arXiv subjects

Chris H. Greene

Publications and source records attributed to Chris H. Greene.

At least 91 records · Page 5Linked to original sources

arXiv2015

Probing a scattering resonance in Rydberg molecules with a Bose-Einstein condensate

We present spectroscopy of a single Rydberg atom excited within a Bose-Einstein condensate. We not only observe the density shift as discovered by Amaldi and Segre in 1934, but a line shape which changes with the principal quantum number n. The line broadening depends precisely on the interaction potential energy curves of the Rydberg electron with the neutral atom perturbers. In particular, we show the relevance of the triplet p-wave shape resonance in the Rydberg electron-Rb(5S) scattering, which significantly modifies the interaction potential. With a peak density of 5.5x10^14 cm^-3, and therefore an inter-particle spacing of 1300 a0 within a Bose-Einstein condensate, the potential energy curves can be probed at these Rydberg ion - neutral atom separations. We present a simple microscopic model for the spectroscopic line shape by treating the atoms overlapped with the Rydberg orbit as zero-velocity, uncorrelated, point-like particles, with binding energies associated with their ion-neutral separation, and good agreement is found.

physics.atom-ph↗

arXiv2015

On the Appearance of Families of Efimov States in the Spinor Three-Body Problem

Few-body systems with access to multiple internal levels exhibit richness beyond that typically found in their single-level counterparts. One example is that of Efimov states in strongly-correlated spinor three-body systems. In [V. E. Colussi, C. H. Greene, and J. P. D'Incao, Phys. Rev. Lett. {\bf 113}, 045302 (2014)] this problem was analyzed for spinor condensates finding a complex level structure as in an early work [Bulgac and Efimov, Sov. J. Nucl. Phys. 22, 153 (1976)] in nuclear physics, and the impact of Efimov physics on the general form of the scattering observables was worked out. In this paper we discuss the appearance of novel families of Efimov states in the spinor three-body problem.

quant-ph↗

arXiv2015

Hyperspherical theory of the quantum Hall effect: the role of exceptional degeneracy

By separating the Schrödinger equation for $N$ noninteracting spin-polarized fermions in two-dimensional hyperspherical coordinates, we demonstrate that fractional quantum Hall (FQH) states emerge naturally from degeneracy patterns of the antisymmetric free-particle eigenfunctions. In the presence of Coulomb interactions, the FQH states split off from a degenerate manifold and become observable as distinct quantized energy eigenstates with an energy gap. This alternative classification scheme is based on an approximate separability of the interacting $N$-fermion Schrödinger equation in the hyperradial coordinate, which sheds light on the emergence of Laughlin states as well as other FQH states. An approximate good collective quantum number, the grand angular momentum $K$ from $K$-harmonic few-body theory, is shown to correlate with known FQH states at many filling factors observed experimentally.

cond-mat.str-el↗

arXiv2015

Universal few-body physics in resonantly interacting spinor condensates

Optical trapping techniques allow for the formation of bosonic condensates with internal degrees of freedom, so-called spinor condensates. Mean-field models of spinor condensates highlight the sensitivity of the quantum phases of the system to the relative strength of the two-body interaction in the different spin-channels. Such a description captures the regime where these interactions are weak. In the opposite and largely unexplored regime of strongly correlated spinor condensates, three-body interactions can play an important role through the Efimov effect, producing possible novel phases. Here, we study the three-body spinor problem using the hyperspherical adiabatic representation for spin-1, -2 and -3 condensates in the strongly-correlated regime. We characterize the Efimov physics for such systems and the relevant three-body mean-field parameters. We find that the Efimov effect can strongly affect the spin dynamics and three-body mean-field contributions to the possible quantum phases of the condensate through universal contributions to scattering observables.

quant-ph↗

arXiv2015

Multichannel long-range Rydberg molecules

A generalized class of ultra-long-range Rydberg molecules is proposed which consist of a multichannel Rydberg atom whose outermost electron creates a chemical bond with a distant ground state atom. Such multichannel Rydberg molecules exhibit favorable properties for laser excitation, because states exist where the quantum defect varies strongly with the principal quantum number. The resulting occurrence of near degeneracies with states of high orbital angular momentum promotes the admixture of low $l$ into the high $l$ deeply bound `trilobite' molecule states, thereby circumventing the usual difficulty posed by electric dipole selection rules. Such states also can exhibit multi-scale binding possibilities that could present novel options for quantum manipulation.

physics.atom-ph↗

arXiv2015

Universal threshold law for ion-neutral-neutral three-body recombination

A very recently method for classical trajectory calculations for three-body collision [J. Pérez-Ríos, S. Ragole, J. Wang and C. H. Greene, J. Chem. Phys. {\bf 140}, 044307 (2014)] has been applied to describe ion-neutral-neutral ternary processes for low energy collisions: 0.1 mK - 10 mK. As a result, a threshold law for the three-body recombination cross section is obtained and corroborated both, experimentally and numerically. The derived threshold law predicts the formation of weakly bound dimers, with binding energies comparable to the collision energy of the collisional partners. In this low energy range, this analysis predicts that molecular ions should dominate over molecular neutrals as the most products formed.

