Physics - Atomic Physics Publications (50)

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Physics - Atomic Physics Publications

A Stark decelerator is an effective tool for controlling motional degrees of freedom of polar molecules. Due to technical limitations, many of the current Stark decelerators focus on molecules in low-field-seeking quantum states and are built based on a fixed electrode size and spacing (type-A architecture). Here, we present an alternative method based on a different architecture, so-called type-B, with microstructured electrodes and a simpler electric field pulse timing with the prospect of producing cold, quasi-CW molecular beams. Read More


Coherent many-body quantum dynamics lies at the heart of quantum simulation and quantum computation. Both require coherent evolution in the exponentially large Hilbert space of an interacting many-body system. To date, trapped ions have defined the state of the art in terms of achievable coherence times in interacting spin chains. Read More


We report on the observation of the motional Stark effect of highly excited $^{87}$Rb Rydberg atoms moving in the presence of a weak homogeneous magnetic field in a vapor cell. Employing electromagnetically induced transparency for spectroscopy of an atomic vapor, we observe the velocity, quantum state and magnetic field dependent transition frequencies between the ground and Rydberg excited states. For atoms with the principal quantum number $n=100$ moving at velocities around 400m/s and a magnetic field of $B=100\mathrm{G}$, we measure a motional Stark shift of $\sim10\mathrm{MHz}$. Read More


2017May

Radiofrequency multipole traps have been used for some decades in cold collision experiments, and are gaining interest for precision spectroscopy due to their low mi-cromotion contribution, and the predicted unusual cold-ion structures. However, the experimental realisation is not yet fully controlled, and open questions in the operation of these devices remain. We present experimental observations of symmetry breaking of the trapping potential in a macroscopic octupole trap with laser-cooled ions. Read More


Coherent interactions between electromagnetic and matter waves lie at the heart of quantum science and technology. However, the diffraction nature of light has limited the scalability of many atom-light based quantum systems. Here, we use the optical fields in a hollow-core photonic crystal fiber to spatially split, reflect, and recombine a coherent superposition state of free-falling 85Rb atoms to realize an inertia-sensitive atom interferometer. Read More


We report on the alteration of photon emission properties of a single trapped ion coupled to a high finesse optical fiber cavity. We show that the vacuum field of the cavity can simultaneously affect the emissions in both the infrared (IR) and ultraviolet (UV) branches of the $\Lambda-$type level system of $^{40}\mathrm{Ca}^+$ despite the cavity coupling only to the IR transition. The cavity induces strong emission in the IR transition through the Purcell effect resulting in a simultaneous suppression of the UV fluorescence. Read More


We use the sensitive response to electric fields of Rydberg atoms to characterize all three vector components of the local electric field close to an atom-chip surface. We measured Stark-Zeeman maps of $S$ and $D$ Rydberg states using an elongated cloud of ultracold Rubidium atoms ($T\sim2.5$ $\mu$K) trapped magnetically $100$ $\mu$m from the chip surface. Read More


Cooling and trapping of dilute gases, both neutral and charged, have enabled extremely precise and controlled experimentation with these systems$^{1}$. The two most widely used ion cooling methods$^{2}$ are laser cooling and sympathetic cooling by elastic collisions (ECs). Recent experiments with interacting trapped ion-atom mixtures$^{3-12}$ have extensively studied ion cooling or heating through elastic ion-atom collisions$^{4-6,9-11}$. Read More


We theoretically examine neon atoms in ultrashort and intense x rays from free electron lasers and compare our results with data from experiments conducted at the Linac Coherent Light Source (LCLS). For this purpose, we treat in detail the electronic structure in all possible nonrelativistic cationic configurations using a relativistic multiconfiguration approach. The interaction with the x rays is described in rate-equation approximation. Read More


Polaritons are an emerging platform for exploration of synthetic materials [1] and quantum information processing [2] that draw properties from two disparate particles: a photon and an atom. Cavity polaritons are particularly promising, as they are long-lived and their dispersion and mass are controllable through cavity geometry [3]. To date, studies of cavity polaritons have operated in the mean-field regime, using short-range interactions between their matter components [4]. Read More


Nuclear resonant excitation of the 29.19-keV level in $^{229}$Th with high-brilliance synchrotron- radiation and detection of its decay signal, are proposed with the aim of populating the extremely low-energy isomeric state of $^{229}$Th.The proposed experiment, known as nuclear resonant scattering (NRS), has the merit of being free from uncertainties about the isomer level energy. Read More


We explore the non-equilibrium evolution and stationary states of an open many-body system which displays epidemic spreading dynamics in a classical and a quantum regime. Our study is motivated by recent experiments conducted in strongly interacting gases of highly excited Rydberg atoms where the facilitated excitation of Rydberg states competes with radiative decay. These systems approximately implement open quantum versions of models for population dynamics or disease spreading where species can be in a healthy, infected or immune state. Read More


