Arxiv Selection Oct 2018

Oct 1- Oct 7 Xuguang Yue, Oct 8- Oct 16 Haiyuan Zou, Oct 17- Oct 23 Zehan Li, Oct 24-Oct 30 Jiansong Pan

Oct. 5

1. arXiv:1810.02337 [pdf, other]

Topological Devil's staircase in atomic two-leg ladders

S. Barbarino, D. Rossini, M. Rizzi, R. Fazio, G. E. Santoro, M. Dalmonte

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

We show that a hierarchy of topological phases in one dimension - a topological Devil's staircase - can emerge at fractional filling fractions in interacting systems, whose single-particle band structure describes a topological or a crystalline topological insulator. Focusing on a specific example in the BDI class, we present a field-theoretical argument based on bosonization that indicates how the system phase diagram, as a function of the filling fraction, hosts a series of density waves. Subsequently, based on a numerical investigation of spectral properties, Wilczek-Zee phases, and entanglement spectra, we show that these phases can support symmetry-protected topological order. In sharp contrast to the non-interacting limit, these topological density waves do not follow the boundary-edge correspondence, as their edge modes are gapped. We then discuss how these results are immediately applicable to models in the AIII class, and to crystalline topological insulators protected by inversion symmetry. Our findings are immediately relevant to cold atom experiments with alkaline-earth atoms in optical lattices, where the band structure properties we exploit have been recently realized.

2. arXiv:1810.02287 (cross-list from cond-mat.stat-mech) [pdf, other]

Entanglement and relative entropies for low-lying excited states in inhomogeneous one-dimensional quantum systems

Sara Murciano, Paola Ruggiero, Pasquale Calabrese

Comments: 27 pages, 7 figures

Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)

Conformal field theories in curved backgrounds have been used to describe inhomogeneous one-dimensional systems, such as quantum gases in trapping potentials and non-equilibrium spin chains. This approach provided, in a elegant and simple fashion, non-trivial analytic predictions for quantities, such as the entanglement entropy, that are not accessible through other methods. Here, we generalise this approach to low-lying excited states, focusing on the entanglement and relative entropies in an inhomogeneous free-fermionic system. Our most important finding is that the universal scaling function characterising these entanglement measurements is the same as the one for homogeneous systems, but expressed in terms of a different variable. This new scaling variable is a non-trivial function of the subsystem length and system's inhomogeneity that is easily written in terms of the curved metric. We test our predictions against exact numerical calculations in the free Fermi gas trapped by a harmonic potential, finding perfect agreement.

Oct. 4

1. arXiv:1810.01852 (cross-list from quant-ph) [pdf, ps, other]

Detecting the entanglement of vortices in ultracold bosons with artificial gauge fields

Li Dai, Lin Xia, Lin Zhuang, Wu-Ming Liu

Comments: 10 pages, 5 figures

Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)

The entanglement of vortices in a two-dimensional Bose-Hubbard model with artificial gauge fields is investigated using the exact diagonalization techniques. We propose an effective Hamiltonian for the spin-spin interactions between vortices responsible for this entanglement, and show that the entanglement can be detected through the quantum interference of the bosons in the vortex centers achieved using the Raman coupling and the quantum gas microscope. The strong bosonic coherence between the vortex centers originates from the charge-density wave order in the vortex core. It is robust against the varying of the pinning strength for the vortices to a wide range, and the coherent bosons can be viewed as a qubit stored in the ground state of the system. Our proposal provides a feasible scheme of quantum memory for storing qubits useful in quantum computation.

2. arXiv:1810.01795 (cross-list from quant-ph) [pdf, ps, other]

Phase Separation Dynamics Induced by an Interaction Quench of a Correlated Fermi-Fermi Mixture in a Double Well

