Atomic Physics

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Floquet Heating in Interacting Atomic Gases with an Oscillating Force (1906.08747v1)

Jun-Ru Li, Boris Shteynas, Wolfgang Ketterle

2019-06-20

We theoretically investigate the collisional heating of a cold atom system subjected to time-periodic forces. We show within the Floquet framework that this heating rate due to two-body collisions has a general semiclassical expression , depending on the kinetic energy associated with the shaking, particle number density , elastic collision cross section , and an effective collisional velocity determined by the dominant energy scale in the system. We further show that the collisional heating is suppressed by Pauli blocking in cold fermionic systems, and by the modified density of states in systems in lower dimensions. Our results provide an exactly solvable example and reveal some general features of Floquet heating in interacting systems.

Transport of light through a dense ensemble of cold atoms in a static electric field (1904.06408v2)

S. E. Skipetrov, I. M. Sokolov

2019-04-03

We demonstrate that the transport of coherent quasiresonant light through a dense cloud of immobile two-level atoms subjected to a static external electric field can be described by a simple diffusion process up to atomic number densities of the order of at least atoms per wavelength cubed. Transport mean free paths well below the wavelength of light in the free space can be reached without inducing any sign of Anderson localization of light or of any other mechanism of breakdown of diffusion.

Reevaluation of the nuclear electric quadrupole moment for 87Sr by hyperfine structures and relativistic atomic theory (1906.08465v1)

Benquan Lu, Tingxian Zhang, Hong Chang, Jiguang Li, Yong Wu, Jianguo Wang

2019-06-20

The values of nuclear electric quadrupole moment are different by about 7% for 87Sr nucleus between the recommended value [N. J. Stone, At. Data Nucl. Data Tables 111-112, 1 (2016); P. Pyykko, Mol. Phys. 116, 1328 (2018)] and earlier results [e.g. A. M. Matensson-Pendrill, J. Phys. B: At. Mol. Opt. Phys. 35, 917 (2002); K. Z. Yu et al., Phys. Rev. A 70, 012506 (2004)]. In this work, we reported a new value, Q(87Sr) = 328(4) mb, making use of our calculated electric field gradients produced by electrons at nucleus in combination with experimental values for hyperfine structures of the 5s5p 3P1,2 states of the neutral Sr atom. In the framework of the multi-configuration Dirac-Hartree-Fock theory, the electron correlations were taken into account systematically so as to control the uncertainties of the electric field gradient at about 1% level. The present result is different from the recommended value, but in excellent agreement with those by Matensson-Pendrill and Yu et al.. We would recommend the present Q value as a reference for 87Sr.

A simple argument that small hydrogen may exist (1906.08243v2)

J. Va'vra

2019-06-04

This paper discusses a possible existence of small hydrogen, which may have been created during the Big Bang before formation of normal hydrogen.

Probing multiphoton light-induced molecular potentials (1906.08285v1)

Matthias Kübel, Michael Spanner, Zack Dube, Andrei Yu. Naumov, Szczepan Chelkowski, Andrei D. Bandrauk, Marc J. J. Vrakking, Paul B. Corkum, David M. Villeuve, A. Staudte

2019-06-19

The strong coupling between intense laser fields and valence electrons in molecules causes a distortion of the potential energy hypersurfaces which determine the motion of nuclei in a molecule and influences possible reaction pathways. The coupling strength varies with the angle between the light electric field and valence orbital, and thereby adds another dimension to the effective molecular potential energy surface, allowing for the emergence of light-induced conical intersections. Here, we demonstrate in theory and experiment that the full complexity of such light-induced potential energy surfaces can be uncovered. In H, the simplest of molecules, we observe a strongly modulated angular distribution of protons which has escaped prior observation. These modulations directly result from ultrafast dynamics on the light-induced molecular potentials and can be modified by varying the amplitude, duration and phase of the mid-infrared dressing field. This opens new opportunities for manipulating the dissociation of small molecules using strong laser fields.