The integrated cross sections of high-energy $e^+e^-$ electroproduction by an electron in an atomic field is studied. Importance of various contributions to these cross sections is discussed. It is shown that the Coulomb corrections are very important both for the differential cross section and for the integrated cross sections even for moderate values of the atomic charge number. Read More


Single atoms form a model system for understanding the limits of single photon detection. Here, we develop a non-Markov theory of single-photon absorption by a two-level atom to place limits on the transduction time. We show the existence of a finite rise time in the probability of excitation of the atom during the absorption event which is infinitely fast in previous Markov theories. Read More


Experimentally the spin dependence of inelastic collisions between ytterbium (Yb) in the metastable 3P0 state and lithium (Li) in the Li ground state manifold is investigated at low magnetic fields. Using selective excitation all magnetic sublevels mJ of 174Yb(3P0) are accessed and four of the six lowest lying magnetic sublevels of 6Li are prepared by optical pumping. On the one hand, mJ-independence of collisions involving Li(F=1/2) atoms is found. Read More


We present absolute frequency measurement of the unperturbed P7 P7 O$_2$ B-band transition with relative standard uncertainty of $2\times10^{-11}$. We reached the level of accuracy typical for Doppler-free techniques, with Doppler-limited spectroscopy. The Doppler-limited shapes of the P7 P7 spectral line were measured with a frequency-stabilized cavity ring-down spectrometer referenced to an $^{88}$Sr optical atomic clock by an optical frequency comb. Read More


In this work we report ab initio calculations for the $H_2^+$ molecule interacting with ultrashort intense laser pulses. We analyse several observables that can, in principle, be available experimentally, in order to get a deeper understanding of the strong field molecular dynamics. In particular, we will focus our attention to the interplay between electronic and nuclear dynamics and how the two motions are correlated. Read More


Strong dipole-dipole interactions between atoms in high-lying Rydberg states can suppress multiple Rydberg excitations within a micron-sized trapping volume and yield sizable Rydberg level shifts at larger distances. Ensembles of atoms in optical microtraps then form Rydberg superatoms with collectively enhanced transition rates to the singly excited state. These superatoms can represent mesoscopic, strongly-interacting spins. Read More


We study the dynamics of vortices generated by an artificial gauge potential in the quasi-2D condensate. For detailed description, we consider a two level system and derive the modified Gross-Pitaevskii (GP) equation. The equilibrium solution of this equation has a vortex Lattice in the ground state when the system is stabilized with a dissipative term. Read More


We propose a method for protecting fragile quantum superpositions in many-particle systems from dephasing by external classical noise. We call superpositions "fragile" if dephasing occurs particularly fast, because the noise couples very differently to the superposed states. The method consists of letting a quantum superposition evolve under the internal thermalization dynamics of the system, followed by a time reversal manipulation known as Loschmidt echo. Read More


A velocity-selective spectroscopy technique for studying the spectra from hot Rydberg gases is presented. This method provides high-resolution measurement of the spectrum interval. Based on this method, the velocity-selective hyperfine splitting of intermediate states is measured, as well as the Doppler-free fine-structure splitting of the Rydberg states via two-photon Rydberg excitation in a room-temperature 133Cs vapor cell. Read More


Trapping cold, chemically important molecules with electromagnetic fields is a useful technique to study small molecules and their interactions. Traps provide long interaction times that are needed to precisely examine these low density molecular samples. However, the trapping fields lead to non-uniform molecular density distributions in these systems. Read More


We describe a novel procedure for the calculation of correction factors for taking into account the effect of target thickness to be applied to the determination of cross sections of X-ray emission induced by heavy ions at MeV energies. We discuss the origin of the correction and describe the calculations, based on simple polynomial fits of both the theoretical cross sections and the ion energy losses. The procedure can be easily implemented. Read More


We explore the feasibility of compact high-precision Hg atomic clock based on the hollow core optical fiber. We evaluate the sensitivity of the $^1S_0$-$^3P_0$ clock transition in Hg and other divalent atoms to the fiber inner core surface at non-zero temperatures. The Casimir-Polder interaction induced $^1S_0$-$^3P_0$ transition frequency shift is calculated for the atom inside the hollow capillary as a function of atomic position, capillary material, and geometric parameters. Read More


A new mechanism of strong laser field induced ionization of an atom is identified which is based on recollisions under the tunneling barrier. Developing an enhanced strong field approximation, the interference of the direct and the under-the-barrier recolliding quantum orbits are shown to induce a measurable shift of the peak of the photoelectron momentum distribution. The scaling of the momentum shift is derived relating the momentum shift to the tunneling delay time according to the Wigner concept. Read More


