arXiv subjects

H. R. Sadeghpour

Publications and source records attributed to H. R. Sadeghpour.

At least 37 records · Page 2Linked to original sources

arXiv2024

Tunneling dynamics of $^{164}$Dy supersolids and droplets

The tunneling dynamics of a magnetic $^{164}$Dy quantum gas in an elongated or pancake skewed double-well trap is investigated with a time-dependent extended Gross-Pitaevskii approach. Upon lifting the energy offset, different tunneling regimes can be identified. In the elongated trap and for sufficiently large offset, the different configurations exhibit collective macroscopic tunneling. For smaller offset, partial reflection from and transmission through the barrier lead to density accumulation in both wells, and eventually to tunneling-locking. One can also reach the macroscopic self-trapping regime for increasing relative dipolar interaction strength, while tunneling vanishes for large barrier heights. A richer dynamical behavior is observed for the pancake-like trap. For instance, the supersolid maintains its shape, while the superfluid density gets distorted signifying the emergence of peculiar excitation patterns in the macroscopic tunneling regime. The findings reported here may offer new ways to probe distinctive dynamical features in the supersolid and droplet regimes.

cond-mat.quant-gas↗

arXiv2024

Multiphoton dressed Rydberg excitations in a microwave cavity with ultracold Rb atoms

We investigate magneto-optical trap loss spectroscopy of Rydberg excited $^{85}$Rb ($66\leq n \leq 68~S_{1/2}$) atoms, placed inside a tailored microwave cavity. The cavity frequency at 13.053 GHz is in resonance with the $67S_{1/2} \rightarrow 66P_{3/2}$ transition, inducing a ladder multiphoton microwave Rydberg absorption and emission. The observed spectra are modeled with an extended Jaynes-Cumming formalism that accounts for multiphoton absorption from and emission into the cavity, the loss from the trap due to Rydberg excitation, and cavity imperfection. We calculate the average photons in each spectral feature and find evidence for fractional photon emission into the cavity modes. The microwave cavity Rydberg spectroscopy in this work should inform the application and technology development of Rydberg based sensors and hybrid Rydberg atom-superconducting resonator quantum gates.

physics.atom-ph↗

arXiv2024

Microwave transitions in atomic sodium: Radiometry and polarimetry using the sodium layer

We calculate, via variational techniques, single- and two-photon Rydberg microwave transitions, as well as scalar and tensor polarizabilities of sodium atom using the parametric one-electron valence potential, including the spin-orbit coupling. The trial function is expanded in a basis set of optimized Slater-type orbitals, resulting in highly accurate and converged eigen-energies up to $n=60$. We focus our studies on the microwave band 90-150 GHz, due to its relevance to laser excitation in the Earth's upper-atmospheric sodium layer for wavelength-dependent radiometry and polarimetry, as precise microwave polarimetry in this band is an important source of systematic uncertainty in searches for signatures of primordial gravitational waves within the anisotropic polarization pattern of photons from the cosmic microwave background. We present the most efficient transition coefficients in this range, as well as the scalar and tensor polarizabilities compared with available experimental and theoretical data.

physics.atom-ph↗

arXiv2024

Ultralong-range Cs-RbCs Rydberg molecules: non-adiabaticity of dipole moments

We consider ultralong-range polyatomic Rydberg molecules formed by combining a Rydberg cesium atom and a ground-state RbCs molecule. We explore the regime where the charge-dipole interaction due to the Rydberg electron with the diatomic polar molecule couples the quantum defect Rydberg states Cs(ns) to the nearest degenerate hydrogenic manifold. We consider polyatomic Rydberg molecules in states which are amenable to production in optical tweezers and study the influence of nonadiabatic coupling on the likelihood of their formation. The decay rates of the vibrational states reflect the interference signature of wave function spread in different coupled potential wells.

