The Experts below are selected from a list of 110838 Experts worldwide ranked by ideXlab platform
Sebastian Wüster - One of the best experts on this subject based on the ideXlab platform.
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van der Waals-stabilized Rydberg aggregates
Physical Review A, 2014Co-Authors: Hashem Zoubi, Alexander Eisfeld, Sebastian WüsterAbstract:Assemblies of Rydberg atoms subject to resonant dipole-dipole interactions form Frenkel excitons. We show that van-der-Waals shifts can significantly modify the exciton wave function, whenever atoms approach each other closely. As a result, attractive excitons and repulsive van-der-Waals interactions can be combined to form stable one-dimensional atom chains, akin to bound aggregates. Here the van-der-Waals shifts ensure a stronger homogeneous delocalisation of a Single Excitation over the whole chain, enabling it to bind up to six atoms. When brought into unstable configurations, such Rydberg aggregates allow the direct monitoring of their dissociation dynamics.
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Breakup of Rydberg-blockaded atom clouds via dipole-dipole interactions
Physical Review A, 2013Co-Authors: S. Möbius, Sebastian Wüster, Alexander Eisfeld, M. Genkin, Jan M. RostAbstract:We investigate resonant dipole-dipole interactions between two "superatoms" of different angular momentum, consisting of two Rydberg-blockaded atom clouds where each of them carries initially a coherently shared Single Excitation. We demonstrate that the dipole-dipole interaction breaks up the superatoms by removing the Excitations from the clouds. The dynamics is akin to an ensemble average over systems where only one atom per cloud participates in entangled motion and Excitation transfer. Our findings should thus facilitate the experimental realization of adiabatic exciton transport in Rydberg systems by replacing Single sites with atom clouds.
Martin Headgordon - One of the best experts on this subject based on the ideXlab platform.
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beyond the coulson fischer point characterizing Single Excitation ci and tddft for excited states in Single bond dissociations
arXiv: Chemical Physics, 2019Co-Authors: Diptarka Hait, Adam Rettig, Martin HeadgordonAbstract:Linear response time dependent density functional theory (TDDFT), which builds upon configuration interaction Singles (CIS) and TD-Hartree-Fock (TDHF), is the most widely used class of excited state quantum chemistry methods and is often employed to study photochemical processes. This paper studies the behavior of the resulting excited state potential energy surfaces beyond the Coulson-Fisher (CF) point in Single bond dissociations, when the optimal reference determinant is spin-polarized. Many excited states exhibit sharp kinks at the CF point, and connect to different dissociation limits via a zone of unphysical concave curvature. In particular, the unrestricted M$_S=0$ lowest triplet T$_1$ state changes character, and does not dissociate into ground state fragments. The unrestricted $M_S=\pm 1$ T$_1$ CIS states better approximate the physical dissociation limit, but their degeneracy is broken beyond the CF point for most Single bond dissociations. On the other hand, the $M_S=\pm 1$ T$_1$ TDHF states reach the asymptote too soon, by merging with the ground state from the CF point onwards. Use of local exchange-correlation functionals causes $M_S=\pm 1$ T$_1$ TDDFT states to resemble their unphysical $M_S= 0$ counterpart. The 2 orbital, 2-electron model system of minimal basis H$_2$ is analytically treated to understand the origin of these issues, revealing that the lack of double Excitations is at the root of these remarkable observations. The behavior of excited state surfaces is also numerically examined for species like H$_2$, NH$_3$, C$_2$H$_6$ and LiH in extended basis sets.
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generalized unitary coupled cluster wave functions for quantum computation
Journal of Chemical Theory and Computation, 2019Co-Authors: Martin Headgordon, William Huggins, Birgitta K WhaleyAbstract:We introduce a unitary coupled-cluster (UCC) ansatz termed k-UpCCGSD that is based on a family of sparse generalized doubles operators, which provides an affordable and systematically improvable unitary coupled-cluster wave function suitable for implementation on a near-term quantum computer. k-UpCCGSD employs k products of the exponential of pair coupled-cluster double Excitation operators (pCCD), together with generalized Single Excitation operators. We compare its performance in both efficiency of implementation and accuracy with that of the generalized UCC ansatz employing the full generalized Single and double Excitation operators (UCCGSD), as well as with the standard ansatz employing only Single and double Excitations (UCCSD). k-UpCCGSD is found to show the best scaling for quantum computing applications, requiring a circuit depth of O(kN), compared with O(N3) for UCCGSD, and O((N−η)2η) for UCCSD, where N is the number of spin orbitals and η is the number of electrons. We analyzed the accuracy of t...
