Atomic Physics
Far-from-equilibrium dynamics of angular momentum in a quantum many-particle system (1906.12238v2)
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.
Time delays from one-photon transitions in the continuum (1907.03607v1)
Jaco Fuchs, Nicolas Douguet, Stefan Donsa, Fernando Martin, Joachim Burgdörfer, Luca Argenti, Laura Cattaneo, Ursula Keller
2019-07-08
Attosecond photoionisation time delays reveal information about the potential energy landscape an outgoing electron wavepacket probes upon ionisation. In this study we experimentally quantify, for the first time, the dependence of the time delay on the angular momentum of the liberated photoelectrons. For this purpose, electron quantum-path interference spectra have been resolved in energy and angle using a two-color attosecond pump-probe photoionisation experiment in helium. A fitting procedure of the angle-dependent interference pattern allows us to disentangle the relative phase of all four quantum pathways that are known to contribute to the final photoelectron signal. In particular, we resolve the dependence on the angular momentum of the delay of one-photon transitions between continuum states, which is an essential and universal contribution to the total photoionization delay observed in attosecond pump-probe measurements. For such continuum-continuum transitions, we measure a delay between outgoing s- and d-electrons as large as 12 as close to the ionisation threshold in helium. Both single-active-electron and first-principles ab initio simulations confirm this observation for helium and hydrogen, demonstrating the universality of the observed delays.
Correlation trends in the hyperfine structure for Rb, Cs, Fr and high-accuracy predictions for hyperfine constants (1907.02657v2)
S. J. Grunefeld, B. M. Roberts, J. S. M. Ginges
2019-07-05
We have performed high-precision calculations of the hyperfine structure for n 2S_1/2 and n 2P_1/2 states of the alkali-metal atoms Rb, Cs, and Fr across principal quantum number n, and studied the trend in the size of the correlations. Our calculations were performed in the all-orders correlation potential method. We demonstrate that the relative correlation corrections fall off quickly with n and tend towards constant and non-zero values for highly-excited states. This trend is supported by experiment, and we utilize the smooth dependence on n to make high-accuracy predictions of the hyperfine constants, with uncertainties to within 0.1% for most states of Rb and Cs.
Pure Molecular Beam of Water Dimer (1904.08716v3)
Helen Bieker, Jolijn Onvlee, Melby Johny, Lanhai He, Thomas Kierspel, Sebastian Trippel, Daniel A. Horke, Jochen Küpper
2019-04-18
Spatial separation of water dimer from water monomer and larger water-clusters through the electric deflector is presented. A beam of water dimer with
purity and a rotational temperature of
K was obtained. Following strong-field ionization using a
fs laser pulse with a wavelength centered around
nm and a peak intensity of
we observed proton transfer and
of the ionized water dimer broke apart into a hydronium ion
and neutral OH.
Discrete time crystal in a finite chain of Rydberg atoms without disorder (1907.03446v1)
Chuhui Fan, D. Rossini, Han-Xiao Zhang, Jin-Hui Wu, M. Artoni, G. C. La Rocca
2019-07-08
We study the collective dynamics of a clean Floquet system of cold atoms, numerically simulating two realistic set-ups based on a regular chain of interacting Rydberg atoms driven by laser fields. In both cases, the population evolution and its Fourier spectrum display clear signatures of a discrete time crystal (DTC), exhibiting the appearance of a robust subharmonic oscillation which persists on a time scale increasing with the chain size, within a certain range of control parameters. We also characterize how the DTC stability is affected by dissipative processes, typically present in this atomic system even though the Rydberg state is very long lived.
Control and imaging of molecular quantum states with second-scale coherence (1907.03413v1)
Yan Zhou, Yuval Shagam, William B. Cairncross, Kia Boon Ng, Tanya S. Roussy, Tanner Grogan, Kevin Boyce, Antonio Vigil, Madeline Pettine, Tanya Zelevinsky, Jun Ye, Eric A. Cornell
2019-07-08
Cold molecules provide a platform for a variety of scientific applications such as quantum computation, simulation, cold chemistry, and searches for physics beyond the Standard Model. Mastering quantum state control and measurement of diverse molecular species is critical for enabling these applications. However, state control and readout are difficult for the majority of molecular species due to the lack of optical cycling transitions. Here we demonstrate internal state cooling and orientation-selective photofragment imaging in a spin precession measurement with multi-second coherence, allowing us to achieve the quantum projection noise (QPN) limit in a large ensemble of trapped molecular ions. We realize this scheme for both HfF+ and ThF+ --- molecules chosen for their sensitivity to beyond Standard Model physics rather than their amenability to state control and readout.