J. Erdmann, S. I. Mistakidis, P. Schmelcher

Comments: 14 pages, 9 figures

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

We explore the interspecies interaction quench dynamics of ultracold spin-polarized few-body mass balanced Fermi-Fermi mixtures confined in a double-well with an emphasis on the beyond Hartree-Fock correlation effects. It is shown that the ground state of particle imbalanced mixtures exhibits a symmetry breaking of the single-particle density for strong interactions in the Hartree-Fock limit, which is altered within the many-body approach. Quenching the interspecies repulsion towards the strongly interacting regime the two species phase separate within the Hartree-Fock approximation while remaining miscible in the many-body treatment. Despite their miscible character on the one-body level the two species are found to be strongly correlated and exhibit a phase separation on the two-body level that suggests the anti-ferromagnetic like behavior of the few-body mixture. For particle balanced mixtures we show that an intrawell fragmentation (filamentation) of the density occurs both for the ground state as well as upon quenching from weak to strong interactions, a result that is exclusively caused by the presence of strong correlations. Inspecting the two-body correlations a phase separation of the two species is unveiled being a precursor towards an anti-ferromagnetic state. Finally, we simulate in-situ single-shot measurements and showcase how our findings can be retrieved by averaging over a sample of single-shot images.

3. arXiv:1810.01584 (cross-list from cond-mat.stat-mech) [pdf, ps, other]

Prethermalization in the transverse-field Ising chain with long-range interactions

Takashi Mori

Comments: 24 pages, 5 figures

Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Nonequilibrium dynamics of an isolated quantum spin chain with long-range Ising interactions that decay as 1/rα (0<α<1) with the distance r is studied. It turns out that long-range interactions give rise to a big timescale separation, which causes prethermalization for all α∈(0,1). This conclusion is deduced by comparing two important timescales relevant for relaxation dynamics; one is the relaxation time of local permutation operators, which are quasi-conserved quantities in this system, and the other is the timescale of the initial relaxation due to the growth of quantum fluctuations. We also explore the entire nonequilibrium dynamics by using the discrete truncated Wigner approximation, which is consistent with the result mentioned above.

Oct. 3

1. arXiv:1810.01362 [pdf, other]

Momentum distribution and coherence of a weakly interacting Bose gas after a quench

Giovanni I. Martone, Pierre-Élie Larré, Alessandro Fabbri, Nicolas Pavloff

Comments: 23 pages, 12 figures

Subjects: Quantum Gases (cond-mat.quant-gas); General Relativity and Quantum Cosmology (gr-qc)

We consider a weakly interacting atomic Bose gas with a time-dependent nonlinear coupling constant. By developing a suitable Bogoliubov treatment we investigate the time evolution of several observables, including the momentum distribution, the degree of coherence in the system, and their dependence on dimensionality and temperature. We rigorously prove that the low-momentum Bogoliubov modes remain frozen during the whole evolution, while the high-momentum ones adiabatically follow the change in time of the interaction strength. At intermediate momenta we point out the occurrence of oscillations, which are analogous to Sakharov oscillations. We identify two wide classes of time-dependent behaviors of the coupling for which an exact solution of the problem can be found, allowing for an analytic computation of all the relevant observables. A special emphasis is put on the study of the coherence property of the system in one spatial dimension. We show that the system exhibits a smooth `light-cone effect,' with typically no prethermalization.

2. arXiv:1810.01089 [pdf, other]

Spin-charge separation effects in the low-temperature transport of 1D Fermi gases

Márton Mestyán, Bruno Bertini, Lorenzo Piroli, Pasquale Calabrese

Comments: 21 pages, 7 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)

We study the transport properties of a one-dimensional spinful Fermi gas, after junction of two semi-infinite sub-systems held at different temperatures. The ensuing dynamics is studied by analysing the space-time profiles of local observables emerging at large distances x and times t, as a function of ζ=x/t. At equilibrium, the system displays two distinct species of quasi-particles, naturally associated with different physical degrees of freedom. By employing the generalised hy- drodynamic approach, we show that when the temperatures are finite no notion of separation can be attributed to the quasi-particles. In this case the profiles can not be qualitatively distinguished by those associated to quasi-particles of a single species that can form bound states. On the contrary, signatures of separation emerge in the low-temperature regime, where two distinct characteristic ve- locities appear. In this regime, we analytically show that the profiles display a piece-wise constant form and can be understood in terms of two decoupled Luttinger liquids.

