Arxiv Selection Jan 2020
Jan 6 - Jan 12 Zehan Li, Jan 13 - Jan 19 Haiping Hu, Jan 22 - Jan 27 Sayan Choudhury
Jan 6
arXiv:2001.00795 (cross-list from quant-ph) [pdf, other]
A subradiant optical mirror formed by a single structured atomic layer
Jun Rui, David Wei, Antonio Rubio-Abadal, Simon Hollerith, Johannes Zeiher, Dan M. Stamper-Kurn, Christian Gross, Immanuel Bloch
Comments: 8 pages, 5 figures + 12 pages Supplementary Infomation
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Optics (physics.optics)
Jan 7
arXiv:2001.01487 (cross-list from nlin.PS) [pdf, other]
Singular solitons
Hidetsugu Sakaguchi, Boris A. Malomed
Comments: to be published in Physical Review E
Subjects: Pattern Formation and Solitons (nlin.PS); Quantum Gases (cond-mat.quant-gas); Optics (physics.optics)
We demonstrate that the commonly known concept, which treats solitons as nonsingular solu- tions produced by the interplay of nonlinear self-attraction and linear dispersion, may be extended to include modes with a relatively weak singularity at the central point, which keeps their inte- gral norm convergent. Such states are generated by self-repulsion, which should be strong enough, namely, represented by septimal, quintic, and usual cubic terms in the framework of the one-, two-, and three-dimensional (1D, 2D, and 3D) nonlinear Schro ̈dinger equations (NLSEs), respectively. Although such solutions seem counterintuitive, we demonstrate that they admit a straightforward interpretation as a result of screening of an additionally introduced attractive delta-functional po- tential by the defocusing nonlinearity. The strength (“bare charge”) of the attractive potential is infinite in 1D, finite in 2D, and vanishingly small in 3D. Analytical asymptotics of the singular solitons at small and large distances are found, entire shapes of the solitons being produced in a numerical form. Complete stability of the singular modes is accurately predicted by the anti- Vakhitov-Kolokolov criterion (under the assumption that it applies to the model), as verified by means of numerical methods. In 2D, the NLSE with a quintic self-focusing term admits singular- soliton solutions with intrinsic vorticity too, but they are fully unstable. We also mention that dissipative singular solitons can be produced by the model with a complex coefficient in front of the nonlinear term.
Jan 8
arXiv:2001.01925 [pdf, other]
Density wave propagation in a two-dimensional random dimer potential: from a single to a bipartite square lattice
Pablo Capuzzi, Patrizia Vignolo
Comments: 9 pages, 7 figures
Journal-ref: Phys. Rev. A 101, 013601 (2020)
Subjects: Quantum Gases (cond-mat.quant-gas); Disordered Systems and Neural Networks (cond-mat.dis-nn)
We study the propagation of a density perturbation in a weakly interacting boson gas confined on a lattice and in the presence of square dimerized impurities. Such a two-dimensional random-dimer model (2D-DRDM), previously introduced in [Capuzzi et al., Phys. Rev. A 92, 053622 (2015)], is the disorder transition from a single square lattice, where impurities are absent, to a bipartite square lattice, where the number of impurities is maximum and coincides with half the number of lattice sites. We show that disorder correlations can play a crucial role in the dynamics for a broad range of parameters by allowing density fluctuations to propagate in the 2D-DRDM lattice, even in the limit of strong disorder. In such a regime, the propagation speed depends on the percentage of impurities, interpolating between the speed in a single monoperiodic lattice and that in a bipartite one.
Jan 9
arXiv:2001.02315 [pdf, ps, other]
Driving Quantum Correlated Atom-Pairs from a Bose-Einstein Condensate
Liang-Ying Chih, Murray Holland
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The ability to cool quantum gases into the quantum degenerate realm has opened up possibilities for an extreme level of quantum-state control. In this paper, we investigate one such control protocol that demonstrates the resonant amplification of quasimomentum pairs from a Bose-Einstein condensate by the periodic modulation of the two-body s-wave scattering length. This shows a capability to selectively amplify quantum fluctuations with a predetermined momentum, where the momentum value can be spectroscopically tuned. A classical external field that excites pairs of particles with the same energy but opposite momenta is reminiscent of the coherently-driven nonlinearity in a parametric amplifier crystal in nonlinear optics. For this reason, it may be anticipated that the evolution will generate a ‘squeezed’ matter-wave state in the quasiparticle mode on resonance with the modulation frequency. Our model and analysis is motivated by a recent experiment by Clark et al. that observed a time-of- flight pattern similar to an exploding firework [1]. Since the drive is a highly coherent process, we interpret the observed firework patterns as arising from a monotonic growth in the two-body correlation amplitude, so that the jets should contain correlated atom pairs with nearly equal and opposite momenta. We propose a potential future experiment based on applying Ramsey interferometry to experimentally probe these pair correlations.
