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arXiv2014

Phase sensitive quantum interference on forbidden transition in ladder scheme

A three level ladder system is analyzed and the coherence of initially electric-dipole forbidden transition is calculated. Due to the presence of two laser fields the initially dipole forbidden transition becomes dynamically permitted due to ac Stark effect. It is shown that such transitions exhibit quantum-interference-related phenomena, such as electromagnetically induced transparency, gain without inversion and enhanced refractive index. Gain and dispersion characteristics of such transitions strongly depend upon the relative phase between the driving and the probe fields. Unlike allowed transitions, gain/absorption behavior of ac-Stark allowed transitions exhibit antisymmetric feature on the Rabi sidebands. It is found that absorption/gain spectra possess extremely narrow sub-natural resonances on these ac Stark allowed forbidden transitions. An interesting finding is simultaneous existence of gain and negative dispersion at Autler-Townes transition which may lead to both reduction of the group velocity and amplification of light.

physics.optics↗

arXiv2014

Coulomb corrections to electron scattering on the extended source and the proton charge radius

It is shown that the account for the proton charge form factor in the Coulomb corrections to the electron-proton scattering cross section noticeably diminishes the difference between the value of the proton charge radius $r_{\mathrm{E}}$, extracted from the $ep$ scattering data, and that following from the muonic hydrogen data. For the electron energy much higher than the electron mass but much smaller than $r_{\mathrm{E}}^{-1}\approx 230$~MeV, the relative correction has the universal form $δr_{\mathrm{E}}/r_{\mathrm{E}}=-πα/2$, where $α$ is the fine structure constant.

hep-ph↗

arXiv2014

Effect of pairwise Dipole - Dipole interaction among three atoms Systems

We present analysis of a system of three two-level atoms interacting with each other through the dipole-dipole interaction. The interaction manifests between excited state of one of the atoms and the ground state of its nearest neighbour. Steady state populations of the density matrix elements are presented and are compared with a situation when only two atoms are present. It can be noticed that the third atom modifies the behaviour of the three atoms. Two configurations are analysed, one in which the three atoms are in a line, with no interaction between atoms at the end points and the other in which the atoms form a closed loop with each atom interacting with both its neighbours.

physics.atom-ph↗

arXiv2014

Photoelectron angular distributions from aligned molecules using the R-matrix method

We present a new extension of the UKRmol electron-molecule scattering code suite, which allows one to compute ab initio photoionization and photorecombination amplitudes for complex molecules, resolved both on the molecular alignment (orientation) and the emission angle and energy of the photoelectron. We illustrate our approach using CO$_2$ as an example, and analyze the importance of multi-channel effects by performing our calculations at different, increasing levels of complexity. We benchmark our method by comparing the results of our calculations with experimental data and with theoretical calculations available in the literature.

physics.chem-ph↗

arXiv2014

Measurement of the scalar third-order electric polarizability of the Cs ground state using CPT-spectroscopy in Ramsey geometry

The AC Stark shift induced by blackbody radiation is a major source of systematic uncertainty in present-day cesium microwave frequency standards. The shift is parametrized in terms of a third-order electric polarizability $α_0^{(3)}$ that can be inferred from the static electric field displacement of the clock transition resonance. In this paper, we report on an all-optical CPT pump-probe experiment measuring the differential polarizability $Δα_0^{(3)} = α_0^{(3)}(F{=}4) - α_0^{(3)}(F{=}3)$ on a thermal Cs atomic beam, from which we infer $ α_0^{(3)}(F{=}4) = 2.023(6)_{stat}(9)_{syst}~Hz/(kV/cm)^2$, which corresponds to a scalar Stark shift parameter $ k_{s} = -2.312(7)_{stat}(10)_{syst}~Hz/(kV/cm)^2$. The result agrees within two standard deviations with a recent measurement in an atomic fountain, and rules out another recent result obtained in a Cs vapor cell.

physics.atom-ph↗

arXiv2014

Power broadening effects on Electromagnetically Induced Transparency in $^{20}$Ne vapor

We report here the first observation of electromagnetically induced transparency (EIT) in $^{20}$Ne. The power broadening of the EIT linewidth is measured as a function of neon pressure and RF excitation power. Doppler effects on the EIT broadening are found even at low pressures and low intensities, where the linewidth should be governed only by homogeneous effects.

physics.optics↗

arXiv2014

Momentum Distribution of Near-Zero-Energy Photoelectrons in the Strong-Field Tunneling Ionization in the Long Wavelength Limit

