Spin-dependent Collisions Research Articles

Coherent spin mixing via spin-orbit coupling in Bose gases

We study beyond-mean-field properties of interacting spin-1 Bose gases with synthetic Rashba-Dresselhaus spin-orbit coupling at low energies. We derive a many-body Hamiltonian following a tight-binding approximation in quasi-momentum space, where the effective spin dependence of the collisions that emerges from spin-orbit coupling leads to dominant correlated tunneling processes that couple the different bound states. We discuss the properties of the spectrum of the derived Hamiltonian and its experimental signatures. In a certain region of the parameter space, the system becomes integrable, and its dynamics becomes analogous to that of a spin-1 condensate with spin-dependent collisions. Remarkably, we find that such dynamics can be observed in existing experimental setups through quench experiments that are robust against magnetic fluctuations.

Superfluid–Mott-insulator transition of spin-1 bosons in optical resonators

We consider an antiferromagnetic spin-1 Bose-Einstein condensate confined in a Fabry-P\'erot optical resonator in which the intracavity light field forms an optical lattice potential for the atoms. Special emphasis is paid to the cavity-mediated superfluid--Mott-insulator transition. We find that exotic phase diagrams can appear due to the competition between cavity-induced nonlinear interactions and the atomic spin-dependent collision interactions.

Generation of Massive Entanglement through an Adiabatic Quantum Phase Transition in a Spinor Condensate

We propose a method to generate massive entanglement in a spinor Bose-Einstein condensate from an initial product state through an adiabatic sweep of the magnetic field across a quantum phase transition induced by competition between the spin-dependent collision interaction and the quadratic Zeeman effect. The generated many-body entanglement is characterized by the experimentally measurable entanglement depth in the proximity of the Dicke state. We show that the scheme is robust to practical noise and experimental imperfection and under realistic conditions it is possible to generate genuine entanglement for hundreds of atoms.

Laser-catalyzed spin-exchange process in a Bose-Einstein condensate

We show theoretically that it is possible to optically control collective spin-exchange processes in spinor Bose condensates through virtual photoassociation. The interplay between optically induced spin exchange and spin-dependent collisions provides a flexible tool for the control of atomic spin dynamics, including enhanced or inhibited quantum spin oscillations, the optically-induced ferromagnetic-to-antiferromagnetic transition, and coherent matter-wave spin conversion.

Frequency response and origin of the spin-1∕2photoluminescence-detected magnetic resonance in aπ-conjugated polymer

We model the frequency responses of the photoinduced absorption (PA) and the spin-$1∕2$ photoluminescence-detected magnetic resonance (PLDMR) in the archetypal $\ensuremath{\pi}$-conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]. We show that the frequency response of the resonance is consistent with a quenching model mediated by spin-dependent interactions between triplet excitons and polarons. Two polaron populations are identified: short-lived paired polarons that may recombine after spin-dependent collisions with triplet excitons, and long-lived unpaired polarons that are unaffected by microwave resonance. The large density of unpaired polarons dominates the frequency response of PA measurements, but does not influence the frequency response of the PLDMR, which instead probes the dynamics of triplet excitons and paired polarons.

Magnetic field dependence of the dynamics ofRb87spin-2 Bose-Einstein condensates

We experimentally studied the spin-dependent collision dynamics of $^{87}\mathrm{Rb}$ spin-2 Bose-Einstein condensates confined in an optical trap. The condensed atoms were initially populated in the $\ensuremath{\mid}F=2,{m}_{F}=0⟩$ state, and their time evolutions in the trap were measured in the presence of external magnetic field strengths ranging from 0.1 to $3.0\phantom{\rule{0.3em}{0ex}}\mathrm{G}$. The atom loss rate due to inelastic two-body collisions was found to be $1.4(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{3}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Spin mixing in the $F=2$ manifold developed dramatically for the first few tens of milliseconds, and the oscillations in the population distribution between different magnetic components were observed over a limited range of magnetic field strengths. The antiferromagnetic property of this system was deduced from the magnetic field dependence on the evolution of relative populations for each ${m}_{F}$ component.

Chiral effects in spin-dependent elastic electron scattering from molecules

A general theory of elastic spin-dependent collisions between electrons and spinless molecules is developed. The main emphasis is on scattering from oriented, chiral and achiral molecules, although results for isotropic target systems are also derived. Spin-dependent phenomena are predicted and illustrated with several examples. In particular, chiral effects are discussed in detail and classified according to their behaviour under spatial inversion and time reversal. The authors identify two types of chiral phenomena associated with systems exhibiting 'time-even' and 'time-odd' chirality. The corresponding observables are calculated for a chiral model molecule. It is concluded from the numerical results that the predicted new spin-dependent effects could be measured experimentally.

