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QLM Physics and Astronomy

University of Southampton

Quantum, Light and Matter Research at Southampton

The research of the Quantum, Light and Matter (QLM) Group emphasizes themes of

nano-structured materials, quantum coherence and photonics. QLM was formed in 2004,

bringing into one unit all the “mainstream1” research of the Physics and Astronomy

Department, including all the in-house experimental work.

Our work on nanostructured materials includes templated materials, and a range of hybrid

organic/inorganic systems for photonic and bio-nano applications based on combinations

of III-V quantum wells, polymers and liquid crystals and colloidal quantum dots. Work

on quantum coherence includes the experimental and theoretical study of exciton-

polaritons in semiconductor microcavities, cold molecules, matter-wave interferometry

and cold atoms, as well as atom chips. Individual projects are described in more detail

below. The QLM group has extensive international collaborations (EU networks, US Air

Force), joint projects with other UK universities (Cardiff, Cambridge, Nottingham,

Sheffield…), as well as collaborations with other departments at Southampton (ORC,

Chemistry, ECS, Mathematics, Engineering Sciences).

QLM currently has 13 academic staff members including two EPSRC Early Career

Fellows and a Royal Academy of Engineering Fellow. We occupy about 430 m2 of

laboratory space, supported by an integrated technical team that provides mechanical

workshop, electronic workshop, cryogenics, fabrication, laser facility and laboratory

infrastructure support.

Recent QLM successes include:

The award of Early Career Fellowships to Keith Wilcox and Otto Muskens in

the first round of the new EPSRC Fellowship competition, for work on future

frequency combs and nanophotonics respectively.

award to Pavlos Lagoudakis of the inaugural IUPAP Quantum Electronics

Young Scientist Prize, which he will accept at IQEC in Sydney this August, in

acknowledgement of his pioneering work in hybrid optoelectronics;

award of a £6M Programme Grant jointly with Chemistry (Phil Bartlett PI) to

fund continuing research on the deposition of device quality semiconductor

material from supercritical fluids. The activity originated at this University in a

Basic Technology Grant led by David Smith.

1 i.e. not particle physics or astronomy

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award to Hendrik Ulbricht of $140k from the Foundational Questions Institute

for experimental tests of quantum theory by de Broglie interference of large

particles - polystyrene spheres and viruses. Hendrik won the largest award on a

list that includes of the world’s leading quantum gravity researchers. More

recently Hendrik has been awarded £400k for work on Nonclassicalities and

Quantum Control at the Nanoscale as part of a large EPSRC-funded project

involving also UCL, Imperial and Warwick.

award to Dorota Bartczak, PhD student of Antonis Kanaras, of the Mendel

Medal, which is First Prize in Biological and Biomedical Sciences at the SET for

Britain 2010 poster exhibition at the House of Commons

award to Matt Himsworth of a Royal Academy of Engineering Fellowship

entitled Atom-Chip Integration for Quantum-Enabled Devices;

award to Anne Tropper of a 1-year Leverhulme/Royal Society Senior Research

Fellowship for work on femtosecond semiconductor lasers.

award to Alexey Kavokin of a 1-year Leverhulme/Royal Society Senior Research

Fellowship for work on strong light-matter coupling in semiconductor

microcavities.

The QLM group runs 1st, 2

nd and 3

rd year undergraduate teaching laboratories and

contributes a wide range of dissertation and project teaching, as well as delivering core

physics lecture courses and specialist teaching for the Masters “with Photonics” and

Masters “with Nano” programmes. The Masters in Physics with a Year of Research

programme, offered to a few high-achieving undergraduates, allows students to work full

time on a research project for one year in a QLM research laboratory.

The research programmes of individual staff members are described in more detail

below.

Nanomaterials group

http://www.nanotech.soton.ac.uk

The Nanomaterials Group headed by David C. Smith focuses on the rational design,

production and characterisation of a range of nanostructured materials. The group has

strong links with Chemistry and Electronic and Computer Science in Southampton.

