@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{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},
}