physics.atom-ph↗

arXiv2023

Polaritonic ultracold reactions: cavity controlled molecular photoassociation

We introduce a prototypical model for cavity polaritonic control of ultracold photochemistry by considering the resonant vibrational strong coupling of a rubidium dimer to a terahertz cavity. We demonstrate that at avoided crossings between a vibrational excitation and the vacuum photon absorption, the resulting polaritonic states between the molecule and photons can efficiently control the molecular vibrational Franck-Condon (FC) factors. Due to the entanglement between light and matter, FC factor is transferred from one polaritonic branch to other, leading to a polariton with a substantially enhanced FC factor. Utilizing this polariton state for photoassociation results in the enhanced formation of ultracold molecules. This work suggests a path to controlling photoassociation with cavity vacuum fields, and lays the ground for the emerging subfield of polaritonic ultracold chemistry.

cond-mat.quant-gas↗

arXiv2023

Engineering chiral spin interactions with Rydberg atoms

We propose to simulate the anisotropic and chiral Dzyaloshinskii-Moriya (DM) interaction with Rydberg atom arrays. The DM Hamiltonian is engineered in a one-dimensional optical lattice or trap array with effective long-range Rydberg spins, interacting indirectly via a mobile mediator Rydberg atom. A host of XXZ and DM Hamiltonians can be simulated with out-of-phase sign periodic coupling strengths; for initial states in a stationary condensate, the DM interaction vanishes. This theory allows for determination of the DM interaction (DMI) vector components from first principles. The inherent anisotropy of the Rydberg-Rydberg interactions, facilitates the DMI coupling to be tuned so as to be comparable to the XXZ interaction. Our results make plausible the formation of non-trivial topological spin textures with Rydberg atom arrays.

physics.atom-ph↗

arXiv2023

Many-body quantum chaos in stroboscopically-driven cold atoms

In quantum chaotic systems, the spectral form factor (SFF), defined as the Fourier transform of the two-level spectral correlation function, is known to follow random matrix theory (RMT), namely a 'ramp' followed by a 'plateau' in sufficiently late times. Recently, a generic early-time deviation from the RMT behavior, which we call the 'bump', was shown to exist in random quantum circuits and spin chains as toy models for many-body quantum chaotic systems. Here we demonstrate the existence of the 'bump-ramp-plateau' behavior in the SFF for a number of paradigmatic and stroboscopically-driven 1D cold atom models: (i) Bose-Hubbard model, (ii) spin$-1/2$ Bose-Hubbard model, and (iii) nonintegrable spin-$1$ condensate with contact or dipolar interactions. We find that the scaling of the many-body Thouless time $t_{\textrm{Th}}$ -- the onset of RMT -- , and the bump amplitude are more sensitive to variations in atom number than the lattice size regardless of the hyperfine structure, the symmetry classes, or the choice of driving protocol. Moreover, $t_{\textrm{Th}}$ scaling and the increase of the bump amplitude in atom number are significantly slower in spinor gases than interacting bosons in 1D optical lattices, demonstrating the role of locality. We obtain universal scaling functions of SFF which suggest power-law behavior for the bump regime in quantum chaotic cold-atom systems, and propose an interference measurement protocol.

cond-mat.quant-gas↗

arXiv2023

Sympathetic cooling and slowing of molecules with Rydberg atoms

We propose to sympathetically slow and cool polar molecules in a cold, low-density beam using laser-cooled Rydberg atoms. The elastic collision cross sections between molecules and Rydberg atoms are large enough to efficiently thermalize the molecules even in a low density environment. Molecules traveling at 100 m/s can be stopped in under 30 collisions with little inelastic loss. Our method does not require photon scattering from the molecules and can be generically applied to complex species for applications in precision measurement, quantum information science, and controlled chemistry.

