| 1. |
- Fernandez-Vidal, Sonia, et al.
(författare)
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Quantum ground state of self-organized atomic crystals in optical resonators
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 81:4, s. 43407-
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Tidskriftsartikel (refereegranskat)abstract
- Cold atoms, driven by a laser and simultaneously coupled to the quantum field of an optical resonator, may self-organize in periodic structures. These structures are supported by the optical lattice, which emerges from the laser light they scatter into the cavity mode and form when the laser intensity exceeds a threshold value. We study theoretically the quantum ground state of these structures above the pump threshold of self-organization by mapping the atomic dynamics of the self-organized crystal to a Bose-Hubbard model. We find that the quantum ground state of the self-organized structure can be the one of a Mott insulator, depending on the pump strength of the driving laser. For very large pump strengths, where the intracavity-field intensity is maximum and one would expect a Mott-insulator state, we find intervals of parameters where the phase is compressible. These states could be realized in existing experimental setups.
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| 2. |
- Joshi, C., et al.
(författare)
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Entanglement of distant optomechanical systems
- 2012
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Ingår i: Physical Review A. - 1050-2947 .- 1094-1622. ; 85:3
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically investigate the possibility to generate nonclassical states of optical and mechanical modes of optical cavities, distant from each other. A setup comprised of two identical cavities, each with one fixed and one movable mirror and coupled by an optical fiber, is studied in detail. We show that with such a setup there is potential to generate entanglement between the distant cavities, involving both optical and mechanical modes. The scheme is robust with respect to dissipation, and nonlocal correlations are found to exist in the steady state at finite temperatures.
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| 3. |
- Krutitsky, Konstantin V., et al.
(författare)
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Dark solitons near the Mott-insulator-superfluid phase transition
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 82:3, s. 33618-
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Tidskriftsartikel (refereegranskat)abstract
- Dark solitons of ultracold bosons in the vicinity of the Mott-insulator-superfluid phase transition are studied. Making use of the Gutzwiller ansatz we have found antisymmetric eigenstates corresponding to standing solitons, as well as propagating solitons created by phase imprinting. Near the phase boundary, superfluidity has either a particle or a hole character depending on the system parameters, which greatly affects the characteristics of both types of solitons. Within the insulating Mott regions, soliton solutions are prohibited by lack of phase coherence between the lattice sites. Linear and modulational stability show that the soliton solutions are sensitive to small perturbations and, therefore, unstable. In general, their lifetimes differ for on-site and off-site modes. For the on-site modes, there are small areas between the Mott-insulator regions where the lifetime is very large, and in particular much larger than that for the off-site modes.
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| 4. |
- Larson, Jonas
(författare)
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Analog of the spin-orbit-induced anomalous Hall effect with quantized radiation
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 81:5, s. 51803-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how the term describing the interaction between a single two-level atom and two cavity field modes may attain a Rashba form. As an outcome, cavity QED provides a testbed for studies of phenomena reminiscent of the spin-orbit induced anomalous Hall effect. The effective magnetic field, deriving from the non-Abelian gauge potentials rendered by the Rashba coupling, induces a transverse force acting on the phase space distributions. Thereby, the phase space distributions build up a transverse motion manifesting itself in spiral trajectories, rather than circular ones obtained for a zero magnetic field as one would acquire for the corresponding Abelian gauge potentials. Utilizing realistic experimental parameters, the phenomenon is numerically verified, ascertain that it should be realizable with current techniques.
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| 5. |
- Larson, Jonas
(författare)
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Anomalous decoherence and absence of thermalization in a photonic many-body system
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 83:5, s. 052103-
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Tidskriftsartikel (refereegranskat)abstract
- The intention of this work is twofold: first, to present a most simple system capable of simulating the intrinsic bosonic Josephson effect with photons and, second, to study various outcomes deriving from inherent or external decoherence. A qubit induces an effective coupling between two externally pumped cavity modes. Without cavity losses and in the dispersive regime, intrinsic Josephson oscillations of photons between the two modes occurs. In this case, contrary to regular Markovian decoherence, the qubit purity shows a Gaussian decay and recurrence of its coherence. Due to intrinsic nonlinearities, both the Josephson oscillations as well as the qubit properties display a rich collapse-revival structure, where, however, the complexity of the qubit evolution is in some sense stronger. The qubit as a meter of the photon dynamics is considered, and it is shown that qubit dephasing, originating, for example, from nondemolition measurements, results in an exponential destruction of the oscillations which manifests the collectiveness of the Josephson effect. Nonselective qubit measurements, on the other hand, render a Zeno effect seen in a slowing down of the Josephson oscillations. Contrary to dephasing, cavity dissipation results in a Gaussian decay of the scaled Josephson oscillations. Finally, following Ponomarev et al. [Phys. Rev. Lett. 106, 010405 (2011)], we analyze aspects of thermalization. In particular, despite similarities with the generic model studied by Ponomarev et al., our system does not seem to thermalize.
