@phdthesis{7514,
abstract = {We study the interacting homogeneous Bose gas in two spatial dimensions in the thermodynamic limit at fixed density. We shall be concerned with some mathematical aspects of this complicated problem in many-body quantum mechanics. More specifically, we consider the dilute limit where the scattering length of the interaction potential, which is a measure for the effective range of the potential, is small compared to the average distance between the particles. We are interested in a setting with positive (i.e., non-zero) temperature. After giving a survey of the relevant literature in the field, we provide some facts and examples to set expectations for the two-dimensional system. The crucial difference to the three-dimensional system is that there is no Bose–Einstein condensate at positive temperature due to the Hohenberg–Mermin–Wagner theorem. However, it turns out that an asymptotic formula for the free energy holds similarly to the three-dimensional case.
We motivate this formula by considering a toy model with δ interaction potential. By restricting this model Hamiltonian to certain trial states with a quasi-condensate we obtain an upper bound for the free energy that still has the quasi-condensate fraction as a free parameter. When minimizing over the quasi-condensate fraction, we obtain the Berezinskii–Kosterlitz–Thouless critical temperature for superfluidity, which plays an important role in our rigorous contribution. The mathematically rigorous result that we prove concerns the specific free energy in the dilute limit. We give upper and lower bounds on the free energy in terms of the free energy of the non-interacting system and a correction term coming from the interaction. Both bounds match and thus we obtain the leading term of an asymptotic approximation in the dilute limit, provided the thermal wavelength of the particles is of the same order (or larger) than the average distance between the particles. The remarkable feature of this result is its generality: the correction term depends on the interaction potential only through its scattering length and it holds for all nonnegative interaction potentials with finite scattering length that are measurable. In particular, this allows to model an interaction of hard disks.},
author = {Mayer, Simon},
issn = {2663-337X},
pages = {148},
publisher = {IST Austria},
title = {{The free energy of a dilute two-dimensional Bose gas}},
doi = {10.15479/AT:ISTA:7514},
year = {2020},
}
@article{7508,
abstract = {In this paper, we introduce a novel method for deriving higher order corrections to the mean-field description of the dynamics of interacting bosons. More precisely, we consider the dynamics of N d-dimensional bosons for large N. The bosons initially form a Bose–Einstein condensate and interact with each other via a pair potential of the form (N−1)−1Ndβv(Nβ·)forβ∈[0,14d). We derive a sequence of N-body functions which approximate the true many-body dynamics in L2(RdN)-norm to arbitrary precision in powers of N−1. The approximating functions are constructed as Duhamel expansions of finite order in terms of the first quantised analogue of a Bogoliubov time evolution.},
author = {Bossmann, Lea and Pavlović, Nataša and Pickl, Peter and Soffer, Avy},
issn = {1572-9613},
journal = {Journal of Statistical Physics},
publisher = {Springer Nature},
title = {{Higher order corrections to the mean-field description of the dynamics of interacting bosons}},
doi = {10.1007/s10955-020-02500-8},
year = {2020},
}
@article{7611,
abstract = {We consider a system of N bosons in the limit N→∞, interacting through singular potentials. For initial data exhibiting Bose–Einstein condensation, the many-body time evolution is well approximated through a quadratic fluctuation dynamics around a cubic nonlinear Schrödinger equation of the condensate wave function. We show that these fluctuations satisfy a (multi-variate) central limit theorem.},
author = {Rademacher, Simone Anna Elvira},
issn = {0377-9017},
journal = {Letters in Mathematical Physics},
publisher = {Springer Nature},
title = {{Central limit theorem for Bose gases interacting through singular potentials}},
doi = {10.1007/s11005-020-01286-w},
year = {2020},
}
@article{80,
abstract = {We consider an interacting, dilute Bose gas trapped in a harmonic potential at a positive temperature. The system is analyzed in a combination of a thermodynamic and a Gross–Pitaevskii (GP) limit where the trap frequency ω, the temperature T, and the particle number N are related by N∼ (T/ ω) 3→ ∞ while the scattering length is so small that the interaction energy per particle around the center of the trap is of the same order of magnitude as the spectral gap in the trap. We prove that the difference between the canonical free energy of the interacting gas and the one of the noninteracting system can be obtained by minimizing the GP energy functional. We also prove Bose–Einstein condensation in the following sense: The one-particle density matrix of any approximate minimizer of the canonical free energy functional is to leading order given by that of the noninteracting gas but with the free condensate wavefunction replaced by the GP minimizer.},
author = {Deuchert, Andreas and Seiringer, Robert and Yngvason, Jakob},
journal = {Communications in Mathematical Physics},
number = {2},
pages = {723--776},
publisher = {Springer},
title = {{Bose–Einstein condensation in a dilute, trapped gas at positive temperature}},
doi = {10.1007/s00220-018-3239-0},
volume = {368},
year = {2019},
}
@article{6840,
abstract = {We discuss thermodynamic properties of harmonically trapped
imperfect quantum gases. The spatial inhomogeneity of these systems imposes
a redefinition of the mean-field interparticle potential energy as compared
to the homogeneous case. In our approach, it takes the form a
2N2 ωd, where
N is the number of particles, ω—the harmonic trap frequency, d—system’s
dimensionality, and a is a parameter characterizing the interparticle interaction.
We provide arguments that this model corresponds to the limiting case of
a long-ranged interparticle potential of vanishingly small amplitude. This
conclusion is drawn from a computation similar to the well-known Kac scaling
procedure, which is presented here in a form adapted to the case of an isotropic
harmonic trap. We show that within the model, the imperfect gas of trapped
repulsive bosons undergoes the Bose–Einstein condensation provided d > 1.
