@article{7594,
abstract = {The concept of the entanglement between spin and orbital degrees of freedom plays a crucial role in our understanding of various phases and exotic ground states in a broad class of materials, including orbitally ordered materials and spin liquids. We investigate how the spin-orbital entanglement in a Mott insulator depends on the value of the spin-orbit coupling of the relativistic origin. To this end, we numerically diagonalize a one-dimensional spin-orbital model with Kugel-Khomskii exchange interactions between spins and orbitals on different sites supplemented by the on-site spin-orbit coupling. In the regime of small spin-orbit coupling with regard to the spin-orbital exchange, the ground state to a large extent resembles the one obtained in the limit of vanishing spin-orbit coupling. On the other hand, for large spin-orbit coupling the ground state can, depending on the model parameters, either still show negligible spin-orbital entanglement or evolve to a highly spin-orbitally-entangled phase with completely distinct properties that are described by an effective XXZ model. The presented results suggest that (i) the spin-orbital entanglement may be induced by large on-site spin-orbit coupling, as found in the 5d transition metal oxides, such as the iridates; (ii) for Mott insulators with weak spin-orbit coupling of Ising type, such as, e.g., the alkali hyperoxides, the effects of the spin-orbit coupling on the ground state can, in the first order of perturbation theory, be neglected.},
author = {Gotfryd, Dorota and Paerschke, Ekaterina and Chaloupka, Jiri and Oles, Andrzej M. and Wohlfeld, Krzysztof},
journal = {Physical Review Research},
number = {1},
publisher = {American Physical Society},
title = {{How spin-orbital entanglement depends on the spin-orbit coupling in a Mott insulator}},
doi = {10.1103/PhysRevResearch.2.013353},
volume = {2},
year = {2020},
}
@article{7428,
abstract = {In the superconducting regime of FeTe(1−x)Sex, there exist two types of vortices which are distinguished by the presence or absence of zero-energy states in their core. To understand their origin, we examine the interplay of Zeeman coupling and superconducting pairings in three-dimensional metals with band inversion. Weak Zeeman fields are found to suppress intraorbital spin-singlet pairing, known to localize the states at the ends of the vortices on the surface. On the other hand, an orbital-triplet pairing is shown to be stable against Zeeman interactions, but leads to delocalized zero-energy Majorana modes which extend through the vortex. In contrast, the finite-energy vortex modes remain localized at the vortex ends even when the pairing is of orbital-triplet form. Phenomenologically, this manifests as an observed disappearance of zero-bias peaks within the cores of topological vortices upon an increase of the applied magnetic field. The presence of magnetic impurities in FeTe(1−x)Sex, which are attracted to the vortices, would lead to such Zeeman-induced delocalization of Majorana modes in a fraction of vortices that capture a large enough number of magnetic impurities. Our results provide an explanation for the dichotomy between topological and nontopological vortices recently observed in FeTe(1−x)Sex.},
author = {Ghazaryan, Areg and Lopes, P. L.S. and Hosur, Pavan and Gilbert, Matthew J. and Ghaemi, Pouyan},
issn = {24699969},
journal = {Physical Review B},
number = {2},
publisher = {APS},
title = {{Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors}},
doi = {10.1103/PhysRevB.101.020504},
volume = {101},
year = {2020},
}
@article{7190,
abstract = {We investigate the ground-state energy of a one-dimensional Fermi gas with two bosonic impurities. We consider spinless fermions with no fermion-fermion interactions. The fermion-impurity and impurity-impurity interactions are modeled with Dirac delta functions. First, we study the case where impurity and fermion have equal masses, and the impurity-impurity two-body interaction is identical to the fermion-impurity interaction, such that the system is solvable with the Bethe ansatz. For attractive interactions, we find that the energy of the impurity-impurity subsystem is below the energy of the bound state that exists without the Fermi gas. We interpret this as a manifestation of attractive boson-boson interactions induced by the fermionic medium, and refer to the impurity-impurity subsystem as an in-medium bound state. For repulsive interactions, we find no in-medium bound states. Second, we construct an effective model to describe these interactions, and compare its predictions to the exact solution. We use this effective model to study nonintegrable systems with unequal masses and/or potentials. We discuss parameter regimes for which impurity-impurity attraction induced by the Fermi gas can lead to the formation of in-medium bound states made of bosons that repel each other in the absence of the Fermi gas.},
author = {Huber, D. and Hammer, H.-W. and Volosniev, Artem},
issn = {2643-1564},
journal = {Physical Review Research},
number = {3},
publisher = {APS},
title = {{In-medium bound states of two bosonic impurities in a one-dimensional Fermi gas}},
doi = {10.1103/physrevresearch.1.033177},
volume = {1},
year = {2019},
}
@article{6786,
abstract = {Dipolar coupling plays a fundamental role in the interaction between electrically or magnetically polarized species such as magnetic atoms and dipolar molecules in a gas or dipolar excitons in the solid state. Unlike Coulomb or contactlike interactions found in many atomic, molecular, and condensed-matter systems, this interaction is long-ranged and highly anisotropic, as it changes from repulsive to attractive depending on the relative positions and orientation of the dipoles. Because of this unique property, many exotic, symmetry-breaking collective states have been recently predicted for cold dipolar gases, but only a few have been experimentally detected and only in dilute atomic dipolar Bose-Einstein condensates. Here, we report on the first observation of attractive dipolar coupling between excitonic dipoles using a new design of stacked semiconductor bilayers. We show that the presence of a dipolar exciton fluid in one bilayer modifies the spatial distribution and increases the binding energy of excitonic dipoles in a vertically remote layer. The binding energy changes are explained using a many-body polaron model describing the deformation of the exciton cloud due to its interaction with a remote dipolar exciton. The surprising nonmonotonic dependence on the cloud density indicates the important role of dipolar correlations, which is unique to dense, strongly interacting dipolar solid-state systems. Our concept provides a route for the realization of dipolar lattices with strong anisotropic interactions in semiconductor systems, which open the way for the observation of theoretically predicted new and exotic collective phases, as well as for engineering and sensing their collective excitations.},
author = {Hubert, Colin and Baruchi, Yifat and Mazuz-Harpaz, Yotam and Cohen, Kobi and Biermann, Klaus and Lemeshko, Mikhail and West, Ken and Pfeiffer, Loren and Rapaport, Ronen and Santos, Paulo},
issn = {2160-3308},
journal = {Physical Review X},
number = {2},
publisher = {APS},
title = {{Attractive dipolar coupling between stacked exciton fluids}},
doi = {10.1103/PhysRevX.9.021026},
volume = {9},
year = {2019},
}
@article{6940,
abstract = {We study the effect of a linear tunneling coupling between two-dimensional systems, each separately
exhibiting the topological Berezinskii-Kosterlitz-Thouless (BKT) transition. In the uncoupled limit, there
are two phases: one where the one-body correlation functions are algebraically decaying and the other with
exponential decay. When the linear coupling is turned on, a third BKT-paired phase emerges, in which one-body correlations are exponentially decaying, while two-body correlation functions exhibit power-law
