|
 |
|
"Superchemistry": coherent conversion of an atomic
Bose-Einstein condensate into a molecular BEC
These pictures demonstrate the dynamics of the formation of a molecular Bose-Einstein condensate (BEC) (right) from an atomic BEC (left), and subsequent coherent oscillations between the coupled condensates. Shown are the particle number densities versus the time and the radial distance from the origin. We dubbed this phenomenon 'superchemistry', reflecting the fact that the process of molecule formation taking place in a BEC at ultralow temperatures occurs at greatly enhanced chemical reaction rates due to the effect of bosonic stimulation. In the case of diatomic molecules, the process of coherent dimerization requires a specific coupling mechanism, such as Raman photoassociation in two external laser fields or a magnetically tuned Feshbach resonance. When taking place in a BEC, coherent dimerization represents a matter-wave analog of the second-harmonic generation in nonlinear optics with photons.
|
Top of Page 
Coupled atomic-molecular solitons in 3D
These pictures show the dynamics of stable propagation of coupled atomic and molecular solitons in free space. Solitons are localized wave forms -- in this case matter waves in a BEC -- that can propagate over long distances (or for long time durations) without changing their shape. Usually this requires a nonlinear coupling mechanism that can compete against repulsive 'forces' (e.g. dispersion/diffraction), thus preventing the initial wave from spreading. In this example, the stable 'propagation' of the coupled atomic and molecular solitary BECs refers to their localized behavior in free space; it is self-maintained (in the absence of gravity) over long time scales, without the need of external confining potentials.
|
Top of Page
Top of Page
Formation of a Bose-Einstein condensate by evaporative cooling
  
These images are not the results of my own research; the original work is due to P. D. Drummond and J. F. Corney, while the data represented here are due to the work of T. G. Vaughan. My acknowledgments go to all of them. The pictures are 'snapshots' of a quantum dynamical simulation of the formation of a BEC by evaporative cooling. This is the first calculation of its type, showing a sharp peak in momentum space as the temperature reduces.
|
Top of Page
|
Quantum state imaging in phase space via Wigner function
 
The concept of quantum mechanical phase space and associated quasiprobability distributions has proven to be extremely useful and appealing in many fundamental applications of quantum mechanics. Yet, for realistic quantum systems with nonlinear interactions and dissipation, the problem of finding exact solutions for the quasiprobability distributions and hence being able to visualize the quantum state of the system in phase space is notoriously difficult. In quantum optics there are only three nonlinear dissipative models for which one can find exact analytical solutions in terms of the Wigner function -- the oldest and most famous quasiprobability distribution function. These pictures represent examples of the Wigner function for a nondegenerate parametric oscillator in the bistable regime of operation (left) and in the above-threshold regime (right). Shown is the Wigner function for the signal mode which is known to possess no well defined phase, hence the radial symmetry of the images.
-
-
K. V. Kheruntsyan, D. S. Krahmer, G. Yu. Kryuchkyan, and K. G. Petrossian, Opt. Comm. 139, 157 (1997); Wigner function for generalized model of parametric oscillator: phase-space tristability, competition and nonclassical effects.
|
Top of Page
|
