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Search Results: 1 - 10 of 118201 matches for " T. Pohl "
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Strong-coupling effects in the relaxation dynamics of ultracold neutral plasmas
T. Pohl,T. Pattard
Physics , 2005, DOI: 10.1088/1742-6596/11/1/022
Abstract: We describe a hybrid molecular dynamics approach for the description of ultracold neutral plasmas, based on an adiabatic treatment of the electron gas and a full molecular dynamics simulation of the ions, which allows us to follow the long-time evolution of the plasma including the effect of the strongly coupled ion motion. The plasma shows a rather complex relaxation behavior, connected with temporal as well as spatial oscillations of the ion temperature. Furthermore, additional laser cooling of the ions during the plasma evolution drastically modifies the expansion dynamics, so that crystallization of the ion component can occur in this nonequilibrium system, leading to lattice-like structures or even long-range order resulting in concentric shells.
Rydberg atom formation in strongly correlated ultracold plasmas
G. Bannasch,T. Pohl
Physics , 2011, DOI: 10.1103/PhysRevA.84.052710
Abstract: In plasmas at very low temperatures formation of neutral atoms is dominated by collisional three-body recombination, owing to the strong ~ T^(-9/2) scaling of the corresponding recombination rate with the electron temperature T. While this law is well established at high temperatures, the unphysical divergence as T -> 0 clearly suggest a breakdown in the low-temperature regime. Here, we present a combined molecular dynamics-Monte-Carlo study of electron-ion recombination over a wide range of temperatures and densities. Our results reproduce the known behavior of the recombination rate at high temperatures, but reveal significant deviations with decreasing temperature. We discuss the fate of the kinetic bottleneck and resolve the divergence-problem as the plasma enters the ultracold, strongly coupled domain.
Kinetic modelling and molecular dynamics simulation of ultracold neutral plasmas including ionic correlations
T. Pohl,T. Pattard,J. M. Rost
Physics , 2004, DOI: 10.1103/PhysRevA.70.033416
Abstract: A kinetic approach for the evolution of ultracold neutral plasmas including interionic correlations and the treatment of ionization/excitation and recombination/deexcitation by rate equations is described in detail. To assess the reliability of the approximations inherent in the kinetic model, we have developed a hybrid molecular dynamics method. Comparison of the results reveals that the kinetic model describes the atomic and ionic observables of the ultracold plasma surprisingly well, confirming our earlier findings concerning the role of ion-ion correlations [Phys. Rev. A {\bf 68}, 010703]. In addition, the molecular dynamics approach allows one to study the relaxation of the ionic plasma component towards thermodynamical equilibrium.
Influence of electron-ion collisions on Coulomb crystallization of ultracold neutral plasmas
T. Pohl,T. Pattard,J. M. Rost
Physics , 2004, DOI: 10.1088/0953-4075/38/2/025
Abstract: While ion heating by elastic electron-ion collisions may be neglected for a description of the evolution of freely expanding ultracold neutral plasmas, the situation is different in scenarios where the ions are laser-cooled during the system evolution. We show that electron-ion collisions in laser-cooled plasmas influence the ionic temperature, decreasing the degree of correlation obtainable in such systems. However, taking into account the collisions increases the ion temperature much less than what would be estimated based on static plasma clouds neglecting the plasma expansion. The latter leads to both adiabatic cooling of the ions as well as, more importantly, a rapid decrease of the collisional heating rate.
Strongly Coupled Plasmas via Rydberg-Blockade of Cold Atoms
G. Bannasch,T. C. Killian,T. Pohl
Physics , 2013, DOI: 10.1103/PhysRevLett.110.253003
Abstract: We propose and analyze a new scheme to produce ultracold neutral plasmas deep in the strongly coupled regime. The method exploits the interaction blockade between cold atoms excited to high-lying Rydberg states and therefore does not require substantial extensions of current ultracold plasma experiments. Extensive simulations reveal a universal behavior of the resulting Coulomb coupling parameter, providing a direct connection between the physics of strongly correlated Rydberg gases and ultracold plasmas. The approach is shown to reduce currently accessible temperatures by more than an order of magnitude, which opens up a new regime for ultracold plasma research and cold ion-beam applications with readily available experimental techniques.
