 |
Quantum nonlinear dynamics of trapped atoms.(Theory: Milburn, Experiment: Rubinsztein-Dunlop, Heckenberg)
The primary experimental project is to demonstrate quantum tunnelling of a trapped atom. Quantum tunnelling, in which a particle can access a dynamical state forbidden by classical mechanics, has long been regarded as the most nonclassical prediction of quantum mechanics. It is the focus of suggestions for testing the validity of quantum mechanics, forms the basis of the new technology of scanning tunnelling microscopy, and will very likely be exploited in the next generation of nanoscopic circuits. Vital to such applications is a thorough understanding of the effect of noise. The tunnelling of a laser cooled atom between two classically inaccessible states provides an ideal experimental context in which to investigate the effect of noise on tunnelling.
In our experiment the laser cooled Rb atoms are moving in a standing wave optical potential the amplitude of which is periodically modulated. Our preliminary experiments on trapped Rb and cooling with diode lasers clearly demonstrate the atoms are well prepared for such a quantum tunnelling experiment.
Theory of cold atoms in modulated potentials. (Milburn, Dyrting, Theory)
The motion of cold atoms in modulated potentials has provided the clearest experimental context in which to determine quantum nonlinear dynamics. Raizen's group at University of Texas (UT) leads the world in this field. The UQ theory group, in collaboration with the UT, is providing the theoretical foundation of this field.
Our aims are; to characterise the effect of laser and quantum noise on quantum nonlinear dynamics in optical potentials, particularly deep quantum effects such as quantum tunnelling, to determine quantum phase-space transport in globally chaotic systems with possible applications to new cooling schemes.
Theory of Bose-Einstein Condensation (BEC).(Milburn)
Theoretical work on BEC at UQ is based on two projects: (i) macroscopic tunnelling of a BEC in a double well potential, (ii) Floquet state BEC. The aim in the first of these projects is to formulate the theory of macroscopic quantum tunnelling of BEC in a nonlinear potential. For many years now this phenomenon has been sought in condensed matter physics, with limited success. Our preliminary calculations indicate that an atomic BEC is likely to be more successful. We are proposing a new mechanism for BEC in which irreversible processes lead to Bose-Einstein condensation into the Floquet state of time periodic potential.
Mesoscopic quantum circuits (Theory:Milburn, Sun).
In recent years microfabrication techniques have advanced to the stage where it is possible to build semiconductor circuits so free from defects and so small the charge carriers propagate through the device with almost no chance of an inelastic collision. When operated at low temperatures, charge transport in these devices are determined entirely by quantum mechanical rules.
Our objective in this project is to apply the well developed techniques for treating quantum noise used in quantum optics, to these new mesoscopic electronic devices. The first three years of this project are entirely theoretical. A second objective is to develop a proposal for a class of optoelectronic mesoscopic devices which combine the low noise properties of mesoscopic devices with photonic devices such as LEDs (light emitting diodes) and laser diodes. Such hybrid circuits may find applications in quantum limited communications systems of the future.
With the establishment of a centre we will include an experimental component, in year 4 largely directed by Dr Sun. We will use our collaboration with Macquarie University (Dr B. Sanders) and The University of New South Wales (Dr Taylor) to provide fabricated samples for measurements of the noise spectrum of both RTDs (resonant tunnelling diodes) and split gate 2DEG (two dimensional electron gas) devices.
Compatibility of Quantum and Classical Mechanics at Mesoscopic Levels (Reid)
There has been a substantial development of experimental laser technology enabling the manipulation of quantum effects. These advances provide an opportunity to test, and probe, for new features of quantum mechanics in mesoscopic/macroscopic regimes that were previously not investigated.
This investigation into the nonclassical nature of quantum mechanics at mesoscopic particle number levels, will initially follow two approaches. We will determine the degree of compatibility of quantum mechanics with local realism, for quadrature phase measurements at large photon number. We will determine the validity of degrees of local realism, corresponding to different levels of the measurement precision (from microscopic, through mesoscopic, to macroscopic).
This research is primarily a fundamental investigation into quantum theory, but will give insight into quantum cryptography, quantum computing, and quantum communication, for mesoscopic systems in the quantum/classical interface. The experimental program in parametric systems will provide an experimental context in which to tests the predictions of this project.