TY - JOUR AB - 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. AU - Yakaboylu, Enderalp AU - Midya, Bikashkali AU - Deuchert, Andreas AU - Leopold, Nikolai K AU - Lemeshko, Mikhail ID - 5983 IS - 22 JF - Physical Review B SN - 2469-9950 TI - Theory of the rotating polaron: Spectrum and self-localization VL - 98 ER - TY - JOUR AB - 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. AU - Midya, Bikashkali AU - Konotop, Vladimir ID - 435 IS - 3 JF - Optics Letters TI - Coherent-perfect-absorber and laser for bound states in a continuum VL - 43 ER - TY - JOUR AB - 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. AU - Midya, Bikashkali AU - Konotop, Vladimir ID - 939 IS - 3 JF - Physical Review Letters SN - 00319007 TI - Waveguides with absorbing boundaries: Nonlinearity controlled by an exceptional point and solitons VL - 119 ER - TY - JOUR AB - We use recently developed angulon theory [R. Schmidt and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.203001] to study the rotational spectrum of a cyanide molecular anion immersed into Bose-Einstein condensates of rubidium and strontium. Based on ab initio potential energy surfaces, we provide a detailed study of the rotational Lamb shift and many-body-induced fine structure which arise due to dressing of molecular rotation by a field of phonon excitations. We demonstrate that the magnitude of these effects is large enough in order to be observed in modern experiments on cold molecular ions. Furthermore, we introduce a novel method to construct pseudopotentials starting from the ab initio potential energy surfaces, which provides a means to obtain effective coupling constants for low-energy polaron models. AU - Midya, Bikashkali AU - Tomza, Michał AU - Schmidt, Richard AU - Lemeshko, Mikhail ID - 1286 IS - 4 JF - Physical Review A - Atomic, Molecular, and Optical Physics TI - Rotation of cold molecular ions inside a Bose-Einstein condensate VL - 94 ER - TY - JOUR AB - A planar waveguide with an impedance boundary, composed of nonperfect metallic plates, and with passive or active dielectric filling, is considered. We show the possibility of selective mode guiding and amplification when a homogeneous pump is added to the dielectric and analyze differences in TE and TM mode propagation. Such a non-conservative system is also shown to feature exceptional points for specific and experimentally tunable parameters, which are described for a particular case of transparent dielectric. AU - Midya, Bikashkali AU - Konotop, Vladimir ID - 1287 IS - 20 JF - Optics Letters TI - Modes and exceptional points in waveguides with impedance boundary conditions VL - 41 ER -