decay. We perform numerical simulations in the paradigmatic case of two coupled XY models at finite
temperature, finding evidences that for any finite value of the interlayer coupling, the BKT-paired phase is
present. We provide a picture of the phase diagram using a renormalization group approach.},
author = {Bighin, Giacomo and Defenu, Nicolò and Nándori, István and Salasnich, Luca and Trombettoni, Andrea},
issn = {1079-7114},
journal = {Physical Review Letters},
number = {10},
publisher = {American Physical Society (APS)},
title = {{Berezinskii-Kosterlitz-Thouless paired phase in coupled XY models}},
doi = {10.1103/physrevlett.123.100601},
volume = {123},
year = {2019},
}
@article{6092,
abstract = {In 1915, Einstein and de Haas and Barnett demonstrated that changing the magnetization of a magnetic material results in mechanical rotation and vice versa. At the microscopic level, this effect governs the transfer between electron spin and orbital angular momentum, and lattice degrees of freedom, understanding which is key for molecular magnets, nano-magneto-mechanics, spintronics, and ultrafast magnetism. Until now, the timescales of electron-to-lattice angular momentum transfer remain unclear, since modeling this process on a microscopic level requires the addition of an infinite amount of quantum angular momenta. We show that this problem can be solved by reformulating it in terms of the recently discovered angulon quasiparticles, which results in a rotationally invariant quantum many-body theory. In particular, we demonstrate that nonperturbative effects take place even if the electron-phonon coupling is weak and give rise to angular momentum transfer on femtosecond timescales.},
author = {Mentink, Johann H and Katsnelson, Mikhail and Lemeshko, Mikhail},
journal = {Physical Review B},
number = {6},
publisher = {APS},
title = {{Quantum many-body dynamics of the Einstein-de Haas effect}},
doi = {10.1103/PhysRevB.99.064428},
volume = {99},
year = {2019},
}
@article{6632,
abstract = {We consider a two-component Bose gas in two dimensions at a low temperature with short-range repulsive interaction. In the coexistence phase where both components are superfluid, interspecies interactions induce a nondissipative drag between the two superfluid flows (Andreev-Bashkin effect). We show that this behavior leads to a modification of the usual Berezinskii-Kosterlitz-Thouless (BKT) transition in two dimensions. We extend the renormalization of the superfluid densities at finite temperature using the renormalization-group approach and find that the vortices of one component have a large influence on the superfluid properties of the other, mediated by the nondissipative drag. The extended BKT flow equations indicate that the occurrence of the vortex unbinding transition in one of the components can induce the breakdown of superfluidity also in the other, leading to a locking phenomenon for the critical temperatures of the two gases.},
author = {Karle, Volker and Defenu, Nicolò and Enss, Tilman},
issn = {24699934},
journal = {Physical Review A},
number = {6},
publisher = {APS},
title = {{Coupled superfluidity of binary Bose mixtures in two dimensions}},
doi = {10.1103/PhysRevA.99.063627},
volume = {99},
year = {2019},
}
@article{5886,
abstract = {Problems involving quantum impurities, in which one or a few particles are interacting with a macroscopic environment, represent a pervasive paradigm, spanning across atomic, molecular, and condensed-matter physics. In this paper we introduce new variational approaches to quantum impurities and apply them to the Fröhlich polaron–a quasiparticle formed out of an electron (or other point-like impurity) in a polar medium, and to the angulon–a quasiparticle formed out of a rotating molecule in a bosonic bath. We benchmark these approaches against established theories, evaluating their accuracy as a function of the impurity-bath coupling.},
author = {Li, Xiang and Bighin, Giacomo and Yakaboylu, Enderalp and Lemeshko, Mikhail},
issn = {00268976},
journal = {Molecular Physics},
publisher = {Taylor and Francis},
title = {{Variational approaches to quantum impurities: from the Fröhlich polaron to the angulon}},
doi = {10.1080/00268976.2019.1567852},
year = {2019},
}
@article{6955,
abstract = {We study few-body bound states of charged particles subject to attractive zero-range/short-range plus repulsive Coulomb interparticle forces. The characteristic length scales of the system at zero energy are set by the Coulomb length scale D and the Coulomb-modified effective range r eff. We study shallow bound states of charged particles with D >> r eff and show that these systems obey universal scaling laws different from neutral particles. An accurate description of these states requires both the Coulomb-modified scattering length and the effective range unless the Coulomb interaction is very weak (D -> ). Our findings are relevant for bound states whose spatial extent is significantly larger than the range of the attractive potential. These states enjoy universality – their character is independent of the shape of the short-range potential.},
author = {Schmickler, C.H. and Hammer, H.-W. and Volosniev, Artem},
issn = {0370-2693},
journal = {Physics Letters B},
publisher = {Elsevier},
title = {{Universal physics of bound states of a few charged particles}},
doi = {10.1016/j.physletb.2019.135016},
volume = {798},
year = {2019},
}
@inproceedings{6646,
abstract = {We demonstrate robust retention of valley coherence and its control via polariton pseudospin precession through the optical TE-TM splitting in bilayer WS2 microcavity exciton polaritons at room temperature.},
author = {Khatoniar, Mandeep and Yama, Nicholas and Ghazaryan, Areg and Guddala, Sriram and Ghaemi, Pouyan and Menon, Vinod},
booktitle = {CLEO: Applications and Technology},
isbn = {9781943580576},
location = {San Jose, CA, United States},
publisher = {OSA},
title = {{Room temperature control of valley coherence in bilayer WS2 exciton polaritons}},
doi = {10.1364/cleo_at.2019.jtu2a.52},
year = {2019},
}
@article{7396,
abstract = {The angular momentum of molecules, or, equivalently, their rotation in three-dimensional space, is ideally suited for quantum control. Molecular angular momentum is naturally quantized, time evolution is governed by a well-known Hamiltonian with only a few accurately known parameters, and transitions between rotational levels can be driven by external fields from various parts of the electromagnetic spectrum. Control over the rotational motion can be exerted in one-, two-, and many-body scenarios, thereby allowing one to probe Anderson localization, target stereoselectivity of bimolecular reactions, or encode quantum information to name just a few examples. The corresponding approaches to quantum control are pursued within separate, and typically disjoint, subfields of physics, including ultrafast science, cold collisions, ultracold gases, quantum information science, and condensed-matter physics. It is the purpose of this review to present the various control phenomena, which all rely on the same underlying physics, within a unified framework. To this end, recall the Hamiltonian for free rotations, assuming the rigid rotor approximation to be valid, and summarize the different ways for a rotor to interact with external electromagnetic fields. These interactions can be exploited for control—from achieving alignment, orientation, or laser cooling in a one-body framework, steering bimolecular collisions, or realizing a quantum computer or quantum simulator in the many-body setting.},
author = {Koch, Christiane P. and Lemeshko, Mikhail and Sugny, Dominique},
issn = {0034-6861},
journal = {Reviews of Modern Physics},
number = {3},
publisher = {APS},
title = {{Quantum control of molecular rotation}},
doi = {10.1103/revmodphys.91.035005},
volume = {91},
year = {2019},
}
@article{294,
