Atom-molecule Bose-Einstein Condensate Research Articles

Dynamical quantum phase transitions in an atom-molecule system

We conduct an investigation on the dynamical quantum phase transition within an atom-molecule Bose–Einstein condensate. We explore the dynamics of atom-molecule conversion and utilize the fraction population of the atom as an order parameter for probing dynamical quantum phase transitions. It is shown that the quench dynamics of the atom presents a non-analytical change regarding the atom binding energy, and it is demonstrated that this dynamics can detect both the quantum phase transition at the ground state and at the highest energy level. Furthermore, we analyze the dynamics of the Loschmidt echo and present its connection with the dynamical quantum phase transitions.

Robust control of unstable nonlinear quantum systems

Adiabatic passage is a standard tool for achieving robust transfer in quantum systems. We show that, in the context of driven nonlinear Hamiltonian systems, adiabatic passage becomes highly non-robust when the target is unstable. We show this result for a generic (1:2) resonance, for which the complete transfer corresponds to a hyperbolic fixed point in the classical phase space featuring an adiabatic connectivity strongly sensitive to small perturbations of the model. By inverse engineering, we devise high-fidelity and robust partially non-adiabatic trajectories. They localize at the approach of the target near the stable manifold of the separatrix, which drives the dynamics towards the target in a robust way. These results can be applicable to atom-molecule Bose-Einstein condensate conversion and to nonlinear optics.

Nonclassicality in an atom–molecule Bose–Einstein condensate: Higher-order squeezing, antibunching and entanglement

Abstract The transient quantum statistical properties of the atoms and molecules in an atom–molecule BEC system are investigated by obtaining a third-order perturbative solution of the Heisenberg’s equations of motion corresponding to the Hamiltonian of the system, where two atoms can collide to form a molecule. Time dependent quantities, like two boson correlation, entanglement, squeezing, antibunching, etc., are computed, and their properties are compared. It is established that the atom–molecule BEC system is highly nonclassical as lower-order and higher-order squeezing and antibunching in pure (atomic and molecular) modes, squeezing and antibunching in compound mode, and lower-order and higher-order entanglement in compound mode can be observed in the atom–molecule BEC system. Exact numerical results are also reported and the analytic results obtained using the perturbative technique are shown to agree with the exact numerical results.

Quantum Zeno control of coherent dissociation

We study the effect of dephasing on the coherent dissociation dynamics of an atom-molecule Bose-Einstein condensate. We show that when phase-noise intensity is strong with respect to the inverse correlation time of the stimulated process, dissociation is suppressed via a Bose enhanced Quantum Zeno effect. This is complementary to the quantum zeno control of phase-diffusion in a bimodal condensate by symmetric noise (Phys. Rev. Lett. {\bf 100}, 220403 (2008)) in that the controlled process here is phase-{\it formation} and the required decoherence mechanism for its suppression is purely phase noise.

Phases of Atom-Molecule Vortex Matter

We study ground state vortex configurations in a rotating atom-molecule Bose-Einstein condensate. It is found that the coherent coupling between the atomic and molecular condensates can render a pairing of atomic and molecular vortices into a composite structure that resembles a carbon dioxide molecule. Structural phase transitions of vortex lattices are also explored through different physical parameters including the rotational frequency of the system.

Improvement of Conversion Efficiency of Atom-Molecule Bose-Einstein Condensate

We investigate the stimulated Raman adiabatic passage in two-color photoassociation for a atom-molecule Bose-Einstein condensate. By applying two time-varying Guassian laser pulses that fulfill generalized two-photon resonance condition, we obtain highly efficient atom-molecule conversion. The efficiency depends on the free-bound detuning and the delay time between the two pulses. By adjusting the parameters optimally, we achieve 92% conversion efficiency.

Electromagnetically Induced Transparency in an Atom-MoleculeBose–Einstein Condensate

We propose a new measurement scheme for the atom-molecule darkstate by using electromagnetically induced transparency (EIT)technique. Based on a density-matrix formalism, we calculate theabsorption coefficient numerically. The appearance of the EIT dipin the spectra profile gives clear evidence for the creation ofthe dark state in the atom-molecule Bose–Einstein condensate.

Quantum dynamics and statistical properties of atom-molecule Bose-Einstein condensates

Based on a two-mode boson model, we study nonclassical properties of the atom-molecule Bose-Einstein condensate. The effects of nonlinear collisions on the dynamics of the molecular formation is studied both in classical and quantum treatments. We find that the conversion from atoms to molecules can be suppressed strongly due to nonlinearity-induced localization of the atomic population. In addition, we study statistical properties of the atom-molecule condensed system by calculating the intensity correlation functions numerically. We find that the effect of nonlinearity leads to the appearance of superchaotic molecular pulses, while maintaining the atomic field sub-Poissonian. The joint quantum statistical properties of the atoms and the molecules always show anti-bunching.

Entanglement of two-mode Bose-Einstein condensates

We investigate the entaglement characteristics of two general bimodal Bose-Einstein condensates - a pair of tunnel-coupled Bose-Einstein condensates and the atom-molecule Bose-Einstein condensate. We argue that the entanglement is only physically meaningful if the system is viewed as a bipartite system, where the subsystems are the two modes. The indistinguishibility of the particles in the condensate means that the atomic constituents are physically inaccessible and thus the degree of entanglement between individual particles, unlike the entanglement between the modes, is not experimentally relevant so long as the particles remain in the condensed state. We calculate the entanglement between the modes for the exact ground state of the two bimodal condensates and consider the dynamics of the entanglement in the tunnel-coupled case.

Stability of an atom-molecule Bose-Einstein condensate against collapse

We investigate the coupled atom-molecule Bose-Einstein condensate, as would ensue in an attempt to control the scattering length by means of either the Feshbach resonance or coherent photoassociation. In a mean-field model with a photoassociative coupling between the condensates, we demonstrate that the system is structurally stable. The sign of the effective scattering length notwithstanding, neither condensate will collapse.