Atomic Physics

---

How to Directly Measure Floquet Topological Invariants in Optical Lattices (1812.04636v2)

F. Nur Ünal, Babak Seradjeh, André Eckardt

2018-12-11

The classification of topological Floquet systems with time-periodic Hamiltonians transcends that of static systems. For example, spinless fermions in periodically driven two-dimensional lattices are not completely characterized by the Chern numbers of the quasienergy bands, but rather by a set of winding numbers associated with the quasienergy gaps. We propose a scheme for measuring these winding numbers in a system of fermionic cold atoms in a periodically driven optical lattice efficiently and directly. It is based on the construction of a one-parameter family of experimentally feasible drives, continuously connecting the Floquet system of interest to a trivial reference system. The winding numbers are then determined by the identification and the tomography of the band-touching singularities occurring on the way. As a byproduct, we also propose a method for probing spectral properties of time evolution operators via a time analog of crystallography.

Long-range vs. short-range effects in cold molecular ion-neutral collisions: Charge exchange of Rb with N and O (1906.12285v1)

Alexander D. Dörfler, Pascal Eberle, Debasish Koner, Michal Tomza, Markus Meuwly, Stefan Willitsch

2019-06-28

We report a study of cold charge-transfer (CT) collisions of Rb atoms with N and O ions in the mK regime using a dynamic ion-neutral hybrid trapping experiment. State- and collision-energy- dependent reaction rate coefficients have been measured for both systems. We observe markedly different charge-transfer kinetics and dynamics for the different systems and reaction channels. While the kinetics in some channels are consistent with classical capture theory for the rate coefficient, others show distinct non-universal dynamics. The experimental results are interpreted with the help of classical capture, quasiclassical trajectory and quantum scattering calculations using state-of-the-art ab-initio potentials for the highly excited molecular states involved. The theoretical analysis reveals an intricate interplay between short- and long-range effects in the different reaction channels which ultimately determines the CT dynamics and rates. At short range, CT was found to occur via both single and multiple collision events with the latter typically showing pronounced large-amplitude internal motions of the collision complex. Our results illustrate salient mechanisms that determine the efficiency of cold molecular CT reactions.

Far-from-equilibrium dynamics of angular momentum in a quantum many-particle system (1906.12238v1)

Igor N. Cherepanov, Giacomo Bighin, Lars Christiansen, Anders Vestergaard Jørgensen, Richard Schmidt, Henrik Stapelfeldt, Mikhail Lemeshko

2019-06-28

We use laser-induced rotation of single molecules embedded in superfluid helium nanodroplets to reveal angular momentum dynamics and transfer in a controlled setting, under far-from-equilibrium conditions. As an unexpected result, we observe pronounced oscillations of time-dependent molecular alignment that have no counterpart in gas-phase molecules. Angulon theory reveals that these oscillations originate from the unique rotational structure of molecules in He droplets and quantum-state-specific transfer of rotational angular momentum to the many-body He environment on picosecond timescales. Our results pave the way to understanding collective effects of macroscopic angular momentum exchange in solid state systems in a bottom-up fashion.

Nature of interference between Autler-Townes peaks in multi-level system (1906.12194v1)

Dangka Shylla, Elijah Ogaro Nyakango, Kirthanaa Indumathi, Kanhaiya Pandey

2019-06-28

In this work we present a theoretical frame work to identify the role and the nature of interference between Autler-Townes (AT) peaks (or dressed states) in generic multi-level system. The destructive interference between the AT peaks, gives rise to sharp transparency window known as electromagnetically induced transparency (EIT). In the three-level system, the two AT peaks interferes pair-wise with each other, almost similar to the two-slit interference. In the four-level system, the interference between the three AT peaks is also pair-wise analogous to three-slit interference but has a bit more complicated nature of interference. However, in many practical situations in atomic systems only the simple form of interference similar to three-level system dominates. In the three-level system, the nature of interference (i.e. constructive, destructive or zero/no interference) between the two AT peaks is purely determined by the natural decay rate of the states coupled by the control laser. However, in four-level system the nature of interference between the two extreme AT peaks can be tuned from constructive to destructive by tuning the power of the control laser.

Streaking strong-field double ionization (1906.12169v1)

Matthias Kübel, Georgios P. Katsoulis, Zack Dube, Andrei Yu Naumov, David M. Villeneuve, Paul B. Corkum, André Staudte, Agapi Emmanouilidou

2019-06-28

Double ionization in intense laser fields can comprise electron correlations, which manifest in the non-independent emission of two electrons from an atom or molecule. However, experimental methods that directly access the electron emission times have been scarce. Here, we explore the application of an all-optical streaking technique to strong-field double ionization both theoretically and experimentally. We show that both sequential and non-sequential double ionization processes lead to streaking delays that are distinct from each other and single ionization. Moreover, coincidence detection of ions and electrons provides access to the emission time difference, which is encoded in the two-electron momentum distributions. The experimental data agree very well with simulations of sequential double ionization. We further test and discuss the application of this method to non-sequential double ionization, which is strongly affected by the presence of the streaking field.