The main result of our analysis is that in d = 1 the gas of attractive imperfect
fermions with a = −aF < 0 is thermodynamically equivalent to the gas of
repulsive bosons with a = aB > 0 provided the parameters aF and aB fulfill
the relation aB + aF = . This result supplements similar recent conclusion
about thermodynamic equivalence of two-dimensional (2D) uniform imperfect
repulsive Bose and attractive Fermi gases.},
author = {Mysliwy, Krzysztof and Napiórkowski, Marek},
issn = {1742-5468},
journal = {Journal of Statistical Mechanics: Theory and Experiment},
number = {6},
publisher = {IOP Publishing},
title = {{Thermodynamics of inhomogeneous imperfect quantum gases in harmonic traps}},
doi = {10.1088/1742-5468/ab190d},
volume = {2019},
year = {2019},
}
@article{7235,
abstract = {We consider the Fröhlich model of a polaron, and show that its effective mass diverges in thestrong coupling limit.},
author = {Lieb, Elliott H. and Seiringer, Robert},
issn = {0022-4715},
journal = {Journal of Statistical Physics},
publisher = {Springer},
title = {{Divergence of the effective mass of a polaron in the strong coupling limit}},
doi = {10.1007/s10955-019-02322-3},
year = {2019},
}
@article{7413,
abstract = {We consider Bose gases consisting of N particles trapped in a box with volume one and interacting through a repulsive potential with scattering length of order N−1 (Gross–Pitaevskii regime). We determine the ground state energy and the low-energy excitation spectrum, up to errors vanishing as N→∞. Our results confirm Bogoliubov’s predictions.},
author = {Boccato, Chiara and Brennecke, Christian and Cenatiempo, Serena and Schlein, Benjamin},
issn = {0001-5962},
journal = {Acta Mathematica},
number = {2},
pages = {219--335},
publisher = {International Press of Boston},
title = {{Bogoliubov theory in the Gross–Pitaevskii limit}},
doi = {10.4310/acta.2019.v222.n2.a1},
volume = {222},
year = {2019},
}
@article{6649,
abstract = {While Hartree–Fock theory is well established as a fundamental approximation for interacting fermions, it has been unclear how to describe corrections to it due to many-body correlations. In this paper we start from the Hartree–Fock state given by plane waves and introduce collective particle–hole pair excitations. These pairs can be approximately described by a bosonic quadratic Hamiltonian. We use Bogoliubov theory to construct a trial state yielding a rigorous Gell-Mann–Brueckner–type upper bound to the ground state energy. Our result justifies the random-phase approximation in the mean-field scaling regime, for repulsive, regular interaction potentials.
},
author = {Benedikter, Niels P and Nam, Phan Thành and Porta, Marcello and Schlein, Benjamin and Seiringer, Robert},
issn = {1432-0916},
journal = {Communications in Mathematical Physics},
publisher = {Springer},
title = {{Optimal upper bound for the correlation energy of a Fermi gas in the mean-field regime}},
doi = {10.1007/s00220-019-03505-5},
year = {2019},
}
@article{6788,
abstract = {We consider the Nelson model with ultraviolet cutoff, which describes the interaction between non-relativistic particles and a positive or zero mass quantized scalar field. We take the non-relativistic particles to obey Fermi statistics and discuss the time evolution in a mean-field limit of many fermions. In this case, the limit is known to be also a semiclassical limit. We prove convergence in terms of reduced density matrices of the many-body state to a tensor product of a Slater determinant with semiclassical structure and a coherent state, which evolve according to a fermionic version of the Schrödinger–Klein–Gordon equations.},
author = {Leopold, Nikolai K and Petrat, Sören P},
issn = {1424-0661},
journal = {Annales Henri Poincare},
number = {10},
pages = {3471–3508},
publisher = {Springer Nature},
title = {{Mean-field dynamics for the Nelson model with fermions}},
doi = {10.1007/s00023-019-00828-w},
volume = {20},
year = {2019},
}
@article{7015,
abstract = {We modify the "floating crystal" trial state for the classical homogeneous electron gas (also known as jellium), in order to suppress the boundary charge fluctuations that are known to lead to a macroscopic increase of the energy. The argument is to melt a thin layer of the crystal close to the boundary and consequently replace it by an incompressible fluid. With the aid of this trial state we show that three different definitions of the ground-state energy of jellium coincide. In the first point of view the electrons are placed in a neutralizing uniform background. In the second definition there is no background but the electrons are submitted to the constraint that their density is constant, as is appropriate in density functional theory. Finally, in the third system each electron interacts with a periodic image of itself; that is, periodic boundary conditions are imposed on the interaction potential.},
author = {Lewin, Mathieu and Lieb, Elliott H. and Seiringer, Robert},
issn = {2469-9950},
journal = {Physical Review B},
number = {3},
publisher = {APS},
title = {{Floating Wigner crystal with no boundary charge fluctuations}},
doi = {10.1103/physrevb.100.035127},
volume = {100},
year = {2019},
}
@article{7100,
abstract = {We present microscopic derivations of the defocusing two-dimensional cubic nonlinear Schrödinger equation and the Gross–Pitaevskii equation starting froman interacting N-particle system of bosons. We consider the interaction potential to be given either by Wβ(x)=N−1+2βW(Nβx), for any β>0, or to be given by VN(x)=e2NV(eNx), for some spherical symmetric, nonnegative and compactly supported W,V∈L∞(R2,R). In both cases we prove the convergence of the reduced density corresponding to the exact time evolution to the projector onto the solution of the corresponding nonlinear Schrödinger equation in trace norm. For the latter potential VN we show that it is crucial to take the microscopic structure of the condensate into account in order to obtain the correct dynamics.},
author = {Jeblick, Maximilian and Leopold, Nikolai K and Pickl, Peter},
issn = {1432-0916},
journal = {Communications in Mathematical Physics},
number = {1},
pages = {1--69},
publisher = {Springer Nature},
title = {{Derivation of the time dependent Gross–Pitaevskii equation in two dimensions}},
doi = {10.1007/s00220-019-03599-x},
volume = {372},
year = {2019},
}
@article{5856,
