@article{8816,
abstract = {Area-dependent quantum field theory is a modification of two-dimensional topological quantum field theory, where one equips each connected component of a bordism with a positive real number—interpreted as area—which behaves additively under glueing. As opposed to topological theories, in area-dependent theories the state spaces can be infinite-dimensional. We introduce the notion of regularised Frobenius algebras in Hilbert spaces and show that area-dependent theories are in one-to-one correspondence to commutative regularised Frobenius algebras. We also provide a state sum construction for area-dependent theories. Our main example is two-dimensional Yang–Mills theory with compact gauge group, which we treat in detail.},
author = {Runkel, Ingo and Szegedy, Lorant},
issn = {14320916},
journal = {Communications in Mathematical Physics},
number = {1},
pages = {83–117},
publisher = {Springer Nature},
title = {{Area-dependent quantum field theory}},
doi = {10.1007/s00220-020-03902-1},
volume = {381},
year = {2021},
}
@article{9005,
abstract = {Studies on the experimental realization of two-dimensional anyons in terms of quasiparticles have been restricted, so far, to only anyons on the plane. It is known, however, that the geometry and topology of space can have significant effects on quantum statistics for particles moving on it. Here, we have undertaken the first step toward realizing the emerging fractional statistics for particles restricted to move on the sphere instead of on the plane. We show that such a model arises naturally in the context of quantum impurity problems. In particular, we demonstrate a setup in which the lowest-energy spectrum of two linear bosonic or fermionic molecules immersed in a quantum many-particle environment can coincide with the anyonic spectrum on the sphere. This paves the way toward the experimental realization of anyons on the sphere using molecular impurities. Furthermore, since a change in the alignment of the molecules corresponds to the exchange of the particles on the sphere, such a realization reveals a novel type of exclusion principle for molecular impurities, which could also be of use as a powerful technique to measure the statistics parameter. Finally, our approach opens up a simple numerical route to investigate the spectra of many anyons on the sphere. Accordingly, we present the spectrum of two anyons on the sphere in the presence of a Dirac monopole field.},
author = {Brooks, Morris and Lemeshko, Mikhail and Lundholm, D. and Yakaboylu, Enderalp},
issn = {10797114},
journal = {Physical Review Letters},
number = {1},
publisher = {American Physical Society},
title = {{Molecular impurities as a realization of anyons on the two-sphere}},
doi = {10.1103/PhysRevLett.126.015301},
volume = {126},
year = {2021},
}
@article{9093,
abstract = {We employ the Gross-Pitaevskii equation to study acoustic emission generated in a uniform Bose gas by a static impurity. The impurity excites a sound-wave packet, which propagates through the gas. We calculate the shape of this wave packet in the limit of long wave lengths, and argue that it is possible to extract properties of the impurity by observing this shape. We illustrate here this possibility for a Bose gas with a trapped impurity atom -- an example of a relevant experimental setup. Presented results are general for all one-dimensional systems described by the nonlinear Schrödinger equation and can also be used in nonatomic systems, e.g., to analyze light propagation in nonlinear optical media. Finally, we calculate the shape of the sound-wave packet for a three-dimensional Bose gas assuming a spherically symmetric perturbation.},
author = {Marchukov, Oleksandr and Volosniev, Artem},
issn = {2542-4653},
journal = {SciPost Physics},
number = {2},
publisher = {SciPost Foundation},
title = {{Shape of a sound wave in a weakly-perturbed Bose gas}},
doi = {10.21468/scipostphys.10.2.025},
volume = {10},
year = {2021},
}
@article{9606,
abstract = {Sound propagation is a macroscopic manifestation of the interplay between the equilibrium thermodynamics and the dynamical transport properties of fluids. Here, for a two-dimensional system of ultracold fermions, we calculate the first and second sound velocities across the whole BCS-BEC crossover, and we analyze the system response to an external perturbation. In the low-temperature regime we reproduce the recent measurements [Phys. Rev. Lett. 124, 240403 (2020)] of the first sound velocity, which, due to the decoupling of density and entropy fluctuations, is the sole mode excited by a density probe. Conversely, a heat perturbation excites only the second sound, which, being sensitive to the superfluid depletion, vanishes in the deep BCS regime and jumps discontinuously to zero at the Berezinskii-Kosterlitz-Thouless superfluid transition. A mixing between the modes occurs only in the finite-temperature BEC regime, where our theory converges to the purely bosonic results.},
