Three-body Recombination Research Articles

A perturbative approach to inelastic collisions in a Bose–Einstein condensate

It has recently been discovered that for certain rates of mode-exchange collisions analytic solutions can be found for a Hamiltonian describing the two-mode Bose–Einstein condensate. We proceed to study the behaviour of the system using perturbation theory if the coupling constants only approximately match these parameter constraints. We find that the model is robust to such perturbations. We study the effects of degeneracy on the perturbations and find that the induced changes differ greatly from the non-degenerate case. We also model inelastic collisions that result in particle loss or condensate decay as external perturbations and use this formalism to examine the effects of three-body recombination and background collisions.

Spinor atom-molecule conversion via laser-induced three-body recombination

We study theoretically several aspects of the dynamics of coherent atom-molecule conversion in spin-1 Bose-Einstein condensates. Specifically, we discuss how for a suitable dark-state condition the interplay of spin-exchange collisions and photoassociation leads to the stable creation of an atom- molecule pairs from three initial spin-zero atoms. This process involves two two-body interactions and can be intuitively viewed as an effective three-body recombination. We investigate the relative roles of photoassociation and of the initial magnetization in the \resonant" case where the dark state condition is perfectly satisfied. We also consider the "non-resonant" regime, where that condition is satisfied either approximately {the so-called adiabatic case {or not at all. In the adiabatic case, we derive an effective non-rigid pendulum model that allows one to conveniently discuss the onset of an antiferromagnetic instability of an \atom-molecule pendulum," as well as large-amplitude pair oscillations and atom-molecule entanglement.

Production of a dual-species Bose-Einstein condensate of Rb and Cs atoms

We report the simultaneous production of Bose-Einstein condensates (BECs) of 87Rb and 133Cs atoms in separate optical traps. The two samples are mixed during laser cooling and loading but are separated by 400 μm for the final stage of evaporative cooling. This is done to avoid considerable interspecies three-body recombination, which causes heating and evaporative loss. We characterize the BEC production process, discuss limitations, and outline the use of the dual-species BEC in future experiments to produce rovibronic ground state molecules, including a scheme facilitated by the superfluid-to-Mott-insulator (SF-MI) phase transition.

Universal three-body physics at finite energy near Feshbach resonances

We find that universal three-body physics extends beyond the threshold regime to non-zero energies. For ultracold atomic gases with a negative two-body s-wave scattering length near a Feshbach resonance, we show that the resonant peaks characteristic of Efimov physics persist in three-body recombination to higher collision energies. For this and other inelastic processes, we use the adiabatic hyperspherical representation to derive universal analytical expressions for their dependence on the scattering length, the collision energy and—for narrow resonances—the effective range. These expressions are supported by full numerical solutions of the Schrödinger equation and display log-periodic dependence on energy characteristic of Efimov physics. This dependence is robust and might be used to experimentally observe several Efimov features.

Numerical Investigation on the X-Ray Production of Aluminum-Wire-Array $Z$-Pinch Implosion

In this paper, the processes and mechanisms of X-ray production are discussed by numerically investigating a typical aluminum-wire-array Z-pinch implosion on the S-300 facility. It is shown that the line emission accounts for over 70% of the total radiation, and the continuum including free-free and free-bound transitions occupies less than 30%. In the line emission, most photons are generated from L-shell transitions which take place everywhere, while high-energy K-shell photons are much fewer and are mainly produced in the interior region, where the electron temperature is relatively high. Corresponding to the variation of plasma conditions in different phases of the implosion, the dominant atomic processes and radiation mechanisms show great difference. In the run-in phase, the ionization and excitation processes dominate with the increase of electron temperature, thus causing a large number of ions in excited states and, in turn, the increase of the line emission. However, the share of the line emission decreases slightly because of the strong self-absorption of lines and much weaker opacity effect on the continuum. At stagnation, the plasma is compressed to the state of high density; three-body recombination plays a key role in determining the populations of ions. Consequently, the populations of some important excited states increase rapidly, resulting in an increase of the share of line emission. After stagnation, the plasma expands, and the electron number density decreases, and the three-body recombination decreases more quickly than the radiation recombination, thus again leading to a gradual decrease in the share of line emission.

Molecular ion–electron recombination in an expanding ultracold neutral plasma of NO+

Using state-selected double-resonant excitation, we create a Rydberg gas of NO molecules excited to the principal quantum number n = 50 of the f-series converging to the ion rotational level, N(+) = 2. This gas evolves to form an ultracold plasma, which expands under the thermal pressure of its electrons, and dissipates by electron-ion recombination. Under conditions chosen for this experiment, the observed rates of expansion vary with selected plasma density. Electron temperatures derived from these expansion rates vary from T(e) = 12 K for the highest density up to 16 K at four-fold lower density. Over this range, the apparent electron coupling parameter, defined as Γ(e) = e(2)/4πε(0)ak(B)T(e), falls from nearly three to about one. The decay of charged-particle density fits with a kinetic model that includes parallel paths of direct two-body and stepwise three-body dissociative recombination. The overall recombinative decay follows a second-order rate law, with an observed rate constant that fits with established scattering-theory estimates for elementary two-body dissociative recombination. A small residual increase in this rate constant with decreasing charged-particle density suggests a growing importance of the three-body recombination channel under conditions of decreasing electron correlation.