abstract = {We give a bound on the ground-state energy of a system of N non-interacting fermions in a three-dimensional cubic box interacting with an impurity particle via point interactions. We show that the change in energy compared to the system in the absence of the impurity is bounded in terms of the gas density and the scattering length of the interaction, independently of N. Our bound holds as long as the ratio of the mass of the impurity to the one of the gas particles is larger than a critical value m∗ ∗≈ 0.36 , which is the same regime for which we recently showed stability of the system.},
author = {Moser, Thomas and Seiringer, Robert},
issn = {14240637},
journal = {Annales Henri Poincare},
number = {4},
pages = {1325–1365},
publisher = {Springer},
title = {{Energy contribution of a point-interacting impurity in a Fermi gas}},
doi = {10.1007/s00023-018-00757-0},
volume = {20},
year = {2019},
}
@article{6906,
abstract = {We consider systems of bosons trapped in a box, in the Gross–Pitaevskii regime. We show that low-energy states exhibit complete Bose–Einstein condensation with an optimal bound on the number of orthogonal excitations. This extends recent results obtained in Boccato et al. (Commun Math Phys 359(3):975–1026, 2018), removing the assumption of small interaction potential.},
author = {Boccato, Chiara and Brennecke, Christian and Cenatiempo, Serena and Schlein, Benjamin},
issn = {0010-3616},
journal = {Communications in Mathematical Physics},
publisher = {Springer},
title = {{Optimal rate for Bose-Einstein condensation in the Gross-Pitaevskii regime}},
doi = {10.1007/s00220-019-03555-9},
year = {2019},
}
@article{7226,
author = {Jaksic, Vojkan and Seiringer, Robert},
issn = {00222488},
journal = {Journal of Mathematical Physics},
number = {12},
publisher = {AIP},
title = {{Introduction to the Special Collection: International Congress on Mathematical Physics (ICMP) 2018}},
doi = {10.1063/1.5138135},
volume = {60},
year = {2019},
}
@unpublished{7524,
abstract = {We prove a lower bound for the free energy (per unit volume) of the two-dimensional Bose gas in the thermodynamic limit. We show that the free energy at density $\rho$ and inverse temperature $\beta$ differs from the one of the non-interacting system by the correction term $4 \pi \rho^2 |\ln a^2 \rho|^{-1} (2 - [1 - \beta_{\mathrm{c}}/\beta]_+^2)$. Here $a$ is the scattering length of the interaction potential, $[\cdot]_+ = \max\{ 0, \cdot \}$ and $\beta_{\mathrm{c}}$ is the inverse Berezinskii--Kosterlitz--Thouless critical temperature for superfluidity. The result is valid in the dilute limit
$a^2\rho \ll 1$ and if $\beta \rho \gtrsim 1$.},
author = {Deuchert, Andreas and Mayer, Simon and Seiringer, Robert},
booktitle = {arXiv:1910.03372},
pages = {61},
publisher = {ArXiv},
title = {{The free energy of the two-dimensional dilute Bose gas. I. Lower bound}},
year = {2019},
}
@inproceedings{11,
abstract = {We report on a novel strategy to derive mean-field limits of quantum mechanical systems in which a large number of particles weakly couple to a second-quantized radiation field. The technique combines the method of counting and the coherent state approach to study the growth of the correlations among the particles and in the radiation field. As an instructional example, we derive the Schrödinger–Klein–Gordon system of equations from the Nelson model with ultraviolet cutoff and possibly massless scalar field. In particular, we prove the convergence of the reduced density matrices (of the nonrelativistic particles and the field bosons) associated with the exact time evolution to the projectors onto the solutions of the Schrödinger–Klein–Gordon equations in trace norm. Furthermore, we derive explicit bounds on the rate of convergence of the one-particle reduced density matrix of the nonrelativistic particles in Sobolev norm.},
author = {Leopold, Nikolai K and Pickl, Peter},
location = {Munich, Germany},
pages = {185 -- 214},
publisher = {Springer},
title = {{Mean-field limits of particles in interaction with quantised radiation fields}},
doi = {10.1007/978-3-030-01602-9_9},
volume = {270},
year = {2018},
}
@article{446,
abstract = {We prove that in Thomas–Fermi–Dirac–von Weizsäcker theory, a nucleus of charge Z > 0 can bind at most Z + C electrons, where C is a universal constant. This result is obtained through a comparison with Thomas-Fermi theory which, as a by-product, gives bounds on the screened nuclear potential and the radius of the minimizer. A key ingredient of the proof is a novel technique to control the particles in the exterior region, which also applies to the liquid drop model with a nuclear background potential.},
author = {Frank, Rupert and Phan Thanh, Nam and Van Den Bosch, Hanne},
journal = {Communications on Pure and Applied Mathematics},
number = {3},
pages = {577 -- 614},
publisher = {Wiley-Blackwell},
title = {{The ionization conjecture in Thomas–Fermi–Dirac–von Weizsäcker theory}},
doi = {10.1002/cpa.21717},
volume = {71},
year = {2018},
}
@article{554,
abstract = {We analyse the canonical Bogoliubov free energy functional in three dimensions at low temperatures in the dilute limit. We prove existence of a first-order phase transition and, in the limit (Formula presented.), we determine the critical temperature to be (Formula presented.) to leading order. Here, (Formula presented.) is the critical temperature of the free Bose gas, ρ is the density of the gas and a is the scattering length of the pair-interaction potential V. We also prove asymptotic expansions for the free energy. In particular, we recover the Lee–Huang–Yang formula in the limit (Formula presented.).},
author = {Napiórkowski, Marcin M and Reuvers, Robin and Solovej, Jan},
issn = {00103616},
journal = {Communications in Mathematical Physics},
number = {1},
pages = {347--403},
publisher = {Springer},
title = {{The Bogoliubov free energy functional II: The dilute Limit}},
doi = {10.1007/s00220-017-3064-x},
volume = {360},
year = {2018},
}
@article{295,
abstract = {We prove upper and lower bounds on the ground-state energy of the ideal two-dimensional anyon gas. Our bounds are extensive in the particle number, as for fermions, and linear in the statistics parameter (Formula presented.). The lower bounds extend to Lieb–Thirring inequalities for all anyons except bosons.},
author = {Lundholm, Douglas and Seiringer, Robert},
journal = {Letters in Mathematical Physics},
number = {11},
pages = {2523--2541},
publisher = {Springer},