Critical Dynamics of Weakly-Dissipative Driven Systems (1906.08278v1)

Daniel A. Paz, Mohammad F. Maghrebi

2019-06-19

Driven quantum systems coupled to an environment typically exhibit an effectively classical behavior with relaxational dynamics at, or near, criticality. A paradigmatic driven-dissipative model is the open Dicke model which describes collective light-matter interactions and features a superradiant phase that is observed in experiments. In this work, we investigate the closely related infinite-range Ising model, in a transverse field, subject to individual atomic dissipation. This effective model governs the open Dicke model in the limit of large cavity detuning. We show that, in the weakly dissipative regime, the system undergoes a dynamical crossover from relaxational dynamics, with a characteristic dynamical exponent , to underdamped critical dynamics described by the exponent . We identify these critical behaviors with the infinite-range classical (stochastic) and quantum (unitary) Ising models at finite temperature, respectively. However, in contrast with the volume law (, the system size) expected at finite temperature, we show that the von Neumann entropy scales logarithmically with the system size at criticality, . We nevertheless obtain a finite value for the entanglement negativity, , thus confirming the purely classical nature of the phase transition. To obtain these results, we introduce a non-equilibrium extension of the Suzuki-Trotter quantum-to-classical mapping in the superoperator space.

Continuous real-time tracking of a quantum phase below the standard quantum limit (1809.08216v3)

Athreya Shankar, Graham P. Greve, Baochen Wu, James K. Thompson, Murray Holland

2018-09-21

We propose a scheme for continuously measuring the evolving quantum phase of a collective spin composed of pseudospins. Quantum non-demolition measurements of a lossy cavity mode interacting with an atomic ensemble are used to directly probe the phase of the collective atomic spin without converting it into a population difference. Unlike traditional Ramsey measurement sequences, our scheme allows for real-time tracking of time-varying signals. As a bonus, spin-squeezed states develop naturally, providing real-time phase estimation significantly more precise than the standard quantum limit of radians.

Resonant single-photon double ionization driven by combined intra- and interatomic electron correlations (1906.08123v1)

A. Eckey, A. B. Voitkiv, C. Müller

2019-06-19

Double ionization of an atom by single-photon absorption in the presence of a neighbouring atom is studied. The latter is, first, resonantly photoexcited and, afterwards, transfers the excitation energy radiationlessly to the other atom, leading to its double ionization. The process relies on the combined effect of interatomic and intraatomic electron correlations. It can dominate over the direct double photoionization by several orders of magnitude at interatomic distances up to few nanometers. The relative position of the neighbouring atom is shown to exert a characteristic influence on the angular distribution of emitted electrons.

Optical properties of magnetized transient low-pressure plasma (1906.08100v1)

Roman Bergert, Slobodan Mitic

2019-06-19

A plasma under the influence of an external magnetic field changes the optical properties due to the Zeeman splitting of the energy levels. This splitting degenerates an initial single spectral line into a system of spectral lines with different transition frequencies defined by the electronic structure of the energy levels. Newly created magnetic sub-levels redefine the spectral profile of the line emission and therefore radiation transport mechanism in optically thick plasma. Self-absorption which defines the excited state-densities is an important mechanism and can be used with other methods to describe the state densities for an optically thick plasma. This method is an established tool to retrieve state-density and plasma parameters. To measure each magnetic sub-level density of argon 1s4 and 1s5 (in Paschen's notation) a tunable diode laser absorption spectroscopy (TDLAS) was used. Based on reconstructed excited state densities, the self-absorption coefficient was calculated for individual magnetic sub-levels. A decrease in self-absorption with an external magnetic field was noticed indicating a higher transparency of the plasma. Furthermore a polarization dependent self-absorption was found. The presented results can help to model optical properties and interpret the absorption of a low-pressure optically thick magnetized plasma.

Quantum dynamics of atomic Rydberg excitation in strong laser fields (1906.08093v1)

Shilin Hu, Xiaolei Hao, Hang Lv, Mingqing Liu, Tianxiang Yang, Haifeng Xu, Mingxing Jin, Dajun Ding, Qianguang Li, Weidong Li, Wilhelm Becker, Jing Chen

2019-06-19

Neutral atoms have been observed to survive intense laser pulses in high Rydberg states with surprisingly large probability. Only with this Rydberg-state excitation (RSE) included is the picture of intense-laser-atom interaction complete. Various mechanisms have been proposed to explain the underlying physics. However, neither one can explain all the features observed in experiments and in time-dependent Schr"{o}dinger equation (TDSE) simulations. Here we propose a fully quantum-mechanical model based on the strong-field approximation (SFA). It well reproduces the intensity dependence of RSE obtained by the TDSE, which exhibits a series of modulated peaks. They are due to recapture of the liberated electron and the fact that the pertinent probability strongly depends on the position and the parity of the Rydberg state. We also present measurements of RSE in xenon at 800 nm, which display the peak structure consistent with the calculations.

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