AtMol Research Seminar Archive
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Seminar Archive

Michaelmas 2010

Date Speaker Institution
Ion trapping
21st September Prof. Christopher Monroe University of Maryland

This was an exceptional seminar on work by the group of Prof. Monroe on Ion trapping.

No seminar
13th October

Precision frequency metrology (cancelled)
20th October Prof. Ben Varcoe University of Leeds

In this talk I will present a line of work that we have been following for the last few years in the development of a system for absolute frequency metrology of atomic lines. The rubidium Rydberg series is the system that we have used as a focal point of our effort, primarily because of its importance to microwave cavity QED and for our experiments in special and general relativity. In developing this system we have found a number of inconsistencies and gaps in the field that we have been able to reconcile, such as a 10 standard deviation difference between two recent measurements of the D1 line and resolving a long standing error in D2 line spectroscopy. We use a combination of a three laser excitation scheme and microwave spectroscopy linked to a GPS disciplined atomic clock and a 250MHz frequency comb. The comb system was tailor made for our application and provides reference light spanning two octaves from 500nm to 2000nm. The system that we have created is capable of performing precision spectroscopy on the Rydberg series, ns, np, nd, nf, ng and nh. Our most recent result is an observation of van der Waals interactions between 5s ground states and np and nf excited states.

From ultracold to ultrahot: quasi-relativistic dynamics in atomic quantum gases
27th October Dr Patrik Öhberg Heriot-Watt University

Artificial electromagnetism is a new tool to manipulate charge neutral quantum gases. In this talk we will look at how spin-orbit coupling arises in these gases and how it can be used to simulate quasi-relativistic dynamics and find connections to phenomena known from high energy physics.

Journal Club talk: David Holdaway
3rd November Mr David Holdaway Durham University

Photosynthesis provides the base nutrients for almost all life on earth, recent experimental and theoretical work on the phenomina has yielded interesting results, suggesting that long lived quantum coherence can be found in light harvesting protein "antenna" is used as a mechanism to transfer excitation energy to reaction center even at room temperature.

This talk focuses on the experimental techniques of three pulse two photon echo (2PE) spectroscopy and the results obtained in the paper "Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature" E. Collini, C. Y. Wong et al, doi:10.1038/nature08811

Manipulating and probing microwave fields in a cavity by quantum nondemolition photon counting
10th November Dr Michel Brune École normale supérieure - Paris

We perform quantum nondemolition photon (QND) counting in a high Q cavity. Microwave photons are stored in a superconducting cavity for time as long as 0.1s. By using Rydberg atoms as clocks whose ticking rate is affected by light shifts induced by the cavity field, we realize an ideal projective measurement of the photon number. The experiment demonstrates all features of quantum measurement theory: random results, state projection and repeatabily.

Measuring the atoms is an efficient way for preparing by projection non-classical states such as number states or Schrödinger cat states. We use the QND measurement method for reconstructing the Wigner function of these states and to monitor their decoherence. These field manipulation methods can be applied to state preparation by quantum feedback and to demonstrate non-locality with two fields located in separated cavities.

Hybrid quantum computing with spin ensembles and super conducting qubits
17th November (Lunch time 13:00-14:00) Prof. Klaus Mølmer Aarhus University

In conventional registers for quantum information processing, quantum bits are associated with individual two-level quantum systems. Separate addressing and interaction with these systems permit one-bit gates, while an interaction between systems is needed to accomplish two-bit gates. I will review a recent proposal to implement quantum computing in collective excitation degrees of freedom in ensembles of identical quantum systems.

In this proposal one does not need to address individual particles, but one needs an interaction between all particles in the system. Such interactions exist in hybrid systems where large spin-ensembles are coupled to superconducting qubit elements via a resonant single mode of the quantized radiation field. We will review the main ideas of ensemble encoding and we will discuss recent results on the effects of unwanted interactions and inhomogeneities in such systems.

Nanoelectromechanical Systems in the Quantum Regime
17th November As Prof. Andrew Armour University of Nottingham

Bose Einstein condensates of Chromium
24th November Dr Bruno Laburthe-Tolra Laboratoire de Physique des Lasers

Optical Trapping and Manipulation of Nanostructures
1st Decemember Dr Phil Jones University College London

In this talk I will present recent work from the UCL Optical Tweezers Group on the application of optical trapping methods to the nanoscale. I will start by describing the working of the single-beam laser trap or optical tweezers and the limitations encountered when trying to trap nanoparticles, before discussing the application to nanomaterials such as gold nanorods, carbon nanotubes, graphene flakes and polymer nanowires.

Our experiments with these objects include measurement of optically induced rotations and force measurements in the femto-Newton regime. I will then go on to discuss how novel beam-shaping techniques can be applied to optical tweezers that could lead to improved trapping of nanoparticles, before presenting our most recent activity aimed at using light-carrying nanostructures for optical trapping and manipulation

Journal club talk: Magnetically Trapped Antihydrogen
8th Decemember Mr Lee Weller Durham University

Based on the paper G. B. Andresen et al. Nature 468, 673–676 (02 December 2010). Antimatter was first predicted1 in 1931, by Dirac. Work with high-energy antiparticles is now commonplace, and anti-electrons are used regularly in the medical technique of positron emission tomography scanning. Antihydrogen, the boundstate of an antiproton and a positron, has been produced2, 3 at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature's fundamental symmetries. The charge conjugation/parity/time reversal (CPT) theorem, a crucial part of the foundation of the standard model of elementary particles and interactions, demands that hydrogen and antihydrogen have the same spectrum. Given the current experimental precision of measurements on the hydrogen atom (about two parts in 1014 for the frequency of the 1s-to-2s transition4), subjecting antihydrogen to rigorous spectroscopic examination would constitute a compelling, model-independent test of CPT.

Antihydrogen could also be used to study the gravitational behaviour of antimatter5. However,so far experiments have produced antihydrogen that is not confined, precluding detailed study of its structure. Here we demonstrate trapping of antihydrogen atoms. From the interaction of about 107 antiprotons and 7×108 positrons, weobserved 38 annihilation events consistent with the controlled release of trapped antihydrogen from our magnetic trap; the measured background is 1.4±1.4 events. This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.

Journal club talk: Quantum Random Walks
15th December Mr Chris Carr Durham University

In my journal club talk, I will review recent work by Jeremy O'Brien at the University of Bristol. O'Brien has shown that lattices of coupled waveguides are an extremely versatile tool that can be used to manipulate the flow of light. The photons undergo random walks in the waveguide lattice and develop non-trivial quantum correlations. Such a system also enables direct observation of optical analogues of many fundamental quantum mechanical effects. Following a review of the applications of random walk analysis, I will look at how classical and random walks are different. A brief encounter with some basic quantum optics will then be followed by a presentation of the experimental results from the waveguide lattice.