# Publications

## Role of the pair potential for the saturation of generalized Pauli constraints

(2017)

The dependence of the (quasi-)saturation of the generalized Pauli constraints on the pair potential is studied for ground states of few-fermion systems. For this, we consider spinless fermions in one dimension which are harmonically confined and interact by pair potentials of the form |xi−xj|^s with −1≤s≤5. Using the Density Matrix Renormalization Group-approach and large orbital basis sets ensures the convergence on more than ten digits of both the variational energy and the natural occupation numbers. Our results confirm that the conflict between energy minimization and fermionic exchange symmetry results in a quasi-saturation of the generalized Pauli constraints (quasipinning), implying structural simplifications of the fermionic ground state. However, a self-consistent perturbation theory reveals that most of that relevance has to be assigned to Pauli's original exclusion principle, except for the harmonic case, i.e., s=2. This emphasizes the unique nature of the strong, non-trivial quasipinning found recently for the Harmonium model.

## Exact matrix product decay modes of a boundary driven cellular automaton

Journal of Physics A: Mathematical and Theoretical **50** (2017)

© 2017 IOP Publishing Ltd. We study integrability properties of a reversible deterministic cellular automaton (Rule 54 of (Bobenko et al 1993 Commun. Math. Phys. 158 127)) and present a bulk algebraic relation and its inhomogeneous extension which allow for an explicit construction of Liouvillian decay modes for two distinct families of stochastic boundary driving. The spectrum of the many-body stochastic matrix defining the time propagation is found to separate into sets, which we call orbitals, and the eigenvalues in each orbital are found to obey a distinct set of Bethe-like equations. We construct the decay modes in the first orbital (containing the leading decay mode) in terms of an exact inhomogeneous matrix product ansatz, study the thermodynamic properties of the spectrum and the scaling of its gap, and provide a conjecture for the Bethe-like equations for all the orbitals and their degeneracy.

## Charge and spin current statistics of the open Hubbard model with weak coupling to the environment.

Physical review. E **95** (2017) 052141-

Based on generalization and extension of our previous work [Phys. Rev. Lett. 112, 067201 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.067201] to multiple independent Markovian baths we will compute the charge and spin current statistics of the open Hubbard model with weak system-bath coupling up to next-to-leading order in the coupling parameter. Only the next-to-leading and higher orders depend on the Hubbard interaction parameter. The physical results are related to those for the XXZ model in the analogous setup implying a certain universality, which potentially holds in this class of nonequilibrium models.

## Species-selective confinement of atoms dressed with multiple radiofrequencies

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS **50** (2017) ARTN 094002

## Universal upper bounds on the Bose-Einstein condensate and the Hubbard star

PHYSICAL REVIEW B **96** (2017) ARTN 064502

## Reconstructing quantum states from single-party information

Physical Review A: Atomic, Molecular and Optical Physics American Physical Society **96** (2017)

The possible compatibility of density matrices for single-party subsystems is described by linear constraints on their respective spectra. Whenever some of those quantum marginal constraints are saturated, the total quantum state has a specific, simplified structure. We prove that these remarkable global implications of extremal local information are stable; i.e., they hold approximately for spectra close to the boundary of the allowed region. Application of this general result to fermionic quantum systems allows us to characterize natural extensions of the Hartree-Fock ansatz and to quantify their accuracy by resorting to one-particle information, only: The fraction of the correlation energy not recovered by such an ansatz can be estimated from above by a simple geometric quantity in the occupation number picture.

## Topological spin models in Rydberg lattices

APPLIED PHYSICS B-LASERS AND OPTICS **123** (2017) ARTN 46

## Influence of the fermionic exchange symmetry beyond Pauli's exclusion principle

PHYSICAL REVIEW A **95** (2017) ARTN 022336

## Relating correlation measures: The importance of the energy gap

(2017)

## Relating correlation measures: The importance of the energy gap

Physical Review A American Physical Society **95** (2017) 032507

The concept of correlation is central to all approaches that attempt the description of many-body effects in electronic systems. Multipartite correlation is a quantum information theoretical property that is attributed to quantum states independent of the underlying physics. In quantum chemistry, however, the correlation energy (the energy not seized by the Hartree-Fock ansatz) plays a more prominent role. We show that these two different viewpoints on electron correlation are closely related. The key ingredient turns out to be the energy gap within the symmetry-adapted subspace. We then use a few-site Hubbard model and the stretched H2 to illustrate this connection and to show how the corresponding measures of correlation compare.

## Enhancement of superexchange pairing in the periodically driven Hubbard model

PHYSICAL REVIEW B **96** (2017) ARTN 085104

## Terahertz field control of interlayer transport modes in cuprate superconductors

PHYSICAL REVIEW B **96** (2017) ARTN 064526

## Connected correlations, fluctuations and current of magnetization in the steady state of boundary driven XXZ spin chains

Journal of Statistical Mechanics: Theory and Experiment **2016** (2016)

© 2016 IOP Publishing Ltd and SISSA Medialab srl. We show how to exploit algebraic relations among the operators (or matrices) which constitute the non-equilibrium matrix product steady state of a boundary driven quantum spin chain to find partial differential equations determining all the m-point correlation functions in the continuum (or thermodynamic) limit. These partial differential equations, the order of which is determined by scaling of the non-equilibrium partition function, are readily solved if we also know the boundary conditions. In this way we can avoid resorting to representation theory of the matrix product algebra. We apply our methods to study the distributions, or moments, of the magnetization and the spin current observables in boundary driven open XXZ spin chains, as well as some connected correlation functions. Interestingly, we find that the transverse connected correlation functions are thermodynamically non-decaying and long range at the isotropic point Δ = 1.

## Two-way interconversion of millimeter-wave and optical fields in Rydberg gases

NEW JOURNAL OF PHYSICS **18** (2016) ARTN 093030

## Pinning of fermionic occupation numbers: General concepts and one spatial dimension

PHYSICAL REVIEW A **93** (2016) ARTN 042126

## Number-parity effect for confined fermions in one dimension

PHYSICAL REVIEW A **93** (2016) ARTN 021601

## Systematic construction of density functionals based on matrix product state computations

NEW JOURNAL OF PHYSICS **18** (2016) ARTN 083039

## Quantum mechanical calculation of Rydberg-Rydberg autoionization rates

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS **49** (2016) ARTN 204004

## Natural Extension of Hartree-Fock Through Extremal 1-Fermion Information: Overview and Application to the Lithium Atom

ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS **230** (2016) 703-717

## Two-way interconversion of millimeter-wave and optical fields in Rydberg gases (vol 18, 093030, 2016)

NEW JOURNAL OF PHYSICS **18** (2016) ARTN 109502