One particular strength of this group is the deposition of high quality semiconductors and

metals into nanostructured templates using supercritical fluids. This work came out of a

Basic Technology grant (£3.4M pre-FEC) led by David which demonstrated for the first

time the thermal deposition of optoelectronic quality compound semiconductors from

supercritical fluids [Adv. Matt. 21, 4115 (2009).] and the first generally applicable

method for electrodepositing from a supercritical fluid [PNAS 106, 14768 (2009).] . The

latter has been used to produce high density thin films of 3nm diameter >100nm long

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copper nanowires. This work has led to a translation grant (£1M) to apply supercritical

fluid electrodeposition to magnetic, MEMS and plasmonic applications and a recently

announced Programme Grant (£6M) to enable the technique to be extended to higher

temperatures (~350OC), reactive materials, e.g. silicon, extreme nanopores (1nm in

diameter) to enable the deposition of materials with

crystalline forms which are not stable in bulk, and

to epitaxial heterostructures.

Other areas of research include vapour-liquid-solid

growth of semiconductor nanowires[NATURE 415

(6872), 617-620 (2002).], anodic alumina templated

nanowires for single/few molecule electronics

[ANAL. CHEM. 78 (3), 951 (2006]] and

electrically contacted nano-antennas, growth of carbon nanotubes using non-metallic

precursors, and liquid crystal photorefractive systems for controlling plasmons.

David leads, and is one of the main users, of the nanomaterials rapid prototyping facility

and often advises others on how to get the best from the facility.

Quantum Nanophysics and Matter Wave Interferometry

http://www.phys.soton.ac.uk/matterwave/html/index.html

The Quantum Nanophysics Group headed by Hendrik Ulbricht focuses on the

experimental demonstration of mesoscopic quantum effects to probe the limits of

quantum mechanics in the context of our interest in the foundations of physics. Main

experiments are concentrated on de Broglie interferometry to test quantum superposition

of large particles, such as

organic molecules and

nanospheres. The latter

effort was recently funded

by the Foundational

Questions Institute (FQXi).

Particles of a mass of

106dalton will test

spontaneous localisation

models, which represent an

extension of Schrödinger’s

quantum mechanics.

We are running Talbot-Lau

molecule interferometry [1]

to investigate the centre of mass motion of organic molecules up to 10.000 Dalton.

Interests also include molecule metrology by interferometric deflection. We make use of

the high degree of control on the transverse motion of the molecules and their coupling to

external forces and field for metrology, for example to investigate Casimir-Polder van der

Walls interactions forces, dielectric properties of the molecules [3], but also their optical

properties [5]. Interestingly, the internal state dynamics of molecules can be mapped onto

Figure 1: Talbot-Lau molecule interferometer at our labs.

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its motion, which may open new perspectives for coherent control techniques [4]. On the

molecular quantum optics side we are interested to the reconstruct the Wigner function of

the motion quantum state of molecules. To increase the control on the motion of

molecules we are interested in manipulation of molecules by for example light, particle

collisions and meta-materials for guiding, deceleration and cooling [2].

Another interest is the matter wave interference of electrons in graphene aiming towards

quantum entangling motion degrees of freedom of the electrons and other use of the wave

behaviour of electrons in this material. We are working on the realisation of a quantum

point contact device in graphene by carving the carbon film with the Orion He-ion

microscope. We have widespread collaboration ranging from nanofabrication at

Southampton to quantum theory and experiments within the UK and the EU.

[1] S. Gerlich et al., Nature Physics 3, 711 - 715 (2007).

[2] S. Deachapunya, EJPD 46, 307-313 (2008).

[3] S. Gerlich et al., Angew. Chem. 47, 6195-6198 (2008).

[4] M. Gring et al., Phys. Rev. A 81, 031604(R) (2010).

[5] S. Nimmrichter et al., Phys. Rev. A 063607 (2008

Functional Optical Materials Laboratory

http://www.phys.soton.ac.uk/funcoptmat

The Functional Optical Materials Laboratory led by Malgosia Kaczmarek, pursues

research on the development and charaterisation of hybrid optical materials. The range of

materials currently investigated includes photosensitive and nonlinear polymers, liquid

crystals and hybrid organic-inorganic structures. The group’s research on functional

materials focuses on gaining fundamental understanding of their performance, as well as

on creating material platforms ready for applications in photonic switching, signal

processing and sensing.

