Publications (126)360.97 Total impact

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ABSTRACT: We show that a Gaussian Process model can be combined with a small number of scattering calculations to provide an accurate multidimensional dependence of scattering observables on the experimentally controllable parameters (such as the collision energy, temperature or external fields) as well as the potential energy surface parameters. This can be used for solving the inverse scattering problem, the prediction of collision properties of a specific molecular system based on the information for another molecule, the efficient calculation of thermally averaged observables and for reducing the error of the molecular dynamics calculations by averaging over the potential energy surface variations. We show that, trained by a combination of classical and quantum dynamics calculations, the model provides an accurate description of the scattering cross sections, even near scattering resonances. In this case, the classical calculations stabilize the model against uncertainties arising from wildly varying correlations of resonantly enhanced quantum results. 
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ABSTRACT: We consider the dynamics of rotational excitations placed on a single molecule in spatially disordered 1D, 2D and 3D ensembles of ultracold molecules trapped in optical lattices. The disorder arises from incomplete populations of optical lattices with molecules. We show that for realistic experimental parameters this specific type of disorder leads to disorderinduced localization in 1D and 2D systems on a time scale $t \sim 1$ sec. For 3D lattices with $55$ sites in each dimension and vacancy concentrations $\leq 90 \%$, the rotational excitations generated in the middle of the lattice diffuse to the edges of the lattice. We observe that the diffusion of rotational excitations in highly disordered 2D and 3D lattices has three distinct time scales. At short times, the rotational excitations diffuse as quantum particles expanding ballistically. At later times, the diffusion character changes to be the same as for the classical particles in Brownian motion. At still later times, the rotational excitations transition to a subdiffusive regime. While the ballistic expansion is brief ($\sim 10$ ms), the classicallike diffusion can last as long as 200300 ms. We also examine the role of the longrange tunnelling amplitudes allowing for transfer of rotational excitations between distant lattice sites. Our results show that the longrange tunnelling has little impact on the dynamics in the diffusive regime but affects significantly the localization dynamics in lattices with large concentrations of vacancies, enhancing the width of the localized distributions in 2D lattices by more than a factor of 2. 
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ABSTRACT: We use classical trajectory calculations to study the effects of the interaction strength and the geometry of rigid polyatomic molecules on the formation of longlived collision complexes at low collision energies. We first compare the results of the calculations for collisions of benzene molecules with rare gas atoms He, Ne, Ar, Kr, and Xe. The comparison illustrates that the mean lifetimes of the collision complexes increase monotonically with the strength of the atommolecule interaction. We then compare the results of the atombenzene calculations with those for benzenebenzene collisions. The comparison illustrates that the mean lifetimes of the benzenebenzene collision complexes are significantly reduced due to nonergodic effects prohibiting the molecules from sampling the entire configuration space. We find that the thermally averaged lifetimes of the benzenebenzene collisions are much shorter than those for Xe with benzene and similar to those for Ne with benzene.The Journal of Chemical Physics 10/2014; 141(16):164315. DOI:10.1063/1.4898796 · 3.12 Impact Factor 
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ABSTRACT: We develop a theoretical method for solving the quantum mechanical reactive scattering problem in the presence of external fields based on a hyperspherical coordinate description of the reaction complex combined with the total angular momentum representation for collisions in external fields. The method allows us to obtain converged results for the chemical reaction LiF + H > Li + HF in an electric field. Our calculations demonstrate that, by inducing couplings between states of different total angular momenta, electric fields with magnitudes <150 kV/cm give rise to resonant scattering and a significant modification of the total reaction probabilities, product state distributions and the branching ratios for reactive vs inelastic scattering. 
