Atomic Physics

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Discrete time crystal in a finite chain of Rydberg atoms without disorder (1907.03446v2)

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.

Transfer of orbital angular momentum superposition from asymmetric Laguerre-Gaussian beam to Bose-Einstein Condensate (1907.04090v1)

Subrata Das, Anal Bhowmik, Koushik Mukherjee, Sonjoy Majumder

2019-07-09

In this paper, we have formulated a theory for the microscopic interaction of the asymmetric Laguerre-Gaussian (aLG) beam with the atomic Bose-Einstein condensate (BEC) in a harmonic trap. Here the asymmetry is introduced to an LG beam considering a complex-valued shift in the Cartesian plane keeping the axis of the beam and its vortex states co-axial to the trap axis of the BEC. Due to the inclusion of the asymmetric nature, multiple quantized circulations are generated in the beam. We show how these quantized circulations are transferred to the BEC resulting in a superposition of matter vortex states. The calculated Rabi frequencies for the dipole as well as quadrupole transitions during the transfer process show distinct variability with the shift parameters of the beam. A significant enhancement of the quadrupole Rabi frequency for higher vorticity states is observed compared to symmetric single orbital angular momentum (OAM) mode beam at a particular range of the shift parameters. We also demonstrate the variation of superposition of matter vortex states and observe its distinct feature compared to the superposition of the LG modes for different shift parameters. The first order spatial correlation of the superposed states supports this feature and highlights asymmetry in degree of transverse coherence along orthogonal directions on the surface.

Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks (1907.02661v2)

B. M. Roberts, P. Delva, A. Al-Masoudi, A. Amy-Klein, C. Bærentsen, C. F. A. Baynham, E. Benkler, S. Bilicki, S. Bize, W. Bowden, J. Calvert, V. Cambier, E. Cantin, E. A. Curtis, S. Dörscher, M. Favier, F. Frank, P. Gill, R. M. Godun, G. Grosche, C. Guo, A. Hees, I. R. Hill, R. Hobson, N. Huntemann, J. Kronjäger, S. Koke, A. Kuhl, R. Lange, T. Legero, B. Lipphardt, C. Lisdat, J. Lodewyck, O. Lopez, H. S. Margolis, H. Álvarez-Martínez, F. Meynadier, F. Ozimek, E. Peik, P. -E. Pottie, N. Quintin, C. Sanner, L. De Sarlo, M. Schioppo, R. Schwarz, A. Silva, U. Sterr, Chr. Tamm, R. Le Targat, P. Tuckey, G. Vallet, T. Waterholter, D. Xu, P. Wolf

2019-07-05

We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation in alpha to <5*10^-17 for transients of duration 10^3 s. This analysis also presents a possibility to search for dark matter, the mysterious substance hypothesised to explain galaxy dynamics and other astrophysical phenomena that is thought to dominate the matter density of the universe. At the current sensitivity level, we find no evidence for dark matter in the form of topological defects (or, more generally, any macroscopic objects), and we thus place constraints on certain potential couplings between the dark matter and standard model particles, substantially improving upon the existing constraints, particularly for large (>~10^4 km) objects.

Gravity surveys using a mobile atom interferometer (1904.09084v3)

Xuejian Wu, Zachary Pagel, Bola S. Malek, Timothy H. Nguyen, Fei Zi, Daniel S. Scheirer, Holger Müller

2019-04-19

Mobile gravimetry is important in metrology, navigation, geodesy, and geophysics. Atomic gravimeters could be among the most accurate mobile gravimeters, but are currently constrained by being complex and fragile. Here, we demonstrate a mobile atomic gravimeter, measuring tidal gravity variations in the laboratory as well as surveying gravity in the field. The tidal gravity measurements achieve a sensitivity of 37 Gal/ and a long-term stability of better than 2 Gal, revealing ocean tidal loading effects and recording several distant earthquakes. We survey gravity in the Berkeley Hills with an accuracy of around 0.04 mGal and determine the density of the subsurface rocks from the vertical gravity gradient. With simplicity and sensitivity, our instrument paves the way for bringing atomic gravimeters to field applications.