title = {{Fermionic behavior of ideal anyons}},
doi = {10.1007/s11005-018-1091-y},
volume = {108},
year = {2018},
}
@article{400,
abstract = {We consider the two-dimensional BCS functional with a radial pair interaction. We show that the translational symmetry is not broken in a certain temperature interval below the critical temperature. In the case of vanishing angular momentum, our results carry over to the three-dimensional case.},
author = {Deuchert, Andreas and Geisinge, Alissa and Hainzl, Christian and Loss, Michael},
journal = {Annales Henri Poincare},
number = {5},
pages = {1507 -- 1527},
publisher = {Springer},
title = {{Persistence of translational symmetry in the BCS model with radial pair interaction}},
doi = {10.1007/s00023-018-0665-7},
volume = {19},
year = {2018},
}
@article{455,
abstract = {The derivation of effective evolution equations is central to the study of non-stationary quantum many-body systems, and widely used in contexts such as superconductivity, nuclear physics, Bose–Einstein condensation and quantum chemistry. We reformulate the Dirac–Frenkel approximation principle in terms of reduced density matrices and apply it to fermionic and bosonic many-body systems. We obtain the Bogoliubov–de Gennes and Hartree–Fock–Bogoliubov equations, respectively. While we do not prove quantitative error estimates, our formulation does show that the approximation is optimal within the class of quasifree states. Furthermore, we prove well-posedness of the Bogoliubov–de Gennes equations in energy space and discuss conserved quantities},
author = {Benedikter, Niels P and Sok, Jérémy and Solovej, Jan},
journal = {Annales Henri Poincare},
number = {4},
pages = {1167 -- 1214},
publisher = {Birkhäuser},
title = {{The Dirac–Frenkel principle for reduced density matrices and the Bogoliubov–de Gennes equations}},
doi = {10.1007/s00023-018-0644-z},
volume = {19},
year = {2018},
}
@article{5983,
abstract = {We study a quantum impurity possessing both translational and internal rotational degrees of freedom interacting with a bosonic bath. Such a system corresponds to a “rotating polaron,” which can be used to model, e.g., a rotating molecule immersed in an ultracold Bose gas or superfluid helium. We derive the Hamiltonian of the rotating polaron and study its spectrum in the weak- and strong-coupling regimes using a combination of variational, diagrammatic, and mean-field approaches. We reveal how the coupling between linear and angular momenta affects stable quasiparticle states, and demonstrate that internal rotation leads to an enhanced self-localization in the translational degrees of freedom.},
author = {Yakaboylu, Enderalp and Midya, Bikashkali and Deuchert, Andreas and Leopold, Nikolai K and Lemeshko, Mikhail},
issn = {2469-9950},
journal = {Physical Review B},
number = {22},
publisher = {American Physical Society},
title = {{Theory of the rotating polaron: Spectrum and self-localization}},
doi = {10.1103/physrevb.98.224506},
volume = {98},
year = {2018},
}
@phdthesis{52,
abstract = {In this thesis we will discuss systems of point interacting fermions, their stability and other spectral properties. Whereas for bosons a point interacting system is always unstable this ques- tion is more subtle for a gas of two species of fermions. In particular the answer depends on the mass ratio between these two species. Most of this work will be focused on the N + M model which consists of two species of fermions with N, M particles respectively which interact via point interactions. We will introduce this model using a formal limit and discuss the N + 1 system in more detail. In particular, we will show that for mass ratios above a critical one, which does not depend on the particle number, the N + 1 system is stable. In the context of this model we will prove rigorous versions of Tan relations which relate various quantities of the point-interacting model. By restricting the N + 1 system to a box we define a finite density model with point in- teractions. In the context of this system we will discuss the energy change when introducing a point-interacting impurity into a system of non-interacting fermions. We will see that this change in energy is bounded independently of the particle number and in particular the bound only depends on the density and the scattering length. As another special case of the N + M model we will show stability of the 2 + 2 model for mass ratios in an interval around one. Further we will investigate a different model of point interactions which was discussed before in the literature and which is, contrary to the N + M model, not given by a limiting procedure but is based on a Dirichlet form. We will show that this system behaves trivially in the thermodynamic limit, i.e. the free energy per particle is the same as the one of the non-interacting system.},
author = {Moser, Thomas},
pages = {115},
publisher = {IST Austria},
title = {{Point interactions in systems of fermions}},
doi = {10.15479/AT:ISTA:th_1043},
year = {2018},
}
@article{180,
abstract = {In this paper we define and study the classical Uniform Electron Gas (UEG), a system of infinitely many electrons whose density is constant everywhere in space. The UEG is defined differently from Jellium, which has a positive constant background but no constraint on the density. We prove that the UEG arises in Density Functional Theory in the limit of a slowly varying density, minimizing the indirect Coulomb energy. We also construct the quantum UEG and compare it to the classical UEG at low density.},
author = {Lewi, Mathieu and Lieb, Élliott and Seiringer, Robert},
journal = {Journal de l'Ecole Polytechnique - Mathematiques},
pages = {79 -- 116},
publisher = {Ecole Polytechnique},
title = {{Statistical mechanics of the uniform electron gas}},
doi = {10.5802/jep.64},
volume = {5},
year = {2018},
}
@article{399,
abstract = {Following an earlier calculation in 3D, we calculate the 2D critical temperature of a dilute, translation-invariant Bose gas using a variational formulation of the Bogoliubov approximation introduced by Critchley and Solomon in 1976. This provides the first analytical calculation of the Kosterlitz-Thouless transition temperature that includes the constant in the logarithm.},
author = {Napiórkowski, Marcin M and Reuvers, Robin and Solovej, Jan},
journal = {EPL},
number = {1},
publisher = {IOP Publishing Ltd.},