Calculation of Stokes' parameters for inelastic electron-mercury scattering

The relativistic R-matrix method is applied to the excitation of the 63P1 state of Hg by polarised electrons. The Stokes' parameters of the light emitted in the subsequent atomic decay, are calculated from threshold to 6.5 eV and are compared with experiment. The physical importance of these observables for spin-dependent collisions is discussed.

Hyperfine Structure of the Ground State ofHe+3by the Ion-Storage Exchange-Collision Technique

The hfs of the ground state of $^{3}\mathrm{He}^{+}$ has been studied using the spin-dependent collision processes between stored $^{3}\mathrm{He}^{+}$ ions and a polarized beam of Cs atoms. All possible hfs transitions have been measured in a magnetic field of about 7.13 G. A consecutive-pulse multiple-resonance scheme was developed to detect the only weakly field-dependent transition $(F=0, {m}_{F}=0)\ensuremath{\leftrightarrow}(F=1, {m}_{F}=0)$ in an almost ideally isolated and pure atomic system. Magnetic-resonance disorientation is observed as a change in the number of ions remaining in the rf quadrupole ion trap after a fixed interaction time with both the resonant rf fields and the polarized atomic beam. For the detection of an ion-number signal, the ion macromotion at ${\overline{\ensuremath{\omega}}}_{z}$ was coherently excited by a homogeneous electric field at ${\overline{\ensuremath{\omega}}}_{z}+\ensuremath{\Omega}$, where $\ensuremath{\Omega}$ is the frequency of the inhomogeneous rf field used for trapping. Linewidths of 10 Hz have been measured for the (0, 0) \ensuremath{\leftrightarrow} (1, 0) hfs transition, when the transition was induced during a time of the order of half the electron-spin orientation time in a weak atomic beam. The value for the zero-magnetic-field hfs splitting is $\ensuremath{\Delta}\ensuremath{\nu}=(8665649867\ifmmode\pm\else\textpm\fi{}10)$ Hz. Rate equations for the populations of the hfs Zeeman levels in the presence of the polarized atomic beam and transitions caused by various rf fields are given. Features of the line shape caused by the consecutive-pulse multiple-resonance scheme are also considered. Several mechanisms which may ultimately limit the precision are discussed. A comparison of the experimental result with current theories of the hfs of hydrogenic systems is presented.

Method for Measuring the Cyclotron and Spin Resonance of Free Electrons

The cyclotron and spin resonance of free electrons field confined in a small volume in ultrahigh vacuum have been observed via the rapid loss of electrons when their cyclotron motion is excited by the rf field and spin-dependent collision processes with polarized Na atoms in a beam, respectively. The electrons were polarized by spin exchange and then monitored through the spin dependence of the excitation process $e+\mathrm{Na}(3S)\ensuremath{\rightarrow}e+{\mathrm{Na}}^{*}(3P)$ and hence of their cooling rate.

Exchange-Collision Technique for the rf Spectroscopy of Stored Ions

A description is given of a technique, whose application to ${\mathrm{He}}^{+}$ has previously been briefly reported, whereby the rf spectrum of field-confined paramagnetic ions in ultrahigh vacuum is observed through spin-dependent collision processes with a spin-polarized beam of neutral particles. A rf electric quadrupole ion trap is used, and a description of the ion motion, based on the adiabatic approximation, is given, including the effect of randomizing elastic collisions with neutral background particles. With particular reference to the ${({\mathrm{He}}^{3})}^{+}$-Cs system, the rate equations for the magnetic sublevel populations for an ion with $I=\frac{1}{2}$, $J=\frac{1}{2}$ are derived under the simultaneous action of spin exchange and spin-dependent charge exchange with an alkali atom. According to these equations, the relative intensities observed in the $\ensuremath{\Delta}F=0$ transitions of ${({\mathrm{He}}^{3})}^{+}$ indicate that a Cs spin polarization of 0.5 was achieved in the optically pumped atomic beam. The ${\mathrm{He}}^{+}$ polarization approached that of the Cs atoms. With on-off modulation of the Cs polarization, a total 2% change in the ${\mathrm{He}}^{+}$ lifetime was observed, with a signal-to-noise ratio of 4, in an interaction period having a duration of 0.8 sec, the optimum value for the observed 0.4-sec lifetime against Cs-induced ion loss. In the absence of the beam, the lifetime was 8 sec at a residual pressure of 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ Torr. The $\ensuremath{\Delta}F=0$ lines obtained with long integration times had a signal-to-noise ratio which indicated that the $\ensuremath{\Delta}F=\ifmmode\pm\else\textpm\fi{}1$ transitions should be observable, as has since been demonstrated.