abstract = {We developed a method to calculate two-photon processes in quantum mechanics that replaces the infinite summation over the intermediate states by a perturbation expansion. This latter consists of a series of commutators that involve position, momentum, and Hamiltonian quantum operators. We analyzed several single- and many-particle cases for which a closed-form solution to the perturbation expansion exists, as well as more complicated cases for which a solution is found by convergence. Throughout the article, Rayleigh and Raman scattering are taken as examples of two-photon processes. The present method provides a clear distinction between the Thomson scattering, regarded as classical scattering, and quantum contributions. Such a distinction lets us derive general results concerning light scattering. Finally, possible extensions to the developed formalism are discussed.},
author = {Fratini, Filippo and Safari, Laleh and Amaro, Pedro and Santos, José},
journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
number = {4},
publisher = {American Physical Society},
title = {{Two-photon processes based on quantum commutators}},
doi = {10.1103/PhysRevA.97.043842},
volume = {97},
year = {2018},
}
@article{427,
abstract = {We investigate the quantum interference induced shifts between energetically close states in highly charged ions, with the energy structure being observed by laser spectroscopy. In this work, we focus on hyperfine states of lithiumlike heavy-Z isotopes and quantify how much quantum interference changes the observed transition frequencies. The process of photon excitation and subsequent photon decay for the transition 2s→2p→2s is implemented with fully relativistic and full-multipole frameworks, which are relevant for such relativistic atomic systems. We consider the isotopes Pb79+207 and Bi80+209 due to experimental interest, as well as other examples of isotopes with lower Z, namely Pr56+141 and Ho64+165. We conclude that quantum interference can induce shifts up to 11% of the linewidth in the measurable resonances of the considered isotopes, if interference between resonances is neglected. The inclusion of relativity decreases the cross section by 35%, mainly due to the complete retardation form of the electric dipole multipole. However, the contribution of the next higher multipoles (e.g., magnetic quadrupole) to the cross section is negligible. This makes the contribution of relativity and higher-order multipoles to the quantum interference induced shifts a minor effect, even for heavy-Z elements.},
author = {Amaro, Pedro and Loureiro, Ulisses and Safari, Laleh and Fratini, Filippo and Indelicato, Paul and Stöhlker, Thomas and Santos, José},
journal = { Physical Review A - Atomic, Molecular, and Optical Physics},
number = {2},
publisher = {American Physical Society},
title = {{Quantum interference in laser spectroscopy of highly charged lithiumlike ions}},
doi = {10.1103/PhysRevA.97.022510},
volume = {97},
year = {2018},
}
@article{415,
abstract = {Recently it was shown that a molecule rotating in a quantum solvent can be described in terms of the “angulon” quasiparticle [M. Lemeshko, Phys. Rev. Lett. 118, 095301 (2017)]. Here we extend the angulon theory to the case of molecules possessing an additional spin-1/2 degree of freedom and study the behavior of the system in the presence of a static magnetic field. We show that exchange of angular momentum between the molecule and the solvent can be altered by the field, even though the solvent itself is non-magnetic. In particular, we demonstrate a possibility to control resonant emission of phonons with a given angular momentum using a magnetic field.},
author = {Rzadkowski, Wojciech and Lemeshko, Mikhail},
journal = {The Journal of Chemical Physics},
number = {10},
publisher = {AIP},
title = {{Effect of a magnetic field on molecule–solvent angular momentum transfer }},
doi = { 10.1063/1.5017591 },
volume = {148},
year = {2018},
}
@article{435,
abstract = {It is shown that two fundamentally different phenomena, the bound states in continuum and the spectral singularity (or time-reversed spectral singularity), can occur simultaneously. This can be achieved in a rectangular core dielectric waveguide with an embedded active (or absorbing) layer. In such a system a two-dimensional bound state in a continuum is created in the plane of a waveguide cross section, and it is emitted or absorbed along the waveguide core. The idea can be used for experimental implementation of a laser or a coherent-perfect-absorber for a photonic bound state that resides in a continuous spectrum.},
author = {Midya, Bikashkali and Konotop, Vladimir},
journal = {Optics Letters},
number = {3},
pages = {607 -- 610},
publisher = {OSA},
title = {{Coherent-perfect-absorber and laser for bound states in a continuum}},
doi = {10.1364/OL.43.000607},
volume = {43},
year = {2018},
}
@article{195,
abstract = {We demonstrate that identical impurities immersed in a two-dimensional many-particle bath can be viewed as flux-tube-charged-particle composites described by fractional statistics. In particular, we find that the bath manifests itself as an external magnetic flux tube with respect to the impurities, and hence the time-reversal symmetry is broken for the effective Hamiltonian describing the impurities. The emerging flux tube acts as a statistical gauge field after a certain critical coupling. This critical coupling corresponds to the intersection point between the quasiparticle state and the phonon wing, where the angular momentum is transferred from the impurity to the bath. This amounts to a novel configuration with emerging anyons. The proposed setup paves the way to realizing anyons using electrons interacting with superfluid helium or lattice phonons, as well as using atomic impurities in ultracold gases.},
author = {Yakaboylu, Enderalp and Lemeshko, Mikhail},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {4},
publisher = {American Physical Society},
title = {{Anyonic statistics of quantum impurities in two dimensions}},
doi = {10.1103/PhysRevB.98.045402},
volume = {98},
year = {2018},
}
@article{417,
abstract = {We introduce a Diagrammatic Monte Carlo (DiagMC) approach to complex molecular impurities with rotational degrees of freedom interacting with a many-particle environment. The treatment is based on the diagrammatic expansion that merges the usual Feynman diagrams with the angular momentum diagrams known from atomic and nuclear structure theory, thereby incorporating the non-Abelian algebra inherent to quantum rotations. Our approach works at arbitrary coupling, is free of systematic errors and of finite size effects, and naturally provides access to the impurity Green function. We exemplify the technique by obtaining an all-coupling solution of the angulon model, however, the method is quite general and can be applied to a broad variety of quantum impurities possessing angular momentum degrees of freedom. },
author = {Bighin, Giacomo and Tscherbul, Timur and Lemeshko, Mikhail},
journal = {Physical Review Letters},
number = {16},
publisher = {APS Physics},
title = {{Diagrammatic Monte Carlo approach to rotating molecular impurities}},
doi = {10.1103/PhysRevLett.121.165301},
volume = {121},
year = {2018},
}
@article{6339,
abstract = {We introduce a diagrammatic Monte Carlo approach to angular momentum properties of quantum many-particle systems possessing a macroscopic number of degrees of freedom. The treatment is based on a diagrammatic expansion that merges the usual Feynman diagrams with the angular momentum diagrams known from atomic and nuclear structure theory, thereby incorporating the non-Abelian algebra inherent to quantum rotations. Our approach is applicable at arbitrary coupling, is free of systematic errors and of finite-size effects, and naturally provides access to the impurity Green function. We exemplify the technique by obtaining an all-coupling solution of the angulon model; however, the method is quite general and can be applied to a broad variety of systems in which particles exchange quantum angular momentum with their many-body environment.},