author = {Tononi, A. and Cappellaro, Alberto and Bighin, Giacomo and Salasnich, L.},
issn = {24699934},
journal = {Physical Review A},
number = {6},
publisher = {American Physical Society},
title = {{Propagation of first and second sound in a two-dimensional Fermi superfluid}},
doi = {10.1103/PhysRevA.103.L061303},
volume = {103},
year = {2021},
}
@article{9679,
abstract = {The relative motion of three impenetrable particles on a ring, in our case two identical fermions and one impurity, is isomorphic to a triangular quantum billiard. Depending on the ratio κ of the impurity and fermion masses, the billiards can be integrable or non-integrable (also referred to in the main text as chaotic). To set the stage, we first investigate the energy level distributions of the billiards as a function of 1/κ ∈ [0, 1] and find no evidence of integrable cases beyond the limiting values 1/κ = 1 and 1/κ = 0. Then, we use machine learning tools to analyze properties of probability distributions of individual quantum states. We find that convolutional neural networks can correctly classify integrable and non-integrable states. The decisive features of the wave functions are the normalization and a large number of zero elements, corresponding to the existence of a nodal line. The network achieves typical accuracies of 97%, suggesting that machine learning tools can be used to analyze and classify the morphology of probability densities obtained in theory or experiment.},
author = {Huber, David and Marchukov, Oleksandr V. and Hammer, Hans Werner and Volosniev, Artem},
issn = {13672630},
journal = {New Journal of Physics},
number = {6},
publisher = {IOP Publishing},
title = {{Morphology of three-body quantum states from machine learning}},
doi = {10.1088/1367-2630/ac0576},
volume = {23},
year = {2021},
}
@article{7956,
abstract = {When short-range attractions are combined with long-range repulsions in colloidal particle systems, complex microphases can emerge. Here, we study a system of isotropic particles, which can form lamellar structures or a disordered fluid phase when temperature is varied. We show that, at equilibrium, the lamellar structure crystallizes, while out of equilibrium, the system forms a variety of structures at different shear rates and temperatures above melting. The shear-induced ordering is analyzed by means of principal component analysis and artificial neural networks, which are applied to data of reduced dimensionality. Our results reveal the possibility of inducing ordering by shear, potentially providing a feasible route to the fabrication of ordered lamellar structures from isotropic particles.},
author = {Pȩkalski, J. and Rzadkowski, Wojciech and Panagiotopoulos, A. Z.},
issn = {10897690},
journal = {The Journal of chemical physics},
number = {20},
publisher = {AIP},
title = {{Shear-induced ordering in systems with competing interactions: A machine learning study}},
doi = {10.1063/5.0005194},
volume = {152},
year = {2020},
}
@article{7968,
abstract = {Organic materials are known to feature long spin-diffusion times, originating in a generally small spin–orbit coupling observed in these systems. From that perspective, chiral molecules acting as efficient spin selectors pose a puzzle that attracted a lot of attention in recent years. Here, we revisit the physical origins of chiral-induced spin selectivity (CISS) and propose a simple analytic minimal model to describe it. The model treats a chiral molecule as an anisotropic wire with molecular dipole moments aligned arbitrarily with respect to the wire’s axes and is therefore quite general. Importantly, it shows that the helical structure of the molecule is not necessary to observe CISS and other chiral nonhelical molecules can also be considered as potential candidates for the CISS effect. We also show that the suggested simple model captures the main characteristics of CISS observed in the experiment, without the need for additional constraints employed in the previous studies. The results pave the way for understanding other related physical phenomena where the CISS effect plays an essential role.},
author = {Ghazaryan, Areg and Paltiel, Yossi and Lemeshko, Mikhail},
issn = {1932-7447},
journal = {The Journal of Physical Chemistry C},
number = {21},
pages = {11716--11721},
publisher = {American Chemical Society},
title = {{Analytic model of chiral-induced spin selectivity}},
doi = {10.1021/acs.jpcc.0c02584},
volume = {124},