title = {{Calculation of the critical temperature of a dilute Bose gas in the Bogoliubov approximation}},
doi = {10.1209/0295-5075/121/10007},
volume = {121},
year = {2018},
}
@article{154,
abstract = {We give a lower bound on the ground state energy of a system of two fermions of one species interacting with two fermions of another species via point interactions. We show that there is a critical mass ratio m2 ≈ 0.58 such that the system is stable, i.e., the energy is bounded from below, for m∈[m2,m2−1]. So far it was not known whether this 2 + 2 system exhibits a stable region at all or whether the formation of four-body bound states causes an unbounded spectrum for all mass ratios, similar to the Thomas effect. Our result gives further evidence for the stability of the more general N + M system.},
author = {Moser, Thomas and Seiringer, Robert},
issn = {15729656},
journal = {Mathematical Physics Analysis and Geometry},
number = {3},
publisher = {Springer},
title = {{Stability of the 2+2 fermionic system with point interactions}},
doi = {10.1007/s11040-018-9275-3},
volume = {21},
year = {2018},
}
@article{6002,
abstract = {The Bogoliubov free energy functional is analysed. The functional serves as a model of a translation-invariant Bose gas at positive temperature. We prove the existence of minimizers in the case of repulsive interactions given by a sufficiently regular two-body potential. Furthermore, we prove the existence of a phase transition in this model and provide its phase diagram.},
author = {Napiórkowski, Marcin M and Reuvers, Robin and Solovej, Jan Philip},
issn = {0003-9527},
journal = {Archive for Rational Mechanics and Analysis},
number = {3},
pages = {1037--1090},
publisher = {Springer Nature},
title = {{The Bogoliubov free energy functional I: Existence of minimizers and phase diagram}},
doi = {10.1007/s00205-018-1232-6},
volume = {229},
year = {2018},
}
@article{484,
abstract = {We consider the dynamics of a large quantum system of N identical bosons in 3D interacting via a two-body potential of the form N3β-1w(Nβ(x - y)). For fixed 0 = β < 1/3 and large N, we obtain a norm approximation to the many-body evolution in the Nparticle Hilbert space. The leading order behaviour of the dynamics is determined by Hartree theory while the second order is given by Bogoliubov theory.},
author = {Nam, Phan and Napiórkowski, Marcin M},
issn = {10950761},
journal = {Advances in Theoretical and Mathematical Physics},
number = {3},
pages = {683 -- 738},
publisher = {International Press},
title = {{Bogoliubov correction to the mean-field dynamics of interacting bosons}},
doi = {10.4310/ATMP.2017.v21.n3.a4},
volume = {21},
year = {2017},
}
@article{632,
abstract = {We consider a 2D quantum system of N bosons in a trapping potential |x|s, interacting via a pair potential of the form N2β−1 w(Nβ x). We show that for all 0 < β < (s + 1)/(s + 2), the leading order behavior of ground states of the many-body system is described in the large N limit by the corresponding cubic nonlinear Schrödinger energy functional. Our result covers the focusing case (w < 0) where even the stability of the many-body system is not obvious. This answers an open question mentioned by X. Chen and J. Holmer for harmonic traps (s = 2). Together with the BBGKY hierarchy approach used by these authors, our result implies the convergence of the many-body quantum dynamics to the focusing NLS equation with harmonic trap for all 0 < β < 3/4. },
author = {Lewin, Mathieu and Nam, Phan and Rougerie, Nicolas},
journal = {Proceedings of the American Mathematical Society},
number = {6},
pages = {2441 -- 2454},
publisher = {American Mathematical Society},
title = {{A note on 2D focusing many boson systems}},
doi = {10.1090/proc/13468},
volume = {145},
year = {2017},
}
@article{1198,
abstract = {We consider a model of fermions interacting via point interactions, defined via a certain weighted Dirichlet form. While for two particles the interaction corresponds to infinite scattering length, the presence of further particles effectively decreases the interaction strength. We show that the model becomes trivial in the thermodynamic limit, in the sense that the free energy density at any given particle density and temperature agrees with the corresponding expression for non-interacting particles.},
author = {Moser, Thomas and Seiringer, Robert},
issn = {03779017},
journal = {Letters in Mathematical Physics},
number = {3},
pages = { 533 -- 552},
publisher = {Springer},
title = {{Triviality of a model of particles with point interactions in the thermodynamic limit}},
doi = {10.1007/s11005-016-0915-x},
volume = {107},
year = {2017},
}
@article{997,
abstract = {Recently it was shown that molecules rotating in superfluid helium can be described in terms of the angulon quasiparticles (Phys. Rev. Lett. 118, 095301 (2017)). Here we demonstrate that in the experimentally realized regime the angulon can be seen as a point charge on a 2-sphere interacting with a gauge field of a non-abelian magnetic monopole. Unlike in several other settings, the gauge fields of the angulon problem emerge in the real coordinate space, as opposed to the momentum space or some effective parameter space. Furthermore, we find a topological transition associated with making the monopole abelian, which takes place in the vicinity of the previously reported angulon instabilities. These results pave the way for studying topological phenomena in experiments on molecules trapped in superfluid helium nanodroplets, as well as on other realizations of orbital impurity problems.},
author = {Yakaboylu, Enderalp and Deuchert, Andreas and Lemeshko, Mikhail},
issn = {00319007},
journal = {APS Physics, Physical Review Letters},
number = {23},
publisher = {American Physiological Society},
title = {{Emergence of non-abelian magnetic monopoles in a quantum impurity problem}},
doi = {10.1103/PhysRevLett.119.235301},
volume = {119},
year = {2017},
}
@article{912,
abstract = {We consider a many-body system of fermionic atoms interacting via a local pair potential and subject to an external potential within the framework of Bardeen-Cooper-Schrieffer (BCS) theory. We measure the free energy of the whole sample with respect to the free energy of a reference state which allows us to define a BCS functional with boundary conditions at infinity. Our main result is a lower bound for this energy functional in terms of expressions that typically appear in Ginzburg-Landau functionals.
