TY - JOUR AB - We present a numerical analysis of spin-1/2 fermions in a one-dimensional harmonic potential in the presence of a magnetic point-like impurity at the center of the trap. The model represents a few-body analogue of a magnetic impurity in the vicinity of an s-wave superconductor. Already for a few particles we find a ground-state level crossing between sectors with different fermion parities. We interpret this crossing as a few-body precursor of a quantum phase transition, which occurs when the impurity "breaks" a Cooper pair. This picture is further corroborated by analyzing density-density correlations in momentum space. Finally, we discuss how the system may be realized with existing cold-atoms platforms. AU - Rammelmüller, Lukas AU - Huber, David AU - Čufar, Matija AU - Brand, Joachim AU - Hammer, Hans-Werner AU - Volosniev, Artem ID - 13278 IS - 1 JF - SciPost Physics KW - General Physics and Astronomy SN - 2542-4653 TI - Magnetic impurity in a one-dimensional few-fermion system VL - 14 ER - TY - JOUR AB - The model of a ring threaded by the Aharonov-Bohm flux underlies our understanding of a coupling between gauge potentials and matter. The typical formulation of the model is based upon a single particle picture, and should be extended when interactions with other particles become relevant. Here, we illustrate such an extension for a particle in an Aharonov-Bohm ring subject to interactions with a weakly interacting Bose gas. We show that the ground state of the system can be described using the Bose-polaron concept—a particle dressed by interactions with a bosonic environment. We connect the energy spectrum to the effective mass of the polaron, and demonstrate how to change currents in the system by tuning boson-particle interactions. Our results suggest the Aharonov-Bohm ring as a platform for studying coherence and few- to many-body crossover of quasi-particles that arise from an impurity immersed in a medium. AU - Brauneis, Fabian AU - Ghazaryan, Areg AU - Hammer, Hans-Werner AU - Volosniev, Artem ID - 14246 JF - Communications Physics KW - General Physics and Astronomy SN - 2399-3650 TI - Emergence of a Bose polaron in a small ring threaded by the Aharonov-Bohm flux VL - 6 ER - TY - JOUR AB - We demonstrate that a sodium dimer, Na2(13Σ+u), residing on the surface of a helium nanodroplet, can be set into rotation by a nonresonant 1.0 ps infrared laser pulse. The time-dependent degree of alignment measured, exhibits a periodic, gradually decreasing structure that deviates qualitatively from that expected for gas-phase dimers. Comparison to alignment dynamics calculated from the time-dependent rotational Schrödinger equation shows that the deviation is due to the alignment dependent interaction between the dimer and the droplet surface. This interaction confines the dimer to the tangential plane of the droplet surface at the point where it resides and is the reason that the observed alignment dynamics is also well described by a 2D quantum rotor model. AU - Kranabetter, Lorenz AU - Kristensen, Henrik H. AU - Ghazaryan, Areg AU - Schouder, Constant A. AU - Chatterley, Adam S. AU - Janssen, Paul AU - Jensen, Frank AU - Zillich, Robert E. AU - Lemeshko, Mikhail AU - Stapelfeldt, Henrik ID - 14238 IS - 5 JF - Physical Review Letters SN - 0031-9007 TI - Nonadiabatic laser-induced alignment dynamics of molecules on a surface VL - 131 ER - TY - JOUR AB - We prove the r-spin cobordism hypothesis in the setting of (weak) 2-categories for every positive integer r: the 2-groupoid of 2-dimensional fully extended r-spin TQFTs with given target is equivalent to the homotopy fixed points of an induced Spin 2r -action. In particular, such TQFTs are classified by fully dualisable objects together with a trivialisation of the rth power of their Serre automorphisms. For r=1, we recover the oriented case (on which our proof builds), while ordinary spin structures correspond to r=2. To construct examples, we explicitly describe Spin 2r​-homotopy fixed points in the equivariant completion of any symmetric monoidal 2-category. We also show that every object in a 2-category of Landau–Ginzburg models gives rise to fully extended spin TQFTs and that half of these do not factor through the oriented bordism 2-category. AU - Carqueville, Nils AU - Szegedy, Lorant ID - 14756 IS - 3 JF - Quantum Topology KW - Geometry and Topology KW - Mathematical Physics SN - 1663-487X TI - Fully extended r-spin TQFTs VL - 14 ER - TY - JOUR AB - We study an impurity with a resonance level whose position coincides with the Fermi energy of the surrounding Fermi gas. An impurity causes a rapid variation of the scattering phase shift for fermions at the Fermi surface, introducing a new characteristic length scale into the problem. We investigate manifestations of this length scale in the self-energy of the impurity and in the density of the bath. Our calculations reveal a model-independent deformation of the density of the Fermi gas, which is determined by the width of the resonance. To provide a broader picture, we investigate time evolution of the density in quench dynamics, and study the behavior of the system at finite temperatures. Finally, we briefly discuss implications of our findings for the Fermi-polaron problem. AU - Maslov, Mikhail AU - Lemeshko, Mikhail AU - Volosniev, Artem ID - 10845 JF - Physical Review Research SN - 2643-1564 TI - Impurity with a resonance in the vicinity of the Fermi energy VL - 4 ER - TY - JOUR AB - A critical overview of the theory of the chirality-induced spin selectivity (CISS) effect, that is, phenomena in which the chirality of molecular species imparts significant