Arxiv Selection Jan 2019

Jan 1-Jan 7 Biao Huang, Jan 8- Jan 14 Xuguang Yue, Jan 15-Jan 21 Zehan Li, Jan 22-Jan 28 Jiansong Pan

Jan 14

1. arXiv:1901.03542 [pdf, ps, other]

Few-boson system with a single impurity: Universal bound states tied to Efimov trimers D. Blume

Comments: 14 pages, 7 figures

Subjects: Quantum Gases (cond-mat.quant-gas)

Small weakly-bound droplets determine a number of properties of ultracold Bose and Fermi gases. For example, Efimov trimers near the atom-atom-atom and atom-dimer thresholds lead to enhanced losses from bosonic clouds. Generalizations to four- and higher-body systems have also been considered. Moreover, Efimov trimers have been predicted to play a role in the Bose polaron with large boson-impurity scattering length. Motivated by these considerations, the present work provides a detailed theoretical analysis of weakly-bound N-body clusters consisting of N−1 identical bosons (denoted by "B") of mass m that interact with a single distinguishable impurity particle (denoted by "X") of mass M. The system properties are analyzed as a function of the mass ratio κ (values from κ=1 to 50 are considered), where κ is equal to m/M, and the two-body s-wave scattering length aBX between the bosons and the impurity. To reach the universal Efimov regime in which the size of the BBX trimer as well as those of larger clusters is much larger than the length scales of the underlying interaction model, three different approaches are considered: resonance states are determined in the absence of BB and BBX interactions, bound states are determined in the presence of repulsive three-body boson-boson-impurity interactions, and bound states are determined in the presence of repulsive two-body boson-boson interactions. The universal regime, in which the details of the underlying interaction model become irrelevant, is identified.

2. arXiv:1901.03519 [pdf, ps, other]

Superadiabatic generation of cat states in bosonic Josephson junctions under particle losses

Takuya Hatomura, Krzysztof Pawłowski

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We investigate a superadiabatic scheme to produce a cat state in a bosonic Josephson junction in absence and presence of particle losses. The generation scheme is based on shortcuts to adiabaticity and strongly relies on the parity conservation. The parity conservation also ensures that the produced state is a superposition of cat states with various sizes, i.e., a "cats state". Parity is also the quantity to be measured in order to utilize the produced state in interferometry. The generation scheme still works even if a number of particle losses during generation are substantial.

3. arXiv:1901.03643 (cross-list from nucl-th) [pdf, other]

Efimov universality with Coulomb interaction

C.H. Schmickler, H.-W. Hammer, E. Hiyama

Comments: 17 pages, 9 figures

Subjects: Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Atomic and Molecular Clusters (physics.atm-clus)

The universal properties of charged particles are modified by the presence of a long-range Coulomb interaction. We investigate the modification of Efimov universality as a function of the Coulomb strength using the Gaussian expansion method. The resonant short-range interaction is described by Gaussian potentials to which a Coulomb potential is added. We calculate binding energies and root mean square radii for the three- and four-body systems of charged particles and present our results in a generalised Efimov plot. We find that universal features can still be discerned for weak Coulomb interaction, but break down for strong Coulomb interaction. The root-mean-square radius plateaus at increasingly smaller values for strong Coulomb interaction and the probablity distributions of the states become more concentrated inside the Coulomb barrier. As an example, we apply our universal model to nuclei with an alpha-cluster substructure. Our results point to strong non-universal contributions in that sector.

4. arXiv:1901.03595 (cross-list from cond-mat.mes-hall) [pdf, other]

Bosonic Fractional Quantum Hall States on a Finite Cylinder

Paolo Rosson, Michael Lubasch, Martin Kiffner, Dieter Jaksch

Comments: 9 pages, 8 figures

Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We investigate the ground state properties of a bosonic Harper-Hofstadter model with local interactions on a finite cylindrical lattice with filling fraction ν=1/2. We find that our system supports topologically ordered states by calculating the topological entanglement entropy, and its value is in good agreement with the theoretical value for the ν=1/2 Laughlin state. By exploring the behaviour of the density profiles, edge currents and single-particle correlation functions, we find that the ground state on the cylinder shows all signatures of a fractional quantum Hall state even for large values of the magnetic flux density. Furthermore, we determine the dependence of the correlation functions and edge currents on the interaction strength. We find that depending on the magnetic flux density, the transition towards Laughlin-like behaviour can be either smooth or happens abruptly for some critical interaction strength.