author = {Bighin, Giacomo and Tscherbul, Timur and Lemeshko, Mikhail},
journal = {Physical Review Letters},
number = {16},
publisher = {APS},
title = {{Diagrammatic Monte Carlo approach to angular momentum in quantum many-particle systems}},
doi = {10.1103/physrevlett.121.165301},
volume = {121},
year = {2018},
}
@article{420,
abstract = {We analyze the theoretical derivation of the beyond-mean-field equation of state for two-dimensional gas of dilute, ultracold alkali-metal atoms in the Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein condensate (BEC) crossover. We show that at zero temperature our theory — considering Gaussian fluctuations on top of the mean-field equation of state — is in very good agreement with experimental data. Subsequently, we investigate the superfluid density at finite temperature and its renormalization due to the proliferation of vortex–antivortex pairs. By doing so, we determine the Berezinskii–Kosterlitz–Thouless (BKT) critical temperature — at which the renormalized superfluid density jumps to zero — as a function of the inter-atomic potential strength. We find that the Nelson–Kosterlitz criterion overestimates the BKT temperature with respect to the renormalization group equations, this effect being particularly relevant in the intermediate regime of the crossover.},
author = {Bighin, Giacomo and Salasnich, Luca},
journal = {International Journal of Modern Physics B},
number = {17},
pages = {1840022},
publisher = {World Scientific Publishing},
title = {{Renormalization of the superfluid density in the two-dimensional BCS-BEC crossover}},
doi = {10.1142/S0217979218400222},
volume = {32},
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},
}
@article{5794,
abstract = {We present an approach to interacting quantum many-body systems based on the notion of quantum groups, also known as q-deformed Lie algebras. In particular, we show that, if the symmetry of a free quantum particle corresponds to a Lie group G, in the presence of a many-body environment this particle can be described by a deformed group, Gq. Crucially, the single deformation parameter, q, contains all the information about the many-particle interactions in the system. We exemplify our approach by considering a quantum rotor interacting with a bath of bosons, and demonstrate that extracting the value of q from closed-form solutions in the perturbative regime allows one to predict the behavior of the system for arbitrary values of the impurity-bath coupling strength, in good agreement with nonperturbative calculations. Furthermore, the value of the deformation parameter allows one to predict at which coupling strengths rotor-bath interactions result in a formation of a stable quasiparticle. The approach based on quantum groups does not only allow for a drastic simplification of impurity problems, but also provides valuable insights into hidden symmetries of interacting many-particle systems.},
author = {Yakaboylu, Enderalp and Shkolnikov, Mikhail and Lemeshko, Mikhail},
issn = {00319007},
journal = {Physical Review Letters},
number = {25},
publisher = {American Physical Society},
title = {{Quantum groups as hidden symmetries of quantum impurities}},
doi = {10.1103/PhysRevLett.121.255302},
volume = {121},
year = {2018},
}
@article{1015,
abstract = {Vortices are commonly observed in the context of classical hydrodynamics: from whirlpools after stirring the coffee in a cup to a violent atmospheric phenomenon such as a tornado, all classical vortices are characterized by an arbitrary circulation value of the local velocity field. On the other hand the appearance of vortices with quantized circulation represents one of the fundamental signatures of macroscopic quantum phenomena. In two-dimensional superfluids quantized vortices play a key role in determining finite-temperature properties, as the superfluid phase and the normal state are separated by a vortex unbinding transition, the Berezinskii-Kosterlitz-Thouless transition. Very recent experiments with two-dimensional superfluid fermions motivate the present work: we present theoretical results based on the renormalization group showing that the universal jump of the superfluid density and the critical temperature crucially depend on the interaction strength, providing a strong benchmark for forthcoming investigations.},
author = {Bighin, Giacomo and Salasnich, Luca},
issn = {20452322},
journal = {Scientific Reports},
publisher = {Nature Publishing Group},
title = {{Vortices and antivortices in two-dimensional ultracold Fermi gases}},
doi = {10.1038/srep45702},
volume = {7},
year = {2017},
}
@article{939,
abstract = {We reveal the existence of continuous families of guided single-mode solitons in planar waveguides with weakly nonlinear active core and absorbing boundaries. Stable propagation of TE and TM-polarized solitons is accompanied by attenuation of all other modes, i.e., the waveguide features properties of conservative and dissipative systems. If the linear spectrum of the waveguide possesses exceptional points, which occurs in the case of TM polarization, an originally focusing (defocusing) material nonlinearity may become effectively defocusing (focusing). This occurs due to the geometric phase of the carried eigenmode when the surface impedance encircles the exceptional point. In its turn, the change of the effective nonlinearity ensures the existence of dark (bright) solitons in spite of focusing (defocusing) Kerr nonlinearity of the core. The existence of an exceptional point can also result in anomalous enhancement of the effective nonlinearity. In terms of practical applications, the nonlinearity of the reported waveguide can be manipulated by controlling the properties of the absorbing cladding.},
author = {Midya, Bikashkali and Konotop, Vladimir},
issn = {00319007},
journal = {Physical Review Letters},
number = {3},
publisher = {American Physical Society},
title = {{Waveguides with absorbing boundaries: Nonlinearity controlled by an exceptional point and solitons}},
doi = {10.1103/PhysRevLett.119.033905},
volume = {119},
year = {2017},
}
@article{996,
abstract = {Iodine (I 2 ) molecules embedded in He nanodroplets are aligned by a 160 ps long laser pulse. The highest degree of alignment, occurring at the peak of the pulse and quantified by ⟨cos 2 θ 2D ⟩ , is measured as a function of the laser intensity. The results are well described by ⟨cos 2 θ 2D ⟩ calculated for a gas of isolated molecules each with an effective rotational constant of 0.6 times the gas-phase value, and at a temperature of 0.4 K. Theoretical analysis using the angulon quasiparticle to describe rotating molecules in superfluid helium rationalizes why the alignment mechanism is similar to that of isolated molecules with an effective rotational constant. A major advantage of molecules in He droplets is that their 0.4 K temperature leads to stronger alignment than what can generally be achieved for gas phase molecules -- here demonstrated by a direct comparison of the droplet results to measurements on a ∼ 1 K supersonic beam of isolated molecules. This point is further illustrated for more complex system by measurements on 1,4-diiodobenzene and 1,4-dibromobenzene. For all three molecular species studied the highest values of ⟨cos 2 θ 2D ⟩ achieved in He droplets exceed 0.96. },
author = {Shepperson, Benjamin and Chatterley, Adam and Søndergaard, Anders and Christiansen, Lars and Lemeshko, Mikhail and Stapelfeldt, Henrik},
issn = {00219606},
journal = {The Journal of Chemical Physics},
number = {1},
publisher = {AIP},
title = {{Strongly aligned molecules inside helium droplets in the near-adiabatic regime}},
doi = {10.1063/1.4983703},
volume = {147},
year = {2017},
}
@article{1109,