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| 6. |
- Larson, Jonas, et al.
(författare)
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Cavity-state preparation using adiabatic transfer
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:5
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Tidskriftsartikel (refereegranskat)abstract
- We show how to prepare a variety of cavity field states for multiple cavities. The state preparation technique used is related to the method of stimulated adiabatic Raman passage. The cavity modes are coupled by atoms, making it possible to transfer an arbitrary cavity field state from one cavity to another and also to prepare nontrivial cavity field states. In particular, we show how to prepare entangled states of two or more cavities, such as an Einstein-Podolsky-Rosen state and a W state, as well as various entangled superpositions of coherent states in different cavities, including Schrodinger cat states. The theoretical considerations are supported by numerical simulations.
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| 7. |
- Larson, Jonas, et al.
(författare)
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Chaos-driven dynamics in spin-orbit-coupled atomic gases
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 87:1, s. 013624-
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics, appearing after a quantum quench, of a trapped, spin-orbit coupled, dilute atomic gas is studied. The characteristics of the evolution is greatly influenced by the symmetries of the system, and we especially compare evolution for an isotropic Rashba coupling and for an anisotropic spin-orbit coupling. As we make the spin-orbit coupling anisotropic, we break the rotational symmetry and the underlying classical model becomes chaotic; the quantum dynamics is affected accordingly. Within experimentally relevant time scales and parameters, the system thermalizes in a quantum sense. The corresponding equilibration time is found to agree with the Ehrenfest time, i.e., we numerically verify a similar to ln ( (h) over bar (-1)) scaling. Upon thermalization, we find that the equilibrated distributions show examples of quantum scars distinguished by accumulation of atomic density for certain energies. At shorter time scales, we discuss nonadiabatic effects deriving from the spin-orbit-coupled induced Dirac point. In the vicinity of the Dirac point, spin fluctuations are large and, even at short times, a semiclassical analysis fails.
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| 8. |
- Larson, Jonas, et al.
(författare)
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Effective mass in cavity QED
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:1
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Tidskriftsartikel (refereegranskat)abstract
- We consider propagation of a two-level atom coupled to one electromagnetic mode of a high-Q cavity. The atomic center-of-mass motion is treated quantum mechanically and we use a standing wave shape for the mode. The periodicity of the Hamiltonian leads to a spectrum consisting of bands and gaps, which is studied from a Floquet point of view. Based on the band theory, we introduce a set of effective mass parameters that approximately describe the effect of the cavity on the atomic motion, with the emphasis on one associated with the group velocity and on another one that coincides with the conventional effective mass. Propagation of initially Gaussian wave packets is also studied using numerical simulations and the mass parameters extracted thereof are compared with those predicted by the Floquet theory. Scattering and transmission of the wave packet against the cavity are further analyzed, and the constraints for the effective mass approach to be valid are discussed in detail.
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| 9. |
- Larson, Jonas, et al.
(författare)
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Jahn-Teller-induced Berry phase in spin-orbit-coupled Bose-Einstein condensates
- 2009
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 79, s. 043627-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that Berry phases may greatly affect the dynamics of spin-orbit coupled Bose-Einstein condensates. The effective model Hamiltonian under consideration is shown to be equivalent to the Exe Jahn-Teller model first introduced in molecular physics. The corresponding conical intersection is identified and the Berry phase acquired for a wave packet encircling the intersection is studied. It is found that this phase manifests itself in the density profile of the condensate, making it a directly measurable quantity via time-of-flight detection. Moreover, the non-Abelian gauge structure of the system is addressed and we verify how it affects the dynamics.
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| 10. |
- Larson, Jonas
(författare)
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Level crossings in a cavity QED model
- 2006
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 73:1
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Tidskriftsartikel (refereegranskat)abstract
- In this paper I study the dynamics of a two-level atom interacting with a standing-wave field. When the atom is subjected to a weak linear force, the problem can be turned into a time-dependent one, and the evolution is understood from the band structure of the spectrum. The presence of level crossings in the spectrum gives rise to Bloch oscillations of the atomic motion. Here I investigate the effects of the atom-field detuning parameter. A variety of different level crossings are obtained by changing the magnitude of the detuning, and the behavior of the atomic motion is strongly affected due to this. I also consider the situation in which the detuning is oscillating in time, and its impact on the atomic motion. Wave-packet simulations of the full problem are treated numerically and the results are compared with analytical solutions given by the standard Landau-Zener and the three-level Landau-Zener models.
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