Jan 11

1. arXiv:1901.03172 [pdf, other]

Emergence and stability of spontaneous vortex lattices in exciton-polariton condensates

F. X. Sun, Z. X. Niu, Q. H. Gong, Q. Y. He, W. Zhang

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

The spontaneous formation of lattice structure of quantized vortices is a characteristic feature of superfluidity in closed systems under thermal equilibrium. In exciton-polariton Bose-Einstein condensate, which is a typical example of macroscopic quantum state in open systems, spontaneous vortex lattices have also been proposed by not yet observed. Here, we take into account the finite decay rate of exciton reservoir, and theoretically investigate the vortex structures in circularly pumped polariton Bose-Einstein condensate. Our results show that a decreasing reservoir decay rate can reduce the number of vortices and destabilize the lattice structure, hence is unfavorable to the formation and observation of vortex lattices. These detrimental effects can be prevailed by applying an external angular momentum.

Jan 10

1. arXiv:1901.02829 [pdf, other]

Beyond-mean-field corrections for dipolar bosons in an optical lattice

Jan Kumlin, Krzysztof Jachymski, Hans Peter Büchler

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Recent experiments with ultracold lanthanide atoms which are characterized by a large magnetic moment have revealed the crucial importance of beyond-mean-field corrections in understanding the dynamics of the gas. We study how the presence of an external optical lattice modifies the structure of the corrections. We find that deep in the superfluid regime the equation of state is well described by introducing an anisotropic effective mass. However, for a deep lattice we find terms with anomalous density dependence which do not arise in free space. For a one-dimensional lattice, the relative orientation of the dipole axis with respect to the lattice plays a crucial role and the beyond-mean-field corrections can be either enhanced or suppressed.

2. arXiv:1901.02766 [pdf, other]

Polaron in a p+ip Fermi topological superfluid

Fang Qin, Xiaoling Cui, Wei Yi

Comments: 6 pages, 4 figures

Subjects: Quantum Gases (cond-mat.quant-gas)

We study polaron excitations induced by an impurity interacting with a two-dimensional p+ip Fermi superfluid. As the Fermi-Fermi pairing interaction is tuned, the background Fermi superfluid undergoes a topological phase transition. We show that such a transition is accompanied by a discontinuity in the second derivative of the polaron energy, regardless of the impurity-fermion interaction. We also identify a polaron to trimer crossover when the Fermi superfluid is in the strongly interacting, thus topologically trivial, regime. However, the trimer state is metastable against the molecular state where the impurity binds a Bogoliubov quasiparticle from the Fermi superfluid. By comparing the polaron to molecule transition in our system with that of an impurity in a non-interacting Fermi sea, we find that pairing interactions in the background Fermi superfluid effectively facilitate the impurity-fermion binding. Our results suggest the possibility of using the impurity as a probe for detecting topological phase transitions in the background, they also reveal interesting competitions between various many-body states in the system.

3. arXiv:1901.02595 [pdf, ps, other]

Angular Stripe Phase in Spin-Orbital-Angular-Momentum Coupled Bose Condensates

Xiao-Long Chen, Shi-Guo Peng, Peng Zou, Xia-Ji Liu, Hui Hu

Comments: 5+3 pages, 4+2 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

We propose that novel superfluid with supersolid-like properties - angular stripe phase - can be realized in a two-dimensional spin-1/2 Bose gas with spin-orbital-angular-momentum coupling. We predict a rich ground-state phase diagram, including the vortex-antivortex pair phase, half-skyrmion phase, and two different angular stripe phases. The stripe phases feature modulated angular density-density correlation with sizable contrast and can occupy a relatively large parameter space. The low-lying collective excitations, such as the dipole and breathing modes, show distinct behaviors in different phases. The existence of the novel angular stripe phase is also clearly indicated in the energetic and dynamic instabilities of collective modes near phase transitions. Our predictions of the angular stripe phase could be readily examined in current cold-atom experiments with 87Rb.