One of the main themes of the current work is nanoengineering of liquid crystals.

Dispersing low concentrations of ferroelectric, ferromagnetic or metal nanoparticles in

liquid crystals is a successful, non-synthetic method of improving their optical properties.

For example, incorporating inorganic, ferroelectric nanoparticles into low refractive

index liquid crystals led to the observation of some truly intriguing effects – a dramatic

improvement in their electro-optical parameters, optical anisotropy and nonlinearity. This

project, which includes both fundamental and device driven investigation is carried out in

collaboration with colleagues from DSTL, Kiev University, University of Lille and Penn

State.

Another important research area concerns optically addressed light modulators with

photosensitive polymer layers, such as PVK:C60. In involves a study

of surface and interface effects between liquid crystals and

photoconductive polymers, their dynamic patterning and light

propagation. This project includes both experimental study as well as

modelling and is carried out in collaboration with the Schools of

Mathematics.

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The group also actively pursues applications of functional materials in the exciting and

technologically important area of optoelectronics with the aim of demonstrating practical

applications for optical telecommunications and sensing. A successful demonstration of a

sensor, based liquid crystals overlays on channel waveguides led recently to a patent.

This work is carried out in collaboration with colleagues from the ORC and with

industrial input from Stratophase.

As nonlinearity and reorientation of liquid crystals can be induced with low laser

intensities, they are ideal materials for reconfigurable and adaptive optical interconnects.

In a joint work with University of Rome, tuneable nonlinearity, polarisation effects and

total internal reflection of solitons were successfully demonstrated in tailor-made liquid

crystal cells.

[1] N. Podoliak, et al, Phys. Rev. E, 82, 030701, (2010)

[2] A. Piccardi et al, Appl. Phys. Lett. 94, 091106, (2009)

[3] M. Peccianti et al, Phys. Rev. Lett. 101, 153902, (2008)

[4] N. Podoliak et al, Soft Matter, DOI: 10.1039/C1SM05051F, (2011)

Integrated Nanophotonics group

http://www.phys.soton.ac.uk/muskens

The Integrated Nanophotonics group has started in 2009 and is lead by Otto Muskens.

Our research is aimed toward developing fundamental understanding and new

applications of nanoscale and mesoscopic photonics. The group has received an EPSRC

First Grant and Royal Society funding in 2010, and is currently focusing on the following

topics:

Active control of nanoplasmonic devices: Analogous to radiowave

antennas, plasmonic nanoantennas have been developed which

provide a high local field enhancement with efficient coupling to

far field radiation. Active control of the resonance spectrum of a

plasmonic nanoantenna is a crucial step toward achieving

transistor-type nanodevices for manipulation of the flow and

emission of light. We have recently proposed new concepts of

photoconductive nanoantenna switches [1] and are currently

working on experimental realisation of these concepts.

Light trapping in photonic nanomaterials: Using novel broadband techniques based on a

supercontinuum light source [2], we are investigating the propagation of light in complex

photonic media such as photonic crystals [3] and random semiconductor nanowires [4].

These methods yield a detailed insight in the static and dynamical transport parameters

and enable studies of the interplay between order and disorder in photonic nanomaterials.

Mesoscopic photonics: Propagation of light through complex photonic media is governed

by the interference of thousands of light paths with random phases. Analogous with the

theory of mesoscopic electron transport at low temperatures, fundamental corrections to

diffuse transport arise related to localization phenomena. We investigate the coherence of

light transport in nanomaterials, including ultrafast control [5] and random lasers [6].

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Biophotonics: In a multidisciplinary collaboration with the Kanaras group and the School

of Medicine, we use optical techniques to image and manipulate living cells. Our first

results have shown the damage and recovery of human endothelial cells following

plasmonically targeted laser treatment [7]. We are developing techniques for real-time

imaging of plasmonic nanoparticles in cells based on single-nanoparticle microscopy [8].

