Microscopic Interaction Potentials Research Articles

Error budgeting for a controlled-phase gate with strontium-88 Rydberg atoms

We study the implementation of a high fidelity controlled-phase gate in a Rydberg quantum computer. The protocol is based on a symmetric gate with respect to the two qubits as experimentally realized by Levine et al [Phys. Rev. Lett. 123, 170503 (2019)], but allows for arbitrary pulse shapes with time-dependent detuning. Optimizing the pulse shapes, we introduce laser pulses which shorten the time spent in the Rydberg state by 10% and reduce the leading contribution to the gate infidelity, i.e., the decay from the Rydberg state. Remarkably, this reduction can be achieved for smooth pulses in detuning and smooth turning on of the Rabi frequency as required in any experimental realization. We carefully analyze the influence of fundamental error sources such as the photon recoil, the microscopic interaction potential, as well as the harmonic trapping of the atoms for an experimentally realistic setup based on strontium-88 atoms. We find that an average gate fidelity above 99.9% is possible for a very conservative estimation of experimental parameters.

Influence of the tensor force on the microscopic heavy-ion interaction potential

Background: The tensor interaction is known to play an important role in the nuclear structure studies of exotic nuclei. However, most microscopic studies of low-energy nuclear reactions neglect the tensor force, resulting in a lack of knowledge concerning the effect of the tensor force on HIC...... Purpose: The theoretical study of the influence of the tensor force on heavy-ion interaction potentials is required to further our understanding of the microscopic mechanisms entailed in fusion dynamics. Method: The full Skyrme tensor force is implemented into the static Hartree-Fock and dynamic density-constrained time-dependent Hartree-Fock (DC-TDHF) theory to calculate both static (frozen density) and dynamic microscopic interaction potentials for reactions involving exotic and stable nuclei. Results: The static potentials are found to be systematically higher than the dynamical results, which are attributed to the microscopic dynamical effects included in TDHF. We also show that the dynamical potential barriers vary more significantly by the inclusion of tensor force than the static barriers. The influence of isoscalar and isovector tensor terms is also investigated with the TIJ set of forces. For light systems, the tensor force is found to have an imperceptible effect on the nucleus-nucleus potential. However, for medium and heavy spin-unsaturated reactions, the potentials may change from a fraction of an MeV to almost 2 MeV by the inclusion of tensor force, indicating a strong impact of the tensor force on sub-barrier fusion. Conclusions: The tensor force could indeed play a large role in the fusion of nuclei, with spin-unsaturated systems seeing a systematic increase in ion-ion barrier height and width. This fusion hindrance is partly due to static, ground state effects from the inclusion of the tensor force, though additional hindrance appears when studying nuclear dynamics.

Sequence correlations shape protein promiscuity

We predict analytically that diagonal correlations of amino acid positions within protein sequences statistically enhance protein propensity for nonspecific binding. We use the term "promiscuity" to describe such nonspecific binding. Diagonal correlations represent statistically significant repeats of sequence patterns where amino acids of the same type are clustered together. The predicted effect is qualitatively robust with respect to the form of the microscopic interaction potentials and the average amino acid composition. Our analytical results provide an explanation for the enhanced diagonal correlations observed in hubs of eukaryotic organismal proteomes [J. Mol. Biol. 409, 439 (2011)]. We suggest experiments that will allow direct testing of the predicted effect.

Cytoskeletal Polymer Networks: Viscoelastic Properties are Determined by the Microscopic Interaction Potential of Cross-links

Although the structure of cross-linking molecules mainly determines the structural organization of actin filaments and with that the static elastic properties of the cytoskeleton, it is largely unknown how the biochemical characteristics of transiently cross-linking proteins (actin-binding proteins (ABPs)) affect the viscoelasticity of actin networks. In this study, we show that the macroscopic network response of reconstituted actin networks can be traced back to the microscopic interaction potential of an individual actin/ABP bond. The viscoelastic response of cross-linked actin networks is set by the cross-linker off-rate, the binding energy, and the characteristic bond length of individual actin/ABP interactions.

Topology and phase transitions II. Theorem on a necessary relation

In this second paper, we prove a necessity theorem about the topological origin of phase transitions. We consider physical systems described by smooth microscopic interaction potentials V N ( q ) , among N degrees of freedom, and the associated family of configuration space submanifolds { M v } v ∈ R , with M v = { q ∈ R N | V N ( q ) ⩽ v } . On the basis of an analytic relationship between a suitably weighed sum of the Morse indexes of the manifolds { M v } v ∈ R and thermodynamic entropy, the theorem states that any possible unbound growth with N of one of the following derivatives of the configurational entropy S ( − ) ( v ) = ( 1 / N ) log ∫ M v d N q , that is of | ∂ k S ( − ) ( v ) / ∂ v k | , for k = 3 , 4 , can be entailed only by the weighed sum of Morse indexes. Since the unbound growth with N of one of these derivatives corresponds to the occurrence of a first- or of a second-order phase transition, and since the variation of the Morse indexes of a manifold is in one-to-one correspondence with a change of its topology, the Main Theorem of the present paper states that a phase transition necessarily stems from a topological transition in configuration space. The proof of the theorem given in the present paper cannot be done without Main Theorem of paper I.

Dynamical deformation effects in subbarrier fusion ofNi64+Sn132

We show that dynamical deformation effects play an important role in fusion reactions involving the $^{64}\mathrm{Ni}$ nucleus, in particular the $^{64}\mathrm{Ni}+^{132}\mathrm{Sn}$ system. We calculate fully microscopic interaction potentials and the corresponding subbarrier fusion cross-sections.

