AtMol Research Seminars
Seminar Archive

Unless otherwise advertised, all talks are in room Ph30 at 1:00pm on Wednesdays.

Michaelmas Term 2014

Date Speaker Institution
Quantum simulators: physics fad or something useful?
Wed 8 Oct 2014 Charles Adams Durham University

The purpose of this talk is to introduce what is meant by the term 'quantum simulator', and what kinds of problems such a device might solve. Then we will consider where we are research wise in trying to produce a quantum simulator based on various platforms such as ions, atoms, molecules and superconductors.

Journal Club: Imaging through Quantum Optics
Wed 15 Oct 2014 Simon Ball Durham University

Classical imaging has relied on direct detection of photons since the first photoreceptive cells mutated approximately two thirds of a billion years ago. Over the last century, our understanding of the quantum nature of light has allowed alternative schemes to be developed, allowing indirect detection of illuminated objects through entanglement of photons. Ghost imaging uses correlations between direct and indirect photons, while quantum photography uses entirely indirect methods to produce images. References: Pittman et al, Phys. Rev. A 52, R3429 (1995) Zou et al, Phys. Rev. Lett. 67, 318 (1991) Barreto-Lemos et al, Nature 512, 409 (2014)

Engineering Ultracold Quantum Technologies
Wed 22 Oct 2014 Matt Himsworth Southampton University

There is expected to be a second quantum technology revolution in the coming decade in which the weirder aspects of quantum physics, such as entanglement, superposition and matter-waves, are used for practical applications beyond the laboratory. These may include communication, navigation, geo-prospecting, defence, environmental monitoring, medical imaging, computing and archaeology. To do this we must overcome the current stage of chip-in-a-lab components to produce integrated and robust lab-in-a-chip systems. Commercial pressure will always drive development to reduce size, weight and power and therefore there is a large amount of engineering required to miniaturise current laboratory setups. Our groups approach to this problem is to look at the materials and processes developed in the microfabrication industry and adapt them to the roles of cold atom and ion systems. We constrain ourselves to methods which can be used for wafer level mass-production instead of bespoke demonstrations. This talk will focus on our efforts to develop a microliter magneto-optical trap including vacuum systems, optics, and atom sources which passively maintain ultrahigh vacuum for several years.

Journal Club: A Real-Time High Resolution Laser-Based Brain Tumour Imaging Technique
Wed 29 Oct 2014 Alistair Bounds Durham University

There is a dynamic and very rapidly growing field of medical imaging using lasers. We consider two techniques, Raman imaging (frequency changes in scattered light), and photoacoustic (PA) imaging (mapping an ultrasound image from ultrasound generated by light absorption). We then consider a method for merging these techniques with magnetic resonance imaging (MRI) to obtain a triple-modality brain tumour imaging technique. This technique can be performed in real-time during surgery with imaging depths of a few cm and resolution of tens of microns, and is capable of detecting microscopic tumour traces invisible to the naked eye. References: Going deeper than microscopy: the optical imaging frontier in biology, V. Ntziachristos, Nature Methods, 7, 603-614, (2010) Raman based imaging in biological application- a perspective, P. P. Kundu, C. Narayana, J. Med. Allied Sci, 2 (2), 41-48, (2012) Sensitivity of photoacoustic microscopy, J. Yao, L. V. Wang, Photoacoustics, 2, 87-101, (2014) A brain tumor molecular imaging strategy using a new triple-modality MRI-photoacoustic-Raman nanoparticle, M. F. Kircher et. al, Nature Medicine, 18, 829, (2012)

Impurity Problems with Cold Atoms
Wed 5 Nov 2014 Yvan Castin Laboratoire Kastler Brossel

The problem of 3D propagation of a distinguishable impurity in an ensemble of particles with which it interacts is multiform and of a deceptive simplicity, but by no means purely academic since it can be concretized experimentally with cold atoms. In the talk we shall explore various trails: (i) the impurity is a photon immersed in a periodic ensemble of trapped atoms. Can the spectrum of light exhibit some omnidirectional band gap ? How would an experimental observation be affected by finite size effects or by vacancies ? (ii) the impurity is a mobile atom interacting resonantly (more precisely with an infinite s-wave scattering length) with mobile atoms of another species. Can a few (two, three) majority atoms form bound states with the impurity ? An infinite number of bound states ? And how do these bound states affect the thermodynamic properties of macroscopic ensembles of such atoms and impurities ?