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ABSTRACT: We explore the collision dynamics of complex hydrocarbon molecules (benzene, coronene, adamantane, and anthracene) containing carbon rings in a cold buffer gas of (3)He. For benzene, we present a comparative analysis of the fully classical and fully quantum calculations of elastic and inelastic scattering cross sections at collision energies between 1 and 10 cm(1). The quantum calculations are performed using the timeindependent coupled channel approach and the coupledstates approximation. We show that the coupledstates approximation is accurate at collision energies between 1 and 20 cm(1). For the classical dynamics calculations, we develop an approach exploiting the rigidity of the carbon rings and including lowenergy vibrational modes without holonomic constraints. Our results illustrate the effect of the molecular shape and the vibrational degrees of freedom on the formation of longlived resonance states that lead to lowtemperature clustering.The Journal of Chemical Physics 09/2014; 141(10):104317. DOI:10.1063/1.4894793 · 3.12 Impact Factor 
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ABSTRACT: Magnetic Feshbach resonances play a central role in experimental research on atomic gases at ultracold temperatures, as they allow one to control the microscopic interactions between ultracold atoms by tuning an applied magnetic field. These resonances arise due to strong hyperfine interactions between the unpaired electron and the nuclear magnetic moment of the alkali metal atoms. A major thrust of current research is to create an ultracold gas of diatomic alkali metal molecules in the ground rovibrational state of the ground electronic 1Σ state. Unlike alkali metal atoms, 1Σ diatomic molecules have no unpaired electrons. However, the hyperfine interactions of molecules may give rise to magnetic Feshbach resonances. We use quantum scattering calculations to study the possible width of these resonances. Our results show that the widths of magnetic Feshbach resonances in ultracold moleculemolecule collisions for 1Σ molecules may exceed 1 mG, rendering such resonances experimentally detectable. We hope that this work will stimulate the experimental search of these resonances.Physical Review A 02/2014; 89(3). DOI:10.1103/PhysRevA.89.032716 · 2.99 Impact Factor 
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ABSTRACT: We show that the interaction of polar alkalimetal dimers in the quintet spin state leads to the formation of a deeply bound reaction complex. The reaction complex can decompose adiabatically into homonuclear alkalimetal dimers (for all molecules except KRb) and into alkalimetal trimers (for all molecules). We show that there are no barriers for these chemical reactions. This means that all alkalimetal dimers in the a^{3}Σ^{+} state are chemically unstable at ultracold temperature, and the use of an optical lattice to segregate the molecules and suppress losses may be necessary. In addition, we calculate the minimumenergy path for the chemical reactions of alkalimetal hydrides. We find that the reaction of two molecules is accelerated by a strong attraction between the alkalimetal atoms, leading to a barrierless process that produces hydrogen atoms with large kinetic energy. We discuss the unique features of the chemical reactions of ultracold alkalimetal dimers in the a^{3}Σ^{+} electronic state.Physical Review A 11/2013; 88(5). DOI:10.1103/PhysRevA.88.050701 · 2.99 Impact Factor 
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ABSTRACT: We calculate the cross sections for elastic scattering and Zeeman relaxation in binary collisions of molecules in the rovibrational ground state of a $^2\Sigma$ electronic state and the Zeeman state with the electron spin projection $M_S=1/2$ on the magnetic field axis. This is the lowestenergy state of $^2\Sigma$ molecules confined in a magnetic trap. The results are averaged over calculations with multiple molecule  molecule interaction potentials, which yields the expectation intervals for the cross sections and the elastictoinelastic cross section ratios. We find that the elastictoinelastic cross section ratios under conditions corresponding to trapped molecular ensembles at $T \sim 10^{3}$ K exceed 100 for the majority of $^2\Sigma$ molecules. The range of $^2\Sigma$ molecules expected to be collisionally unstable in magnetic traps at $T < 10^{3}$ K is limited to molecules with the spinrotation interaction constant $\gamma_{\rm SR} > 0.5$ cm$^{1}$ and the rotational constant $B_e < 4$ cm$^{1}$.Physical Review A 08/2013; 88(4). DOI:10.1103/PhysRevA.88.042705 · 2.99 Impact Factor 