A Bridge between the Microscopic Interaction Potentials in a Fluid and Effective Long-wavelength Hamiltonians

The asymptotic and preasymptotic critical behavior of the three-dimensional Ising universality class, which includes easy axis magnets and fluids, is believed to be described by effective ψ 4 scalar field theory with suitable, non-universal, coupling constants. Universal properties do not depend on the specific values of these coupling constants but this is not so for the non-universal properties. Here we show that the coupling constants dependence on microscopic potentials can be studied using the Hierarchical Reference Theory (HRT), which implements the basic ideas of Wilson momentum renormalization group to microscopic Hamiltonians. We discuss the application of this method to two different microscopic models of intermolecular potential of a simple fluid and to the Ising model. Also the wetting phase transition in a fluid near a wall is described by an effective Hamiltonian. This Hamiltonian contains an effective interfacial potential, which describes the effective interaction of interface with the wall. Here we show how to extend the HRT formalism to inhomogeneous system and how, in such theory, we can extract the interfacial quantities and study their behavior.

Properties of microscopic nucleus-nucleus interaction for molecular resonance formation in12C+12Cand3α+3αsystems

Properties of microscopic interaction potentials between two ${}^{12}\mathrm{C}$ nuclei are discussed in connection with the formation of ${}^{12}{\mathrm{C}+}^{12}\mathrm{C}$ and $3\ensuremath{\alpha}+3\ensuremath{\alpha}$ molecular resonances. The nucleus-nucleus interactions are calculated by the double-folding procedure based on a realistic nucleon-nucleon interaction (DDM3Y) and microscopic ${}^{12}\mathrm{C}$ transition densities calculated from 3\ensuremath{\alpha}-RGM wave functions. The interaction potential can be written as the sum of the monopole part obtained from the monopole density and the multiple parts generated from the quadrupole component of the density. We discuss the role of the monopole and multipole parts of the potential separately. It is shown that the multipole part is very strong in the channels with $3\ensuremath{\alpha}+3\ensuremath{\alpha}$ structure and the energy positions of the $3\ensuremath{\alpha}+3\ensuremath{\alpha}$ molecular bands generated by the monopole potential are largely modified. The effect is moderate but non-negligible on the molecular bands with the ${}^{12}{\mathrm{C}+}^{12}\mathrm{C}$ dinuclearlike structure and largely modifies the band crossing diagram between the elastic and aligned-inelastic molecular bands. The channel coupling effect among the ${}^{12}{\mathrm{C}+}^{12}\mathrm{C}$ channels, namely, the elastic channel and the single- and mutual-${2}_{1}^{+}$ excitation channels is also investigated. Due to the strong coupling between the ground and ${2}_{1}^{+}$ states of ${}^{12}\mathrm{C},$ the resonance wave functions obtained by the coupled-channel calculation have an additional radial node compared with those of the single-channel resonances. All the results are discussed in connection with the band crossing model which was believed to be successful in describing the ${}^{12}{\mathrm{C}+}^{12}\mathrm{C}$ molecular resonances.

Wetting of curved surfaces

As a first step towards a microscopic understanding of the effective interaction between colloidal particles suspended in a solvent, we study the wetting behavior of one-component fluids at spheres and fibers. We describe these phenomena within density functional theory which keeps track of the microscopic interaction potentials governing these systems. In particular, we properly take into account the power-law decay of both the fluid–fluid interaction potentials and the substrate potentials. The thicknesses of the wetting films as a function of temperature and chemical potential as well as the wetting phase diagrams are determined by minimizing an effective interface potential which we obtain by applying a sharp-kink approximation to the density functional. We compare our results with previous approaches to this problem.

Precise experimental determination of the structure of noble gases: two- and many-body contributions

It is shown that, from recent measurements, the static structure factor S(k) in noble gas fluids can be determined with the precision of a few parts per thousand. Examples for argon at low density and krypton at high density are discussed and comparison with theoretical calculations are reported. The low-density case is analysed and compared with theory in terms of virial expansions, while at high density a refined modified hypernetted chain (MHNC) theory, which includes the three-body interaction, is used for the calculations. From the comparison the authors can conclude that precise information on the detail of the structure of the fluid and its connection with the microscopic interaction potential can be derived.

Inversion of Structural Data for Effective Potentials in Dense Liquids and Colloids

Abstract We address the inverse problem of obtaining microscopic interaction potentials from macroscopic structure, here in the context of liquid-like systems. The proposed method uses a perturbation-theoretic formalism and requires no a priori knowledge of the form of the potential. Very stable and rapidly converging potentials are obtained for widely different classes of fluids, and the results demonstrate the feasibility of inversion. The methodology can be extended to related problems in condensed matter physics and will aid in the analyses of structural data.

Crystallinity in liquid films.

If a solid is covered with a quasi-liquid-film, each Fourier coefficient of the solid density vanishes with a characteristic decay length within the liquid film. A microscopic theory is employed in order to calculate these decay lengths and to study their dependence on the orientation of the surface plane and on the microscopic interaction potential. The results are compared with recent surface experiments on Pb.

Mobility of intermediate sized aqueous ions in a neutral gas

A mobility versus size relationship is calculated for aqueous ions of intermediate size in an argon gas. The method is based on the Chapman-Enskog transport theory. It involves the microscopic interaction potential between the aqueous ion and the neutral gas molecules. A model potential is used that accounts for the water molecules in the cluster-ion as well as its finite size. The results agree with the Langevin small ion theory at the small end of the size spectrum, give a lower mobility for intermediate sized ions, and then agree with the Stokes viscosity theory at the large end of the size spectrum. An explicit function containing adjustable parameters is fitted to the numerical results in the intermediate size region. The results are applied to data from a Wilson cloud chamber ion mobility experiment.