Arxiv Selection Feb 2019
Feb 1-Feb 7 Ahmet Keles, Feb 8- Feb 14 Haiping Hu, Feb 15-Feb 21 Biao Huang, Feb 22-Feb 28 Xuguang Yue
Feb 1-Feb 7
Equilibrium trapping of cold atoms using dipole and radiative forces in an optical trap
Taro Mashimo, Masashi Abe, Satoshi Tojo
We report on highly effective trapping of cold atoms by a new method for a stable single optical trap in the near-optical resonant regime. An optical trap with the near-optical resonance condition consists of not only the dipole but also the radiative forces, while a trap using a far-off resonance dominates only the dipole force. We estimate a near-optical resonant trap for ultracold rubidium atoms in the range between -0.373 and -2.23 THz from the resonance. The time dependence of the trapped atoms indicates some difference of the stable center-of-mass positions in the near-optical resonant trap, and also indicates that the differences are caused by the change of the equilibrium condition of the optical dipole and radiative forces. A stable position depends only on laser detuning due to the change in the radiative force; however, the position is ineffective against the change in the laser intensity, which results in a change in the radiative force.
An Optical Tweezer Array of Ultracold Molecules
Loïc Anderegg, Lawrence W. Cheuk, Yicheng Bao, Sean Burchesky, Wolfgang Ketterle, Kang-Kuen Ni, John M. Doyle
Arrays of single ultracold molecules promise to be a powerful platform for many applications ranging from quantum simulation to precision measurement. Here we report on the creation of an optical tweezer array of single ultracold CaF molecules. By utilizing light-induced collisions during the laser cooling process, we trap single molecules. The high densities attained inside the tweezer traps have also enabled us to observe in the absence of light molecule-molecule collisions of laser cooled molecules for the first time.
Critical Opalescence across the Doping Driven Mott Transition in Optical Lattices of Ultracold Atoms
C. Walsh, P. Sémon, G. Sordi, A.-M. S. Tremblay
Phase transitions and their associated crossovers are imprinted in the behavior of fluctuations. Motivated by recent experiments on ultracold atoms in optical lattices, we compute the thermodynamic density fluctuations δN2 of the two-dimensional fermionic Hubbard model with plaquette cellular dynamical mean-field theory. To understand the length scale of these fluctuations, we separate the local from the nonlocal contributions to δN2. We determine the effects of particle statistics, interaction strength U, temperature T and density n. At high temperature, our theoretical framework reproduces the experimental observations in the doping-driven crossover regime between metal and Mott insulator. At low temperature, there is an increase of thermodynamic density fluctuations, analog to critical opalescence, accompanied by a surprising reduction of the absolute value of their nonlocal contributions. This is a precursory sign of an underlying phase transition between a pseudogap phase and a metallic state in doped Mott insulators, which should play an important role in the cuprate high-temperature superconductors. Predictions for ultracold atom experiments are made.
Quantum spiral spin-tensor magnetism
Xiaofan Zhou, Xi-Wang Luo, Gang Chen, Suotang Jia, Chuanwei Zhang
The characterization of quantum magnetism in a large spin (≥1) system naturally involves both spin-vectors and -tensors. While certain types of spin-vector (e.g., ferromagnetic, spiral) and spin-tensor (e.g., nematic in frustrated lattices) orders have been investigated separately, the coexistence and correlation between them have not been well explored. Here we propose and characterize a novel quantum spiral spin-tensor order on a spin-1 Heisenberg chain subject to a spiral spin-tensor Zeeman field, which can be experimentally realized using a Raman-dressed cold atom optical lattice. Through numerical density-matrix renormalization group (DMRG) simulation, we obtain the phase diagram and characterize the coexistence of spin-vector and spin-tensor orders as well as their correlations. Our results may open an avenue for exploring novel magnetic orders and spin-tensor electronics/atomtronics in large-spin systems.
Bloch oscillations of spin-orbit-coupled cold atoms in an optical lattice and spin current generation
Wei Ji, Keye Zhang, Weiping Zhang, Lu Zhou
We study the Bloch oscillation dynamics of a spin-orbit-coupled cold atomic gas trapped inside a one-dimensioanl optical lattice. The eigenspectra of the system is identified as two interpenetrating Wannier-Stark ladder. Based on that, we carefully analyzed the Bloch oscillation dynamics and found out that intraladder coupling between neighboring rungs of Wannier-Stark ladder give rise to ordinary Bloch oscillation while interladder coupling lead to small amplitude high frequency oscillation superimposed on it. Specifically spin-orbit interaction breaks Galilean invariance, which can be reflected by out-of-phase oscillation of the two spin components in the accelerated frame. The possibility of generating spin current in this system are also explored.
