Atomic Physics

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Sideband cooling of the radial modes of motion of a single ion in a Penning trap (1907.02406v1)

P. Hrmo, M. K. Joshi, V. Jarlaud, O. Corfield, R. C. Thompson

2019-07-04

Doppler and sideband cooling are long standing techniques that have been used together to prepare trapped atomic ions in their ground state of motion. In this paper we study how these techniques can be extended to cool both radial modes of motion of a single ion in a Penning trap. We numerically explore the prerequisite experimental parameters for efficient Doppler cooling in the presence of an additional oscillating electric field to resonantly couple the radial modes. The simulations are supported by experimental data for a single Ca ion Doppler cooled to 100 phonons in both modes at a magnetron frequency of 52 kHz and a modified cyclotron frequency of 677 kHz. For these frequencies, we then show that mean phonon numbers of for the modified cyclotron and for the magnetron motions are achieved after 68 ms of sideband cooling.

Quench dynamics of Rydberg dressed bosons on two-dimensional square lattices (1907.02028v1)

Yijia Zhou, Yongqiang Li, Rejish Nath, Weibin Li

2019-07-03

We study dynamics of bosonic atoms on a two dimensional square lattice, where atomic interactions are long ranged with either a box or soft-core shape. The latter can be realized through laser dressing ground state atoms to electronically excited Rydberg states. When the range of interactions is equal or larger than the lattice constant, the system is governed by an extended Bose-Hubbard model. We propose a quench process by varying the atomic hopping linearly across phase boundaries of the Mott insulator-supersolid and supersolid-superfluid phases. Starting from a Mott insulator state, dynamical evolution exhibits a universal behaviour at the early stage. We numerically find that the universality is largely independent of interactions during this stage. However, dynamical evolution could be significantly altered by long-range interactions at later times. We demonstrate that density wave excitations are important below a critical quench rate, where non-universal dynamics is found. We also show that the quench dynamics can be analysed through time-of-flight images, i.e. measuring the momentum distribution and noise correlations.

Excitation spectrum of a trapped dipolar supersolid and its experimental evidence (1907.01986v1)

G. Natale, R. M. W. van Bijnen, A. Patscheider, D. Petter, M. J. Mark, L. Chomaz, F. Ferlaino

2019-07-03

We study the spectrum of elementary excitations of a trapped dipolar Bose gas across the superfluid-supersolid phase transition. Our calculations, accounting for the experimentally relevant case of confined systems, show that, when entering the supersolid phase, two distinct excitation branches appear, respectively connected to crystal or superfluid orders. These results confirm infinite-system predictions, showing that finite-size effects play only a small qualitative role. Experimentally, we probe compressional excitations in an Er quantum gas across the phase diagram. While in the BEC regime the system exhibits an ordinary quadrupole oscillation, in the supersolid regime, we observe a striking two-frequency response of the system, related to the two spontaneously broken symmetries.

Electromagnetically Induced Transparency of Interacting Rydberg Atoms with Two-Body dephasing (1902.07492v4)

Dong Yan, Binbin Wang, Zhengyang Bai, Weibin Li

2019-02-20

We study electromagnetically induced transparency of a ladder type configuration in ultracold atomic gases, where the upper level is an electronically highly excited Rydberg state. We study a scenario where both dispersive and dissipative long-range interactions between Rydberg atoms are present. This is motivated by recent experimental discovery, where molecular transitions cause an effective two-body dephasing process. It has been shown that long-range van der Waals interactions suppress simultaneous excitations of multiple Rydberg atoms within a blockade volume. We show that the nonlocal, two-body dissipative process enhances the excitation blockade. Through numerical and approximately analytical calculations, we show that transmission of the probe field is reduced drastically in the transparent window, which is accompanied by stronger photon-photon anti-bunching. Around the Autler-Townes splitting, photon bunching is amplified by the two-body dephasing.

Charge dynamics of a molecular ion immersed in a Rydberg-dressed atomic lattice gas (1901.06288v3)

Rick Mukherjee

2019-01-18

Charge dynamics in an ultra-cold setup involving a laser dressed atom and an ion is studied here. This transfer of charge is enabled through molecular Rydberg states that are accessed via a laser. The character of the charge exchange crucially depends on the coupling between the electronic dynamics and the vibrational motion of the atoms and ion. The molecular Rydberg states are characterized and a criterion for distinguishing coherent and incoherent regimes is formulated. Furthermore the concept is generalized to the many-body setup as the ion effectively propagates through a chain of atoms. Aspects of the transport such as its direction can be controlled by the excitation laser. This leads to new directions in the investigation of hybrid atom-ion systems that can be experimentally explored using optically trapped strontium atoms.

