Mohamed Babiker
Emeritus Professor

Profile

Career

BSc (Khartoum), MSc, PhD (Sussex), CPhys, FInstP

Summary of expertise

• Condensed matter theory; semiconductors
• Quantum optics theory;
• Optical and matter vortices
• Quantum field theory

Research

Overview

Research Group: Condensed Matter Physics

Research Interests

• Atom Optics and Quantum Optics
• Laser Cooling and Trapping
• Orbital Angular Momentum of Light
• Bose-Einstein Condensation
• QED in media
• Photonic Band-gap Systems
• Electron-phonon interactions
• Electric Transport in LDS
• Large Band-gap Semiconductors

Projects

Our main research activities are concerned with the study of the consequences of confinement which arises when restricting real space by the introduction of boundaries. Introducing boundaries generates dielectric cavities with walls made of materials with widely differing properties. In general, a cavity exhibits quantisation characteristics whenever the relevant de Broglie wavelength at a typical energy becomes comparable with the dimensions of the confining region. Not surprisingly, this field of research engages a wide range of topics from the fundamental to the applied. It involves disciplines which, at first sight, appear unrelated. Our activities concentrate on two areas: the physics of condensed matter (especially semiconductors) and quantum/atom optics. Broadly speaking, our research seeks to understand:

• the modifications which boundaries introduce to electromagnetic as well as matter fields and, in general, all elementary excitations under confinement conditions, treated within quantum field theory;
• the quantum processes involving interaction with and between these confined fields;
• the means via which confinement effects can be put to good use in practical applications of semiconductor optoelectronics and modern quantum and atom optics.

Low Dimensional Semiconductors

In the context of semiconductor heterostructures, quantum confinement modifies the properties of the charge carriers (conduction electrons and holes) as well as the phonons, the quanta of lattice vibrations. Such confinement effects are key in the realisation of quantum well lasers and other modern optoelectronic devices. An important area we are investigating seeks to characterise the polar optical (PO) phonons which, in most materials of interest, provide the intermediary via which hot carriers, so called when their energy is typically greater than a PO phonon energy, can spontaneously discharge energy and relax to lower energy states by the emission of optical phonons.

Current emphasis is on large band-gap heterostructure materials, especially GaN/AlN systems which are distinguished by a relatively large effective mass mismatch, large PO phonon energies, piezoacoustic effects, high intrinsic carrier densities and high electric fields, among other characteristics. One of our goals is to understand transport in such heterostructures.

Quantum Optics and Atom Optics

The quanta of confined electromagnetic fields are confined photons which behave entirely differently from the usual photons in unbounded space in that they have restricted sets of wavelengths. One major consequence of this is that basic quantum processes, especially spontaneous emission and resonant dipole-dipole cooperative effects, can be drastically modified relative to free space. In fact, spontaneous emission can be completely suppressed. Our current research seeks to investigate spontaneous emission and cooperative phenomena specifically in microstructured dielectric cavities. This often requires the framework of dielectric cavity quantum electrodynamics with the added complication that dielectric media can be both temporally and spatially dispersive.

Another related area of research we are currently working on is 'atom optics'. In this new field of research, atomic motion is controlled by the action of laser fields. It has arisen as a natural progression of laser cooling and trapping in dilute atomic ensembles, culminating in the realisation of Bose-Einstein condensates. Here too, confinement effects are in evidence in a variety of physical situations, particularly atomic mirrors, atom guides and in Bose-Einstein condensation. Current work by the group seeks to study confinement effects in these areas of application of atom optics.

Grants

(1992-2002)

1. M. Babiker: personal travel grant of £900 from the Royal Society to attend a conference in Toulouse France, July 2002.

    

2. M. Babiker,`The interaction of Laguerre-Gaussian laser beams with chiral molecules' £59,552 from EPSRC, June 2001 to June 2004

    

3. M Babiker, 'Tailoring quantum optics - dielectric cavity effects in photonic microstructures', £166,000 from EPSRC, October 1998 - September 2001

    

4. B K Ridley and M Babiker, 'Theory of transport phenomena in large-bandgap semiconductors', EPSRC grant of £169,894 over three years, September 1997 - August 2000

    

5. M Babiker and R Loudon, 'UK Quantum Optics Network in "Burgeoning areas of Physics"', £50,000 from EPSRC; the Essex Quantum Optics Theory Group is one of 12 Groups forming the Network (Essex, IC, Oxford, Sussex, Exeter, Bangor, Belfast, Strathclyde, BT, DERA, HPR and NPL)

    

6. M Babiker and L Allen, 'Translational and rotational quantum effects on atoms in non-uniform light beams', SERC grant of £53,612 over 2 years, July 1994 - June 1996

    

7. B K Ridley and M Babiker, 'Electron interactions with hybrid optical modes - theory of engineering optical vibrations in microstructures', SERC grant of £110,444 over three years, October 1993-97

    

8. B K Ridley and M Babiker, 'Theory of scattering of electrons, holes and phonons in quantum confined crystals', SERC grant supplement of £2,414, 1992

    

9. B K Ridley and M Babiker - 'Electron interactions with hybrid optical modes - theory of engineering optical vibrations in microstructures', SERC grant of £42,915 over two years, April 1991 - April 1993

    

10. M Babiker, Personal travel grant of £800 from Royal Society to attend international conferences in Japan.

     

11. M Babiker, 'Theory of light-induced forces due to gross motion of atoms and ions, SERC grant of £38,784 over two years, January 1992 - 30 December 1993

Collaborators

Quantum and Atom Optics

• Professor Les Allen
• Professor David Andrews FRS
• Professor Stephen Barnett FRS
• Professor Gabriel Barton
• Dr Bryan Dalton
• Professor Christian Fronsdal
• Professor Ali Kamli
• Professor Sir Peter Knight FRS
• Professor Rodney Loudon FRS
• Professor Miles Padgett
• Professor Edwin Power
• Dr Thiru Thirunamachandran

Condensed Matter, Phonons and Transport

• Professor Brian Ridley FRS
• Professor David Tilley
• Professor Mike Cottam

Supervision

• Mr Sam Skipsey
• Mr Andrew Carter
• Mr Simon Horsley