Bose-Einstein condensate in Bloch bands with off-diagonal periodic potential
Yue-Xin Huang, Wei Feng Zhuang, Xiang-Fa Zhou, Han Pu, Guang-Can Guo, Ming Gong
We report the Bose-Einstein condensate (BEC) in the Bloch bands with off-diagonal periodic potential (ODPP), which simultaneously plays the role of spin-orbit coupling (SOC) and Zeeman field. This model can be realized using two independent Raman couplings in the same three level system, in which the time-reversal symmetry ensures the energy degeneracy between the two states with opposite momenta. We find that these two Raman couplings can be used to tune the spin polarization in momentum space, thus greatly modifies the effective scatterings over the Bloch bands. We observe a transition from the Bloch plane wave phase with condensate at one wave vector to the Bloch stripe phase with condensates at the two Bloch states with opposite wave vectors. These two phases will exhibit totally different spin textures and density modulations in real space, which are totally different from that in free space. In momentum space multiple peaks differ by some reciprocal lattice vectors can be observed, reflecting the periodic structure of the ODPP. A three-band effective model is proposed to understand these observations. This system can provide a new platform in investigating of various physics, such as collective excitations, polaron and topological superlfuids, over the Bloch bands.
Entanglement structure of a quantum simulator: the two-component Bose-Hubbard model
Ivan Morera, Artur Polls, Bruno Juliá-Díaz
We consider a quantum simulator of the Heisenberg chain with ferromagnetic interactions based on the two-component 1D Bose-Hubbard model at filling equal to two in the strong coupling regime. The entanglement properties of the ground state are compared between the original spin model and the quantum simulator as the interspecies interaction approaches the intraspecies one. A numerical study of the entanglement properties of the quantum simulator state is supplemented with analytical expressions derived from the simulated Hamiltonian. At the isotropic point, the entanglement properties of the simulated system are not properly predicted by the quantum simulator.
Particle-number scaling of the quantum work statistics and Loschmidt echo in Fermi gases with time-dependent traps
Ettore Vicari
We investigate the particle-number dependence of some features of the out-of-equilibrium dynamics of d-dimensional Fermi gases in the dilute regime. We consider protocols entailing the variation of the external potential which confines the particles within a limited spatial region, in particular sudden changes of the trap size. In order to characterize the dynamic behavior of the Fermi gas, we consider various global quantities such as the ground-state fidelity for different trap sizes, the quantum work statistics associated with the protocol considered, and the Loschmidt echo measuring the overlap of the out-of-equilibrium quantum states with the initial ground state. Their asymptotic particle-number dependences show power laws for noninteracting Fermi gases. We also discuss the effects of short-ranged interactions to the power laws of the average work and its square fluctuations, within the Hubbard model and its continuum limit, arguing that they do not generally change the particle-number power laws of the free Fermi gases, in any spatial dimensions.
Feb 11
arXiv:1902.02912 [pdf]
Nanomechanical characterization of quantum interference in a topological insulator nanowire
Minjin Kim, Jihwan Kim, Yasen Hou, Dong Yu, Yong-Joo Doh, Bongsoo Kim, Kun Woo Kim, Junho Suh Comments: 15+16 pages, 4+11 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
The discovery of two-dimensional gapless Dirac fermions in graphene and topological insulators (TI) has sparked extensive ongoing research toward applications of their unique electronic properties. The gapless surface states in three-dimensional insulators indicate a distinct topological phase of matter with a non-trivial Z2 invariant that can be verified by angle-resolved photoemission spectroscopy or magnetoresistance quantum oscillation. In TI nanowires, the gapless surface states exhibit Aharonov-Bohm (AB) oscillations in conductance, with this quantum interference effect accompanying a change in the number of transverse one-dimensional modes in transport. Thus, while the density of states (DOS) of such nanowires is expected to show such AB oscillation, this effect has yet to be observed. Here, we adopt nanomechanical measurements that reveal AB oscillations in the DOS of a topological insulator. The TI nanowire under study is an electromechanical resonator embedded in an electrical circuit, and quantum capacitance effects from DOS oscillation modulate the circuit capacitance thereby altering the spring constant to generate mechanical resonant frequency shifts. Detection of the quantum capacitance effects from surface-state DOS is facilitated by the small effective capacitances and high quality factors of nanomechanical resonators, and as such the present technique could be extended to study diverse quantum materials at nanoscale.
Feb 12
arXiv:1902.03445 [pdf, other]
A nonlinear, geometric Hall effect without magnetic field
Nicholas B. Schade, David I. Schuster, Sidney R. Nagel Comments: 22 pages, 3 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall) The classical Hall effect, the traditional means of determining charge-carrier sign and density in a conductor, requires a magnetic field to produce transverse voltages across a current-carrying wire. We show that along curved paths -- without any magnetic field -- geometry alone can produce nonlinear transverse potentials that reflect the charge-carrier sign and density. We demonstrate this effect in curved graphene wires where the transverse potentials are consistent with the doping and change polarity as we switch the carrier sign. In straight wires, we measure transverse potential fluctuations with random polarity demonstrating that the current follows a complex, tortuous path. This geometrically-induced potential offers a sensitive characterization of inhomogeneous current flow in thin films.