abstract = {Rotation of molecules embedded in He nanodroplets is explored by a combination of fs laser-induced alignment experiments and angulon quasiparticle theory. We demonstrate that at low fluence of the fs alignment pulse, the molecule and its solvation shell can be set into coherent collective rotation lasting long enough to form revivals. With increasing fluence, however, the revivals disappear -- instead, rotational dynamics as rapid as for an isolated molecule is observed during the first few picoseconds. Classical calculations trace this phenomenon to transient decoupling of the molecule from its He shell. Our results open novel opportunities for studying non-equilibrium solute-solvent dynamics and quantum thermalization. },
author = {Shepperson, Benjamin and Søndergaard, Anders and Christiansen, Lars and Kaczmarczyk, Jan and Zillich, Robert and Lemeshko, Mikhail and Stapelfeldt, Henrik},
journal = {Physical Review Letters},
number = {20},
publisher = {American Physical Society},
title = {{Laser-induced rotation of iodine molecules in helium nanodroplets: Revivals and breaking-free}},
doi = {10.1103/PhysRevLett.118.203203},
volume = {118},
year = {2017},
}
@article{1162,
abstract = {Selected universal experimental properties of high-temperature superconducting (HTS) cuprates have been singled out in the last decade. One of the pivotal challenges in this field is the designation of a consistent interpretation framework within which we can describe quantitatively the universal features of those systems. Here we analyze in a detailed manner the principal experimental data and compare them quantitatively with the approach based on a single-band model of strongly correlated electrons supplemented with strong antiferromagnetic (super)exchange interaction (the so-called t−J−U model). The model rationale is provided by estimating its microscopic parameters on the basis of the three-band approach for the Cu-O plane. We use our original full Gutzwiller wave-function solution by going beyond the renormalized mean-field theory (RMFT) in a systematic manner. Our approach reproduces very well the observed hole doping (δ) dependence of the kinetic-energy gain in the superconducting phase, one of the principal non-Bardeen-Cooper-Schrieffer features of the cuprates. The calculated Fermi velocity in the nodal direction is practically δ-independent and its universal value agrees very well with that determined experimentally. Also, a weak doping dependence of the Fermi wave vector leads to an almost constant value of the effective mass in a pure superconducting phase which is both observed in experiment and reproduced within our approach. An assessment of the currently used models (t−J, Hubbard) is carried out and the results of the canonical RMFT as a zeroth-order solution are provided for comparison to illustrate the necessity of the introduced higher-order contributions.},
author = {Spałek, Jozef and Zegrodnik, Michał and Kaczmarczyk, Jan},
issn = {24699950},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {2},
publisher = {American Physical Society},
title = {{Universal properties of high temperature superconductors from real space pairing t-J-U model and its quantitative comparison with experiment}},
doi = {10.1103/PhysRevB.95.024506},
volume = {95},
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{1163,
abstract = {We investigate the effect of the electron-hole (e-h) symmetry breaking on d-wave superconductivity induced by non-local effects of correlations in the generalized Hubbard model. The symmetry breaking is introduced in a two-fold manner: by the next-to-nearest neighbor hopping of electrons and by the charge-bond interaction - the off-diagonal term of the Coulomb potential. Both terms lead to a pronounced asymmetry of the superconducting order parameter. The next-to-nearest neighbor hopping enhances superconductivity for h-doping, while diminishes it for e-doping. The charge-bond interaction alone leads to the opposite effect and, additionally, to the kinetic-energy gain upon condensation in the underdoped regime. With both terms included, with similar amplitudes, the height of the superconducting dome and the critical doping remain in favor of h-doping. The influence of the charge-bond interaction on deviations from symmetry of the shape of the gap at the Fermi surface in the momentum space is briefly discussed.},
author = {Wysokiński, Marcin and Kaczmarczyk, Jan},
issn = {09538984},
journal = {Journal of Physics: Condensed Matter},
number = {8},
publisher = {IOP Publishing Ltd.},
title = {{Unconventional superconductivity in generalized Hubbard model role of electron–hole symmetry breaking terms}},
doi = {10.1088/1361-648X/aa532f},
volume = {29},
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{1119,
abstract = {Understanding the behavior of molecules interacting with superfluid helium represents a formidable challenge and, in general, requires approaches relying on large-scale numerical simulations. Here we demonstrate that experimental data collected over the last 20 years provide evidence that molecules immersed in superfluid helium form recently-predicted angulon quasiparticles [Phys. Rev. Lett. 114, 203001 (2015)]. Most importantly, casting the many-body problem in terms of angulons amounts to a drastic simplification and yields effective molecular moments of inertia as straightforward analytic solutions of a simple microscopic Hamiltonian. The outcome of the angulon theory is in good agreement with experiment for a broad range of molecular impurities, from heavy to medium-mass to light species. These results pave the way to understanding molecular rotation in liquid and crystalline phases in terms of the angulon quasiparticle.},
author = {Lemeshko, Mikhail},
issn = {00319007},
journal = {Physical Review Letters},
number = {9},
publisher = {American Physical Society},
title = {{Quasiparticle approach to molecules interacting with quantum solvents}},
doi = {10.1103/PhysRevLett.118.095301},
volume = {118},
year = {2017},
}
@article{6013,
abstract = {The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron’s classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the “tunnel exit.”},
author = {Camus, Nicolas and Yakaboylu, Enderalp and Fechner, Lutz and Klaiber, Michael and Laux, Martin and Mi, Yonghao and Hatsagortsyan, Karen Z. and Pfeifer, Thomas and Keitel, Christoph H. and Moshammer, Robert},
issn = {1079-7114},
journal = {Physical Review Letters},
number = {2},
publisher = {American Physical Society},
title = {{Experimental evidence for quantum tunneling time}},
doi = {10.1103/PhysRevLett.119.023201},
volume = {119},
year = {2017},
}
@article{1133,
abstract = {It is a common knowledge that an effective interaction of a quantum impurity with an electromagnetic field can be screened by surrounding charge carriers, whether mobile or static. Here we demonstrate that very strong, "anomalous" screening can take place in the presence of a neutral, weakly polarizable environment, due to an exchange of orbital angular momentum between the impurity and the bath. Furthermore, we show that it is possible to generalize all phenomena related to isolated impurities in an external field to the case when a many-body environment is present, by casting the problem in terms of the angulon quasiparticle. As a result, the relevant observables such as the effective Rabi frequency, geometric phase, and impurity spatial alignment are straightforward to evaluate in terms of a single parameter: the angular-momentum-dependent screening factor.},
author = {Yakaboylu, Enderalp and Lemeshko, Mikhail},
issn = {00319007},
journal = {Physical Review Letters},
number = {8},
publisher = {American Physical Society},
title = {{Anomalous screening of quantum impurities by a neutral environment}},
doi = {10.1103/PhysRevLett.118.085302},
volume = {118},
year = {2017},
}
@article{994,