year = {2020},
}
@article{8170,
abstract = {Alignment of OCS, CS2, and I2 molecules embedded in helium nanodroplets is measured as a function
of time following rotational excitation by a nonresonant, comparatively weak ps laser pulse. The distinct
peaks in the power spectra, obtained by Fourier analysis, are used to determine the rotational, B, and
centrifugal distortion, D, constants. For OCS, B and D match the values known from IR spectroscopy. For
CS2 and I2, they are the first experimental results reported. The alignment dynamics calculated from the
gas-phase rotational Schrödinger equation, using the experimental in-droplet B and D values, agree in
detail with the measurement for all three molecules. The rotational spectroscopy technique for molecules in
helium droplets introduced here should apply to a range of molecules and complexes.},
author = {Chatterley, Adam S. and Christiansen, Lars and Schouder, Constant A. and Jørgensen, Anders V. and Shepperson, Benjamin and Cherepanov, Igor and Bighin, Giacomo and Zillich, Robert E. and Lemeshko, Mikhail and Stapelfeldt, Henrik},
issn = {10797114},
journal = {Physical Review Letters},
number = {1},
publisher = {American Physical Society},
title = {{Rotational coherence spectroscopy of molecules in Helium nanodroplets: Reconciling the time and the frequency domains}},
doi = {10.1103/PhysRevLett.125.013001},
volume = {125},
year = {2020},
}
@article{8587,
abstract = {Inspired by the possibility to experimentally manipulate and enhance chemical reactivity in helium nanodroplets, we investigate the effective interaction and the resulting correlations between two diatomic molecules immersed in a bath of bosons. By analogy with the bipolaron, we introduce the biangulon quasiparticle describing two rotating molecules that align with respect to each other due to the effective attractive interaction mediated by the excitations of the bath. We study this system in different parameter regimes and apply several theoretical approaches to describe its properties. Using a Born–Oppenheimer approximation, we investigate the dependence of the effective intermolecular interaction on the rotational state of the two molecules. In the strong-coupling regime, a product-state ansatz shows that the molecules tend to have a strong alignment in the ground state. To investigate the system in the weak-coupling regime, we apply a one-phonon excitation variational ansatz, which allows us to access the energy spectrum. In comparison to the angulon quasiparticle, the biangulon shows shifted angulon instabilities and an additional spectral instability, where resonant angular momentum transfer between the molecules and the bath takes place. These features are proposed as an experimentally observable signature for the formation of the biangulon quasiparticle. Finally, by using products of single angulon and bare impurity wave functions as basis states, we introduce a diagonalization scheme that allows us to describe the transition from two separated angulons to a biangulon as a function of the distance between the two molecules.},
author = {Li, Xiang and Yakaboylu, Enderalp and Bighin, Giacomo and Schmidt, Richard and Lemeshko, Mikhail and Deuchert, Andreas},
issn = {0021-9606},
journal = {The Journal of Chemical Physics},
keywords = {Physical and Theoretical Chemistry, General Physics and Astronomy},
number = {16},
publisher = {AIP Publishing},
title = {{Intermolecular forces and correlations mediated by a phonon bath}},
doi = {10.1063/1.5144759},
volume = {152},
year = {2020},
}
@article{8588,
abstract = {Dipolar (or spatially indirect) excitons (IXs) in semiconductor double quantum well (DQW) subjected to an electric field are neutral species with a dipole moment oriented perpendicular to the DQW plane. Here, we theoretically study interactions between IXs in stacked DQW bilayers, where the dipolar coupling can be either attractive or repulsive depending on the relative positions of the particles. By using microscopic band structure calculations to determine the electronic states forming the excitons, we show that the attractive dipolar interaction between stacked IXs deforms their electronic wave function, thereby increasing the inter-DQW interaction energy and making the IX even more electrically polarizable. Many-particle interaction effects are addressed by considering the coupling between a single IX in one of the DQWs to a cloud of IXs in the other DQW, which is modeled either as a closed-packed lattice or as a continuum IX fluid. We find that the lattice model yields IX interlayer binding energies decreasing with increasing lattice density. This behavior is due to the dominating role of the intra-DQW dipolar repulsion, which prevents more than one exciton from entering the attractive region of the inter-DQW coupling. Finally, both models shows that the single IX distorts the distribution of IXs in the adjacent DQW, thus inducing the formation of an IX dipolar polaron (dipolaron). While the interlayer binding energy reduces with IX density for lattice dipolarons, the continuous polaron model predicts a nonmonotonous dependence on density in semiquantitative agreement with a recent experimental study [cf. Hubert et al., Phys. Rev. X 9, 021026 (2019)].},