We analyze possible effects of the dark matter environment on the atomic clock stability measurements. The dark matter is assumed to exist in a form of waves of ultralight scalar fields or in a form of topological defects (monopoles and strings). We identify dark matter signal signatures in clock Allan deviation plots that can be used to constrain the dark matter coupling to the Standard Model fields. Read More


2017May
Affiliations: 1The Racah Institute of Physics, the Hebrew University, Jerusalem 91904, Israel, 2A. F. Ioffe Physical-Technical Institute, St. Petersburg 194021, Russian Federation

We investigate positron scattering upon endohedrals and compare it with electron-endohedral scattering. We show that the polarization of the fullerene shell considerably alters the polarization potential of an atom, stuffed inside a fullerene. This essentially affects both the positron and electron elastic scattering phases as well as corresponding cross-sections. Read More


We investigate electron-correlation effects in the $g$-factor of the ground state of Li-like ions. Our calculations are performed within the nonrelativistic quantum electrodynamics (NRQED) expansion up to two leading orders in the fine-structure constant $\alpha$, $\alpha^2$ and $\alpha^3$. The dependence of the NRQED results on the nuclear charge number $Z$ is studied and the individual $1/Z$-expansion contributions are identified. Read More


The waste majority of physical objects we are dealing with is almost exclusively made of fundamental constituents of matter - atoms. At the same time, atoms have proved to be emitters of light field which is incompatible with classical description of electromagnetic waves. This peculiar property is intrinsic consequence of an atom being a fundamental physical unit uncapable of simultaneous emission of more than one photon. Read More


We describe the design, construction, and characterization of a medium-finesse Fabry-P\'erot cavity for simultaneous frequency stabilization of two lasers operating at 960 and 780 nm wavelengths, respectively. The lasers are applied in experiments with ultracold rubidium Rydberg atoms, for which a combined laser linewidth similar to the natural Rydberg linewidth (approximately 10 kHz) is desired. The cavity, with a finesse of approximately 1500, is used to reduce the linewidth of the lasers to below this level. Read More


Ultracold atomic physics experiments offer a nearly ideal context for the investigation of quantum systems far from equilibrium. We describe three related emerging directions of research into extreme non-equilibrium phenomena in atom traps: quantum emulation of ultrafast atom-light interactions, coherent phasonic spectroscopy in tunable quasicrystals, and realization of Floquet matter in strongly-driven lattice systems. We show that all three should enable quantum emulation in parameter regimes inaccessible in solid-state experiments, facilitating a complementary approach to open problems in non-equilibrium condensed matter. Read More


We theoretically study a scheme to develop an atomic based MW interferometry using the Rydberg states in Rb. Unlike the traditional MW interferometry, this scheme is not based upon the electrical circuits, hence the sensitivity of the phase and the amplitude/strength of the MW field is not limited by the Nyquist thermal noise. Further this system has great advantage due to its very high bandwidth, ranging from radio frequency (RF), micro wave (MW) to terahertz regime. Read More


Long-range interactions and, in particular, two-body potentials with power-law long-distance tails are ubiquitous in nature. For two bosons or fermions in one spatial dimension, the latter case being formally equivalent to three-dimensional $s$-wave scattering, we show how generic asymptotic interaction tails can be accounted for in the long-distance limit of scattering wave functions. This is made possible by introducing a generalisation of the collisional phase shifts to include space dependence. Read More


The reduced density matrix (RDM) is a fundamental contraction of the Bose-Einstein condensate wave function, encapsulating its one-body properties. It serves as a major analysis tool with which the condensed component of the density can be identified. Despite its cardinal importance, calculating the ground-state RDM of trapped interacting bosons is challenging and has been fully achieved only for specific models or when the pairwise interaction is weak. Read More


The advent of novel measurement instrumentation can lead to paradigm shifts in scientific research. Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of units (SI). However, to unlock their potential for cross-disciplinary applications such as relativistic geodesy, a major challenge remains. Read More


In this work we study a system of interacting fermions with large spin and SP(N) symmetry. We contrast their behaviour with the case of SU(N) symmetry by analysing the conserved quantities and the dynamics in each case. We also develop the Fermi liquid theory for fermions with SP(N) symmetry. Read More


We study the impact of Rydberg molecule formation on the storage and retrieval of Rydberg polaritons in an ultracold atomic medium. We observe coherent revivals appearing in the retrieval efficiency of stored photons that originate from simultaneous excitation of Rydberg atoms and Rydberg molecules in the system with subsequent interference between the possible storage paths. We show that over a large range of principal quantum numbers the observed results can be described by a two-state model including only the atomic Rydberg state and the Rydberg dimer molecule state. Read More