Exact solution of the three-boson problem at vanishing energy

A zero range approach is used to model resonant two-body interactions between three identical bosons. A dimensionless phase parametrizes the three-body boundary condition while the scattering length enters the Bethe-Peierls boundary condition. The model is solved exactly at zero energy for any value of the scattering length, positive or negative. From this solution, an analytical expression for the rate of three-body recombination to the universal shallow dimer is extracted.

Recombination-pumped triatomic hydrogen infrared lasers

Mid-infrared laser lines observed in hydrogen/rare gas discharges are assigned to three-body recombination processes involving an electron, a rare gas (He or Ne) atom, and the triatomic hydrogen ion (H(3)(+)). Calculations of radiative transitions between neutral H(3) Rydberg states support this interpretation, and link it to recent results for hydrogenic∕rare gas afterglow plasmas. A mechanism for the population inversion is proposed, and the potential generality and astrophysical implications of such molecular recombination laser systems are briefly discussed.

P-wave optical Feshbach resonances inYb171

We study the use of an optical Feshbach resonance to modify the $p$-wave interaction between ultracold polarized $^{171}\mathrm{Yb}$ spin-$1/2$ fermions. A laser exciting two colliding atoms to the ${}^{1}{S}_{0}+{}^{3}{P}_{1}$ channel can be detuned near a purely-long-range excited molecular bound state. Such an exotic molecule has an inner turning point far from the chemical binding region, and thus, three-body recombination in the Feshbach resonance will be highly suppressed in contrast to that typically seen in a ground-state $p$-wave magnetic Feshbach resonance. We calculate the excited molecular bound-state spectrum using a multichannel integration of the Schr\"odinger equation, including an external perturbation by a magnetic field. From the multichannel wave functions, we calculate the Feshbach resonance properties, including the modification of the elastic $p$-wave scattering volume and inelastic spontaneous scattering rate. The use of magnetic fields and selection rules for polarized light yields a highly controllable system. We apply this control to propose a toy model for three-color superfluidity in an optical lattice for spin-polarized $^{171}\mathrm{Yb}$, where the three colors correspond to the three spatial orbitals of the first excited $p$ band. We calculate the conditions under which tunneling and on-site interactions are comparable, at which point quantum critical behavior is possible.

Fluctuation approach to description of nonideal plasma. II: Collisional recombination in nonequilibrium plasma

A model capable of describing the kinetics of collisional recombination in nonideal plasmas by the methods of molecular dynamics is developed. The dependence of the collisional recombination rate on the coupling parameter is found to differ substantially from the extrapolation of the three-body recombination rate in nonideal plasmas. A sharp decrease in the recombination rate in strongly nonideal plasmas is revealed. As the coupling parameter decreases, collisional recombination transforms into three-body recombination.

Allowed energetic pathways for the three-body recombination reaction of nitrogen monoxide with the hydroxyl radical and their potential atmospheric implications

The OH initiated oxidation of nitric oxide (NO) is an important atmospheric reaction being, during the day time, the main channel that leads to the formation of HONO a reservoir species for both OH and odd nitrogen. This work reports ab initio study of the Potential Energy Surface (PES) of NO + OH using density functional theory calculations conducted at the B3LYP level of theory with a 6-311g (d,p) basis set. We confirmed experimental observations pointing out that the main channel for this reaction is the formation the HONO. From the addition of OH to NO both cis and trans isomers of HONO were found to be the formed as stable intermediate, both having a negative enthalpy of formation relative to the reactants, the cis isomer being more stable than the trans one. The ab initio calculations were extended to include the hydrogen extraction mechanism with its respective transition state to investigate the potential existence of a reaction channel leading to the formation of NO2 + H, that was found not to be of significant interest.

Alternative path for bridging the A = 5, 8 gap in neutron-rich nucleosynthesis scenarios

In neutron-rich nucleosynthesis scenarios the mass gaps A = 5, 8 are assumed to be bridged by the three-body electromagnetic recombination reaction 4He(αn, γ)9Be. However, an alternative path, the nuclear four-body neutron-recoil recombination reaction 4He(αnn, n)9Be, is also conceivable in neutron-rich environments. We estimate the rate of the alternative reaction and show that for temperatures of about 109 K it is comparable with the electromagnetic rate if the neutron density is of about 1030 neutrons per cm3. At higher neutron densities the nuclear process dominates.

Runaway evaporation for optically dressed atoms

Forced evaporative cooling in a far-off-resonance optical dipole trap is proved to be an efficient method to produce fermionic- or bosonic-degenerated gases. However, in most of the experiments, the reduction of the potential height occurs with a diminution of the collision elastic rate. Taking advantage of a long-living excited state, like in two-electron atoms, I propose a new scheme, based on an optical knife, where the forced evaporation can be driven independently of the trap confinement. In this context, the runaway regime might be achieved leading to a substantial improvement of the cooling efficiency. The comparison with the different methods for the forced evaporation is discussed in the presence or absence of three-body recombination losses.