We investigate the ionization dynamics of Argon atoms irradiated by an ultrashort intense laser of a wavelength up to 3100 nm, addressing the momentum distribution of the photoelectrons with near-zero-energy. We find a surprising accumulation in the momentum distribution corresponding to meV energy and a \textquotedblleft V"-like structure at the slightly larger transverse momenta. Semiclassical simulations indicate the crucial role of the Coulomb attraction between the escaping electron and the remaining ion at extremely large distance. Tracing back classical trajectories, we find the tunneling electrons born in a certain window of the field phase and transverse velocity are responsible for the striking accumulation. Our theoretical results are consistent with recent meV-resolved high-precision measurements.

physics.atom-ph↗

arXiv2014

Intersection of low-energy electron-atom scattering and photodetachment of negative ions

We propose to use the near-threshold electron scattering data for atoms to guide the reliable experimental determination of their electron affinities (EAs), extracted using the Wigner Threshold Law, from laser photodetachment threshold spectroscopy measurements. Data from the near-threshold electron elastic scattering from W, Te, Rh, Sb and Sn atoms calculated using our complex angular momentum method, wherein is embedded the electron-electron correlations and core polarization interaction, are used as illustrations. We conclude with a remark on the relativistic effects on the EA calculation for the heavy At atom.

physics.atom-ph↗

arXiv2014

Spin 1/2 systems perturbed by fluctuating, arbitrary fields; relaxation and frequency shifts, a new approach to Redfield theory

The usual approach to considerations of apin relaxation and frequency shifts due to fluctuating fields is through the density matrix Slichter. Here we treat the problem of the influence of fluctuating fields on a spin 1/2 system based on direct solution of the Schroedinger equation in contrast to the usual treatment. Our results are seen to be in agreement with the known results in the literature McGregor, Slichter, Red2, CSH, as they must, but our derivation directly from the Schroedinger equation allows us to see the role of the necessary assumptions in a somewhat clearer way.

physics.atom-ph↗

arXiv2014

Nonlinear Doppler - Free comb-spectroscopy in counter-propagating fields

The method of Doppler - free comb - spectroscopy for dipole transitions was proposed. The calculations for susceptibility spectrum for moving two-level atoms driving by strong counter propagating combs have been done. The used theoretical method based on the Fourier expansion of the components of density matrix on two rows on kv (v-velocity of group of atoms, k-projection of wave vector) and Ω (frequency between comb components). For testing of validity of this method the direct numerical integration was done. The narrow peaks with homogeneous width arise on the background of Doppler counter. The contrast of these peaks is large for largest amplitudes of comb-components. Power broadening is increasing with increase of field amplitudes. The spectral range of absorption spectrum is determined by the spectral range of comb generator and all homogeneous lines arise simultaneously. The spectral resolution is determined by the width of homogeneously-broadening lines. The physical nature of narrow peaks is in the existence of multi-photon transitions between manifolds of quasi-energy levels arising for different groups of atoms moving with velocities that satisfy to the resonant conditions 2kv= (n+l)Ω, where n, l - are integers and Ω - frequency difference between comb teeth.

physics.optics↗

arXiv2014

Benchmarking strong-field ionisation with atomic hydrogen

As the simplest atomic system, the hydrogen atom plays a key benchmarking role in laser and quantum physics. Atomic hydrogen is a widely used atomic test system for theoretical calculations of strong-field ionization, since approximate theories can be directly compared to numerical solutions of the time-dependent Schrödinger equation. However, relatively little experimental data is available for comparison to these calculations, since atomic hydrogen sources are difficult to construct and use. We review the existing experimental results on strong-field ionization of atomic hydrogen in multi-cycle and few-cycle laser pulses. Quantitative agreement has been achieved between experiment and theoretical predictions at the 10% uncertainty level, and has been used to develop an intensity calibration method with 1% uncertainty. Such quantitative agreement can be used to certify experimental techniques as being free from systematic errors, guaranteeing the accuracy of data obtained on species other than H. We review the experimental and theoretical techniques that enable these results.

physics.atom-ph↗

arXiv2014

The electric dipole moment of an electron in H-like ions in an electrostatic storage ring

Theoretical studies are presented how the electric dipole moment (EDM) of the electron in H-like ions in electrostatic storage rings can sensitively be determined. With the proposed experiments a new constraint of about $10^{-29}$ e cm for the electron EDM can be established what is by an order of magnitude more restrictive than the existing bounds. Experiments with H-like ions may provide a possibility to distinguish between the electron EDM effect and the effect of P,T violating interaction between the atomic electron and the nucleus.