physics.atom-ph↗

arXiv2023

Observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule

We demonstrate Rydberg blockade due to the charge-dipole interaction between a single Rb atom and a single RbCs molecule confined in optical tweezers. The molecule is formed by magnetoassociation of a Rb+Cs atom pair and subsequently transferred to the rovibrational ground state with an efficiency of 91(1)\%. Species-specific tweezers are used to control the separation between the atom and molecule. The charge-dipole interaction causes blockade of the transition to the Rb(52s) Rydberg state, when the atom-molecule separation is set to $310(40)$~nm. The observed excitation dynamics are in good agreement with simulations using calculated interaction potentials. Our results open up the prospect of a hybrid platform where quantum information is transferred between individually trapped molecules using Rydberg atoms.

physics.atom-ph↗

arXiv2022

Cavity Induced Collective Behavior in the Polaritonic Ground State

Cavity quantum electrodynamics provides an ideal platform to engineer and control light-matter interactions with polariton quasiparticles. In this work, we investigate collective phenomena in a system of many particles in a harmonic trap coupled to a homogeneous quantum cavity field. The system couples collectively to the cavity field, through its center of mass, and collective polariton states emerge. The cavity field mediates pairwise long-range interactions and enhances the effective mass of the particles. This leads to an enhancement of localization in the matter ground state density, which features a maximum when light and matter are on resonance, and demonstrates a Dicke-like, collective behavior with the particle number. The light-matter interaction also modifies the photonic properties of the polariton system, as the ground state is populated with bunched photons. In addition, it is shown that the diamagnetic $\mathbf{A}^2$ term is necessary for the stability of the system, as otherwise the superradiant ground state instability occurs. We demonstrate that coherent transfer of polaritonic population is possbile with an external magnetic field and by monitoring the Landau-Zener transition probability.

quant-ph↗

arXiv2022

Control of $^{164}$Dy Bose-Einstein condensate phases and dynamics with dipolar anisotropy

We investigate the quench dynamics of quasi-one and two dimensional dipolar Bose-Einstein condensates (dBEC) of $^{164}$Dy atoms under the influence of a fast rotating magnetic field. The magnetic field thus controls both the magnitude and sign of the dipolar potential. We account for quantum fluctuations, critical to formation of exotic quantum droplet and supersolid phases in the extended Gross-Pitaevskii formalism, which includes the so-called Lee-Huang-Yang (LHY) correction. An analytical variational ansatz allows us to obtain the phase diagrams of the superfluid and droplet phases. The crossover from the superfluid to the supersolid phase and to single and droplet arrays is probed with particle number and dipolar interaction. The dipolar strength is tuned by rotating the magnetic field with subsequent effects on phase boundaries. Following interaction quenches across the aforementioned phases, we monitor the dynamical formation of supersolid clusters or droplet lattices. We include losses due to three-body recombination over the crossover regime, where the three-body recombination rate coefficient scales with the fourth power of the scattering length ($a_s$) or the dipole length ($a_{dd}$). For fixed values of the dimensionless parameter, $ε_{dd} = a_{dd}/a_s$, tuning the dipolar anisotropy leads to an enhancement of the droplet lifetimes.

cond-mat.quant-gas↗

arXiv2022

Inducing spin-order with an impurity: phase diagram of the magnetic Bose polaron

We investigate the formation of magnetic Bose polaron, an impurity atom dressed by spin-wave excitations, in a one-dimensional spinor Bose gas. In terms of an effective potential model the impurity is strongly confined by the host excitations which can even overcome the impurity-medium repulsion leading to a self-localized quasi-particle state. The phase diagram of the attractive and self-bound repulsive magnetic polaron, repulsive non-magnetic (Fr{\" o}hlich-type) polaron and impurity-medium phase-separation regimes is explored with respect to the Rabi-coupling between the spin components, spin-spin interactions and impurity-medium coupling. The residue of such magnetic polarons decreases substantially in both strong attractive and repulsive branches with strong impurity-spin interactions, illustrating significant dressing of the impurity. The impurity can be used to probe and maneuver the spin polarization of the magnetic medium while suppressing ferromagnetic spin-spin correlations. It is shown that mean-field theory fails as the spinor gas approaches immiscibility since the generated spin-wave excitations are prominent. Our findings illustrate that impurities can be utilized to generate controllable spin-spin correlations and magnetic polaron states which can be realized with current cold atom setups.