[1] N. Large et al., Nano Lett. 10, 1741 (2010)

[2] O.L. Muskens et al., Opt. Lett. 34, 395 (2009); O.L. Muskens et al., Opt. Expr. 16, 1222 (2008)

[3] O.L. Muskens et al., Phys. Rev. B 83, 155101 (2011)

[4] O.L. Muskens et al., Nano Lett. 9, 930 (2009); O.L. Muskens et al., Nano Lett. 8, 2638 (2008)

[5] M. Abb et al., Phys. Rev. Lett. 106, 143902 (2011)

[6] R.G.S. El-Dardiry et al., Phys. Rev. A 81, 043830 (2010)

[7] D. Bartczak et al., Nano Lett. 11, 1358 (2011)

[8] O.L. Muskens et al., J. Phys. Chem. C 112, 8917 (2008) ; O.L. Muskens et al., Phys. Rev. B 78,

205410 (2008)

Laboratory for Inorganic Colloidal Nanocrystals

www.licn.phys.soton.ac.uk

The laboratory for Inorganic Colloidal Nanocrystals is led by Antonios Kanaras who

joined the group in autumn 2007, having recently worked with Paul Alivisatos at

Berkeley and Mathias Brust at Liverpool.

The main theme of his group is the synthesis and functionalization of new type of

functional materials based on nanoparticles as well as their applications in Physical and

Biomedical Sciences. Nanoparticles are employed in several fields of science ranging

from biology and medicine and the development of new diagnostic methods, drug

delivery, and imaging, to physics and engineering and the fabrication of novel devices for

energy conversion and storage. The major reason for the vast range of applications of

colloidal nanocrystals is the ability to easily tune the density of their electronic states,

which allows the control of their magnetic, optical, electrical, catalytic and mechanical

properties, characteristic for different materials. The control over the properties of these

nanocrystals can be achieved by chemically adjusting their size, shape, and composition

as well as by carefully selecting the organic molecules to coat their surface.

The group is inherently multidisciplinary and Antonios’ students have scientific

backgrounds in molecular biology, neuroscience, physics and materials chemistry.

Some of the major projects running at the group at the moment are in the areas of

nanomaterial synthesis and biophysics/biophotonics:

1) Manipulation of angiogenesis using functional plasmonic nanoparticles and their

properties. Angiogenesis is a major biological process related to the growth of new blood

vessels from existing ones. This process is strongly correlated with cancer growth and

metastasis. In this project, we synthesize new functional plasmonic materials that serve as

drug carriers, biomarkers and therapeutic agents (via laser hyperthermia) with the aim to

deliberately block cancer angiogenesis.

2) Nanoparticles’ penetration through skin: In this project we study the penetration of

nanoparticles with different sizes, shapes and charge through human skin explants. The

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outcomes of this research will be important for identifying new ways of drug delivery

through skin and for assessing the toxicity of near market products.

3) Morphological manipulation of neurons using nanoparticles: The aim of this project is

to influence neuron characteristics using newly developed types of plasmonic and

magnetic nanoparticles. We synthesize functional and biocompatible particles, which we

interact with different types of neurons.

More secondary themes related to the applications of nanoparticles to build smart

nanocomposites and to alter device functions are being developed.

[1] D. Bartczak et al., Small 7 (3) 388 (2011)

[2] D. Bartczak et al., Nano Lett. 11 (3) 1358 (2011)

[3] R. Fernandes et al. ChemComm (46) 7602 (2010)

[4] D. Bartczak et al. Langmuir 26 (17) 13760 (2010)

[5] Puigmartí-Luis J. et al. Angew. Chem. Int. Ed., 47 (10) 1861 (2008)

[6] Gur I. et al., Nano Lett. 7 (2) 409 (2007)

[7] A. G. Kanaras et al., Nano Lett. 5 (11) 2164 (2005)

[8] A. G. Kanaras et al., Angew. Chem. Int. Ed. 42 (2, 191 (2003)

Laboratories for Hybrid Optoelectronics

http://hybrid.phys.soton.ac.uk

In the Laboratories for Hybrid Optoelectronics we combine the purity of inorganic

semiconductors and the versatility of organic materials and colloidal nanoparticles in

novel hybrid configurations, and explore the properties and possible applications of this

amalgamation. The group, led by Richard Harley and Pavlos Lagoudakis, comprises

three postdoctoral fellows and four PhD students. There are four core activities:

Hybrid semiconductor nanostructures: Hybrid systems inspired by natural biological

nanostructures can use energy transfer and recycling to transform light into chemical

energy. Using ultrafast spectroscopy we investigate methods of transferring carriers from

efficient absorbers of low carrier mobility, such as organic semiconductors and

nanocrystal quantum dots, into high mobility single crystal inorganic semiconductors. We

recently demonstrated record exciton transfer efficiency of 65% and, applying novel

technologies developed in our group to excitonic solar cells, have achieved a threefold

enhancement of the overall efficiency of a single junction photovoltaic device. [1]

Spintronics: The ability to control the spin of electrons in semiconductors has brought a

new class of optoelectronic devices, with MRAMs being the latest to be commercialized.

The mechanisms that govern spin dynamics in semiconductors offer a fascinating field of

research highlighted by the 2007 Nobel prize for the discovery of Giant Magneto-

Resistance. Here we subject electrons to quantum confinement in zero, one and two

dimensions and study the spin dynamics under the influence of strong external fields. [2]

Nanoscale optoelectronics: The whole gamut of nanoscience consists of investigations on

the nanoscale and nano-engineering of artificial structures that give rise to desirable

macroscopic physical properties. In collaboration with synthetic chemists we explore the

possibility to actively tune the interaction of solid state quantum structures with the

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environment, a route to nanoscale manipulations of the optical and electronic properties.

The ultimate applications range from electric-field nanosensors, single photon tunable

sources to optical memory elements and all optical parallel processing. [3]

Strong light-matter coupling in nanostructures: Light-matter interactions in an environ-

ment of strong optical and electronic confinement boost a new range of optoelectronic

effects not seen in conventional devices. Spatially localised photons and electrons can be

engineered to produce polaritons: bosonic quasi-particles that can coalesce and form

Bose Einstein condensates, similar to those seen in cold atoms but in the solid state. Our

recent observation of room-temperature polariton lasing signalled a new era of devices

that exploit strong coupling; we have now built a new lab to investigate how polariton

condensates interact under strong magnetic fields (9 T) in GaAs microcavities. [4]

[1] S. Rohrmoser et al., Appl. Phys. Lett. 91, 092126 (2007); G. Itskos et al., Phys. Rev. B 76 035344

(2007); K. Becker et al.,Angewandte Chemie Int. Ed. 46, 3450 (2007)

[2] W. J. H. Leyland et al., Phys. Rev. B 75, 165309 (2007); M. Reufer et al., Nature Mat. 4 340 (2005);

O. Z. Karimov et al., Phys.Rev.Lett. 91 246601 (2003)

[3] R. M. Kraus et al., Phys. Rev. Lett. 98, 017401 (2007); J. Müller et al., Nano Lett., 5 2044 (2005); P.

G. Lagoudakis et al., Phys. Rev. Lett. 93 257401 (2004)

[4] S. Christopoulos et al., Phys. Rev. Lett. 98 126405 (2007); P. G. Lagoudakis et al., Phys. Rev. Lett. 90

206401 (2003)

Theory of Light-Matter Coupling in Nanostructures

http://hybrid.phys.soton.ac.uk/QLM/index_files/Page960.htm

Our world-leading group in the theoretical description of light-matter coupling

phenomena in low-dimensional semiconductor structures is led by Alexey Kavokin and

comprises 2 PhD students, and a postdoctoral fellow.

A large variety of intriguing optical phenomena take place in monolithic solid state

structures called microcavities [1] which can confine both light and charge carriers and

provide a laboratory for semiconductor quantum optics and photonics. The central object

of study in this laboratory is the exciton-polariton; a half-light-half-matter quasiparticle

exhibiting very specific properties and playing a key role in a number of beautiful effects

including superfluidity, super-radiance and entanglement. Exciton-polaritons are

excitations of a crystal obeying bosonic statistics and can Bose-condense at high

temperatures due to their extremely light effective mass. The Bose-Einstein condensation

(BEC) of exciton polaritons that was experimentally observed in 2006 opens the way

towards the realization of a new generation of optoelectronic devices exploiting

collective quantum effects at room temperature. Polaritonics, a newly emerging supra-

disciplinary field involving fundamental and applied semiconductor physics, photonics,

band structure engineering, crystal growth and device fabrication, is now expanding at a

rapid pace. At present, tens of research teams worldwide work on fabrication, optical

spectroscopy, theory, and applications of microcavities for the polaritonics.