},
author = {Deuchert, Andreas},
issn = {00222488},
journal = { Journal of Mathematical Physics},
number = {8},
publisher = {AIP},
title = {{A lower bound for the BCS functional with boundary conditions at infinity}},
doi = {10.1063/1.4996580},
volume = {58},
year = {2017},
}
@article{1120,
abstract = {The existence of a self-localization transition in the polaron problem has been under an active debate ever since Landau suggested it 83 years ago. Here we reveal the self-localization transition for the rotational analogue of the polaron -- the angulon quasiparticle. We show that, unlike for the polarons, self-localization of angulons occurs at finite impurity-bath coupling already at the mean-field level. The transition is accompanied by the spherical-symmetry breaking of the angulon ground state and a discontinuity in the first derivative of the ground-state energy. Moreover, the type of the symmetry breaking is dictated by the symmetry of the microscopic impurity-bath interaction, which leads to a number of distinct self-localized states. The predicted effects can potentially be addressed in experiments on cold molecules trapped in superfluid helium droplets and ultracold quantum gases, as well as on electronic excitations in solids and Bose-Einstein condensates. },
author = {Li, Xiang and Seiringer, Robert and Lemeshko, Mikhail},
issn = {24699926},
journal = {Physical Review A},
number = {3},
publisher = {American Physical Society},
title = {{Angular self-localization of impurities rotating in a bosonic bath}},
doi = {10.1103/PhysRevA.95.033608},
volume = {95},
year = {2017},
}
@article{1079,
abstract = {We study the ionization problem in the Thomas-Fermi-Dirac-von Weizsäcker theory for atoms and molecules. We prove the nonexistence of minimizers for the energy functional when the number of electrons is large and the total nuclear charge is small. This nonexistence result also applies to external potentials decaying faster than the Coulomb potential. In the case of arbitrary nuclear charges, we obtain the nonexistence of stable minimizers and radial minimizers.},
author = {Nam, Phan and Van Den Bosch, Hanne},
issn = {13850172},
journal = {Mathematical Physics, Analysis and Geometry},
number = {2},
publisher = {Springer},
title = {{Nonexistence in Thomas Fermi-Dirac-von Weizsäcker theory with small nuclear charges}},
doi = {10.1007/s11040-017-9238-0},
volume = {20},
year = {2017},
}
@article{741,
abstract = {We prove that a system of N fermions interacting with an additional particle via point interactions is stable if the ratio of the mass of the additional particle to the one of the fermions is larger than some critical m*. The value of m* is independent of N and turns out to be less than 1. This fact has important implications for the stability of the unitary Fermi gas. We also characterize the domain of the Hamiltonian of this model, and establish the validity of the Tan relations for all wave functions in the domain.},
author = {Moser, Thomas and Seiringer, Robert},
issn = {00103616},
journal = {Communications in Mathematical Physics},
number = {1},
pages = {329 -- 355},
publisher = {Springer},
title = {{Stability of a fermionic N+1 particle system with point interactions}},
doi = {10.1007/s00220-017-2980-0},
volume = {356},
year = {2017},
}
@article{739,
abstract = {We study the norm approximation to the Schrödinger dynamics of N bosons in with an interaction potential of the form . Assuming that in the initial state the particles outside of the condensate form a quasi-free state with finite kinetic energy, we show that in the large N limit, the fluctuations around the condensate can be effectively described using Bogoliubov approximation for all . The range of β is expected to be optimal for this large class of initial states.},
author = {Nam, Phan and Napiórkowski, Marcin M},
issn = {00217824},
journal = {Journal de Mathématiques Pures et Appliquées},
number = {5},
pages = {662 -- 688},
publisher = {Elsevier},
title = {{A note on the validity of Bogoliubov correction to mean field dynamics}},
doi = {10.1016/j.matpur.2017.05.013},
volume = {108},
year = {2017},
}
@article{1267,
abstract = {We give a simplified proof of the nonexistence of large nuclei in the liquid drop model and provide an explicit bound. Our bound is within a factor of 2.3 of the conjectured value and seems to be the first quantitative result.},
author = {Frank, Rupert and Killip, Rowan and Nam, Phan},
journal = {Letters in Mathematical Physics},
number = {8},
pages = {1033 -- 1036},
publisher = {Springer},
title = {{Nonexistence of large nuclei in the liquid drop model}},
doi = {10.1007/s11005-016-0860-8},
volume = {106},
year = {2016},
}
@article{1143,
abstract = {We study the ground state of a dilute Bose gas in a scaling limit where the Gross-Pitaevskii functional emerges. This is a repulsive nonlinear Schrödinger functional whose quartic term is proportional to the scattering length of the interparticle interaction potential. We propose a new derivation of this limit problem, with a method that bypasses some of the technical difficulties that previous derivations had to face. The new method is based on a combination of Dyson\'s lemma, the quantum de Finetti theorem and a second moment estimate for ground states of the effective Dyson Hamiltonian. It applies equally well to the case where magnetic fields or rotation are present.},
author = {Nam, Phan and Rougerie, Nicolas and Seiringer, Robert},
journal = {Analysis and PDE},
number = {2},
pages = {459 -- 485},
publisher = {Mathematical Sciences Publishers},
title = {{Ground states of large bosonic systems: The gross Pitaevskii limit revisited}},
doi = {10.2140/apde.2016.9.459},
volume = {9},
year = {2016},
}
@article{1491,