cond-mat.quant-gas↗

arXiv2022

A Precise Photometric Ratio via Laser Excitation of the Sodium Layer I: One-photon Excitation Using 342.78 nm Light

The largest uncertainty on measurements of dark energy using type Ia supernovae is presently due to systematics from photometry; specifically to the relative uncertainty on photometry as a function of wavelength in the optical spectrum. We show that a precise constraint on relative photometry between the visible and near-infrared can be achieved in upcoming surveys (such as in LSST at the Vera C. Rubin Observatory) via a mountaintop-located laser source tuned to the 342.78 nm vacuum excitation wavelength of neutral sodium atoms. Using a high-power (500 W) laser modified from laser guide star studies, this excitation will produce an artificial star (which we term a "laser photometric ratio star," or LPRS) of de-excitation light in the mesosphere that is observable from the ground at approximately 20 magnitude (i.e., well within the expected single-image magnitude limit of LSST) at wavelengths in vacuum of 589.16 nm, 589.76 nm, 818.55 nm, and 819.70 nm, with the sum of the numbers of 589.16 nm and 589.76 nm photons produced by this process equal to the sum of the numbers of 818.55 nm and 819.70 nm photons, establishing a precise calibration ratio between, for example, the LSST r and z filters. This technique can thus provide a novel mechanism for establishing a spectrophotometric calibration ratio of unprecedented precision, from above most of the Earth's atmosphere, for upcoming telescopic observations across astronomy and atmospheric physics. This article is the first in a pair of articles on this topic. The second article of the pair describes an alternative technique to achieve a similar, but brighter, LPRS than the technique described in this paper, by using two mountaintop-located lasers, at optical frequencies approximately 4 GHz away from resonances at wavelengths in vacuum of 589.16 nm and 819.71 nm respectively.

astro-ph.IM↗

arXiv2022

From atomic physics, to upper-atmospheric chemistry, to cosmology: A "laser photometric ratio star" to calibrate telescopes at major observatories

The expansion of our Universe is accelerating, due to dark energy. But the nature of dark energy has been a mystery since its discovery at the end of the past century. In Research Highlight https://doi.org/10.1002/ntls.20220003 , Justin Albert, Dmitry Budker and Hossein Sadeghpour provide an overview of how a laser photometric ratio star (a novel light source generated by laser excitation of the Earth's upper-atmospheric sodium layer, which will radiate equally brightly at wavelengths of 589 nm and 820 nm) can help us precisely calibrate telescopes in order to understand the nature of dark energy.

astro-ph.IM↗

arXiv2022

Kinetics and Nucleation Dynamics in Ion-Seeded Atomic Clusters

The time-dependent kinetics of formation and evolution of nano-size atomic clusters is investigated and illustrated with the nucleation dynamics of ion-seed Ar$_n$H$^+$ particles. The rates of growth and degradation of Ar-atomic shells around the seed ion are inferred from Molecular Dynamics (MD) simulations. Simulations of cluster formation have been performed with accurate quantum-mechanical binary interaction potentials. Both the nonequilibrium and equilibrium growth of Ar$_n$H$^+$ are investigated at different temperature and densities of the atomic gas and seed ions. Formation of Ar$_{n\leq 40}$ shells is the main mechanism which regulates the kinetics of nano-cluster growth and the diffusive fluctuations of the cluster size distribution. The time-evolution of the cluster intrinsic energy and cluster size distributions are analyzed at the non-thermal, quasi-equilibrium, and thermal equilibrium stages of Ar$_n$H$^+$ formation. We've determined the self-consistent model parameters for the temporal fluctuations of the cluster size and found coefficients of the diffusive growth mechanism describing the equilibrium distribution of nano-clusters. Nucleation of haze and nano-dust particles in astrophysical and atmospheric ionized gases are discussed.

physics.atm-clus↗

arXiv2021

Formation and quench of homonuclear and heteronuclear quantum droplets in one dimension