author = {Hubert, C. and Cohen, K. and Ghazaryan, Areg and Lemeshko, Mikhail and Rapaport, R. and Santos, P. V.},
issn = {2469-9950},
journal = {Physical Review B},
number = {4},
publisher = {American Physical Society},
title = {{Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids}},
doi = {10.1103/physrevb.102.045307},
volume = {102},
year = {2020},
}
@article{8644,
abstract = {Determining the phase diagram of systems consisting of smaller subsystems 'connected' via a tunable coupling is a challenging task relevant for a variety of physical settings. A general question is whether new phases, not present in the uncoupled limit, may arise. We use machine learning and a suitable quasidistance between different points of the phase diagram to study layered spin models, in which the spin variables constituting each of the uncoupled systems (to which we refer as layers) are coupled to each other via an interlayer coupling. In such systems, in general, composite order parameters involving spins of different layers may emerge as a consequence of the interlayer coupling. We focus on the layered Ising and Ashkin–Teller models as a paradigmatic case study, determining their phase diagram via the application of a machine learning algorithm to the Monte Carlo data. Remarkably our technique is able to correctly characterize all the system phases also in the case of hidden order parameters, i.e. order parameters whose expression in terms of the microscopic configurations would require additional preprocessing of the data fed to the algorithm. We correctly retrieve the three known phases of the Ashkin–Teller model with ferromagnetic couplings, including the phase described by a composite order parameter. For the bilayer and trilayer Ising models the phases we find are only the ferromagnetic and the paramagnetic ones. Within the approach we introduce, owing to the construction of convolutional neural networks, naturally suitable for layered image-like data with arbitrary number of layers, no preprocessing of the Monte Carlo data is needed, also with regard to its spatial structure. The physical meaning of our results is discussed and compared with analytical data, where available. Yet, the method can be used without any a priori knowledge of the phases one seeks to find and can be applied to other models and structures.},
author = {Rzadkowski, Wojciech and Defenu, N and Chiacchiera, S and Trombettoni, A and Bighin, Giacomo},
issn = {13672630},
journal = {New Journal of Physics},
number = {9},
publisher = {IOP Publishing},
title = {{Detecting composite orders in layered models via machine learning}},
doi = {10.1088/1367-2630/abae44},
volume = {22},
year = {2020},
}
@article{8652,
abstract = {Nature creates electrons with two values of the spin projection quantum number. In certain applications, it is important to filter electrons with one spin projection from the rest. Such filtering is not trivial, since spin-dependent interactions are often weak, and cannot lead to any substantial effect. Here we propose an efficient spin filter based upon scattering from a two-dimensional crystal, which is made of aligned point magnets. The polarization of the outgoing electron flux is controlled by the crystal, and reaches maximum at specific values of the parameters. In our scheme, polarization increase is accompanied by higher reflectivity of the crystal. High transmission is feasible in scattering from a quantum cavity made of two crystals. Our findings can be used for studies of low-energy spin-dependent scattering from two-dimensional ordered structures made of magnetic atoms or aligned chiral molecules.},
author = {Ghazaryan, Areg and Lemeshko, Mikhail and Volosniev, Artem},
issn = {2399-3650},
journal = {Communications Physics},
publisher = {Springer Nature},
title = {{Filtering spins by scattering from a lattice of point magnets}},
doi = {10.1038/s42005-020-00445-8},
volume = {3},
year = {2020},
}
@article{8699,