abstract = {We study the ground state of a trapped Bose gas, starting from the full many-body Schrödinger Hamiltonian, and derive the non-linear Schrödinger energy functional in the limit of a large particle number, when the interaction potential converges slowly to a Dirac delta function. Our method is based on quantitative estimates on the discrepancy between the full many-body energy and its mean-field approximation using Hartree states. These are proved using finite dimensional localization and a quantitative version of the quantum de Finetti theorem. Our approach covers the case of attractive interactions in the regime of stability. In particular, our main new result is a derivation of the 2D attractive non-linear Schrödinger ground state.},
author = {Lewin, Mathieu and Nam, Phan and Rougerie, Nicolas},
journal = {Transactions of the American Mathematical Society},
number = {9},
pages = {6131 -- 6157},
publisher = {American Mathematical Society},
title = {{The mean-field approximation and the non-linear Schrödinger functional for trapped Bose gases}},
doi = {10.1090/tran/6537},
volume = {368},
year = {2016},
}
@article{1422,
abstract = {We study the time-dependent Bogoliubov–de-Gennes equations for generic translation-invariant fermionic many-body systems. For initial states that are close to thermal equilibrium states at temperatures near the critical temperature, we show that the magnitude of the order parameter stays approximately constant in time and, in particular, does not follow a time-dependent Ginzburg–Landau equation, which is often employed as a phenomenological description and predicts a decay of the order parameter in time. The full non-linear structure of the equations is necessary to understand this behavior.},
author = {Frank, Rupert and Hainzl, Christian and Schlein, Benjamin and Seiringer, Robert},
journal = {Letters in Mathematical Physics},
number = {7},
pages = {913 -- 923},
publisher = {Springer},
title = {{Incompatibility of time-dependent Bogoliubov–de-Gennes and Ginzburg–Landau equations}},
doi = {10.1007/s11005-016-0847-5},
volume = {106},
year = {2016},
}
@article{1620,
abstract = {We consider the Bardeen–Cooper–Schrieffer free energy functional for particles interacting via a two-body potential on a microscopic scale and in the presence of weak external fields varying on a macroscopic scale. We study the influence of the external fields on the critical temperature. We show that in the limit where the ratio between the microscopic and macroscopic scale tends to zero, the next to leading order of the critical temperature is determined by the lowest eigenvalue of the linearization of the Ginzburg–Landau equation.},
author = {Frank, Rupert and Hainzl, Christian and Seiringer, Robert and Solovej, Jan},
journal = {Communications in Mathematical Physics},
number = {1},
pages = {189 -- 216},
publisher = {Springer},
title = {{The external field dependence of the BCS critical temperature}},
doi = {10.1007/s00220-015-2526-2},
volume = {342},
year = {2016},
}
@inproceedings{1428,
abstract = {We report on a mathematically rigorous analysis of the superfluid properties of a Bose- Einstein condensate in the many-body ground state of a one-dimensional model of interacting bosons in a random potential.},
author = {Könenberg, Martin and Moser, Thomas and Seiringer, Robert and Yngvason, Jakob},
booktitle = {Journal of Physics: Conference Series},
location = {Shanghai, China},
number = {1},
publisher = {IOP Publishing Ltd.},
title = {{Superfluidity and BEC in a Model of Interacting Bosons in a Random Potential}},
doi = {10.1088/1742-6596/691/1/012016},
volume = {691},
year = {2016},
}
@article{1478,
abstract = {We consider the Tonks-Girardeau gas subject to a random external potential. If the disorder is such that the underlying one-particle Hamiltonian displays localization (which is known to be generically the case), we show that there is exponential decay of correlations in the many-body eigenstates. Moreover, there is no Bose-Einstein condensation and no superfluidity, even at zero temperature.},
author = {Seiringer, Robert and Warzel, Simone},
journal = {New Journal of Physics},
number = {3},
publisher = {IOP Publishing Ltd.},
title = {{Decay of correlations and absence of superfluidity in the disordered Tonks-Girardeau gas}},
doi = {10.1088/1367-2630/18/3/035002},
volume = {18},
year = {2016},
}
@article{1493,
abstract = {We introduce a new method for deriving the time-dependent Hartree or Hartree-Fock equations as an effective mean-field dynamics from the microscopic Schrödinger equation for fermionic many-particle systems in quantum mechanics. The method is an adaption of the method used in Pickl (Lett. Math. Phys. 97 (2) 151–164 2011) for bosonic systems to fermionic systems. It is based on a Gronwall type estimate for a suitable measure of distance between the microscopic solution and an antisymmetrized product state. We use this method to treat a new mean-field limit for fermions with long-range interactions in a large volume. Some of our results hold for singular attractive or repulsive interactions. We can also treat Coulomb interaction assuming either a mild singularity cutoff or certain regularity conditions on the solutions to the Hartree(-Fock) equations. In the considered limit, the kinetic and interaction energy are of the same order, while the average force is subleading. For some interactions, we prove that the Hartree(-Fock) dynamics is a more accurate approximation than a simpler dynamics that one would expect from the subleading force. With our method we also treat the mean-field limit coupled to a semiclassical limit, which was discussed in the literature before, and we recover some of the previous results. All results hold for initial data close (but not necessarily equal) to antisymmetrized product states and we always provide explicit rates of convergence.},
author = {Petrat, Sören P and Pickl, Peter},
journal = {Mathematical Physics, Analysis and Geometry},
number = {1},