abstract = {The formation of vortices is usually considered to be the main mechanism of angular momentum disposal in superfluids. Recently, it was predicted that a superfluid can acquire angular momentum via an alternative, microscopic route -- namely, through interaction with rotating impurities, forming so-called `angulon quasiparticles' [Phys. Rev. Lett. 114, 203001 (2015)]. The angulon instabilities correspond to transfer of a small number of angular momentum quanta from the impurity to the superfluid, as opposed to vortex instabilities, where angular momentum is quantized in units of ℏ per atom. Furthermore, since conventional impurities (such as molecules) represent three-dimensional (3D) rotors, the angular momentum transferred is intrinsically 3D as well, as opposed to a merely planar rotation which is inherent to vortices. Herein we show that the angulon theory can explain the anomalous broadening of the spectroscopic lines observed for CH 3 and NH 3 molecules in superfluid helium nanodroplets, thereby providing a fingerprint of the emerging angulon instabilities in experiment.},
author = {Cherepanov, Igor and Lemeshko, Mikhail},
journal = {Physical Review Materials},
number = {3},
publisher = {American Physical Society},
title = {{Fingerprints of angulon instabilities in the spectra of matrix-isolated molecules}},
doi = {10.1103/PhysRevMaterials.1.035602},
volume = {1},
year = {2017},
}
@article{1076,
abstract = {Signatures of the Coulomb corrections in the photoelectron momentum distribution during laser-induced ionization of atoms or ions in tunneling and multiphoton regimes are investigated analytically in the case of a one-dimensional problem. A high-order Coulomb-corrected strong-field approximation is applied, where the exact continuum state in the S matrix is approximated by the eikonal Coulomb-Volkov state including the second-order corrections to the eikonal. Although without high-order corrections our theory coincides with the known analytical R-matrix (ARM) theory, we propose a simplified procedure for the matrix element derivation. Rather than matching the eikonal Coulomb-Volkov wave function with the bound state as in the ARM theory to remove the Coulomb singularity, we calculate the matrix element via the saddle-point integration method by time as well as by coordinate, and in this way avoiding the Coulomb singularity. The momentum shift in the photoelectron momentum distribution with respect to the ARM theory due to high-order corrections is analyzed for tunneling and multiphoton regimes. The relation of the quantum corrections to the tunneling delay time is discussed.},
author = {Klaiber, Michael and Daněk, Jiří and Yakaboylu, Enderalp and Hatsagortsyan, Karen and Keitel, Christoph},
issn = {24699926},
journal = { Physical Review A - Atomic, Molecular, and Optical Physics},
number = {2},
publisher = {American Physical Society},
title = {{Strong-field ionization via a high-order Coulomb-corrected strong-field approximation}},
doi = {10.1103/PhysRevA.95.023403},
volume = {95},
year = {2017},
}
@inbook{604,
abstract = {In several settings of physics and chemistry one has to deal with molecules interacting with some kind of an external environment, be it a gas, a solution, or a crystal surface. Understanding molecular processes in the presence of such a many-particle bath is inherently challenging, and usually requires large-scale numerical computations. Here, we present an alternative approach to the problem, based on the notion of the angulon quasiparticle. We show that molecules rotating inside superfluid helium nanodroplets and Bose–Einstein condensates form angulons, and therefore can be described by straightforward solutions of a simple microscopic Hamiltonian. Casting the problem in the language of angulons allows us not only to greatly simplify it, but also to gain insights into the origins of the observed phenomena and to make predictions for future experimental studies.},
author = {Lemeshko, Mikhail and Schmidt, Richard},
booktitle = {Cold Chemistry: Molecular Scattering and Reactivity Near Absolute Zero },
editor = {Dulieu, Oliver and Osterwalder, Andreas},
issn = {20413181},
pages = {444 -- 495},
publisher = {The Royal Society of Chemistry},
title = {{Molecular impurities interacting with a many-particle environment: From ultracold gases to helium nanodroplets}},
doi = {10.1039/9781782626800-00444},
volume = {11},
year = {2017},
}
@inproceedings{313,
abstract = {Tunneling of a particle through a potential barrier remains one of the most remarkable quantum phenomena. Owing to advances in laser technology, electric fields comparable to those electrons experience in atoms are readily generated and open opportunities to dynamically investigate the process of electron tunneling through the potential barrier formed by the superposition of both laser and atomic fields. Attosecond-time and angstrom-space resolution of the strong laser-field technique allow to address fundamental questions related to tunneling, which are still open and debated: Which time is spent under the barrier and what momentum is picked up by the particle in the meantime? In this combined experimental and theoretical study we demonstrate that for strong-field ionization the leading quantum mechanical Wigner treatment for the time resolved description of tunneling is valid. We achieve a high sensitivity on the tunneling barrier and unambiguously isolate its effects by performing a differential study of two systems with almost identical tunneling geometry. Moreover, working with a low frequency laser, we essentially limit the non-adiabaticity of the process as a major source of uncertainty. The agreement between experiment and theory implies two substantial corrections with respect to the widely employed quasiclassical treatment: In addition to a non-vanishing longitudinal momentum along the laser field-direction we provide clear evidence for a non-zero tunneling time delay. This addresses also the fundamental question how the transition occurs from the tunnel barrier to free space classical evolution of the ejected electron.},
author = {Camus, Nicolas and Yakaboylu, Enderalp and Fechner, Lutz and Klaiber, Michael and Laux, Martin and Mi, Yonghao and Hatsagortsyan, Karen and Pfeifer, Thomas and Keitel, Cristoph and Moshammer, Robert},
issn = {17426588},
location = {Kazan, Russian Federation},
number = {1},
publisher = {American Physical Society},
title = {{Experimental evidence for Wigner's tunneling time}},
doi = {10.1088/1742-6596/999/1/012004},
volume = {999},
year = {2017},
}
@article{995,
abstract = {Recently it was shown that an impurity exchanging orbital angular momentum with a surrounding bath can be described in terms of the angulon quasiparticle [Phys. Rev. Lett. 118, 095301 (2017)]. The angulon consists of a quantum rotor dressed by a many-particle field of boson excitations, and can be formed out of, for example, a molecule or a nonspherical atom in superfluid helium, or out of an electron coupled to lattice phonons or a Bose condensate. Here we develop an approach to the angulon based on the path-integral formalism, which sets the ground for a systematic, perturbative treatment of the angulon problem. The resulting perturbation series can be interpreted in terms of Feynman diagrams, from which, in turn, one can derive a set of diagrammatic rules. These rules extend the machinery of the graphical theory of angular momentum - well known from theoretical atomic spectroscopy - to the case where an environment with an infinite number of degrees of freedom is present. In particular, we show that each diagram can be interpreted as a 'skeleton', which enforces angular momentum conservation, dressed by an additional many-body contribution. This connection between the angulon theory and the graphical theory of angular momentum is particularly important as it allows to systematically and substantially simplify the analytical representation of each diagram. In order to exemplify the technique, we calculate the 1- and 2-loop contributions to the angulon self-energy, the spectral function, and the quasiparticle weight. The diagrammatic theory we develop paves the way to investigate next-to-leading order quantities in a more compact way compared to the variational approaches.},