physics.chem-ph↗

arXiv2015

Schwinger variational principle theory of collisions in the presence of multiple potentials

A theoretical method for treating collisions in the presence of multiple potentials is developed by employing the Schwinger variational principle. The current treatment agrees with the local (regularized) frame transformation theory and extends its capabilities. Specifically, the Schwinger variational approach gives results without the divergences that need to be regularized in other methods. Furthermore, it provides a framework to identify the origin of these singularities and possibly improve the local frame transformation. We have used the method to obtain the scattering parameters for different confining potentials symmetric in $x,y$. The method is also used to treat photodetachment processes in the presence of various confining potentials, thereby highlighting effects of the infinitely many closed channels. Two general features predicted are the vanishing of the total photoabsorption probability at {\it every} channel threshold and the occurrence of resonances below the channel thresholds for negative scattering lengths. In addition, the case of negative ion photodetachment in the presence of uniform magnetic fields is also considered where unique features emerge at large scattering lengths.

physics.atom-ph↗

arXiv2015

Adiabatic hyperspherical analysis of realistic nuclear potentials

Using the hyperspherical adiabatic method with the realistic nuclear potentials Argonne V14, Argonne V18, and Argonne V18 with the Urbana IX three-body potential, we calculate the adiabatic potentials and the triton bound state energies. We find that a discrete variable representation with the slow variable discretization method along the hyperradial degree of freedom results in energies consistent with the literature. However, using a Laguerre basis results in missing energy, even when extrapolated to an infinite number of basis functions and channels. We do not include the isospin $T=3/2$ contribution in our analysis.

nucl-th↗

arXiv2014

Few-body physics of ultracold atoms and molecules with long-range interactions

The quantum mechanical few-body problem at ultracold energies poses severe challenges to theoretical techniques, particularly when long-range interactions are present that decay only as a power-law potential. In this paper we review the techniques and progress in studies of universal few-body physics for ultracold atoms, particularly those related to long-range interactions.

physics.atom-ph↗

arXiv2014

Two-Photon Total Annihilation of Molecular Positronium

The rate for complete two-photon annihilation of molecular positronium Ps$_{2}$ is reported. This decay channel involves a four-body collision among the fermions forming Ps$_{2}$, and two photons of 1.022 MeV, each, as the final state. The quantum electrodynamics result for the rate of this process is found to be $Γ_{Ps_{2} \rightarrow γγ}$ = 9.0 $\times 10^{-12}$ s$^{-1}$. This decay channel completes the most comprehensive decay chart for Ps$_{2}$ up to date.

physics.atom-ph↗

arXiv2014

General ultracold scattering formalism with isotropic spin orbit coupling

A general treatment of ultracold two-body scattering in the presence of isotropic spin-orbit coupling (SOC) is presented. Owing to the mixing of different partial wave channels, scattering with SOC is in general a coupled multichannel problem. A systematic method is introduced to analytically solve a class of coupled differential equations by recasting the coupled channel problem as a simple eigenvalue problem. The exact Green's matrix in the presence of SOC is found, which readily gives the scattering solutions for any two identical particles in any total angular momentum subspace having negligible center of mass momentum. Application of this formalism to two spin-1 bosons shows the ubiquitous low energy threshold behavior for systems with isotropic SOC. A modified threshold behavior shows up, which does not occur for the spin-orbit coupled spin-1/2 system. We also confirm the parity-breaking mechanism for the spontaneous emergency of handedness, that has been proposed by Duan et. al. [1]. Additionally, a two-body bound state is found for any arbitrarily small and negative scattering length. Our study sheds light on the few-body side of SOC physics and provides one step towards understanding ultracold scattering in a non-Abelian gauge field.

cond-mat.quant-gas↗

arXiv2014

Quantum Defect Theory description of weakly bound levels and Feshbach resonances in LiRb

The multichannel quantum defect theory (MQDT) in combination with the frame transformation (FT) approach is applied to model the Fano-Feshbach resonances measured for $^{7}$Li$^{87}$Rb and $^{6}$Li$^{87}$Rb [Marzok {\it et al.} Phys. Rev. A {\bf 79} 012717 (2009)]. The MQDT results show a level of accuracy comparable to that of previous models based on direct, fully numerical solutions of the the coupled channel Schrödinger equations (CC). Here, energy levels deduced from 2-photon photoassociation spectra for $^{7}$Li$^{85}$Rb are assigned by applying the MQDT approach, obtaining the bound state energies for the coupled channel problem. Our results confirm that MQDT yields a compact description of photoassociation observables as well as the Fano-Feshbach resonance positions and widths.