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ABSTRACT: The goal of the present article is to review the major developments that have led to the current understanding of moleculefield interactions and experimental methods for manipulating molecules with electromagnetic fields. Moleculefield interactions are at the core of several, seemingly distinct, areas of molecular physics. This is reflected in the organization of this article, which includes sections on Field control of molecular beams, External field traps for cold molecules, Control of molecular orientation and molecular alignment, Manipulation of molecules by nonconservative forces, Ultracold molecules and ultracold chemistry, Controlled manybody phenomena, Entanglement of molecules and dipole arrays, and Stability of molecular systems in highfrequency superintense laser fields. The article contains 853 references.Molecular Physics 06/2013; 111(1213). DOI:10.1080/00268976.2013.813595 · 1.64 Impact Factor 
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ABSTRACT: We determine the phase diagram of a polaron model with mixed breathingmode and SuSchriefferHeeger couplings and show that it has two sharp transitions, in contrast to pure models which exhibit one (for SuSchriefferHeeger coupling) or no (for breathingmode coupling) transition. We then show that ultracold molecules trapped in optical lattices can be used as a quantum simulator to study precisely this mixed Hamiltonian, and that the relative contributions of the two couplings can be tuned with external electric fields. The parameters of current experiments place them in the region where one of the transitions occurs. We also propose a scheme to measure the polaron dispersion using stimulated Raman spectroscopy.Physical Review Letters 05/2013; 110(22):223002. DOI:10.1103/PhysRevLett.110.223002 · 7.73 Impact Factor 
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ABSTRACT: An elementary excitation in an aggregate of coupled particles generates a collective excited state. We show that the dynamics of these excitations can be controlled by applying a transient external potential which modifies the phase of the quantum states of the individual particles. The method is based on an interplay of adiabatic and sudden time scales in the quantum evolution of the manybody states. We show that specific phase transformations can be used to accelerate or decelerate quantum energy transfer and spatially focus delocalized excitations onto different parts of arrays of quantum particles. We consider possible experimental implementations of the proposed technique and study the effect of disorder due to the presence of impurities on its fidelity. We further show that the proposed technique can allow control of energy transfer in completely disordered systems.New Journal of Physics 09/2012; 15(6). DOI:10.1088/13672630/15/6/063015 · 3.67 Impact Factor 
Article: Collisional decoherence of superposition states in an ultracold gas near a Feshbach resonance
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ABSTRACT: We present expressions demonstrating that collisional decoherence of ultracold atoms or molecules in a coherent superposition of nondegenerate quantum states is suppressed when both the real and imaginary parts of the scattering lengths for the states in the coherent superposition are equal. We show that the rate of collisional decoherence can be enhanced or suppressed by varying an external magnetic field near a Feshbach resonance. For some resonances, the suppression is very dramatic. We propose a method for measuring the scattering length of ultracold particles in excited quantum states exhibiting Feshbach resonances.Physical Review A 08/2012; 86(2). DOI:10.1103/PhysRevA.86.022703 · 2.99 Impact Factor 
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ABSTRACT: Ultracold polar molecules trapped on an optical lattice is a manybody system that, under appropriate conditions, may support collective excitations reminiscent of excitons in solid state crystals. Here, we discuss the rotational excitations of molecules on an optical lattice leading to rotational Frenkel excitons. Apart from solid hydrogen, there is no other natural system that exhibits rotational excitons. The rotational excitons have unique properties that can be exploited for tuning nonlinear exciton interactions and excitonimpurity scattering by applying an external electric field. We show that this can be used to explore the competing role of the dynamical and kinematic excitonexciton interactions in excitonic energy transfer and to study quantum localization in a dynamically tunable disordered potential. The rotational excitons can also be used as a basis for quantum simulation of condensed matter models that cannot be realized with ultracold atoms. As an example, we discuss the possibility of engineering the Holstein model with polar molecules on an optical lattice. 
Physical Review Letters 07/2012; 109(4). DOI:10.1103/PhysRevLett.109.049901 · 7.73 Impact Factor