publisher = {Springer},
title = {{A new method and a new scaling for deriving fermionic mean-field dynamics}},
doi = {10.1007/s11040-016-9204-2},
volume = {19},
year = {2016},
}
@article{1486,
abstract = {We review recent results concerning the mathematical properties of the Bardeen-Cooper-Schrieffer (BCS) functional of superconductivity, which were obtained in a series of papers, partly in collaboration with R. Frank, E. Hamza, S. Naboko, and J. P. Solovej. Our discussion includes, in particular, an investigation of the critical temperature for a general class of interaction potentials, as well as a study of its dependence on external fields. We shall explain how the Ginzburg-Landau model can be derived from the BCS theory in a suitable parameter regime.},
author = {Hainzl, Christian and Seiringer, Robert},
journal = {Journal of Mathematical Physics},
number = {2},
publisher = {American Institute of Physics},
title = {{The Bardeen–Cooper–Schrieffer functional of superconductivity and its mathematical properties}},
doi = {10.1063/1.4941723},
volume = {57},
year = {2016},
}
@article{1436,
abstract = {We study the time evolution of a system of N spinless fermions in R3 which interact through a pair potential, e.g., the Coulomb potential. We compare the dynamics given by the solution to Schrödinger's equation with the time-dependent Hartree-Fock approximation, and we give an estimate for the accuracy of this approximation in terms of the kinetic energy of the system. This leads, in turn, to bounds in terms of the initial total energy of the system.},
author = {Bach, Volker and Breteaux, Sébastien and Petrat, Sören P and Pickl, Peter and Tzaneteas, Tim},
journal = {Journal de Mathématiques Pures et Appliquées},
number = {1},
pages = {1 -- 30},
publisher = {Elsevier},
title = {{Kinetic energy estimates for the accuracy of the time-dependent Hartree-Fock approximation with Coulomb interaction}},
doi = {10.1016/j.matpur.2015.09.003},
volume = {105},
year = {2016},
}
@article{1291,
abstract = {We consider Ising models in two and three dimensions, with short range ferromagnetic and long range, power-law decaying, antiferromagnetic interactions. We let J be the ratio between the strength of the ferromagnetic to antiferromagnetic interactions. The competition between these two kinds of interactions induces the system to form domains of minus spins in a background of plus spins, or vice versa. If the decay exponent p of the long range interaction is larger than dÂ +Â 1, with d the space dimension, this happens for all values of J smaller than a critical value Jc(p), beyond which the ground state is homogeneous. In this paper, we give a characterization of the infinite volume ground states of the system, for pÂ >Â 2d and J in a left neighborhood of Jc(p). In particular, we prove that the quasi-one-dimensional states consisting of infinite stripes (dÂ =Â 2) or slabs (dÂ =Â 3), all of the same optimal width and orientation, and alternating magnetization, are infinite volume ground states. Our proof is based on localization bounds combined with reflection positivity.},
author = {Giuliani, Alessandro and Seiringer, Robert},
journal = {Communications in Mathematical Physics},
number = {3},
pages = {983 -- 1007},
publisher = {Springer},
title = {{Periodic striped ground states in Ising models with competing interactions}},
doi = {10.1007/s00220-016-2665-0},
volume = {347},
year = {2016},
}
@article{1622,
abstract = {We prove analogues of the Lieb–Thirring and Hardy–Lieb–Thirring inequalities for many-body quantum systems with fractional kinetic operators and homogeneous interaction potentials, where no anti-symmetry on the wave functions is assumed. These many-body inequalities imply interesting one-body interpolation inequalities, and we show that the corresponding one- and many-body inequalities are actually equivalent in certain cases.},
author = {Lundholm, Douglas and Nam, Phan and Portmann, Fabian},
journal = {Archive for Rational Mechanics and Analysis},
number = {3},
pages = {1343 -- 1382},
publisher = {Springer},
title = {{Fractional Hardy–Lieb–Thirring and related Inequalities for interacting systems}},
doi = {10.1007/s00205-015-0923-5},
volume = {219},
year = {2016},
}
@article{1259,
abstract = {We consider the Bogolubov–Hartree–Fock functional for a fermionic many-body system with two-body interactions. For suitable interaction potentials that have a strong enough attractive tail in order to allow for two-body bound states, but are otherwise sufficiently repulsive to guarantee stability of the system, we show that in the low-density limit the ground state of this model consists of a Bose–Einstein condensate of fermion pairs. The latter can be described by means of the Gross–Pitaevskii energy functional.},
author = {Bräunlich, Gerhard and Hainzl, Christian and Seiringer, Robert},
journal = {Mathematical Physics, Analysis and Geometry},
number = {2},
publisher = {Springer},
title = {{Bogolubov–Hartree–Fock theory for strongly interacting fermions in the low density limit}},
doi = {10.1007/s11040-016-9209-x},
volume = {19},
year = {2016},
}
@article{1545,
abstract = {We provide general conditions for which bosonic quadratic Hamiltonians on Fock spaces can be diagonalized by Bogoliubov transformations. Our results cover the case when quantum systems have infinite degrees of freedom and the associated one-body kinetic and paring operators are unbounded. Our sufficient conditions are optimal in the sense that they become necessary when the relevant one-body operators commute.},
author = {Nam, Phan and Napiórkowski, Marcin M and Solovej, Jan},
journal = {Journal of Functional Analysis},
number = {11},
pages = {4340 -- 4368},
publisher = {Academic Press},
title = {{Diagonalization of bosonic quadratic Hamiltonians by Bogoliubov transformations}},
doi = {10.1016/j.jfa.2015.12.007},
volume = {270},
year = {2016},
}