Dissociation of a diatomic molecule produces two quantum mechanically entangled atoms with equal and opposite momenta in the molecule’s rest frame. This phenomena is shown in figure 1 (figure 2 shows the three dimensional case) and is the matter-wave analog of the production of entangled photon pairs. The two atomic beams generated in this way are “twins” in the sense that they have almost exactly the same number of particles, resulting in the reduction of noise in the particle number-difference below the standard quantum limit. In addition, the two beams possess correlations of the type first discussed by Einstein-Podolsky-Rosen in the early days of quantum mechanics.
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Figure 1: Simulation of the
1D dissociation of a BEC of molecular dimers. |
Figure 2: Snapshot of the 3D
momentum distribution of |
Dr Karen Kheruntsyan of the ARC Centre of Excellence for Quantum-Atom Optics (ACQAO) is part of a research group investigating this phenomenon. The correlations found in papers1 published by the group suggest the possibility of demonstration of the famous EPR paradox with a macroscopic number of massive particles, which is of fundamental importance to quantum theory. They are also investigating other many-body dynamics of interacting quantum gases, including coherent molecule formation from atomic Bose-Einstein condensates. Due to the complexity of the problems being studied, high performance computing plays a large role in the group's research.
A typical calculation consists of numerical integration of a set of coupled stochastic differential equations which model the dynamical evolution of the interacting matter-wave fields in one, two, or three space dimensions. This involves parallel runs over a large number of "random" stochastic trajectories, where the results of the individual runs are averaged to give observables that correspond to quantum mechanical ensemble averages. Thus, the technique corresponds to a first-principle dynamical simulation of a quantum many-body system, which is a notoriously difficult problem in quantum physics. The method relies on utilizing the positive P-representation of the quantum density operator and uses a dedicated software called XMDS for solving the stochastic equations of motion. The high level of complexity of the problem along with the large number of possible trajectories to be calculated is computationally very expensive, requiring the use of high performance computing facilities. Dr Kheruntsyan hopes to be able to implement the software on the QCIF supercomputers at UQ in the near future.
Contacts
Dr Karen Kheruntsyan
ARC Centre of Excellence for
Quantum-Atom Optics, University of Queensland
Publications
- K. V. Kheruntsyan, M. K. Olsen, and P. D. Drummond, 'Einstein-Podolsky-Rosen correlations via dissociation of a molecular Bose-Einstein condensate', Phys. Rev. Lett. (2005) 95, 150405.
- C. M. Savage, P. E. Schwenn, and K. V. Kheruntsyan. 'First-principles quantum simulations of dissociation of molecular condensates: Atom correlations in momentum space', cond-mat/0606345.