AtMol Research Seminar Archive
Index Current Seminars

Easter Term 2013

Date Speaker Institution
Resonant scattering processes in nonlinear optics
Wed 24 Apr 2013 Prof Daniele Faccio Heriot Watt University

There a number of known processes in nonlinear optics that can be described in terms of a resonant scattering process between different modes, i.e. frequencies in the spectrum. The most important example is resonant radiation, also known as Cherenkov or dispersive wave radiation from optical fibre solitons. However, it is rather less appreciated how general and ubiquitous these time-dependent scattering processes actually are. We will first overview the general concept of resonant radiation from solitons and then show, both theoretically/numerically and experimentally that resonant radiation occurs in rather unexpected situations. A clear link is also established between the emission of resonant radiation and the formation of shock fronts in nonlinearly propagating pulses. We then move on to discuss the role of the negative frequency components in scattering processes from time-dependent media. Negative frequencies are a natural component of any real-valued field but usually neglected in light of the fact that in linear optics, a Fourier Transform always delivers a perfectly symmetric spectrum. However, in nonlinear optics we show that the negative and positive frequency components can lead to scattering into separate and distinguishable output modes. These findings are supported by both numerics and experiments. Finally, we briefly examine the relevance of these scattering processes in terms of reconstructing analogues of black hole event horizons alongside other examples of optical scattering from time-dependent media.

Room-temperature solid-state masers based on molecular intersystem crossing (ISC)
Wed 1 May 2013 Dr Mark Oxborrow Imperial College, London

Like lasers, masers exploit the quantum mechanical process of stimulated emission to amplifier electromagnetic waves –though at microwave frequencies (i.e. around a few GHz) as opposed to optical ones (several hundreds of THz). Since microwave photons individually carry little energy, a maser can amplifier a weak signal whilst imparting very little deleterious (Schawlow-Townes) shot noise onto it. Masers made out of solid-state gain materials such as ruby were invented in the mid. 1950s. They became key to the success of NASA’s deep space network, as used for receiving spectacular images of the rings of Saturn back from its distant Voyager 1 & 2 space probes, as well as supporting other missions (like those to Mars) since. But ruby masers can only operate advantageously at liquid-helium temperatures. This prevented their uptake in a great many applications that could have otherwise taken advantage of their superior noise performance. Compared to semiconductor-based amplifiers, which do work –albeit noisily– at room temperature, masers have languished in the backwaters.

In my talk, I shall describe a solid-state maser1 that does work at room temperature. In contrast to ruby, this new maser’s gain medium is an organic mixed molecular crystal, namely p-terphenyl, which is lightly doped with pentacene. Upon photo-exciting the latter species with yellow pump light from a pulsed dye laser, molecular intersystem crossing (ISC) into pentacene’s triplet ground state provides a strong population inversion across the upper and lower sub-levels of this state, sufficient for masing at ~1.45 GHz on the TE01δ mode of a high-Q sapphire-loaded cylindrical microwave cavity, with an output (saturation) power of around –10 dBm. As the ISC process provides negative spin temperatures of the order of a few tens of mK, microwaves can in principle be amplified at a residual noise temperature of this same order, even though the maser crystal is at room temperature. In other words: a cryogenic amplifier that isn’t. The general prospects of organic masers based on ISC shall be discussed.

1 “Room-temperature solid-state maser”, M. Oxborrow, J. D Breeze & N. McN. Alford, Nature 488, 353-356 (2012).

Universal few-body physics in ultracold atoms
Wed 8 May 2013 Lev Khaykovich Bar-llan University

Few-body systems with resonantly enhanced two-body interactions display universal properties in the sense that they are independent of the details of the short-range interaction potential. The central paradigm in the three-body domain, predicted in the early 1970s by V. Efimov, is associated with the infinite ladder of universal bound states with discrete scaling invariance. This curious prediction avoided experimental verification in different systems for decades, and only recently and exclusively surrendered to ultracold atoms. I will describe the remarkable progress in experimental investigation of the Efimov scenario with the emphasize to our studies performed with ultracold bosonic lithim.

Stirring up entanglement: quantum metrology with rotating matter waves
Wed 15 May 2013 Dr Jacob Dunningham Leeds University

Quantum metrology makes use of entanglement to achieve measurement precisions beyond what could be achieved by conventional classical methods and is rapidly emerging as an exciting and feasible new technology. I will give a brief introduction to the field before focusing on the particular case of atomic Bose-Einstein condensates (BECs) trapped in rotating potentials. These are appealing because they are within reach of current experiments, provide a conceptually simple way of generating many-body entanglement, and have the prospect of leading to the development of ultra-precise gyroscopes.

In order to employ such a system for metrology, it is important to understand the detailed form of the entangled states that can be created. I will present a study that goes beyond the Landau level (LLL) approximation. I will demonstrate that whilst the LLL can identify reasonably the critical frequency for a quantum phase transition and entangled state generation, it is vital to go beyond the LLL to identify the details of the state and quantify the quantum Fisher information (which bounds the accuracy of the phase measurement). We thus identify a new parameter regime for entangled state generation, amenable to experimental investigation.

A lifetime in luminescence
Wed 22 May 2013 Andy Beeby Durham University

Abstract TBA

Thin-film magnetism and spintronics
Wed 29 May 2013 Aidan Hindmarch Durham University

Abstract TBA

First Year Talk: Title TBA
Wed 5 Jun 2013 Peter Molony Durham University

Abstract TBA

First Year Talk: Talk Title TBA
Wed 12 Jun 2013 Rob Bettles Durham University

Abstract TBA

[No Seminar]
Wed 19 Jun 2013 [No Seminar] [University]

Abstract TBA