physics.atom-ph↗

arXiv2014

Photoionization microscopy in terms of local frame transformation theory

Two-photon ionization of an alkali-metal atom in the presence of a uniform electric field is investigated using a standardized form of local frame transformation and generalized quantum defect theory. The relevant long-range quantum defect parameters in the combined Coulombic plus Stark potential is calculated with eigenchannel R-matrix theory applied in the downstream parabolic coordinate $η$. The present formulation permits us to express the corresponding microscopy observables in terms of the local frame transformation, and it gives a critical test of the accuracy of the Harmin-Fano theory permitting a scholastic investigation of the claims presented in Zhao {\it et al.} [Phys. Rev. A 86, 053413 (2012)].

quant-ph↗

arXiv2014

Scattering properties of the $2e^-2e^+$ polyelectronic system

We study the $2e^-2e^+$ equal-mass charge-neutral four-body system in the adiabatic hyperspherical framework. The lowest few adiabatic potentials are calculated for zero orbital angular momentum, positive parity, and charge conjugation symmetries. Propagating the R-matrix, the low-energy $s$-wave scattering lengths of the singlet-singlet and triplet-triplet spin configurations are calculated. Lastly, we calculate the S-matrix for energies above the ionic threshold to estimate the transition rates between the single ionic fragmentation channel and the lowest few dimer-dimer fragmentation channels.

physics.atom-ph↗

arXiv2014

Tunable Landau-Zener transitions in a spin-orbit coupled Bose-Einstein condensate

The Landau-Zener (LZ) transition is one of the most fundamental phenomena in quantum dynamics. It describes nonadiabatic transitions between quantum states near an avoided crossing that can occur in diverse physical systems. Here we report experimental measurements and tuning of LZ transitions between the dressed eigenlevels of a Bose-Einstein condensate (BEC) that is synthetically spin-orbit (SO) coupled. We measure the transition probability as the BEC is accelerated through the SO avoided crossing and study its dependence on the coupling between the diabatic (bare) states, eigenlevel slope, and eigenstate velocity--the three parameters of the LZ model that are independently controlled in our experiments. Furthermore, we performed time-resolved measurements to demonstrate the breaking down of the spin-momentum locking of the spin-orbit-coupled BEC in the nonadiabatic regime, and we determined the diabatic switching time of the LZ transitions. Our observations show quantitative agreement with the LZ model and numerical simulations of the quantum dynamics in the quasimomentum space. The tunable LZ transition may be exploited to enable a spin-dependent atomtronic transistor.

cond-mat.quant-gas↗

arXiv2014

Analyzing Feshbach resonances -- A $^6$Li -$^{133}$Cs case study

We provide a comprehensive comparison of a coupled channels calculation, the asymptotic bound state model (ABM), and the multichannel quantum defect theory (MQDT). Quantitative results for $^6$Li -$^{133}$Cs are presented and compared to previously measured $^6$Li -$^{133}$Cs Feshbach resonances (FRs) [M. Repp et al., Phys. Rev. A 87 010701(R) (2013)]. We demonstrate how the accuracy of the ABM can be stepwise improved by including magnetic dipole-dipole interactions and coupling to a non-dominant virtual state. We present a MQDT calculation, where magnetic dipole-dipole and second order spin-orbit interactions are included. A frame transformation formalism is introduced, which allows the assignment of measured FRs with only three parameters. All three models achieve a total rms error of < 1G on the observed FRs. We critically compare the different models in view of the accuracy for the description of FRs and the required input parameters for the calculations.

cond-mat.quant-gas↗

arXiv2014

Three-body Physics in Strongly Correlated Spinor Condensates

Spinor condensates have proven to be a rich area for probing many-body phenomena richer than that of an ultracold gas consisting of atoms restricted to a single spin state. In the strongly correlated regime, the physics controlling the possible novel phases of the condensate remains largely unexplored, and few-body aspects can play a central role in the properties and dynamics of the system through manifestations of Efimov physics. The present study solves the three-body problem for bosonic spinors using the hyperspherical adiabatic representation and characterizes the multiple families of Efimov states in spinor systems as well as their signatures in the scattering observables relevant for spinor condensates. These solutions exhibit a rich array of possible phenomena originating in universal few-body physics, which can strongly affect the spin dynamics and three-body mean-field contributions for spinor condensates. The collisional aspects of atom-dimer spinor condensates are also analyzed and effects are predicted that derive from Efimov physics.

quant-ph↗

arXiv2013

Tunable lattice Induced Opacity in atom-lattice interaction

A lattice-induced opacity is identified in the scattering process of a normally-incident matter wave from a two dimensional lattice of atoms. This system can be treated as an analogue of a confinement induced resonance. Specifically by modifying the s-wave scattering length between atoms in the incident matter wave and the lattice-confined atoms, the transmission of the matter wave can be tuned controllably from zero to one. Based on this, we propose a possible scheme for a matter wave transistor. When the transmission of the matter wave is tuned to zero, a matter wave cavity can be formed by placing two such lattice planes of atoms parallel to one another. At higher kinetic energies, the two dimensional lattice of atoms can also serve as a matter wave beam splitter and a wave plate.

physics.atom-ph↗