We exemplify the impact of beyond Lee-Huang-Yang (LHY) physics, especially due to intercomponent correlations, in the ground state and the quench dynamics of one-dimensional so-called quantum droplets using an ab-initio nonperturbative approach. It is found that the droplet Gaussian-shaped configuration arising for intercomponent attractive couplings becomes narrower for stronger intracomponent repulsion and transits towards a flat-top structure either for larger particle numbers or weaker intercomponent attraction. Additionally, a harmonic trap prevents the flat-top formation. At the balance point where mean-field interactions cancel out, we show that a correlation hole is present in the few particle limit of these fluids as well as for flat-top droplets. Introducing mass-imbalance, droplets experience intercomponent mixing and excitation signatures are identified for larger masses. Monitoring the droplet expansion (breathing motion) upon considering interaction quenches to stronger (weaker) attractions we explicate that beyond LHY correlations result in a reduced velocity (breathing frequency). Strikingly, the droplets feature two-body anti-correlations (correlations) at the same position (longer distances). Our findings pave the way for probing correlation-induced phenomena of droplet dynamics in current ultracold atom experiments.

cond-mat.quant-gas↗

arXiv2021

A Precise Photometric Ratio via Laser Excitation of the Sodium Layer II: Two-photon Excitation Using Lasers Detuned from 589.16 nm and 819.71 nm Resonances

This article is the second in a pair of articles on the topic of the generation of a two-color artificial star (which we term a "laser photometric ratio star," or LPRS) of de-excitation light from neutral sodium atoms in the mesosphere, for use in precision telescopic measurements in astronomy and atmospheric physics, and more specifically for the calibration of measurements of dark energy using type Ia supernovae. The two techniques respectively described in both this and the previous article would each generate an LPRS with a precisely 1:1 ratio of yellow (589/590 nm) photons to near-infrared (819/820 nm) photons produced in the mesosphere. Both techniques would provide novel mechanisms for establishing a spectrophotometric calibration ratio of unprecedented precision, from above most of Earth's atmosphere, for upcoming telescopic observations across astronomy and atmospheric physics. The technique described in this article has the advantage of producing a much brighter (specifically, brighter by approximately a factor of 1000) LPRS, using lower-power (<30 W average power) lasers, than the technique using a single 500 W average power laser described in the first article of this pair. However, the technique described here would require polarization filters to be installed into the telescope camera in order to sufficiently remove laser atmospheric Rayleigh backscatter from telescope images, whereas the technique described in the first article would only require more typical wavelength filters in order to sufficiently remove laser Rayleigh backscatter.

astro-ph.IM↗

arXiv2021

Radiofrequency spectroscopy of one-dimensional trapped Bose polarons: crossover from the adiabatic to the diabatic regime

We investigate the crossover of the impurity-induced dynamics, in trapped one-dimensional Bose polarons subject to radio frequency (rf) pulses of varying intensity, from an adiabatic to a diabatic regime. Utilizing adiabatic pulses for either weak repulsive or attractive impurity-medium interactions, a multitude of polaronic excitations or mode-couplings of the impurity-bath interaction with the collective breathing motion of the bosonic medium are spectrally resolved. We find that for strongly repulsive impurity-bath interactions, a temporal orthogonality catastrophe manifests in resonances in the excitation spectra where impurity coherence vanishes. When two impurities are introduced, impurity-impurity correlations, for either attractive or strong repulsive couplings, induce a spectral shift of the resonances with respect to the single impurity. For a heavy impurity, the polaronic peak is accompanied by a series of equidistant side-band resonances, related to interference of the impurity spin dynamics and the sound waves of the bath. In all cases, we enter the diabatic transfer regime for an increasing bare Rabi frequency of the rf field with a Lorentzian spectral shape featuring a single polaronic resonance. The findings in this work on the effects of external trap, rf pulse and impurity-impurity interaction should have implications for the new generations of cold-atom experiments.

cond-mat.quant-gas↗