author = {Bighin, Giacomo and Lemeshko, Mikhail},
issn = {24699950},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {8},
publisher = {American Physical Society},
title = {{Diagrammatic approach to orbital quantum impurities interacting with a many-particle environment}},
doi = {10.1103/PhysRevB.96.085410},
volume = {96},
year = {2017},
}
@article{1286,
abstract = {We use recently developed angulon theory [R. Schmidt and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.203001] to study the rotational spectrum of a cyanide molecular anion immersed into Bose-Einstein condensates of rubidium and strontium. Based on ab initio potential energy surfaces, we provide a detailed study of the rotational Lamb shift and many-body-induced fine structure which arise due to dressing of molecular rotation by a field of phonon excitations. We demonstrate that the magnitude of these effects is large enough in order to be observed in modern experiments on cold molecular ions. Furthermore, we introduce a novel method to construct pseudopotentials starting from the ab initio potential energy surfaces, which provides a means to obtain effective coupling constants for low-energy polaron models.},
author = {Midya, Bikashkali and Tomza, Michał and Schmidt, Richard and Lemeshko, Mikhail},
journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
number = {4},
publisher = {American Physical Society},
title = {{Rotation of cold molecular ions inside a Bose-Einstein condensate}},
doi = {10.1103/PhysRevA.94.041601},
volume = {94},
year = {2016},
}
@article{1368,
abstract = {Superconductivity in heavy-fermion systems has an unconventional nature and is considered to originate from the universal features of the electronic structure. Here, the Anderson lattice model is studied by means of the full variational Gutzwiller wave function incorporating nonlocal effects of the on-site interaction. We show that the d-wave superconducting ground state can be driven solely by interelectronic correlations. The proposed microscopic mechanism leads to a multigap superconductivity with the dominant contribution due to f electrons and in the dx2−y2-wave channel. Our results rationalize several important observations for CeCoIn5.},
author = {Wysokiński, Marcin and Kaczmarczyk, Jan and Spałek, Jozef},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {2},
publisher = {American Physical Society},
title = {{Correlation driven d wave superconductivity in Anderson lattice model: Two gaps}},
doi = {10.1103/PhysRevB.94.024517},
volume = {94},
year = {2016},
}
@article{1419,
abstract = {We study the superconducting phase of the Hubbard model using the Gutzwiller variational wave function (GWF) and the recently proposed diagrammatic expansion technique (DE-GWF). The DE-GWF method works on the level of the full GWF and in the thermodynamic limit. Here, we consider a finite-size system to study the accuracy of the results as a function of the system size (which is practically unrestricted). We show that the finite-size scaling used, e.g. in the variational Monte Carlo method can lead to significant, uncontrolled errors. The presented research is the first step towards applying the DE-GWF method in studies of inhomogeneous situations, including systems with impurities, defects, inhomogeneous phases, or disorder.},
author = {Tomski, Andrzej and Kaczmarczyk, Jan},
journal = {Journal of Physics: Condensed Matter},
number = {17},
publisher = {IOP Publishing Ltd.},
title = {{Gutzwiller wave function for finite systems: Superconductivity in the Hubbard model}},
doi = {10.1088/0953-8984/28/17/175701},
volume = {28},
year = {2016},
}
@article{1206,
abstract = {We study a polar molecule immersed in a superfluid environment, such as a helium nanodroplet or a Bose–Einstein condensate, in the presence of a strong electrostatic field. We show that coupling of the molecular pendular motion, induced by the field, to the fluctuating bath leads to formation of pendulons—spherical harmonic librators dressed by a field of many-particle excitations. We study the behavior of the pendulon in a broad range of molecule–bath and molecule–field interaction strengths, and reveal that its spectrum features a series of instabilities which are absent in the field-free case of the angulon quasiparticle. Furthermore, we show that an external field allows to fine-tune the positions of these instabilities in the molecular rotational spectrum. This opens the door to detailed experimental studies of redistribution of orbital angular momentum in many-particle systems. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim},
author = {Redchenko, Elena and Lemeshko, Mikhail},
journal = {ChemPhysChem},
number = {22},
pages = {3649 -- 3654},
publisher = {Wiley-Blackwell},
title = {{Libration of strongly oriented polar molecules inside a superfluid}},
doi = {10.1002/cphc.201601042},
volume = {17},
year = {2016},
}
@article{1287,
abstract = {A planar waveguide with an impedance boundary, composed of nonperfect metallic plates, and with passive or active dielectric filling, is considered. We show the possibility of selective mode guiding and amplification when a homogeneous pump is added to the dielectric and analyze differences in TE and TM mode propagation. Such a non-conservative system is also shown to feature exceptional points for specific and experimentally tunable parameters, which are described for a particular case of transparent dielectric.},
author = {Midya, Bikashkali and Konotop, Vladimir},
journal = {Optics Letters},
number = {20},
pages = {4621 -- 4624},
publisher = {OSA},
title = {{Modes and exceptional points in waveguides with impedance boundary conditions}},
doi = {10.1364/OL.41.004621},
volume = {41},
year = {2016},
}
@article{1352,
abstract = {We study the interplay of nematic and superconducting order in the two-dimensional Hubbard model and show that they can coexist, especially when superconductivity is not the energetically dominant phase. Due to a breaking of the C4 symmetry, the coexisting phase inherently contains admixture of the s-wave pairing components. As a result, the superconducting gap exhibits nonstandard features including changed nodal directions. Our results also show that in the optimally doped regime the pure superconducting phase is typically unstable towards developing nematicity (breaking of the C4 symmetry). This has implications for the cuprate high-Tc superconductors, for which in this regime the so-called intertwined orders have recently been observed. Namely, the coexisting phase may be viewed as a precursor to such more involved patterns of symmetry breaking.},
author = {Kaczmarczyk, Jan and Schickling, Tobias and Bünemann, Jörg},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {8},
publisher = {American Physical Society},
title = {{Coexistence of nematic order and superconductivity in the Hubbard model}},
doi = {10.1103/PhysRevB.94.085152},
volume = {94},
year = {2016},
}
@article{1496,
abstract = {The two-photon 1s2 2s 2p 3P0 1s22s2 1S0 transition in berylliumlike ions is theoretically investigated within a fully relativistic framework and a second-order perturbation theory. We focus our analysis on how electron correlation, as well as the negative-energy spectrum, can affect the forbidden E1M1 decay rate. For this purpose, we include the electronic correlation via an effective local potential and within a single configuration-state model. Due to its experimental interest, evaluations of decay rates are performed for berylliumlike xenon and uranium. We find that the negative-energy contribution can be neglected at the present level of accuracy in the evaluation of the decay rate. On the other hand, if contributions of electronic correlation are not carefully taken into account, it may change the lifetime of the metastable state by up to 20%. By performing a full-relativistic jj-coupling calculation, we found a decrease of the decay rate by two orders of magnitude compared to non-relativistic LS-coupling calculations, for the selected heavy ions.},
