Positrons are the antimatter version of electrons and so their fate in a matter world is ultimately to annihilate. However, prior to this, a positron may combine with an electron to form a matter-antimatter hybrid called positronium. This is akin to a hydrogen atom with the proton replaced by a positron. Fundamental to our understanding of the physical universe, positron and positronium are these days also acknowledged as being fantastically useful in practical applications such as probing material properties and medical diagnostics. However, there is still much that we do not know for sure about the details of the interactions of these particles with ordinary matter. For example if, in a collision with an atom or molecule, a positron captures an electron, in which directions is the positronium likely to travel and with what probability? More...
Published: Jun 17, 2015 12:35:19 PM
How light of different colours is absorbed by carbon dioxide (CO2) can now be accurately predicted using new calculations developed by a UCL-led team of scientists. This will help climate scientists studying Earth’s greenhouse gas emissions to better interpret data collected from satellites and ground stations measuring CO2. More...
Published: Jun 15, 2015 10:29:10 AM
New research from UCL has uncovered additional second laws of thermodynamics which complement the ordinary second law of thermodynamics, one of the most fundamental laws of nature. These new second laws are generally not noticeable except on very small scales, at which point, they become increasingly important. More...
Published: Feb 10, 2015 11:55:53 AM
Professor Peter Barker
I have a background in atomic and molecular laser spectroscopy, non-linear optics, and laser trapping and cooling. Within the last 10 years my research has concentrated on the study of molecular cooling and trapping and on quantum cavity optomechanics. I have expertise in developing applications from more basic optical physics research. I was awarded a PhD in Physics from the University of Queensland, Australia in 1996. From 1997 to 2001 I was a Postdoctoral Research Associate, and then a Research Scientist and Lecturer in the Applied Physics Group in the Mechanical and Aerospace Engineering Department at Princeton University. At Princeton, I began to study the manipulation of atoms and molecules in pulsed optical fields by studying coherent Rayleigh scattering from molecules trapped in optical lattices. During this time I was part of a multidisciplinary team of physicists and engineers from Princeton University, Sandia National Laboratories and Lawrence Livermore developing a new type of wind tunnel for accelerating gases to hypersonic speeds using lasers and electron beams. In 2001 I took up the position of Lecturer in the Physics Department at Heriot-Watt University and became a Senior Lecturer in 2004. In October 2006 I joined the AMOP group at UCL as a Reader and was promoted to Professor in October 2007. Currently I have projects in cavity optomechanics using nanoparticles levitated in vacuum and larger microscale clamped systems based on whispering gallery mode resonators for studying fundamental quantum mechanics and for development of sensors.
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NEW - Fully funded PhD Studentship in Levitated quantum cavity optomechanics is now available
Processes in the microscopic world are extremely well described by quantum theory, but yet little is known about the transition to the classical world at macroscopic scales. For example, can a macroscopic object such as a virus be put into a quantum superposition, and if not, what are the processes at these length and mass scales that prevent this? These types of questions are not only important for our fundamental understanding of the world but they will also impact on the development of future engineered macroscopic quantum systems. Until very recently these questions remained a primarily theoretical pursuit because the experimental methods required to prepare and maintain the delicate macroscopic quantum states in the presence of environmental noise did not exist. New experimental techniques now offer the prospect for laboratory tests of macroscopic quantum mechanics. This field, collectively known as quantum cavity optomechanics, uses the controlled interaction of light with the mechanical motion of nanoscale and microscale oscillators, to coherently control their motion. To date quantum ground state cooling has been demonstrated in only a handful of these solid-state devices but a macroscopic superposition, and even non-classical motion, has yet to be observed.
We have developed a new optomechanical oscillator system that is levitated in vacuum. It uses a novel configuration of electric and optical fields to achieve extremely good isolation from the environment. Cooling from room temperatures down to milliKelvin temperatures has been achieved for the first time, by employing a technique called cavity cooling, with quantum ground state cooling now within reach. Our aim in this research programme is to explore macroscopic quantum mechanics by preparing and measuring its nonclassical motion. For the first time, we will undertake laboratory tests of theoretical models for macroscopic wavefunction collapse. This will be possible even when the system is not in the ground state. The very low noise and high mechanical Q of this oscillator system also offers significant promise for sensing applications.
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