The June 2012 research newsletter
This edition marks the end of an era, and the beginning of another. Due to the restructuring of the university and departmental webpages, the newsletter will be changing its form, going towards a more continuously updated format compared to the episodic versions. In future, articles and notices will appear on the physics website as they come in, leading to reduced latency. The new format will also be more flexible in the form of the articles which can be presented. But until then, please enjoy the last "edition" of the Research Newsletter.
Stratospheric Balloon Test of Satellite Quantum Experiment
A collaboration between the University of Strathclyde and the Centre for Quantum Technologies (Singapore) successfully tested components for a satellite quantum entanglement experiment due for launch next year. On the 18th May, a prototype experiment was lofted into the stratosphere by a helium microballoon in order to test its operation at low temperatures, pressures, as well as confirm remote operations.
Balloon launch. A helium balloon carried the prototype quantum entanglement experiment to an altitude of 37.5km. A GPS and radio packet system allowed the balloon and its payload to be tracked to a landing spot 64km from the launch.
Daniel Oi (Strathclyde) first proposed the use of nanosatellites to test quantum entanglement in space as a precursor to a global spanning quantum network for secure quantum communications. This idea is being developed in conjunction with Alexander Ling at the Centre for Quantum Technologies who heads the experimental effort. Along with technician Yue Chuan Tan, Daniel and Alex teamed up with Christian Wildfeuer at the Suso Gymnasium, Konstanz, secondary school students, and a team of amateur radio volunteers to launch, track and recover the experiment. The project has received coverage from the Economist, Space.com, and local newspapers and TV.
Locking Micro-Lasers Made of Cavity Solitons
Laser cavity solitons are spatially localised beams of light on a homogeneous background. They correspond to bright spots of coherent light that can be switched on and off at pleasure by the operator thus making them ideal components for optical memories and delay lines. It is then natural and useful for applications to investigate their interaction properties.
In a strategic collaboration between theory, simulation and experiment, Craig McIntyre, Yoann Noblet, Neal Radwell, William Firth, Thorsten Ackemann, and Gian-Luca Oppo in a collaboration with Pavel Paulau in Berlin and Pere Colet in Majorca have demonstrated that the pinning of laser cavity solitons to background defects changes drastically their interaction properties so that they can lock their phases and frequencies to form bound couples.
Two laser cavity solitons in a vertical cavity semiconductor laser (VCSEL) with feedback provided by a volume Bragg grating (VBG). Cavity solitons are the dark spots in the inset that displays the cross section of the output intensity. They synchronize their frequencies and phases to common values.
Adler Synchronization. Theoretical model (top) shows the phase difference controlled by the detuning proportional to the relative depth of the trapping defects. Experiments (bottom), see green curve within the locking range where the detuning is controlled by the tilting angle of the VBG.
The important news for photonic applications in information and quantum processing is that arrays of phase locked micro-lasers such as our cavity solitons maintain independence (each of them can still be created and erased at will by the operator) while coupled by long-range correlations through their locked phases.
Finally, it is relevant to note that cavity solitons studied here and in absorbing semiconductor micro-cavities are composite structures consisting intrinsically of both a light and a material component as we pointed out recently in a correspondence to Nature Photonics (Volume 6, page 204, 2012). Numerical analyses have shown that forcing a spatial separation of the material and optical components of a cavity soliton causes it to disappear. The composite nature of cavity solitons has also been exploited in experiments that involve their control by optically manipulating their material component.