spin selectivity to various electron processes, is provided. Based on discussions in a recently held workshop, and further work published since, the status of CISS effects—in electron transmission, electron transport, and chemical reactions—is reviewed. For each, a detailed discussion of the state-of-the-art in theoretical understanding is provided and remaining challenges and research opportunities are identified. AU - Evers, Ferdinand AU - Aharony, Amnon AU - Bar-Gill, Nir AU - Entin-Wohlman, Ora AU - Hedegård, Per AU - Hod, Oded AU - Jelinek, Pavel AU - Kamieniarz, Grzegorz AU - Lemeshko, Mikhail AU - Michaeli, Karen AU - Mujica, Vladimiro AU - Naaman, Ron AU - Paltiel, Yossi AU - Refaely-Abramson, Sivan AU - Tal, Oren AU - Thijssen, Jos AU - Thoss, Michael AU - Van Ruitenbeek, Jan M. AU - Venkataraman, Latha AU - Waldeck, David H. AU - Yan, Binghai AU - Kronik, Leeor ID - 10771 IS - 13 JF - Advanced Materials SN - 09359648 TI - Theory of chirality induced spin selectivity: Progress and challenges VL - 34 ER - TY - JOUR AB - Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed femtosecond probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules. AU - Qiang, Junjie AU - Zhou, Lianrong AU - Lu, Peifen AU - Lin, Kang AU - Ma, Yongzhe AU - Pan, Shengzhe AU - Lu, Chenxu AU - Jiang, Wenyu AU - Sun, Fenghao AU - Zhang, Wenbin AU - Li, Hui AU - Gong, Xiaochun AU - Averbukh, Ilya Sh AU - Prior, Yehiam AU - Schouder, Constant A. AU - Stapelfeldt, Henrik AU - Cherepanov, Igor AU - Lemeshko, Mikhail AU - Jäger, Wolfgang AU - Wu, Jian ID - 11552 IS - 24 JF - Physical Review Letters SN - 00319007 TI - Femtosecond rotational dynamics of D2 molecules in superfluid helium nanodroplets VL - 128 ER - TY - JOUR AB - We investigate the ground-state properties of weakly repulsive one-dimensional bosons in the presence of an attractive zero-range impurity potential. First, we derive mean-field solutions to the problem on a finite ring for the two asymptotic cases: (i) all bosons are bound to the impurity and (ii) all bosons are in a scattering state. Moreover, we derive the critical line that separates these regimes in the parameter space. In the thermodynamic limit, this critical line determines the maximum number of bosons that can be bound by the impurity potential, forming an artificial atom. Second, we validate the mean-field results using the flow equation approach and the multi-layer multi-configuration time-dependent Hartree method for atomic mixtures. While beyond-mean-field effects destroy long-range order in the Bose gas, the critical boson number is unaffected. Our findings are important for understanding such artificial atoms in low-density Bose gases with static and mobile impurities. AU - Brauneis, Fabian AU - Backert, Timothy G. AU - Mistakidis, Simeon I. AU - Lemeshko, Mikhail AU - Hammer, Hans Werner AU - Volosniev, Artem ID - 11590 IS - 6 JF - New Journal of Physics SN - 1367-2630 TI - Artificial atoms from cold bosons in one dimension VL - 24 ER - TY - JOUR AB - We compare recent experimental results [Science 375, 528 (2022)] of the superfluid unitary Fermi gas near the critical temperature with a thermodynamic model based on the elementary excitations of the system. We find good agreement between experimental data and our theory for several quantities such as first sound, second sound, and superfluid fraction. We also show that mode mixing between first and second sound occurs. Finally, we characterize the response amplitude to a density perturbation: Close to the critical temperature both first and second sound can be excited through a density perturbation, whereas at lower temperatures only the first sound mode exhibits a significant response. AU - Bighin, Giacomo AU - Cappellaro, Alberto AU - Salasnich, L. ID - 11592 IS - 6 JF - Physical Review A SN - 2469-9926 TI - Unitary Fermi superfluid near the critical temperature: Thermodynamics and sound modes from elementary excitations VL - 105 ER - TY - JOUR AB - Recently it became possible to study highly excited rotational states of molecules in superfluid helium through nonadiabatic alignment experiments (Cherepanov et al 2021 Phys. Rev. A 104 L061303). This calls for theoretical approaches that go beyond explaining renormalized values of molecular spectroscopic constants, which suffices when only the lowest few rotational states are involved. As the first step in this direction, here we present a basic quantum mechanical model describing highly excited rotational states of molecules in superfluid helium nanodroplets. We show that a linear molecule immersed in a superfluid can be seen as an effective symmetric top, similar to the rotational structure of radicals, such as OH or NO, but with the angular momentum of the superfluid playing the role of the electronic angular momentum in free molecules. The simple theory sheds light onto what happens when the rotational angular momentum of the molecule increases beyond the lowest excited states accessible by infrared spectroscopy. In addition, the model allows to estimate the effective rotational and centrifugal distortion constants for a broad range of species and to explain the crossover between light and heavy molecules in superfluid 4He in terms of the many-body wavefunction structure. Some of the above mentioned insights can be acquired by analyzing a simple 2 × 2 matrix. AU - Cherepanov, Igor AU - Bighin, Giacomo AU - Schouder, Constant A. AU - Chatterley, Adam S. AU - Stapelfeldt, Henrik AU - Lemeshko, Mikhail ID - 11998 IS - 7 JF - New Journal of Physics SN - 1367-2630 TI - A simple model for high rotational excitations of molecules in a superfluid VL - 24 ER -