author = {Amaro, Pedro and Fratini, Filippo and Safari, Laleh and Machado, Jorge and Guerra, Mauro and Indelicato, Paul and Santos, José},
journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
number = {3},
publisher = {American Physical Society},
title = {{Relativistic evaluation of the two-photon decay of the metastable 1s22s2p3P0 state in berylliumlike ions with an effective-potential model}},
doi = {10.1103/PhysRevA.93.032502},
volume = {93},
year = {2016},
}
@article{1416,
abstract = {Anisotropic dipole-dipole interactions between ultracold dipolar fermions break the symmetry of the Fermi surface and thereby deform it. Here we demonstrate that such a Fermi surface deformation induces a topological phase transition - the so-called Lifshitz transition - in the regime accessible to present-day experiments. We describe the impact of the Lifshitz transition on observable quantities such as the Fermi surface topology, the density-density correlation function, and the excitation spectrum of the system. The Lifshitz transition in ultracold atoms can be controlled by tuning the dipole orientation and, in contrast to the transition studied in crystalline solids, is completely interaction driven.},
author = {Van Loon, Erik and Katsnelson, Mikhail and Chomaz, Lauriane and Lemeshko, Mikhail},
journal = {Physical Review B - Condensed Matter and Materials Physics},
number = {19},
publisher = {American Physical Society},
title = {{Interaction-driven Lifshitz transition with dipolar fermions in optical lattices}},
doi = {10.1103/PhysRevB.93.195145},
volume = {93},
year = {2016},
}
@article{1347,
abstract = {During the past 70 years, the quantum theory of angular momentum has been successfully applied to describing the properties of nuclei, atoms, and molecules, and their interactions with each other as well as with external fields. Because of the properties of quantum rotations, the angular-momentum algebra can be of tremendous complexity even for a few interacting particles, such as valence electrons of an atom, not to mention larger many-particle systems. In this work, we study an example of the latter: A rotating quantum impurity coupled to a many-body bosonic bath. In the regime of strong impurity-bath couplings, the problem involves the addition of an infinite number of angular momenta, which renders it intractable using currently available techniques. Here, we introduce a novel canonical transformation that allows us to eliminate the complex angular-momentum algebra from such a class of many-body problems. In addition, the transformation exposes the problem's constants of motion, and renders it solvable exactly in the limit of a slowly rotating impurity. We exemplify the technique by showing that there exists a critical rotational speed at which the impurity suddenly acquires one quantum of angular momentum from the many-particle bath. Such an instability is accompanied by the deformation of the phonon density in the frame rotating along with the impurity.},
author = {Schmidt, Richard and Lemeshko, Mikhail},
journal = {Physical Review X},
number = {1},
publisher = {American Physical Society},
title = {{Deformation of a quantum many-particle system by a rotating impurity}},
doi = {10.1103/PhysRevX.6.011012},
volume = {6},
year = {2016},
}
@article{1204,
abstract = {In science, as in life, "surprises" can be adequately appreciated only in the presence of a null model, what we expect a priori. In physics, theories sometimes express the values of dimensionless physical constants as combinations of mathematical constants like π or e. The inverse problem also arises, whereby the measured value of a physical constant admits a "surprisingly" simple approximation in terms of well-known mathematical constants. Can we estimate the probability for this to be a mere coincidence, rather than an inkling of some theory? We answer the question in the most naive form.},
author = {Amir, Ariel and Lemeshko, Mikhail and Tokieda, Tadashi},
journal = {American Mathematical Monthly},
number = {6},
pages = {609 -- 612},
publisher = {Mathematical Association of America},
title = {{Surprises in numerical expressions of physical constants}},
doi = {10.4169/amer.math.monthly.123.6.609},
volume = {123},
year = {2016},
}
@article{1343,
abstract = {The Fermi-Hubbard model is one of the key models of condensed matter physics, which holds a
potential for explaining the mystery of high-temperature superconductivity. Recent progress in
ultracold atoms in optical lattices has paved the way to studying the model’s phase diagram using
the tools of quantum simulation, which emerged as a promising alternative to the numerical
calculations plagued by the infamous sign problem. However, the temperatures achieved using
elaborate laser cooling protocols so far have been too high to show the appearance of
antiferromagnetic (AF) and superconducting quantum phases directly. In this work, we demonstrate
that using the machinery of dissipative quantum state engineering, one can observe the emergence of
the AF order in the Fermi-Hubbard model with fermions in optical lattices. The core of the approach
is to add incoherent laser scattering in such a way that the AF state emerges as the dark state of
the driven-dissipative dynamics. The proposed controlled dissipation channels described in this work
are straightforward to add to already existing experimental setups.},
author = {Kaczmarczyk, Jan and Weimer, Hendrik and Lemeshko, Mikhail},
journal = {New Journal of Physics},
number = {9},
publisher = {IOP Publishing Ltd.},
title = {{Dissipative preparation of antiferromagnetic order in the Fermi-Hubbard model}},
doi = {10.1088/1367-2630/18/9/093042},
volume = {18},
year = {2016},
}
@article{1700,
abstract = {We use the dual boson approach to reveal the phase diagram of the Fermi-Hubbard model with long-range dipole-dipole interactions. By using a large-scale finite-temperature calculation on a 64×64 square lattice we demonstrate the existence of a novel phase, possessing an "ultralong-range" order. The fingerprint of this phase - the density correlation function - features a nontrivial behavior on a scale of tens of lattice sites. We study the properties and the stability of the ultralong-range-ordered phase, and show that it is accessible in modern experiments with ultracold polar molecules and magnetic atoms.},
author = {Van Loon, Erik and Katsnelson, Mikhail and Lemeshko, Mikhail},
journal = {Physical Review B},
number = {8},
publisher = {American Physical Society},
title = {{Ultralong-range order in the Fermi-Hubbard model with long-range interactions}},
doi = {10.1103/PhysRevB.92.081106},
volume = {92},
year = {2015},
}
@article{1813,
abstract = {We develop a microscopic theory describing a quantum impurity whose rotational degree of freedom is coupled to a many-particle bath. We approach the problem by introducing the concept of an “angulon”—a quantum rotor dressed by a quantum field—and reveal its quasiparticle properties using a combination of variational and diagrammatic techniques. Our theory predicts renormalization of the impurity rotational structure, such as that observed in experiments with molecules in superfluid helium droplets, in terms of a rotational Lamb shift induced by the many-particle environment. Furthermore, we discover a rich many-body-induced fine structure, emerging in rotational spectra due to a redistribution of angular momentum within the quantum many-body system.},
author = {Schmidt, Richard and Lemeshko, Mikhail},
journal = {Physical Review Letters},
number = {20},
publisher = {American Physical Society},
title = {{Rotation of quantum impurities in the presence of a many-body environment}},
doi = {10.1103/PhysRevLett.114.203001},
volume = {114},
year = {2015},
}