The group of A. Kavokin in Southampton has made key contributions to the theoretical

understanding of the polariton, including the prediction of the optical spin Hall effect in

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2005, the description of the superfluid phase transition in microcavities in 2006 and the

prediction of polarization multistability and optical switching in microcavities in 2007.

Science [5], Nature Physics [6], Nature Photonics [7], 20 Physical Review Letter papers

and two text books on exciton polaritons have been published by the group. A. Kavokin

coordinated the FP5 and FP6 research-training network projects “Clermont” and

“Clermont2”. Now he coordinates the FP7 network “Exciton-polaritons: physics and

applications” (Clermont4) which is composed by 15 research groups from 5 countries.

The group actively collaborates with universities of Rome, Paris, Montpellier,

Cambridge, Durham, Grenoble, Madrid, Brasilia and Clermont-Ferrand. Our present

research is aimed at studies of charged polariton superfluids (supported by the EPSRC

grant in 2007), exciton supersolids and spin superfluidity.

[1] For a recent review see the textbook by A. Kavokin and G. Malpuech, Cavity polaritons, Elsevier,

Amsterdam (2003)

[2] A. Kavokin, M. Glazov, G. Malpuech, Optical spin Hall effect, Phys. Rev. Lett., 95 136601 (2005)

[3] I.A. Shelykh, Yu.G. Rubo, G. Malpuech, D. Solnyshkov, A. Kavokin, Polarization and propagation

of polariton condensates, Phys. Rev. Lett., 97 066402 (2006)

[4] A. Kavokin, Exciton-polaritons in microcavities: present and future, Applied Physics A – Materials

Science and Processing 89 241 (2007)

[5] K. Lagoudakis, T. Ostatnicky, A.V. Kavokin, Y.G. Rubo, R. Andre, and B. Deveaud-Pledran,

Observation of Half-Quantum Vortices in an Exciton-Polariton Condensate, Science, 326, 974

(2009).

[6] C. Leyder, M. Romanelli, J.Ph. Karr, E. Giacobino, T.C.H. Liew, M.M. Glazov, A.V. Kavokin, G.

Malpuech, A. Bramati, A., Observation of the optical spin Hall effect, Nature Physics 3, 628 (2007).

[7] A. Amo, T.C.H. Liew, C. Adrados, R. Houdre, E. Giacobino, A.V. Kavokin and A. Bramati, Exciton-

polariton spin switches, Nature Photonics, 4, 361 (2010).

Magnetism and superconductivity

http://www.phys.soton.ac.uk/super/

In Magnetism and Superconductivity our research ranges from investigations of

magnetisation dynamics, spin-transport and the statistical mechanics of superconducting

vortices, to the development of model structures for potential data storage and device

applications. This effort is led by Peter de Groot. He has published over 250 refereed

papers in this research area. In recent years de Groot has chaired the Magnetism Group of

the Institute of Physics and he was a panel member for the BLADE beamline (I10) which

is currently nearing completion at Diamond. The group’s research on magnetic and

superconducting materials is part of a close collaboration with engineering schools at

Southampton and with collaborators at Diamond Light Source, ILL, Oxford University,

UAM Madrid, Regensburg University, IoP Beijing, etc. De Groot is a partner in the

recently established Southampton Centre for Photonic Metamaterials which was set up

with substantial EPSRC funding and which is strongly linked to the Southampton

Nanofabrication Centre. In this context we are using patterned, magnetic and

superconducting materials to reduce losses, introduce non-linearities and quantum

coherence, exploit field and temperature control, etc. in microwave, THz and photonic

metamaterial structures.

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Fluorescing rubidium atoms at the

centre of a magneto-optical trap.

In-house magnetometry, transport, magneto-optics, MFM and microwave studies, and

measurements at neutron, synchrotron and high-field facilities are combined with

computational modelling. Achievements include the discovery of novel states and

dynamics of vortex matter [1,2], reorientation [3] and spin transport [4] phenomena in

exchange-spring multilayers, and the first observation of fano resonances in

superconducting metamaterials [5].