On the possibility of "correlation cooling" of ultracold neutral plasmas
T. Pohl,T. Pattard,J. M. Rost
Physics , 2004, DOI: 10.1088/0953-4075/37/9/L01
Abstract: Recent experiments with ultracold neutral plasmas show an intrinsic heating effect based on the development of spatial correlations. We investigate whether this effect can be reversed, so that imposing strong spatial correlations could in fact lead to cooling of the ions. We find that cooling is indeed possible. It requires, however, a very precise preparation of the initial state. Quantum mechanical zero-point motion sets a lower limit for ion cooling.
Plasma formation from ultracold Rydberg gases
T. Pohl,T. Pattard,J. M. Rost
Physics , 2003, DOI: 10.1103/PhysRevA.68.010703
Abstract: Recent experiments have demonstrated the spontaneous evolution of a gas of ultracold Rydberg atoms into an expanding ultracold plasma, as well as the reverse process of plasma recombination into highly excited atomic states. Treating the evolution of the plasma on the basis of kinetic equations, while ionization/excitation and recombination are incorporated using rate equations, we have investigated theoretically the Rydberg-to-plasma transition. Including the influence of spatial correlations on the plasma dynamics in an approximate way we find that ionic correlations change the results only quantitatively but not qualitatively.
Coulomb crystallization in expanding laser-cooled neutral plasmas
T. Pohl,T. Pattard,J. M. Rost
Physics , 2003, DOI: 10.1103/PhysRevLett.92.155003
Abstract: We present long-time simulations of expanding ultracold neutral plasmas, including a full treatment of the strongly coupled ion dynamics. Thereby, the relaxation dynamics of the expanding laser-cooled plasma is studied, taking into account elastic as well as inelastic collisions. It is demonstrated that, depending on the initial conditions, the ionic component of the plasma may exhibit short-range order or even a superimposed long-range order resulting in concentric ion shells. In contrast to ionic plasmas confined in traps, the shell structures are built up from the center of the plasma cloud rather than from the periphery.
Relaxation to non-equilibrium in expanding ultracold neutral plasmas
T. Pohl,T. Pattard,J. M. Rost
Physics , 2005, DOI: 10.1103/PhysRevLett.94.205003
Abstract: We investigate the strongly correlated ion dynamics and the degree of coupling achievable in the evolution of freely expanding ultracold neutral plasmas. We demonstrate that the ionic Coulomb coupling parameter $\Gamma_{\rm i}$ increases considerably in later stages of the expansion, reaching the strongly coupled regime despite the well-known initial drop of $\Gamma_{\rm i}$ to order unity due to disorder-induced heating. Furthermore, we formulate a suitable measure of correlation and show th at $\Gamma_{\rm i}$ calculated from the ionic temperature and density reflects the degree of order in the system if it is sufficiently close to a quasisteady state. At later times, however, the expansion of the plasma cloud becomes faster than the relaxation of correlations, and the system does not reach thermodynamic equilibrium anymore.
Dynamical Crystallization in the Dipole Blockade of Ultracold Atoms
T. Pohl,E. Demler,M. D. Lukin
Physics , 2009, DOI: 10.1103/PhysRevLett.104.043002
Abstract: We describe a method for controlling many-body states in extended ensembles of Rydberg atoms, forming crystalline structures during laser excitation of a frozen atomic gas. Specifically, we predict the existence of an excitation number staircase in laser excitation of atomic ensembles into Rydberg states. Each step corresponds to a crystalline state with a well-defined of regularly spaced Rydberg atoms. We show that such states can be selectively excited by chirped laser pulses. Finally, we demonstarte that, sing quantum state transfer from atoms to light, such crystals can be used to create crystalline photonic states and can be probed via photon correlation measurements.
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