Jan 9

1. arXiv:1901.02325 [pdf, ps, other]

Tail-free self-accelerating solitons and vortices

Jieli Qin, Zhaoxin Liang, Boris A. Malomed, Guangjiong Dong

Comments: Accepted by Phys. Rev. A

Subjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS); Optics (physics.optics)

Self-accelerating waves in conservative systems, which usually feature slowly decaying tails, such as Airy waves, have drawn great interest in studies of quantum and classical wave dynamics. They typically appear in linear media, while nonlinearities tend to deform and eventually destroy them. We demonstrate, by means of analytical and numerical methods, the existence of robust one- and two-dimensional (1D and 2D) self-accelerating tailless solitons and solitary vortices in a model of two-component Bose-Einstein condensates, dressed by a microwave (MW) field, whose magnetic component mediates long-range interaction between the matter-wave constituents, with the feedback of the matter waves on the MW field taken into account. In particular, self-accelerating 2D solitons may move along a curved trajectory in the coordinate plane. The system may also include the spin-orbit coupling between the components, leading to similar results for the self-acceleration. The effect persists if the contact cubic nonlinearity is included. A similar mechanism may generate 1D and 2D self-accelerating solitons in optical media with thermal nonlinearity.

2. arXiv:1901.02268 [pdf, other]

A coherent superposition of Feshbach dimers and Efimov trimers

Yaakov Yudkin, Roy Elbaz, P. Giannakeas, Chris H. Greene, Lev Khaykovich

Comments: 7 pages, 4 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

In the domain of few-body physics, the laws of quantum mechanics allow formation of peculiar loosely bound states. Being insensitive to the details of the short range inter-particle interactions, they display a variety of universal properties. In recent years ultracold atoms emerged as a main experimental platform to explore universality in few-body systems. In the two-body domain, weakly bound dimers are now routinely used for the characterization of Feshbach resonances and serve as the initial state for the production of ultra-cold molecules in their ro-vibrational ground state. In the three-body domain, the captivating subject of Efimov-related physics has been explored in a variety of atomic systems. But, interestingly, experimental techniques used in these explorations have been limited to the study of inter-atomic inelastic processes, such as three-body recombination. Such an approach is best suited for the region of negative scattering lengths, where trimers can be associated from the three-atom continuum. In contrast, for positive scattering lengths the presence of dimers shifts the association related loss features into the atom-dimer continuum and Efimov resonances remain inaccessible for direct observation. Here we demonstrate a powerful experimental approach which turns the presence of the dimers into an advantage. We use them as a local reference for Efimov trimers by creating a coherent superposition of both states. Measurement of its coherent evolution provides information on the binding energy of the trimers with unprecedented precision. Even more importantly, it yields access to previously inaccessible parameters of the system such as the Efimov trimers' lifetime and the elastic processes between atoms and the constituents of the superposition state. Thus, our technique opens a new perspective on Efimov physics in a broad domain, where the main open questions persist.

Jan 8

arXiv:1901.01661 [pdf, other]

Time fractals and discrete scale invariance with trapped ions

Dean Lee, Jacob Watkins, Dillon Frame, Gabriel Given, Rongzheng He, Ning Li, Bing-Nan Lu, Avik Sarkar

Comments: 6 + 6 pages (main + supplemental materials), 2 + 3 figures (main + supplemental materials)

Subjects: Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)

We show that a one-dimensional chain of trapped ions can be engineered to produce a quantum mechanical system with discrete scale invariance and fractal-like time dependence. By discrete scale invariance we mean a system that replicates itself under a rescaling of distance for some particular scale factor. Similarly, a time fractal is a signal that is invariant under the rescaling of time. These features are reminiscent of the Efimov effect, which has been predicted and observed in bound states of three-body systems. We demonstrate that discrete scale invariance in the trapped ion system can be controlled with two independently tunable parameters and discuss the extension to many-body states where the discrete scaling symmetry is local and heterogeneous. The results we present can be realized using existing technologies developed for trapped ion quantum simulators.