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ABSTRACT: We study the growth dynamics of ordered structures of strongly interacting polar molecules in optical lattices. Using a dipole blockade of microwave excitations, we map the system onto an interacting spin1/2 model possessing ground states with crystalline order, and describe a way to prepare these states by nonadiabatically driving the transitions between molecular rotational levels. The proposed technique bypasses the need to cross a phase transition and allows for the creation of ordered domains of considerably larger size compared to approaches relying on adiabatic preparation.Physical Review Letters 07/2012; 109(3):035301. DOI:10.1103/PhysRevLett.109.035301 · 7.73 Impact Factor 
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ABSTRACT: We show that the cross sections for moleculemolecule collisions in the presence of an external field can be computed efficiently using a total angular momentum basis, defined either in the bodyfixed frame or in the spacefixed coordinate system. This method allows for computations with much larger basis sets than previously possible. We present calculations for (15)NH(15)NH collisions in a magnetic field. Our results support the conclusion of the previous study that the evaporative cooling of rotationally ground (15)NH molecules in a magnetic trap has a prospect of success.The Journal of Chemical Physics 07/2012; 137(2):024103. DOI:10.1063/1.4733288 · 3.12 Impact Factor 
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ABSTRACT: Magnetic Feshbach scattering resonances play a central role in experimental research of atomic gases at ultracold temperatures. A major thrust of current research is to create an ultracold gas of diatomic alkalimetal molecules in the ground rovibrational state of the ground electronic ^1σ state. Can ultracold ^1σ molecules be controlled by means of magnetic Feshbach resonances? Unlike alkali metal atoms, ^1σ diatomic molecules have no unpaired electrons. The response of ^1σ molecules to an external magnetic field is determined entirely by the spin structure of the atomic nuclei. We present the first calculations of moleculemolecule collisions for ^1σ molecules in a magnetic field. In particular, we calculate the rates of hyperfine relaxation in molecule  molecule collisions and explore the possibility of tuning magnetic Feshbach resonances in an ultracold gas of ^87Rb^133Cs(X^1&+circ;) molecules. 
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ABSTRACT: Rotational excitation of ultracold polar molecules trapped on an optical lattice produces rotational Frenkel excitons (collective rotational excitations) [1]. We show that nonlinear interactions between these excitons can be tuned by applying a dc electric field. We show that, at electric fields greater than a critical value, rotational Frenkel excitons form bound pairs  biexcitons [2]. Frenkel biexcitons are strongly correlated states of two collective excitations in a molecular crystal, which are exceedingly hard to create and observe in solidstate crystals. We demonstrate that the binding energy of the rotational biexcitons can be controlled by tuning the angle between the applied field and the molecular array. Frenkel biexcitons can be used for many applications ranging from the controlled preparation of entanglement between quasiparticles to the study of bipolarons. [4pt] [1] ``Frenkel biexcitons in optical lattices with polar molecules,'' Ping Xiang, M. Litinskaya, R. V. Krems; condmat/1112.3942. [0pt] [2] ``Tunable disorder in a crystal of cold polar molecules,'' F. Herrera, M. Litinskaya, R. V. Krems, Phys. Rev. A 82, 033428 (2010). 
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ABSTRACT: We show that a strong offresonant optical pulse can be used to create entanglement in an ensemble of polar molecules. The laser field modifies the rotational structure of molecules, enhancing the effect of the dipoledipole interaction between molecules. This generates entanglement between molecules in different rotational states after the pulse is over. The degree of entanglement can be controlled by shaping the intensity and duration of the pulse. We show that a single nanosecond pulse can be used to produce an entangled state of molecules separated by several hundreds of nanometers, and that a sequence of pulses generate entanglement between molecules separated by tens of micrometers. We describe the possibility of using molecules trapped on an optical lattice to test Bell's inequalities by measuring orientation and alignment correlations. We also analyze the main sources of decoherence in the system and estimate the efficiency of twoqubit quantum gates for universal quantum computation with trapped polar molecules. Reference: F. Herrera, Ph.D. thesis, University of British Columbia, 2012 
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ABSTRACT: We propose a method for sensitive parallel detection of lowfrequency electromagnetic fields based on the fine structure interactions in paramagnetic polar molecules. Compared to the recently implemented scheme employing ultracold $^{87}$Rb atoms [B{\"o}hi \textit{et al.}, Appl. Phys. Lett. \textbf{97}, 051101 (2010)], the technique based on molecules offers a 100fold higher sensitivity, the possibility to measure both the electric and magnetic field components, and a probe of a wide range of frequencies from the dc limit to the THz regime.Physical Review A 02/2012; 86(1). DOI:10.1103/PhysRevA.86.013409 · 2.99 Impact Factor
Publication Stats
2k  Citations  
360.97  Total Impact Points  
Top Journals
Institutions

2006–2015

University of British Columbia  Vancouver
 Department of Chemistry
Vancouver, British Columbia, Canada


2013

University of California, Santa Barbara
 Kavli Institute for Theoretical Physics
Santa Barbara, California, United States


2002–2012

HarvardSmithsonian Center for Astrophysics
 Institute for Theoretical Atomic, Molecular and Optical Physics
Cambridge, Massachusetts, United States


2010

Radboud University Nijmegen
 Department of Theoretical Chemistry
Nijmegen, Provincie Gelderland, Netherlands


2003–2005

Harvard University
 Department of Physics
Cambridge, Massachusetts, United States


2000

University of Gothenburg
Goeteborg, Västra Götaland, Sweden 
Moscow State Forest University
Mytishi, Moskovskaya, Russia