Jan10
arXiv:2001.02686 [pdf, other]
Observation of Dynamical Quantum Phase Transition with Correspondence in Excited State Phase Diagram
T. Tian, H.-X. Yang, L.-Y. Qiu, H.-Y. Liang, Y.-B. Yang, Y. Xu, L.-M. Duan
Comments: 7 pages; 6 figures; Physical Review Letters accepted
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Dynamical quantum phase transitions are closely related to equilibrium quantum phase transitions for ground states. Here, we report an experimental observation of a dynamical quantum phase transition in a spinor con- densate with correspondence in an excited state phase diagram, instead of the ground state one. We observe that the quench dynamics exhibits a non-analytical change with respect to a parameter in the final Hamiltonian in the absence of a corresponding phase transition for the ground state there. We make a connection between this sin- gular point and a phase transition point for the highest energy level in a subspace with zero spin magnetization of a Hamiltonian. We further show the existence of dynamical phase transitions for finite magnetization corre- sponding to the phase transition of the highest energy level in the subspace with the same magnetization. Our results open a door for using dynamical phase transitions as a tool to probe physics at higher energy eigenlevels of many-body Hamiltonians.
Jan13
arXiv:2001.03419
Universal Error Bound for Constrained Quantum Dynamics
Zongping Gong, Nobuyuki Yoshioka, Naoyuki Shibata, Ryusuke Hamazaki
Comments: 5 pages, 3 figures. Accompanying paper arXiv:2001.03421.
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph)
It is well known in quantum mechanics that a large energy gap can suppress transitions due to additional couplings and lead to a constrained dynamics within a Hilbert subspace. However, a general and quantitative justification of this statement stays lacking. Here we establish an observable-based error bound for such constrained dynamics in generic gapped quantum systems. This universal bound is a linear function of time that only involves the energy gap and coupling strength, provided that the latter is much smaller than the former. We demonstrate that both the intercept and the slope in the bound can asymptotically be saturated by simple models. We generalize the result to quantum many-body systems with local interactions, for which the coupling strength diverges in the thermodynamic limit while the error is found to grow no faster than a power law td+1 in d dimensions. Our work establishes a universal and rigorous result concerning nonequilibrium quantum dynamics.
Jan14
arXiv:2001.04331
Superfluid phases and excitations in a cold gas of d-wave interacting bosonic atoms and molecules
Zehan Li, Jian-Song Pan, W. Vincent Liu
Comments: 9 pages, 6 figures
Motivated by recent advance in orbitally tuned Feshbach resonance experiments, we analyze the ground-state phase diagram and related low-energy excitation spectra of a d-wave interacting Bose gas. A two-channel model with d-wave symmetric interactions and background s-wave interactions is adopted to characterize the gas. The ground state is found to show three interesting phases: atomic, molecular, and atomic-molecular superfluidity. Remarkably differently from what was previously known in the p-wave case, the atomic superfluid is found to be momentum-independent in the present d-wave case. Bogoliubov spectra above each superfluid phase are obtained both analytically and numerically.
arXiv:2001.03841
The Bulk-boundary Correspondence in Non-Hermitian Hopf-link Exceptional Line Semimetals
Zhicheng Zhang, Zhesen Yang, Jiangping Hu
Comments: 9 pages, 5 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
We consider a 3-dimensional (3D) non-Hermitian exceptional line semimetal model and take open boundary conditions in x, y, and z directions separately. In each case, we calculate the parameter regions where the bulk-boundary correspondence is broken. The breakdown of the bulk-boundary correspondence is manifested by the deviation from unit circles of generalized Brillouin zones (GBZ) and the discrepancy between spectra calculated with open boundary conditions (OBC) and periodic boundary conditions (PBC). The consistency between OBC and PBC spectra can be recovered if the PBC spectra are calculated with GBZs. We use both unit-circle Brillouin zones (BZ) and GBZs to plot the topological phase diagrams. The systematic analysis of the differences between the two phase diagrams suggests that it is necessary to use GBZ to characterize the bulk-boundary correspondence of non-Hermitian models.
Jan15
arXiv:2001.04969
Non-Hermitian band topology in active and dissipative mechanical metamaterials
Colin Scheibner, William T. M. Irvine, Vincenzo Vitelli
Networks of masses with transverse spring-like interactions provide a simple model of solids with energetic gain and loss. In this Letter, we study the non-Hermitian band topology of this model, which applies not only to active solids but also to gyroscopic metamaterials with dissipation. We examine a family of lattices in which topologically charged bands arise as activity (dissipation) is increased (decreased). The topological transition proceeds by a mechanism absent in Hermitian systems: Dirac cones spread out into exceptional rings rather than acquiring a gap. Above the transition, we observe chiral edge modes with a penetration depth that does not diverge even when the band gap closes.
Jan16
arXiv:2001.05688
Diagnosis of bulk phase diagram of non-reciprocal topological lattices by impurity modes
Yanxia Liu, Shu Chen
We study the single impurity problem in the non-Hermitian lattice described by the non-reciprocal Su-Schrieffer-Heeger model and obtain the phase diagram of localized bound states induced by the impurity. The existence of analytical results permits us to determine the phase boundaries exactly, which separate regions with different number of bound states. Particularly, in the limit of strong impurity potential, we find that the phase boundaries of mid-gap bound states are identical to the boundaries of topological phase diagrams of the bulk system in the absence of impurity. The existence of correspondence between mid-gap impurity modes and bulk phases indicate that we are able to diagnose the bulk phase diagram of the non-reciprocal topological model by its impurity modes.