Supersonic rotation of a superfluid: a long-lived dynamical ring (1907.01795v1)

Yanliang Guo, Romain Dubessy, Mathieu de Goër de Herve, Avinash Kumar, Thomas Badr, Aurélien Perrin, Laurent Longchambon, Hélène Perrin

2019-07-03

We present the experimental realization of a long-lived superfluid flow of a quantum gas rotating in an anharmonic potential, sustained by its own angular momentum. The gas is set into motion by rotating an elliptical deformation of the trap. An evaporation selective in angular momentum yields an acceleration of rotation until the density vanishes at the trap center, resulting in a dynamical ring with 350 hbar angular momentum per particle. The density profile of the ring corresponds to the one of a quasi two-dimensional superfluid, with a linear velocity reaching Mach 18 and a rotation lasting more than a minute.

Bi-chromatic adiabatic shells for atom interferometry (1907.01775v1)

Hector Mas, Saurabh Pandey, Giorgos Vasilakis, Wolf von Klitzing

2019-07-03

We demonstrate bi-chromatic adiabatic magnetic shell traps as a novel tool for matterwave interferometry. Using two strong RF fields, we dress the and states of Rubidium Bose-Einstein Condensates thus creating two independently controllable shell traps. This allows us to match the two traps and, using microwave pulses, create a state-dependent clock-type interferometer. Given the low horizontal confinement of the interferometer, the atoms can be made to spread out thus yielding a 2D sheet, which could be used in a direct imaging interferometer. This interferometer can be sensitive to spatially varying electric or magnetic fields, which could be DC, AC, RF fields or microwaves, or even local variations in gravity. We demonstrate that the trap-matching afforded by the independent control of the shell traps allows long coherence times which will result in highly sensitive imaging matterwave interferometers.

Detection of radiation torque exerted on an alkali-metal vapor cell (1903.10123v2)

Atsushi Hatakeyama, Runa Yasuda, Yutaka Goto, Natsumi Chikakiyo, Takahiro Kuroda, Yugo Nagata

2019-03-25

We have developed a torsion balance to detect the rotation of a cell containing spin-polarized gaseous atoms to study angular momentum transfer from gaseous atoms to solid. A cesium vapor cell was hung from a thin wire in a vacuum chamber, and irradiated from the bottom with circularly polarized light tuned to the transition to polarize cesium atoms in the cell. By varying the light helicity at the resonance frequency of the torsion balance, we induced forced rotational oscillation of the cell and detected radiation torque exerted on the cesium vapor cell through the cesium atoms inside. The torque was particularly large when both hyperfine levels of cesium atoms were optically pumped with application of a longitudinal magnetic field. Further detailed study will provide new insights into spin-transfer processes at the gas-solid interface.

Multi-Frequency Atom-Photon Interactions (1907.01469v1)

Ben Yuen, Christopher J. Foot

2019-07-02

We present a formalism that enables the analytic calculation of the interaction of a spin-half particle with a polychromatic electromagnetic field. This powerful new approach provides a clear physical picture even for cases with highly degenerate energy levels, which are complicated to interpret in the standard dressed-atom picture. Typically semi-classical methods are used for such problems (leading to equations that are solved by Floquet theory). Our formalism is derived from quantum electrodynamics and thus is more widely applicable. In particular it makes accessible the intermediate regime between quantum and semi-classical dynamics. We give examples of the application to multi-frequency multi-photon processes in strong fields by deriving the Hamiltonians of such systems, and also to the dynamics of weak fields at long times for which semi-classical methods are insufficient.

Gravitational effects on geonium and free electron -factor measurements in a Penning trap (1907.01460v1)

Sebastian Ulbricht, Robert Alexander Müller, Andrey Surzhykov

2019-07-02

We present a theoretical analysis of an electron confined by a Penning trap, also known as geonium, that is affected by gravity. In particular, we investigate the gravitational influence on the electron dynamics and the electromagnetic field of the trap. We consider the special case of a homogeneous gravitational field, which is represented by Rindler spacetime. In this spacetime the Hamiltonian of an electron with anomalous magnetic moment is constructed. Based on this Hamiltonian and the exact solution to Maxwell equations for the field of a Penning trap in Rindler spacetime, we derived the transition energies of geonium up to the relativistic corrections of . These transition energies are used to obtain an extension of the well known -factor formula introduced by L. S. Brown and G. Gabrielse [Rev. Mod. Phys. 58, 233 1986].

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