abstract = {In the high spin–orbit-coupled Sr2IrO4, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir–O bond geometry in Sr2IrO4 and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained Sr2IrO4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron–hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr2IrO4, originating from the modified hopping elements between the t2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr2IrO4 and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin–orbit coupling.},
author = {Paris, Eugenio and Tseng, Yi and Paerschke, Ekaterina and Zhang, Wenliang and Upton, Mary H and Efimenko, Anna and Rolfs, Katharina and McNally, Daniel E and Maurel, Laura and Naamneh, Muntaser and Caputo, Marco and Strocov, Vladimir N and Wang, Zhiming and Casa, Diego and Schneider, Christof W and Pomjakushina, Ekaterina and Wohlfeld, Krzysztof and Radovic, Milan and Schmitt, Thorsten},
issn = {10916490},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = {40},
pages = {24764--24770},
publisher = {National Academy of Sciences},
title = {{Strain engineering of the charge and spin-orbital interactions in Sr2IrO4}},
doi = {10.1073/pnas.2012043117},
volume = {117},
year = {2020},
}
@article{8726,
abstract = {Several realistic spin-orbital models for transition metal oxides go beyond the classical expectations and could be understood only by employing the quantum entanglement. Experiments on these materials confirm that spin-orbital entanglement has measurable consequences. Here, we capture the essential features of spin-orbital entanglement in complex quantum matter utilizing 1D spin-orbital model which accommodates SU(2)⊗SU(2) symmetric Kugel-Khomskii superexchange as well as the Ising on-site spin-orbit coupling. Building on the results obtained for full and effective models in the regime of strong spin-orbit coupling, we address the question whether the entanglement found on superexchange bonds always increases when the Ising spin-orbit coupling is added. We show that (i) quantum entanglement is amplified by strong spin-orbit coupling and, surprisingly, (ii) almost classical disentangled states are possible. We complete the latter case by analyzing how the entanglement existing for intermediate values of spin-orbit coupling can disappear for higher values of this coupling.},
author = {Gotfryd, Dorota and Paerschke, Ekaterina and Wohlfeld, Krzysztof and Oleś, Andrzej M.},
issn = {2410-3896},
journal = {Condensed Matter},
number = {3},
publisher = {MDPI},
title = {{Evolution of spin-orbital entanglement with increasing ising spin-orbit coupling}},
doi = {10.3390/condmat5030053},
volume = {5},
year = {2020},
}
@article{8741,
abstract = {In ecology, climate and other fields, (sub)systems have been identified that can transition into a qualitatively different state when a critical threshold or tipping point in a driving process is crossed. An understanding of those tipping elements is of great interest given the increasing influence of humans on the biophysical Earth system. Complex interactions exist between tipping elements, e.g. physical mechanisms connect subsystems of the climate system. Based on earlier work on such coupled nonlinear systems, we systematically assessed the qualitative long-term behaviour of interacting tipping elements. We developed an understanding of the consequences of interactions
on the tipping behaviour allowing for tipping cascades to emerge under certain conditions. The (narrative) application of
these qualitative results to real-world examples of interacting tipping elements indicates that tipping cascades with profound consequences may occur: the interacting Greenland ice sheet and thermohaline ocean circulation might tip before the tipping points of the isolated subsystems are crossed. The eutrophication of the first lake in a lake chain might propagate through the following lakes without a crossing of their individual critical nutrient input levels. The possibility of emerging cascading tipping dynamics calls for the development of a unified theory of interacting tipping elements and the quantitative analysis of interacting real-world tipping elements.},
author = {Klose, Ann Kristin and Karle, Volker and Winkelmann, Ricarda and Donges, Jonathan F.},
issn = {20545703},
journal = {Royal Society Open Science},
number = {6},
title = {{Emergence of cascading dynamics in interacting tipping elements of ecology and climate: Cascading dynamics in tipping elements}},
doi = {10.1098/rsos.200599},
volume = {7},
year = {2020},
}
@article{8769,