It is shown that in the Bohr-Oppenheimer approximation for four lowest electronic states $1s\sigma_g$ and $2p\sigma_u$, $2p \pi_u$ and $3d \pi_g$ of H$_2^+$ and the ground state X$^2\Sigma^+$ of HeH, the potential curves can be well-approximated analytically in full range of internuclear distances $R$ with not less than 4-5-6 figures. Approximation is based on straightforward interpolation of the Taylor-type expansion at small $R$ and a combination of the multipole expansion with one-instanton type expansion at large distances $R$. The position of minimum when exists is predicted within 1$\%$ (or better). Read More


We demonstrate direct laser cooling of a gas of rubidium 87 atoms to quantum degeneracy. The method does not involve evaporative cooling, is fast, and induces little atom loss. The atoms are trapped in a two-dimensional optical lattice that enables cycles of cloud compression to increase the density, followed by degenerate Raman sideband cooling to decrease the temperature. Read More


Wave functions of a new functional kind have been proposed for Helium-like atoms in this work . These functions explicitly depend on interelectronic and hyperspherical coordinates. The best ground state energy for the Helium atom $ -2. Read More


We report on the local control of the transition frequency of a spin-$1/2$ encoded in two Rydberg levels of an individual atom by applying a state-selective light shift using an addressing beam. With this tool, we first study the spectrum of an elementary system of two spins, tuning it from a non-resonant to a resonant regime, where "bright" (superradiant) and "dark" (subradiant) states emerge. We observe the collective enhancement of the microwave coupling to the bright state. Read More


Mercury monohalides are promising candidates for electron electric dipole moment searches. This is due to their extremely large values of effective electric fields, besides other attractive experimental features. We have elucidated the theoretical reasons of our previous work. Read More


The Discrete Truncated Wigner Approximation (DTWA) is a semi-classical phase space method useful for the exploration of Many-body quantum dynamics. In this work, we show that the method is suitable for studying Many-Body Localization (MBL). By taking as a benchmark case a 1D random field Heisenberg spin chain with short range interactions, and by comparing to numerically exact techniques, we show that DTWA is able to reproduce dynamical signatures of the MBL phase such as logarithmic growth of entanglement, even though a pure classical mean-field analysis would lead to no dynamics at all. Read More


We present experimental results demonstrating controllable dispersion in a ring laser by monitoring the lasing-frequency response to cavity-length variations. Pumping on an N-type level configuration in ${}^{87}$Rb, we tailor the intra-cavity dispersion slope by varying experimental parameters such as pump-laser frequency, atomic density, and pump power. As a result, we can tune the pulling factor (PF), i. Read More


We study a squeezed vacuum field generated in hot Rb vapor via the polarization self-rotation effect. Our previous experiments showed that the amount of observed squeezing may be limited by the contamination of the squeezed vacuum output with higher-order spatial modes, also generated inside the cell. Here, we demonstrate that the squeezing can be improved by making the light interact several times with a less dense atomic ensemble. Read More


State-to-state chemistry investigates chemical reactions on the most fundamental level. A primary goal of state-to-state chemistry is to determine the quantum states of the final products given the quantum state of reactants. Using the high level control for preparing reactants in the ultracold domain, we demonstrate here a method for investigating state-to-state chemistry with unprecedented resolution. Read More


We propose an intuitive method, called time-dependent population imaging (TDPI), to map the dynamical processes of high harmonic generation (HHG) in solids by solving the time-dependent Schr\"{o}dinger equation (TDSE). It is shown that the real-time dynamical characteristics of HHG in solids, such as the instantaneous photon energies of emitted harmonics, can be read directly from the energy-resolved population oscillations of electrons in the TDPIs. Meanwhile, the short and long trajectories of solid HHG are illustrated clearly from TDPI. Read More


We investigate roles of electron correlation effects in the determination of the $g_j$ factors of the $4s ~ ^2S_{1/2}$, $4p ~ ^2P_{1/2}$, $4p ~ ^2P_{3/2}$, $3d ~ ^2D_{3/2}$, and $3d ~ ^2D_{5/2}$ states, representing to different parities and angular momenta, of the Ca$^+$ ion. Correlation contributions are highlighted with respect to the mean-field values evaluated using the Dirac-Hartree-Fock method, relativistic second order many-body theory, and relativistic coupled-cluster (RCC) theory with the singles and doubles approximation considering only the linear terms and also accounting for all the non-linear terms. This shows that it is difficult to achieve reasonably accurate results employing an approximated perturbative approach. Read More


Experimental realizations of charged ions and neutral atoms in overlapping traps are gaining increasing interest due to their wide research application ranging from chemistry at the quantum level to quantum simulations of solid-state systems. Here, we describe a system in which we overlap a single ground-state cooled ion trapped in a linear Paul trap with a cloud of ultracold atoms such that both constituents are in the $\mu$K regime. Excess micromotion (EMM) currently limits atom-ion interaction energy to the mK energy scale and above. Read More