Journal Club: Optical Tractor Beams
Wed 12 Nov 2014 Philip Gregory Durham University

Optical tweezers are widely used in physical, chemical and biological experiments requiring access to nanometre-scale distances and piconewton-scale forces. They offer a method of manipulating particles via gradient forces which can hold a particle at the focus of a laser. If you want to move that particle however, you must move the focus by, for example, adjusting a lens. A tractor beam is a solution to this problem which allows the movement of particles either towards or away from the laser source without the use of gradient forces. Over recent years, numerous research groups have demonstrated small scale tractor beams with particle displacements ranging from micrometre to centimetre length scales. In this talk, I will outline three different methods which have been developed experimentally to overcome the force of radiation pressure on a particle which has traditionally negated the possibility of motion of a particle towards the laser source. References: S.-H. Lee et al., Opt. Express 18 6988 (2010) O. Brzobohaty et al., Nature Photonics 7, 123 (2013) V. G. Shvedov et al., Nature Photonics 8 846 (2014)

Holographic Generation of Optical Traps for Ultracold Atoms
Wed 19 Nov 2014 Donatella Cassettari St Andrews University

A recent area of interest in the field of cold atomic physics is the development of non-trivial spatially- and temporally-varying optical trapping geometries. Optical traps generally offer increased trap complexity at small length-scales, but at the disadvantage of increased likelihood of small-scale potential roughness. Recently, a new calculation method for phase-only holograms of arbitrary complexity directly addressed the issue of roughness. This algorithm, the Mixed-Region Amplitude Freedom (MRAF) [1] algorithm, calculates smooth and accurate light patterns for use as optical atom traps. However the output of this algorithm, when applied to real devices, often does not give high-quality optical traps and this output must be further adjusted. In this presentation, we introduce a simple and robust feedback-enhanced algorithm to improve the accuracy of optical traps generated by phase-only spatial light modulators (SLMs). In addition to the feedback-enhanced algorithm, we present a new method for the generation of holograms based on the direct minimisation of a cost function by a conjugate gradient local search algorithm [2]. We show that this approach successfully combines computational efficiency and algorithm versatility, allowing the accurate reproduction of a variety of target intensity profiles. References: [1] M. Pasienski and B. DeMarco, Opt. Express 16, 2176 (2008). [2] T. Harte et al., Opt. Express 22, pp.26548-26558 (2014).

Quantum Stochastic Behaviour in Cold Fermi gases
Wed 26 Nov 2014 Ray Rivers Imperial College London

In this talk I shall describe condensate formation in a cold Fermi gas tunable through a narrow Feshbach resonance. The spontaneous breaking of the global U(1) charge symmetry leads to a Goldstone-Higgs model in which the gapless phonon is the Goldstone mode and the gapped diatom density fluctuation mode the Higgs. These quantum density fluctuations provide a stochastic component to the speed of sound and I shall discuss some consequences of this for times of flight and dispersion relations. This stochastic component to a 'Lorentzian' metric depends crucially on the underlying Galilean invariance of the system and it is essential that this is preserved in the necessary approximations. To further exemplify this, I shall use the relation between Galilean and sound-cone Lorentzian invariance to show how the phonon, the Higgs and the diatom field are related, particularly in the BEC regime.

Seminar postponed: Strong Interactions in Alkaline-Earth Rydberg Ensembles
Wed 3 Dec 2014 Rick Mukherjee Max Planck Institute for the Physics of Complex Systems

Ultra-cold atoms in optical lattices provide a versatile and robust platform to study fundamental condensed-matter physics problems and have applications in quantum optics as well as quantum information processing. For many of these applications, Rydberg atoms (atoms excited to large principal quantum numbers) are ideal due to its long coherence times and strong interactions. However, one of the pre-requisite for such applications is identical confinement of ground state atoms with Rydberg atoms. This is challenging for conventionally used alkali atoms. In this talk, I would like to discuss the potential of using alkaline-earth Rydberg atoms for many-body physics by implementing simultaneous trapping for the relevant internal states. In particular, I will discuss a scheme for generating multi-particle entanglement and explore charge transport in a one dimensional atomic lattice.

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