Self-Organization in Cold Atoms Mediated by Diffractive Coupling

This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the 2D plane transverse to the pump. We elucidate how diffractive ripples couple sites on the self-induced atomic lattice. The nonlinear phase shift of the atomic cloud imprinted onto the optical beam is the parameter determining coupling strength. The interaction can be tailored to operate either on external degrees of freedom leading to atomic crystallization for thermal atoms and supersolids for a quantum degenerate gas, or on internal degrees of freedom like populations of the excited state or Zeeman sublevels. Using the light polarization degrees of freedom on the Poincaré sphere (helicity and polarization direction), specific irreducible tensor components of the atomic Zeeman states can be coupled leading to spontaneous magnetic ordering of states of dipolar and quadrupolar nature. The requirements for critical interaction strength are compared for the different situations. Connections and extensions to longitudinally pumped cavities, counterpropagating beam schemes and the CARL instability are discussed.

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Reversibly Sampling Conformations and Binding Modes Using Molecular Darting

10.26434/chemrxiv.12670676.v2 ◽

2020 ◽

Author(s):

Samuel C. Gill ◽

David Mobley

Keyword(s):

Monte Carlo ◽

Ligand Binding ◽

Binding Sites ◽

Degrees Of Freedom ◽

Dynamics Simulation ◽

Hiv Integrase ◽

Binding Modes ◽

System A ◽

Multiple Binding ◽

Internal Degrees Of Freedom

<div>Sampling multiple binding modes of a ligand in a single molecular dynamics simulation is difficult. A given ligand may have many internal degrees of freedom, along with many different ways it might orient itself a binding site or across several binding sites, all of which might be separated by large energy barriers. We have developed a novel Monte Carlo move called Molecular Darting (MolDarting) to reversibly sample between predefined binding modes of a ligand. Here, we couple this with nonequilibrium candidate Monte Carlo (NCMC) to improve acceptance of moves.</div><div>We apply this technique to a simple dipeptide system, a ligand binding to T4 Lysozyme L99A, and ligand binding to HIV integrase in order to test this new method. We observe significant increases in acceptance compared to uniformly sampling the internal, and rotational/translational degrees of freedom in these systems.</div>

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A novel class of translationally invariant spin chains with long-range interactions

Journal of High Energy Physics ◽

10.1007/jhep08(2020)099 ◽

2020 ◽

Vol 2020 (8) ◽

Author(s):

B. Basu-Mallick ◽

F. Finkel ◽

A. González-López

Keyword(s):

Long Range ◽

Degrees Of Freedom ◽

Spin Chains ◽

Open Chain ◽

New Class ◽

Spin Interactions ◽

Long Range Interactions ◽

Spin Reversal ◽

Twisted Yangian ◽

Internal Degrees Of Freedom

Abstract We introduce a new class of open, translationally invariant spin chains with long-range interactions depending on both spin permutation and (polarized) spin reversal operators, which includes the Haldane-Shastry chain as a particular degenerate case. The new class is characterized by the fact that the Hamiltonian is invariant under “twisted” translations, combining an ordinary translation with a spin flip at one end of the chain. It includes a remarkable model with elliptic spin-spin interactions, smoothly interpolating between the XXX Heisenberg model with anti-periodic boundary conditions and a new open chain with sites uniformly spaced on a half-circle and interactions inversely proportional to the square of the distance between the spins. We are able to compute in closed form the partition function of the latter chain, thereby obtaining a complete description of its spectrum in terms of a pair of independent su(1|1) and su(m/2) motifs when the number m of internal degrees of freedom is even. This implies that the even m model is invariant under the direct sum of the Yangians Y (gl(1|1)) and Y (gl(0|m/2)). We also analyze several statistical properties of the new chain’s spectrum. In particular, we show that it is highly degenerate, which strongly suggests the existence of an underlying (twisted) Yangian symmetry also for odd m.