[1] A.N. Grigorenko et al., Phys. Rev. Lett. 90 237001 (2003)

[2] A.A. Zhukov et al., Phys. Rev. Lett. 87 017006 (2001)

[3] K.N.Martin et al., Appl. Phys. Lett. 89 132511. (2006)

[4] S.N. Gordeev et al., Phys. Rev. Lett. 87 186808. (2001)

[5] V. A. Fedotov et al., Opt. Express 18 9015 (2010)

Quantum Control

http://www.phys.soton.ac.uk/quantum/

The Quantum Control group led by Tim Freegarde

investigates new methods for the optical cooling and

manipulation of atoms and molecules. This experimental

activity, backed by theoretical work within the group and

collaborations with both theoreticians and fabricators, falls

roughly into three areas.

A first set of experiments investigate pulsed manipulation

schemes using the coherent interaction between atoms and

laser fields of programmable frequency, intensity and

direction. Such schemes include high fidelity state transfer using Raman chirped

adiabatic passage and velocity selective excitation by atom interferometry [1],

interferometric cooling and amplified cooling [2], and their extension to algorithmic

cooling and a momentum-state quantum computer [3]. Using cold rubidium atoms as test

species, our aim is to develop methods of cooling and manipulation suitable for a wider

range of atomic/molecular species than are currently accessible.

We have previously examined the use of spatially varying light fields for atomic

manipulation [4, 5]. A second experimental activity extends these methods to the

microscale and exploits the optical fields within nanostructured environments for a range

of microscopic trapping and cooling processes [6]. These include dipole force and

magneto-optical trapping within mesoscopic hemispherical mirrors, which also offer

Doppler and polarization-gradient cooling mechanisms. We also plan to investigate a new

process of mirror-mediated cooling - proposed and analysed by the group in collaboration

with the Optoelectronics Research Centre [7, 8] - based upon the retarded interaction

between an optically polarized atom and its own reflection, which could offer a robust

and direct route to the optical cooling of molecules. In this area, we have recently led a

€2M ESF collaboration on Cavity-Mediated Molecular Cooling.

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Together with colleagues in the Schools of Electronics & Computer Science and

Engineering Sciences, we are also developing the practical techniques and technologies

that will enable so-called ‘atom chips’ to be packaged into miniature, integrated, self-

contained devices. The development of miniature pumps and gauges, atom sources,

stabilized and tunable lasers and vacuum-tight chambers draws together a varied

expertise in bonding and MEMS fabrication with techniques from experimental atomic

physics, and exploits the planar microfabrication capability of the University's

Mountbatten cleanrooms.

We are also exploring applications of our optical manipulation techniques to

optomechanical structures [9] that can be built using the University's NanoScribe two-

photon photopolymerization apparatus. By combining optical forces with the resonant

enhancement of periodic structures, we envisage a new class of optomechanical actuators

based around microfabricated flexible photonic crystals.

[1] J. Bateman, T. Freegarde, Phys. Rev. A 76 013416 (2007)

[2] T. Freegarde, G. Daniell, D. Segal, Phys. Rev. A 73 033409 (2006)

[3] T. Freegarde, D. Segal, Phys. Rev. Lett. 91 037904 (2003)

[4] T. Freegarde, K. Dholakia, Phys. Rev. A 66 013413 (2002)

[5] D. Rhodes et al., J. Mod. Opt. 53 547 (2006)

[6] H. Ohadi et al., Opt. Express 17 23003 (2009)

[7] A. Xuereb et al., Phys. Rev. A 79 053810 (2009)

[8] A. Xuereb et al., Phys. Rev. A 80 013836 (2009)

[9] A. Xuereb et al., Phys. Rev. Lett. 105 013602 (2010)

Surface-emitting semiconductor lasers

http://www.vecsel.phys.soton.ac.uk/

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The surface-emitting semiconductor laser

group led by Anne Tropper investigates

quantum well lasers with vertical external

cavities – VECSELs – with particular interest in

their properties as mode-locked laser sources of

ultrashort pulses. The optically-pumped

VECSEL is essentially the semiconductor

equivalent of a diode-pumped solid state laser;

unlike edge-emitting diodes these lasers can combine high output power with diffraction-

limited beam quality. Our group reported the first passively mode-locked VECSEL in

