing in our counter-propagating particle trap, and outline the work I have been doing in trying to understand the origin of these effects.

First-year talk: Gravity
July 11th Mr Mark Saunders Durham University

A new method for measuring the local acceleration due to gravity has been proposed theoretically. Using phenomenon first discovered in optics, the momentum of a cloud of atoms is found to resonate when the pulses from a laser beam are delivered at a particular frequency. I will present the developments over the last 9 months, and discuss the future plans of where I intend to take this project.

Special seminar: Resonant control of cold atomic collisions
July 25th Dr Paul Julienne NIST

4:15 pm in Ph327

Tunable scattering resonances in ultracold atomic collisions have proved to be extraordinarily successful in controling the properties of cooled and trapped atomic gases. This talk will offer an overview of the basic properties of such magnetically and optically tunable Feshbach resonance states, and the corresponding bound molecular states that can be formed from a pair of cold atoms. The basic freatures of such resonances can understood in term of a few parameters and the properties of the long range potential. Several resonances that have been successfully used in experimental studies will be used to illustrate the basic concepts.