SAGE: A Proposal for a Space Atomic Gravity Explorer (1907.03867v1)

G. M. Tino, A. Bassi, G. Bianco, K. Bongs, P. Bouyer, L. Cacciapuoti, S. Capozziello, X. Chen, M. L. Chiofalo, A. Derevianko, W. Ertmer, N. Gaaloul, P. Gill, P. W. Graham, J. M. Hogan, L. Iess, M. A. Kasevich, H. Katori, C. Klempt, X. Lu, L. -S. Ma, H. Muller, N. R. Newbury, C. Oates, A. Peters, N. Poli, E. Rasel, G. Rosi, A. Roura, C. Salomon, S. Schiller, W. Schleich, D. Schlippert, F. Schreck, C. Schubert, F. Sorrentino, U. Sterr, J. W. Thomsen, G. Vallone, F. Vetrano, P. Villoresi, W. von Klitzing, D. Wilkowski, P. Wolf, J. Ye, N. Yu, M. S. Zhan

2019-07-08

The proposed mission "Space Atomic Gravity Explorer" (SAGE) has the scientific objective to investigate gravitational waves, dark matter, and other fundamental aspects of gravity as well as the connection between gravitational physics and quantum physics using new quantum sensors, namely, optical atomic clocks and atom interferometers based on ultracold strontium atoms.

Purely long-range polar molecules composed of identical lanthanide atoms (1907.03853v1)

Hui Li, Goulven Quéméner, Jean-François Wyart, Olivier Dulieu, Maxence Lepers

2019-07-08

Doubly polar molecules, possessing an electric dipole moment and a magnetic dipole moment, can strongly couple to both an external electric field and a magnetic field, providing unique opportunities to exert full control of the system quantum state at ultracold temperatures. We propose a method for creating a purely long-range doubly polar homonuclear molecule from a pair of strongly magnetic lanthanide atoms, one atom being in its ground level and the other in a superposition of quasi-degenerate opposite-parity excited levels [Phys.~Rev.~Lett.~\textbf{121}, 063201 (2018)]. The electric dipole moment is induced by coupling the excited levels with an external electric field. We derive the general expression of the long-range, Stark, and Zeeman interaction energies in the properly symmetrized and fully-coupled basis describing the diatomic complex. Taking the example of holmium, our calculations predict shallow long-range wells in the potential energy curves that may support vibrational levels accessible by direct photoassociation from pairs of ground-level atoms.

O()+CO scattering cross sections at superthermal collision energies for planetary aeronomy (1906.11368v2)

Marko Gacesa, Robert J. Lillis, Kevin J. Zahnle

2019-06-26

We report new elastic and inelastic cross sections for O()+CO scattering at collision energies from 0.03 to 5 eV, of major importance to O escape from Mars, Venus, and CO-rich atmospheres. The cross sections were calculated from first principles using three newly constructed ab-initio potential energy surfaces correlating to the lowest energy asymptote of the complex. The surfaces were restricted to a planar geometry with the CO molecule assumed to be in linear configuration fixed at equilibrium. Quantum-mechanical coupled-channel formalism with a large basis set was used to compute state-to-state integral and differential cross sections for elastic and inelastic O()+CO scattering between all pairs of rotational states of CO molecule. The elastic cross sections are 35% lower at 0.5 eV and more than 50% lower at 4+ eV than values commonly used in studies of processes in upper and middle planetary atmospheres of Mars, Earth, Venus, and CO-rich planets. Momentum transfer cross sections, of interest for energy transport, were found to be lower than predicted by mass-scaling.

Seed and vacuum pair production in strong laser field (1907.03786v1)

Huayu Hu

2019-07-08

Researches on the electron-positron pair production in the presence of the intense laser field are reviewed, motivated by the theoretical importance of the nonperturbative QED problem and the worldwide development of the strong laser facilities. According to distinct experimental requirements and theoretical methods, two types of pair production are elaborated, which are respectively the pair production in the combination of a seed particle and the strong laser, and vacuum pair production without a seed particle. The origin of the nonperturbative problem caused by the strong field is analyzed. The main idea, realization, achievements, validity, challenges and bottleneck problems of the nonperturbative methods developed for each type of the pair production problem are discussed.

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.

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