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time dependent density functional theory for radicals an improved description of excited states with substantial double Excitation character
Chemical Physics Letters, 1999Co-Authors: So Hirata, Martin HeadgordonAbstract:Abstract Spin-unrestricted time-dependent density functional theory (TDDFT) is applied to calculate vertical Excitation energies for the first several excited states of four diatomic radicals and methyl, nitromethyl, benzyl, anilino, and phenoxyl radicals. While the Excitation energies of Rydberg states computed by TDDFT are significantly inferior to the results of Hartree–Fock-based Single Excitation theories, TDDFT performs slightly better than the HF-based theories for valence states with dominant Single Excitation character. For valence states with substantial double Excitation character, TDDFT is a striking improvement over the HF-based theories, the latter being qualitatively incorrect descriptions for these states.
Hashem Zoubi - One of the best experts on this subject based on the ideXlab platform.
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van der Waals-stabilized Rydberg aggregates
Physical Review A, 2014Co-Authors: Hashem Zoubi, Alexander Eisfeld, Sebastian WüsterAbstract:Assemblies of Rydberg atoms subject to resonant dipole-dipole interactions form Frenkel excitons. We show that van-der-Waals shifts can significantly modify the exciton wave function, whenever atoms approach each other closely. As a result, attractive excitons and repulsive van-der-Waals interactions can be combined to form stable one-dimensional atom chains, akin to bound aggregates. Here the van-der-Waals shifts ensure a stronger homogeneous delocalisation of a Single Excitation over the whole chain, enabling it to bind up to six atoms. When brought into unstable configurations, such Rydberg aggregates allow the direct monitoring of their dissociation dynamics.
Alexander Eisfeld - One of the best experts on this subject based on the ideXlab platform.
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van der Waals-stabilized Rydberg aggregates
Physical Review A, 2014Co-Authors: Hashem Zoubi, Alexander Eisfeld, Sebastian WüsterAbstract:Assemblies of Rydberg atoms subject to resonant dipole-dipole interactions form Frenkel excitons. We show that van-der-Waals shifts can significantly modify the exciton wave function, whenever atoms approach each other closely. As a result, attractive excitons and repulsive van-der-Waals interactions can be combined to form stable one-dimensional atom chains, akin to bound aggregates. Here the van-der-Waals shifts ensure a stronger homogeneous delocalisation of a Single Excitation over the whole chain, enabling it to bind up to six atoms. When brought into unstable configurations, such Rydberg aggregates allow the direct monitoring of their dissociation dynamics.
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Breakup of Rydberg-blockaded atom clouds via dipole-dipole interactions
Physical Review A, 2013Co-Authors: S. Möbius, Sebastian Wüster, Alexander Eisfeld, M. Genkin, Jan M. RostAbstract:We investigate resonant dipole-dipole interactions between two "superatoms" of different angular momentum, consisting of two Rydberg-blockaded atom clouds where each of them carries initially a coherently shared Single Excitation. We demonstrate that the dipole-dipole interaction breaks up the superatoms by removing the Excitations from the clouds. The dynamics is akin to an ensemble average over systems where only one atom per cloud participates in entangled motion and Excitation transfer. Our findings should thus facilitate the experimental realization of adiabatic exciton transport in Rydberg systems by replacing Single sites with atom clouds.
Antoine Browaeys - One of the best experts on this subject based on the ideXlab platform.
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Demonstration of strong Rydberg blockade in three-atom systems with anisotropic interactions
Physical Review Letters, 2014Co-Authors: Daniel Barredo, Sylvain Ravets, Henning Labuhn, Lucas Béguin, Aline Vernier, Florence Nogrette, Thierry Lahaye, Antoine BrowaeysAbstract:We study the Rydberg blockade in a system of three atoms arranged in different 2D geometries (linear and triangular configurations). In the strong blockade regime, we observe high-contrast, coherent collective oscillations of the Single Excitation probability, and an almost perfect van der Waals blockade. Our data is consistent with a total population in doubly and triply excited states below 2%. In the partial blockade regime, we directly observe the anisotropy of the van der Waals interactions between $|nD\rangle$ Rydberg states in the triangular configuration. A simple model, that only uses independently measured two-body van der Waals interactions, fully reproduces the dynamics of the system without any adjustable parameter. These results are extremely promising for scalable quantum information processing and quantum simulation with neutral atoms.