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Kinetic Moment Equations for a Gas of Polyatomic Molecules with Many Internal Degrees of Freedom

The Physics of Fluids ◽

10.1063/1.1693100 ◽

1970 ◽

Vol 13 (6) ◽

pp. 1446 ◽

Cited By ~ 7

Author(s):

Francis J. McCormack

Keyword(s):

Degrees Of Freedom ◽

Polyatomic Molecules ◽

Moment Equations ◽

Internal Degrees Of Freedom ◽

Kinetic Moment

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Dissipative dynamics of a particle coupled to a field via internal degrees of freedom

Physical Review D ◽

10.1103/physrevd.103.056023 ◽

2021 ◽

Vol 103 (5) ◽

Author(s):

Kanupriya Sinha ◽

Adrián Ezequiel Rubio López ◽

Yiğit Subaşı

Keyword(s):

Degrees Of Freedom ◽

Dissipative Dynamics ◽

Internal Degrees Of Freedom

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Optimal Relabeling of Water Molecules and Single-Molecule Entropy Estimation

Biophysica ◽

10.3390/biophysica1030021 ◽

2021 ◽

Vol 1 (3) ◽

pp. 279-296

Author(s):

Federico Fogolari ◽

Gennaro Esposito

Keyword(s):

Single Molecule ◽

Degrees Of Freedom ◽

Water Molecules ◽

Maximum Information ◽

Nearest Neighbours ◽

Biomolecular Simulations ◽

Solvent Molecules ◽

Solvation Entropy ◽

Dynamics Simulations ◽

Internal Degrees Of Freedom

Estimation of solvent entropy from equilibrium molecular dynamics simulations is a long-standing problem in statistical mechanics. In recent years, methods that estimate entropy using k-th nearest neighbours (kNN) have been applied to internal degrees of freedom in biomolecular simulations, and for the rigorous computation of positional-orientational entropy of one and two molecules. The mutual information expansion (MIE) and the maximum information spanning tree (MIST) methods were proposed and used to deal with a large number of non-independent degrees of freedom, providing estimates or bounds on the global entropy, thus complementing the kNN method. The application of the combination of such methods to solvent molecules appears problematic because of the indistinguishability of molecules and of their symmetric parts. All indistiguishable molecules span the same global conformational volume, making application of MIE and MIST methods difficult. Here, we address the problem of indistinguishability by relabeling water molecules in such a way that each water molecule spans only a local region throughout the simulation. Then, we work out approximations and show how to compute the single-molecule entropy for the system of relabeled molecules. The results suggest that relabeling water molecules is promising for computation of solvation entropy.

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Emergent long-range magnetic order in ultrathin (111)-oriented LaNiO3 films

npj Quantum Materials ◽

10.1038/s41535-021-00345-2 ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Margaret M. Kane ◽

Arturas Vailionis ◽

Lauren J. Riddiford ◽

Apurva Mehta ◽

Alpha T. N’Diaye ◽

...

Keyword(s):

Long Range ◽

Degrees Of Freedom ◽

Magnetic Order ◽

Magnetic Ordering ◽

Anomalous Hall Effect ◽

X Ray Diffraction ◽

X Ray ◽

Range Magnetic Order ◽

Film Substrate ◽

Long Range Magnetic Order

AbstractThe emergence of ferromagnetism in materials where the bulk phase does not show any magnetic order demonstrates that atomically precise films can stabilize distinct ground states and expands the phase space for the discovery of materials. Here, the emergence of long-range magnetic order is reported in ultrathin (111) LaNiO3 (LNO) films, where bulk LNO is paramagnetic, and the origins of this phase are explained. Transport and structural studies of LNO(111) films indicate that NiO6 octahedral distortions stabilize a magnetic insulating phase at the film/substrate interface and result in a thickness-dependent metal–insulator transition at t = 8 unit cells. Away from this interface, distortions relax and bulk-like conduction is regained. Synchrotron x-ray diffraction and dynamical x-ray diffraction simulations confirm a corresponding out-of-plane unit-cell expansion at the interface of all films. X-ray absorption spectroscopy reveals that distortion stabilizes an increased concentration of Ni2+ ions. Evidence of long-range magnetic order is found in anomalous Hall effect and magnetoresistance measurements, likely due to ferromagnetic superexchange interactions among Ni2+–Ni3+ ions. Together, these results indicate that long-range magnetic ordering and metallicity in LNO(111) films emerges from a balance among the spin, charge, lattice, and orbital degrees of freedom.

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