abstract = {One of the hallmarks of quantum statistics, tightly entwined with the concept of topological phases of matter, is the prediction of anyons. Although anyons are predicted to be realized in certain fractional quantum Hall systems, they have not yet been unambiguously detected in experiment. Here we introduce a simple quantum impurity model, where bosonic or fermionic impurities turn into anyons as a consequence of their interaction with the surrounding many-particle bath. A cloud of phonons dresses each impurity in such a way that it effectively attaches fluxes or vortices to it and thereby converts it into an Abelian anyon. The corresponding quantum impurity model, first, provides a different approach to the numerical solution of the many-anyon problem, along with a concrete perspective of anyons as emergent quasiparticles built from composite bosons or fermions. More importantly, the model paves the way toward realizing anyons using impurities in crystal lattices as well as ultracold gases. In particular, we consider two heavy electrons interacting with a two-dimensional lattice crystal in a magnetic field, and show that when the impurity-bath system is rotated at the cyclotron frequency, impurities behave as anyons as a consequence of the angular momentum exchange between the impurities and the bath. A possible experimental realization is proposed by identifying the statistics parameter in terms of the mean-square distance of the impurities and the magnetization of the impurity-bath system, both of which are accessible to experiment. Another proposed application is impurities immersed in a two-dimensional weakly interacting Bose gas.},
author = {Yakaboylu, Enderalp and Ghazaryan, Areg and Lundholm, D. and Rougerie, N. and Lemeshko, Mikhail and Seiringer, Robert},
issn = {2469-9950},
journal = {Physical Review B},
number = {14},
publisher = {American Physical Society},
title = {{Quantum impurity model for anyons}},
doi = {10.1103/physrevb.102.144109},
volume = {102},
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{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{7882,
abstract = {A few-body cluster is a building block of a many-body system in a gas phase provided the temperature at most is of the order of the binding energy of this cluster. Here we illustrate this statement by considering a system of tubes filled with dipolar distinguishable particles. We calculate the partition function, which determines the probability to find a few-body cluster at a given temperature. The input for our calculations—the energies of few-body clusters—is estimated using the harmonic approximation. We first describe and demonstrate the validity of our numerical procedure. Then we discuss the results featuring melting of the zero-temperature many-body state into a gas of free particles and few-body clusters. For temperature higher than its binding energy threshold, the dimers overwhelmingly dominate the ensemble, where the remaining probability is in free particles. At very high temperatures free (harmonic oscillator trap-bound) particle dominance is eventually reached. This structure evolution appears both for one and two particles in each layer providing crucial information about the behavior of ultracold dipolar gases. The investigation addresses the transition region between few- and many-body physics as a function of temperature using a system of ten dipoles in five tubes.},
author = {Armstrong, Jeremy R. and Jensen, Aksel S. and Volosniev, Artem and Zinner, Nikolaj T.},
issn = {22277390},
journal = {Mathematics},
number = {4},
publisher = {MDPI},
title = {{Clusters in separated tubes of tilted dipoles}},
doi = {10.3390/math8040484},
volume = {8},
year = {2020},
}
@article{7919,
abstract = {We explore the time evolution of two impurities in a trapped one-dimensional Bose gas that follows a change of the boson-impurity interaction. We study the induced impurity-impurity interactions and their effect on the quench dynamics. In particular, we report on the size of the impurity cloud, the impurity-impurity entanglement, and the impurity-impurity correlation function. The presented numerical simulations are based upon the variational multilayer multiconfiguration time-dependent Hartree method for bosons. To analyze and quantify induced impurity-impurity correlations, we employ an effective two-body Hamiltonian with a contact interaction. We show that the effective model consistent with the mean-field attraction of two heavy impurities explains qualitatively our results for weak interactions. Our findings suggest that the quench dynamics in cold-atom systems can be a tool for studying impurity-impurity correlations.},
author = {Mistakidis, S. I. and Volosniev, Artem and Schmelcher, P.},
issn = {2643-1564},
journal = {Physical Review Research},
publisher = {American Physical Society},
title = {{Induced correlations between impurities in a one-dimensional quenched Bose gas}},
doi = {10.1103/physrevresearch.2.023154},
volume = {2},
year = {2020},
}
@article{7933,