physics.atom-ph↗

arXiv2017

Dynamical control of atoms with polarized bichromatic weak field

We propose ultranarrow dynamical control of population oscillation (PO) between ground states through the polarization content of an input bichromatic field. Appropriate engineering of classical interference between optical fields results in PO arising exclusively from optical pumping. Contrary to the expected broad spectral response associated with optical pumping, we obtain subnatural linewidth in complete absence of quantum interference. The ellipticity of the light polarizations can be used for temporal shaping of the PO leading to generation of multiple sidebands even at low light level.

physics.atom-ph↗

arXiv2017

Progress on the ARIADNE axion experiment

The Axion Resonant InterAction Detection Experiment (ARIADNE) is a collaborative effort to search for the QCD axion using techniques based on nuclear magnetic resonance. In the experiment, axions or axion-like particles would mediate short-range spin-dependent interactions between a laser-polarized 3He gas and a rotating (unpolarized) tungsten source mass, acting as a tiny, fictitious "magnetic field". The experiment has the potential to probe deep within the theoretically interesting regime for the QCD axion in the mass range of 0.1-10 meV, independently of cosmological assumptions. The experiment relies on a stable rotary mechanism and superconducting magnetic shielding, required to screen the 3He sample from ordinary magnetic noise. Progress on testing the stability of the rotary mechanism is reported, and the design for the superconducting shielding is discussed.

astro-ph.IM↗

arXiv2017

Interference-induced phenomena in high-order harmonic generation from bulk solids

We consider a quantum mechanical model for the high-order harmonic generation in bulk solids. The bandgap is assumed to be considerably larger than the exciting photon energy. Using dipole approximation, the dynamical equations for different initial Bloch states are decoupled in the velocity gauge. Although there is no quantum mechanical interference between the time evolution of different initial states, the complete harmonic radiation results from the interference of fields emitted by all the initial (valence band) states. In particular, this interference is shown to be responsible for the suppression of the even order harmonics. The number of the observable harmonics (essentially the cutoff) is also determined by electromagnetic field interference.

quant-ph↗

arXiv2017

Demonstration of a passive photon-atom swap gate

Deterministic quantum interactions between single photons and single quantum emitters are a vital building block towards the distribution of quantum information between remote systems. Deterministic photon-atom state transfer has been demonstrated by using protocols that include active feedback or synchronized control pulses. Here we demonstrate a completely passive swap gate between the states of a single photon and a single atom. The underlying mechanism is single-photon Raman interaction (SPRINT) - an interference-based effect in which a photonic qubit deterministically controls the state of a material qubit encoded in the two ground states of a Λ system, and vice versa. Using a nanofiber-coupled microsphere resonator coupled to single Rb atoms we swap a photonic qubit into the atom and back, demonstrating nonclassical fidelities in both directions. Requiring no control fields or feedback protocol, the gate takes place automatically at the timescale of the atom's cavity- enhanced spontaneous emission time. Applicable to any waveguide-coupled Λ system, this scheme provides a versatile building block for the modular scaling up of quantum information processing systems.

quant-ph↗

arXiv2018

Effective Collision Strengths for Allowed Transitions Among the $n \le$ 5 Degenerate Levels of Atomic Hydrogen

We report calculations of collision strengths and effective collision strengths for 26 allowed transitions among the $n \le$ 5 degenerate levels of atomic hydrogen for which the close-coupling (CC) and Born approximations have been used. Results are listed over a wide range of energies (up to 50~Ryd) and temperatures (up to 10$^7$~K), sufficient for applications over a variety of plasmas, including fusion. Similar results have also been calculated for deuterium, but they negligibly differ with those of hydrogen.

physics.atom-ph↗

arXiv2021

An optical tweezer array of ground-state polar molecules

Fully internal and motional state controlled and individually manipulable polar molecules are desirable for many quantum science applications leveraging the rich state space and intrinsic interactions of molecules. While prior efforts at assembling molecules from their constituent atoms individually trapped in optical tweezers achieved such a goal for exactly one molecule, here we extend the technique to an array of five molecules, unlocking the ability to study molecular interactions. We detail the technical challenges and solutions inherent in scaling this system up. With parallel preparation and control of multiple molecules in hand, this platform now serves as a starting point to harness the vast resources and long-range dipolar interactions of molecules.

physics.atom-ph↗