Optimizing configurations for determining the magnetic model based on ab-initio calculations (1907.03376v1)
J. M. Matera, C. A. Lamas, L. A. Errico, A. V. Gil Rebaza, V. I. Fernández
2019-07-08
In this paper, it is presented a novel strategy to optimize the determination of magnetic couplings by using ab-initio calculations of the energy. This approach allows determining efficiently, in terms of a proposed effective magnetic spin model, an optimal set of magnetic configurations to be simulated by DFT methods. Moreover, a procedure to estimate the values of the coupling constants and their error bounds from the estimated energies is proposed. This method, based on Monte Carlo sampling, takes into account the accuracy of the ab - initio simulations. A strategy to refine models reusing previously computed configuration energies is also presented. We apply the method to determine a magnetic model for the recently synthesized material Bi
Mn
O
(NO
Two-photon photoassociation spectroscopy of the 
YbLi molecular ground state (1903.00603v2)
Alaina Green, Jun Hui See Toh, Richard Roy, Ming Li, Svetlana Kotochigova, Subhadeep Gupta
2019-03-02
We report on measurements of the binding energies of several weakly bound vibrational states of the paramagnetic
Yb
Li molecule in the electronic ground state using two-photon spectroscopy in an ultracold atomic mixture confined in an optical dipole trap. We theoretically analyze the experimental spectrum to obtain an accurate description of the long-range potential of the ground state molecule. Based on the measured binding energies, we arrive at an improved value of the interspecies
-wave scattering length
. Employing coherent two-photon spectroscopy we also observe the creation of ''dark'' atom-molecule superposition states in the heteronuclear Yb-Li system. This work is an important step towards the efficient production of ultracold YbLi molecules via association from an ultracold atomic mixture.
Hyperfine Splitting in Muonium: Accuracy of the Theoretical Prediction (1812.10881v3)
Michael I. Eides
2018-12-28
In the last twenty years, the theory of hyperfine splitting in muonium developed without any experimental input. Finally, this situation is changing and a new experiment on measuring hyperfine splitting in muonium is now in progress at J-PARC. The goal of the MuSEUM experiment is to improve by an order of magnitude experimental accuracy of the hyperfine splitting and muon-electron mass ratio. Uncertainty of the theoretical prediction for hyperfine splitting will be crucial for comparison between the forthcoming experimental data and the theory in search of a possible new physics. In the current literature estimates of the error bars of the theoretical prediction differ roughly by a factor of two. We explain the origin of this discrepancy and obtain the theoretical prediction for the muonium hyperfine splitting
.
Optimization of the atom interferometer phase produced by the set of cylindrical source masses to measure the Newtonian gravity constant (1907.03352v1)
B. Dubetsky
2019-07-07
An analytical expression for the gravitational field of a homogeneous cylinder is derived. The phase of the atom interferometer produced by the gravity field of the set of cylinders has been calculated. The optimal values of the initial positions and velocities of atomic clouds were obtained. It is shown that at equal sizes of the atomic cloud in the vertical and transverse directions, as well as at equal atomic vertical and transverse temperatures, systematic errors due to the finite size and temperature of the cloud disappear. It is shown that, although the gravitational field of the Earth does not affect the phase double difference, it continues to affect the measurement accuracy of this signal. To overcome this influence, it is proposed to use the technique of eliminating gravity-gradient terms. Nonlinear dependences of the phase on the uncertainties of atomic positions and velocities required us to modify the expression for the standard phase deviation. Moreover, such dependencies lead to a phase shift, which was also calculated. The relative accuracy of measurements of Newtonian gravitational constant 10^{-4} and 2*10^{-5} is predicted for sets of 24 and 630 cylinders, respectively.