abstract = {We study a mobile quantum impurity, possessing internal rotational degrees of freedom, confined to a ring in the presence of a many-particle bosonic bath. By considering the recently introduced rotating polaron problem, we define the Hamiltonian and examine the energy spectrum. The weak-coupling regime is studied by means of a variational ansatz in the truncated Fock space. The corresponding spectrum indicates that there emerges a coupling between the internal and orbital angular momenta of the impurity as a consequence of the phonon exchange. We interpret the coupling as a phonon-mediated spin-orbit coupling and quantify it by using a correlation function between the internal and the orbital angular momentum operators. The strong-coupling regime is investigated within the Pekar approach, and it is shown that the correlation function of the ground state shows a kink at a critical coupling, that is explained by a sharp transition from the noninteracting state to the states that exhibit strong interaction with the surroundings. The results might find applications in such fields as spintronics or topological insulators where spin-orbit coupling is of crucial importance.},
author = {Maslov, Mikhail and Lemeshko, Mikhail and Yakaboylu, Enderalp},
issn = {24699969},
journal = {Physical Review B},
number = {18},
publisher = {American Physical Society},
title = {{Synthetic spin-orbit coupling mediated by a bosonic environment}},
doi = {10.1103/PhysRevB.101.184104},
volume = {101},
year = {2020},
}
@phdthesis{8958,
abstract = {The oft-quoted dictum by Arthur Schawlow: ``A diatomic molecule has one atom too many'' has been disavowed. Inspired by the possibility to experimentally manipulate and enhance chemical reactivity in helium nanodroplets, we investigate the rotation of coupled cold molecules in the presence of a many-body environment.
In this thesis, 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.
With this theoretical toolbox, we reveal the self-localization transition for the angulon quasiparticle. We show that, unlike for 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 symmetry breaking is dictated by the symmetry of the microscopic impurity-bath interaction, which leads to a number of distinct self-localized states.
For the system containing multiple impurities, by analogy with the bipolaron, we introduce the biangulon quasiparticle describing two rotating molecules that align with respect to each other due to the effective attractive interaction mediated by the excitations of the bath. We study this system from the strong-coupling regime to the weak molecule-bath interaction regime. We show that the molecules tend to have a strong alignment in the ground state, the biangulon shows shifted angulon instabilities and an additional spectral instability, where resonant angular momentum transfer between the molecules and the bath takes place. Finally, we introduce a diagonalization scheme that allows us to describe the transition from two separated angulons to a biangulon as a function of the distance between the two molecules.},
author = {Li, Xiang},
issn = {2663-337X},
pages = {125},
publisher = {IST Austria},
title = {{Rotation of coupled cold molecules in the presence of a many-body environment}},
doi = {10.15479/AT:ISTA:8958},
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{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{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{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},
}
@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{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{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},
}
@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{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{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{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{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{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{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{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{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{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{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{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},
}
@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},
}
@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{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},
}
@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{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{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{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{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},
}