2000 [1], in collaboration with Ursula Keller’s group at ETH Zürich, using a

semiconductor saturable absorber mirror (SESAM) of the type that the Keller group has

developed to a high degree for solid state laser mode-locking. With a SESAM specially

designed to exploit the optical Stark effect nonlinearity it is possible to generate trains of

transform-limited 260-fs pulses from VECSELs [2], at repetition rates up to 1 GHz. We

have shown for the first time that it is possible for a semiconductor laser to generate 60-fs

transform-limited pulses, of duration comparable with the timescale of carrier-carrier

scattering [3]. These lasers can reach levels of pulse quality and peak power [4] that are

not accessible to mode-locked edge-emitting lasers, and can achieve repetition rates

>100GHz in harmonically mode-locked operation [5]. They have the potential to be

cheap compact sources for applications such as optical clocking and sampling, time-

domain THz spectroscopy (see next section), and are of interest as stable seed pulses for

high-power fibre amplifiers, opening a new route towards the generation of high

frequency optical combs.

[1] S. Hoogland et al., IEEE Photonics Technology Letters 12 1135 (2000)

[2] K. G. Wilcox et al. Optics Letters 33 (23) 2797 (2008)

[3] A. H. Quarterman et al. Nature Photonics 3 (12) 729 (2009)

[4] K. Wilcox et al., Photonics Technology Letters 22 (14) 1021 (2010)

[5] A. H. Quarterman et al., Applied Physics Letters 17 267 (2010)

Teraherz Laboratories group

http://sites.google.com/site/terahertzlaboratories/

A new activity in terahertz spectroscopy began in autumn 2007 with the arrival in QLM of Vasilis Apostolopoulos who joined us from the Quantum Cascade Lasers group at Cavendish. Terahertz time domain spectroscopy (THz-TDS) has brought a revolution in terahertz science. THz-TDS is a synchronous technique where the emitter and receiver are usually semiconductor photoconductive antennas, which are gated by an ultrafast pulse to excite carriers in the conduction band. The carriers can be used either to generate or to measure a THz electromagnetic pulse. Due to the synchronous nature of the technique pulses

VECSEL

1

VECSEL

1

13

below the blackbody radiation level can be measured and this results to a signal to noise ratio, which is higher than that of synchrotron experiments. A significant advantage is also that the transient electric field itself is measured therefore the complex refractive index is obtained as a function of frequency.

Miniature THz-TDS: In the Terahertz laboratories we are working into making a new miniature terahertz spectrometer where the pump laser sources will be VECSEL laser sources from our collaborators (Anne Tropper)1. We already have demonstrated an all semiconductor THz spectrometer2. This research is funded from the EPSRC from the first grant EP/G05536X/1. The next step will be integration of the emitter and receiver on the same chip with a plasmon waveguide for terahertz wave propagation. Plasmon waveguides at THz frequencies have low loss in the order of some dBs per cm and can be designed to have a custom evanescent field to interact with a sample placed on top of the chip.

Material Parameter extraction: In most THz-TDS apparatus the sample is placed in the focus of a THz beam, however, the material parameter extraction method commonly used is based on a plane wave transfer function. This restricts the accuracy of the algorithm when strongly converging THz beams are used, e.g. in THz imaging. Here we demonstrate an algorithm that uses a theoretical transfer function calculated for a converging beam to extract material parameters3.

Photo-Dember effect: We have started working using the lateral photo-Dember effect in semiconductors for THz emitters. We specifically are working in different semiconductor materials and excitation wavelengths and finally on nanostructured arrays of emitters to increase power output. We have already a model for the lateral photo-Dember effect to simulate how different nano-emitters would perform.

1 Adrian H Quarterman et al., Nature Photonics 3 (12), 729 (2009).

2 Zakaria Mihoubi et al., Optics Letters 33 (18), 2125 (2008).

3 A. L. Chung et al., presented at the 2010 35th International Conference on Infrared, Millimeter, and

Terahertz Waves (IRMMW-THz 2010), Rome, Italy, 2010 (unpublished).