[TA] & [GLO]
C. Trager-Cowan 1/7/12-31/8/15
EPSRC Awarded £435293
N. Hunt 1/6/12-31/5/15
EPSRC Awarded £179061
O Rolinski 4/5/12-31/3/13 Awarded £2000
K. Ronald 1/4/12-31/3/16
STFC Awarded £306591
C. Trager-Cowan 26/3/12-25/6/12 Strathclyde - Research development fund Awarded £5926
M. Fedorov 1/3/12-28/2/13
Industry Awarded £38735
N. Hunt 1/3/12-30/6/12 Strathclyde - Research Contract Awarded £20000
F. Papoff 27/1/12-27/1/13 Awarded £2500
H. Summers 1/1/12-31/12/12
EPSRC Awarded £40000
Maxim Fedorov has been awarded the 2012 International Association for the Properties of Water and Steam (IAPWS) Helmholtz Award. He was nominated for work on the Integral Equation Theory of Molecular Liquids that allowed the development of fast and accurate modelling of efficient 'in-silico' screening of solvation properties of biologically and pharmaceutically relevant compounds. Maxim will present the Helmholtz Lecture at the IAPWS Annual Meeting in Boulder, Colorado. He is the first winner from the UK.
On Monday 14 May 2012, Ken Ledingham (above top, right) and Gian-Luca Oppo (above, bottom, right) were formally elected Fellows of the Royal Society of Edinburgh (RSE). The RSE is Scotland's National Academy. Its mission is to advance learning and useful knowledge and by doing so it supports the cultural, economic and social well-being of Scotland and its people.
[KL] & [GLO]
EPSRC Award for Nitride Research
An EPSRC grant £843K (Strathclyde Share: £482K) has just been awarded to a research collaboration led by Strathclyde University to develop novel electron microscopy techniques to support the development of new nitride based materials with applications ranging from new light sources to the high power electronics required for electric cars. The grant "Nanoscale characterisation of nitride semiconductor thin films using electron backscatter diffraction, electron channelling contrast imaging, cathodoluminescence and electron beam induced current" is in collaboration with Oxford, Imperial, Bath, Sheffield and Nottingham Universities.
The award follows hot on the heels of the publication of a paper in Physical Review Letters: G Naresh-Kumar, B Hourahine, P R Edwards, A P Day, A Winkelmann, A J Wilkinson, P J Parbrook, G England and C Trager-Cowan 2012 "Rapid nondestructive analysis of threading dislocations in wurtzite materials using the scanning electron microscope", Phys. Rev. Lett. 108, 135503.
Defects in a crystal revealed by new technique
The paper describes a simple, non-destructive technique which allows the efficient, unambiguous identification of common defects in materials with the wurtzite crystal structure (e.g., GaN, ZnO and SiC): namely threading edge, screw and mixed dislocations. The team applies the scanning electron microscopy technique of electron channelling contrast imaging (ECCI). In ECCI images are produced from electrons which channel along crystal planes; defects cause deviations from the perfect crystal lattice and give rise to contrast in the electron channelling contrast image with threading dislocations appearing as spots with black-white contrast (see figure). The paper describes a simple geometric procedure which exploits the differences observed in the direction of this contrast for the different types of threading dislocations, when comparing two electron channelling contrast images acquired from symmetrically equivalent crystal planes. This procedure requires no sophisticated sample preparation and reduces, by an order of magnitude, the time required to obtain quantitative and statistically significant information on dislocations compared to presently available techniques.
Between the Sheets
Melanins are ubiquitous pigments. They are present in skin, hair, the eye and the brain though it is their function as a natural sunscreen for which they are perhaps best known. Although it is established that melanins are largely composed of dihydroxyindoles (relatively small molecules closely linked to several amino acids), their non-repeating polymer structure has remained elusive. This lack of structural knowledge is a barrier to progress in several areas, most notably in understanding the causes of malignant melanoma, the most virulent form of skin cancer.
Recent work in the Photophysics Group (Sutter et. al. Appl. Phys. Lett. 100, 113701, 2012) studied eumelanin synthesis using the fluorescence of thioflavin T (ThT); a dye known increase its fluorescence when rotational modes are constrained between sheet structures. Although the detailed structure remains unknown the work revealed a sigmoidal temporal dependence of assembly that is consistent with protomolecule formation and assembly into a stacked sheet structure analogous to that of graphite (below).