Optimal pulse propagation in an inhomogeneously gas-filled hollow-core fiber (1905.02807v2)

Roman Sulzbach, Thorsten Peters, Reinhold Walser

2019-05-07

We study optical pulse propagation through a hollow-core fiber filled with a radially inhomogeneous cloud of cold atoms. A co-propagating control field establishes electromagnetically induced transparency. In analogy to a graded index fiber, the pulse experiences micro-lensing and the transmission spectrum becomes distorted. Based on a two-layer model of the complex index of refraction, we can analytically understand the cause of the aberration, which is corroborated by numerical simulations for a radial Gaussian-shaped function. With these insights, we show that the spectral distortions can be rectified by choosing an optimal detuning from one-photon resonance.

It is all about phases: ultrafast holographic photoelectron imaging (1906.11781v1)

C. Figueira de Morisson Faria, A. S. Maxwell

2019-06-27

Photoelectron holography constitutes a powerful tool for the ultrafast imaging of matter, as it combines high electron currents with subfemtosecond resolution, and gives information about transition amplitudes and phase shifts. Similarly to light holography, it uses the phase difference between the probe and the reference waves associated with qualitatively different ionization events for the reconstruction of the target and for ascertaining any changes that may occur. These are major advantages over other attosecond imaging techniques, which require elaborate interferometric schemes in order to extract phase differences. For that reason, ultrafast photoelectron holography has experienced a huge growth in activity, which has led to a vast, but fragmented landscape. The present review is an organizational effort towards unifying this landscape. This includes a historic account in which a connection with laser-induced electron diffraction (LIED) is established, a summary of the main holographic structures encountered and their underlying physical mechanisms, a broad discussion of the theoretical methods employed, and of the key challenges and future possibilities. We delve deeper in our own work, and place a strong emphasis on quantum interference, and on the residual Coulomb potential.

Signatures of the optical angular momentum of light in attosecond chronoscopy of photoionisation (1906.11771v1)

Sucharita Giri, Misha Ivanov, Gopal Dixit

2019-06-27

We describe attosecond chronoscopy of photo-ionisation in the presence of a vortex beam. In a pump-probe setup, an extreme ultraviolet or an X-ray pump pulse triggers ionisation, which is probed by a synchronized infrared pulse with non-zero orbital angular momentum. We show how this property of the probe pulse affects the electron dynamics upon ionisation, in a way that is universal and independent of the initial and final angular momentum states of the ionising system.

A low-energy compact Shanghai-Wuhan electron beam ion trap for extraction of highly charged ions (1906.10927v2)

Shiyong Liang, Qifeng Lu, Xincheng Wang, Yang Yang, Ke Yao, Yang Shen, Baoren Wei, Jun Xiao, Shaolong Chen, Pengpeng Zhou, Wei Sun, Yonghui Zhang, Yao Huang, Hua Guan, Chengbin Li, Yaming Zou, Tingyun Shi, Kelin Gao

2019-06-26

A low-energy, compact, high-temperature superconducting, the Shanghai-Wuhan electron beam ion trap (SW-EBIT) for extraction of highly charged ions (HCIs) is reported. The magnetic field in the central drift tube of the SW-EBIT is approximately 0.21 T produced by a pair of high-temperature superconducting coils. The electron-beam energy of the SW-EBIT is in the range of 30-4000 eV, and the maximum electron-beam current is up to over nine mA. For acting as an HCIs source, the ion-beam optics for extraction is integrated including an ion extractor and an Einzel lens. A Wien filter is then used to measure the charge-state distributions of the extracted ions. In this work, the tungsten ions below 15 charge state are produced, extracted, and analyzed. The charge-state distributions and spectra in the range of 530-580 nm of tungsten ions are measured simultaneously with the electron-beam energy of 266 eV and 286 eV, which preliminary proves that the 549.9 nm line comes from .

The effect of Coulomb field on laser-induced ultrafast imaging methods (1906.11503v1)

XiaoLei Hao, YuXing Bai, XiaoYun Zhao, Chan Li, JingYu Zhang, JiLing Wang, WeiDong Li, ChuanLiang Wang, Wei Quan, XiaoJun Liu, Zheng Shu, Mingqing Liu, Jing Chen

2019-06-27

The deconvolution procedure of the laser-induced ultrafast imaging schemes is usually based on strong field approximation (SFA) wherein the Coulomb interaction between the parent ion and the freed electron is ignored after ionization. In the laser-induced electron diffraction (LIED) approach, for example, the high energy part of the above-threshold ionization (ATI) spectrum used for analysis is assumed to be produced mostly by the 1st-return-recollision trajectories according to the SFA. By performing a joint theoretical and experimental investigation on the ATI spectrum, the dominant role of the 3rd-return-recollision trajectories in the high energy part of the spectrum due to the ionic Coulomb field is identified, which invalidates the key assumption adopted in the conventional LIED approach. Since the incident (return) electron beams produced by the 1st and 3rd returns possess distinct characteristics of beam energy, beam diameter and temporal evolution law due to the influence of Coulomb field, the extracted results in the LIED will be significantly altered. Such Coulomb field effect should be taken into account in all kinds of laser-induced imaging schemes based on recollision.

---

Keeping updated in the latest research in atomic and molecular clusters!