Blue photoluminescence of highly photoexcited rutileTiO2: Nearly degenerate conduction-band effects

We report the observation of blue photoluminescence (PL) from highly photoexcited rutile ${\text{TiO}}_{2}$ single crystals at room temperature. Under extremely high-density excitation, we found an anomalous dependence of the PL dynamics and intensity on the excitation density. By considering the nearly degenerate conduction bands of rutile, we revealed that the PL behavior is determined by the electron density in the lower-energy conduction band. The PL decay dynamics is well explained by the simple model involving two-body radiative recombination and three-body Auger recombination processes. We discuss the origin of the blue PL band.

Nuclear-Spin-Independent Short-Range Three-Body Physics in Ultracold Atoms

We investigate three-body recombination loss across a Feshbach resonance in a gas of ultracold 7Li atoms prepared in the absolute ground state and perform a comparison with previously reported results of a different nuclear-spin state [N. Gross, Phys. Rev. Lett. 103, 163202 (2009)]. We extend the previously reported universality in three-body recombination loss across a Feshbach resonance to the absolute ground state. We show that the positions and widths of recombination minima and Efimov resonances are identical for both states which indicates that the short-range physics is nuclear-spin independent.

Green’s functions and the adiabatic hyperspherical method

We address the few-body problem using the adiabatic hyperspherical representation. A general form for the hyperangular Green's function in $d$ dimensions is derived. The resulting Lippmann-Schwinger equation is solved for the case of three particles with $s$-wave zero-range interactions. Identical particle symmetry is incorporated in a general and intuitive way. Complete semianalytic expressions for the nonadiabatic channel couplings are derived. Finally, a model to describe the atom loss due to three-body recombination for a three-component Fermi gas of $^{6}\mathrm{Li}$ atoms is presented.

Absolute ground-state nitrogen atom density in a N2/CH4 late afterglow: TALIF experiments and modelling studies

Following a first study on a late afterglow in flowing pure nitrogen post discharge, we report new two-photon absorption laser-induced fluorescence (TALIF) measurements of the absolute ground-state atomic nitrogen density N(4S) and investigate the influence of methane introduced downstream from the discharge by varying the CH4 mixing ratio from 0% up to 50%. The N (4S) maximum density is about 2.2 × 1015 cm−3 in pure N2 for a residence time of 22 ms and does not change significantly for methane mixing ratio up to ∼15%, while above, a drastic decrease is observed. The influence of the residence time has been studied.A kinetic model has been developed to determine the elementary processes responsible for the evolution of the N (4S) density in N2/CH4 late afterglow. This model shows the same decrease as the experimental results even though absolute density values are always larger by about a factor of 3. In the late afterglow three-body recombination dominates the loss of N (4S) atoms whatever the CH4 mixing ratio. For high CH4 mixing ratio, the destruction process through collisions with CH3, H2CN and NH becomes important and is responsible for the observed decrease of the N (4S) density.

Dissipation-Managed Bright Soliton in a 1D Bose–Einstein Condensate in an Optical-Lattice Potential

We study the formation of a dynamically-stabilized dissipation-managed bright soliton in a quasi-one-dimensional Bose–Einstein condensate by including an imaginary three-body recombination loss term and an imaginary linear feeding one in the Gross–Pitaevskii equation, trapped in a shallow optical-lattice potential. Based on the direct approach of perturbation theory for the nonlinear Schrödinger equation, we demonstrate that the height (as well as width) of bright soliton may have little change through selecting experimental parameters.

Lattice-Boltzmann simulation of laser interaction with weakly ionized helium plasmas

This paper presents a lattice Boltzmann method for laser interaction with weakly ionized plasmas considering electron impact ionization and three-body recombination. To simulate with physical properties of plasmas, the authors' previous work on the rescaling of variables is employed and the electromagnetic fields are calculated from the Maxwell equations by using the finite-difference time-domain method. To calculate temperature fields, energy equations are derived separately from the Boltzmann equations. In this way, we attempt to solve the full governing equations for plasma dynamics. With the developed model, the continuous-wave CO2 laser interaction with helium is simulated successfully.

Three Body Recombination of Ultracold Dipoles to Weakly Bound Dimers

We use universality in two-body dipolar physics to study three-body recombination. We present results for the universal structure of weakly bound two-dipole states that depend only on the s-wave scattering length (a). We study threshold three-body recombination rates into weakly bound dimer states as a function of the scattering length. A Fermi golden rule analysis is used to estimate rates for different events mediated by the dipole-dipole interaction and a phenomenological contact interaction. The three-body recombination rate in the limit where a≫D contains terms which scale as a{4}, a{2}D{2}, and D4, where D is the dipolar length. When a≪D, the three-body recombination rate scales as D4.