3. arXiv:1810.00888 [pdf, other]

Exact Strong-ETH Violating Eigenstates in the Rydberg-blockaded Atom Chain

Cheng-Ju Lin, Olexei I. Motrunich

Comments: 5.5 pages main text (including 2 figures)+5pages of appendices

Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)

A recent experiment in the Rydberg atom chain observed unusual oscillatory quench dynamics with a charge density wave initial state, and theoretical works identified a set of many-body `scar states' in the Hamiltonian as potentially responsible for the atypical dynamics. In the same nonintegrable Hamiltonian, we discover several eigenstates at infinite temperature that can be represented exactly as matrix product states with finite bond dimension, for both periodic boundary conditions (two exact E=0 states) and open boundary conditions (two E=0 states and one each E=±2‾√). This discovery explicitly demonstrates violation of strong eigenstate thermalization hypothesis in this model. These states show signatures of translational symmetry breaking with period-2 bond-centered pattern, despite being in 1d at infinite temperature. We show that the nearby many-body scar states with energies E≈±1.33 and E≈±2.66 can be well approximated as "quasiparticle excitations" on top of our exact E=0 states, and propose a quasiparticle explanation of the strong oscillations observed in experiments.

Oct. 2

1. arXiv:1810.00866 [pdf, other]

A cavity-QED simulator of slow and fast scrambling

J. Marino, A. M. Rey

Comments: 8 pages, 4 figures

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

We study information scrambling, as diagnosed by the out-of-time order correlations (OTOCs), in a system of large spins collectively interacting via spatially inhomogeneous and incommensurate exchange couplings. The model is realisable in a cavity QED system in the dispersive regime. Fast scrambling, signalled by an exponential growth of the OTOCs, is observed when the couplings do not factorise into the product of a pair of local interaction terms, and at the same time the state of the spins points initially coplanar to the equator of the Bloch sphere. When one of these conditions is not realised, OTOCs grow algebraically with an exponent sensitive to the orientation of the spins in the initial state. The impact of initial conditions on the scrambling dynamics is attributed to the presence of a global conserved quantity, which critically slows down the evolution for initial states close to the poles of the Bloch sphere.

2. arXiv:1810.00536 [pdf, other]

Antiferromagnetic Interorbital Spin-Exchange Interaction of 171Yb

Koki Ono, Jun Kobayashi, Yoshiki Amano, Koji Sato, Yoshiro Takahashi

Comments: 7 pages, 7 figures

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

We report on the investigation of the scattering properties between the ground state 1S0 and the metastable state 3P0 of the fermionic isotope of 171Yb. We successfully measure the s-wave scattering lengths in the two-orbital collision channels as a+eg=225(13)a0 and a−eg=355(6)a0, using the clock transition spectroscopy in a three-dimensional optical lattice. The result shows that the interorbital spin-exchange interaction is antiferromagnetic, indicating that 171Yb atom is a promising isotope for the quantum simulation of the Kondo effect with the two-orbital system.

3. arXiv:1810.00325 [pdf, other]

Exactly solvable symmetry protected topological phases of quantum spins on a zig-zag lattice

Haiyuan Zou, Erhai Zhao, Xi-Wen Guan, W. Vincent Liu

Comments: 9 pages, 6 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

A large number of symmetry protected topological phases (SPT) have been hypothesized for strongly interacting spin-1/2 systems in one dimension. The lack of simple, analytical solutions hinders deep understanding and classification. Realizing them often demands experimentally inaccessible fine-tuning. Here we show that two kinds of SPT phases natually arise in the ensemble of ultracold polar molecules confined in a zigzag optical lattice. This system, motivated by recent experiments, is described by an XXZ model whose exchange couplings can be tuned by an external field to connect several limits, previously being studied separately for spin chains and ladders. Away from the Heisenberg model limit, the ground state wave function is obtained exactly along a line and at a special point, for these two phases respectively. These exact solutions provide a clear physical picture for the SPT phases. We further complete numerically the phase diagram by using infinite time-evolving block decimation and discuss phase transitions using effective field theory.

4. arXiv:1810.00625 (cross-list from cond-mat.stat-mech) [pdf, ps, other]

Strong Eigenstate Thermalization within a Generalized Shell in Noninteracting Integrable Systems

Takashi Ishii, Takashi Mori

Comments: 5 pages

Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

Integrable systems do not obey the strong eigenstate thermalization hypothesis (ETH), which has been proposed as a mechanism of thermalization in isolated quantum systems. It has been suggested that an integrable system reaches a steady state described by a generalized Gibbs ensemble (GGE) instead of thermal equilibrium. We prove that a generalized version of the strong ETH holds for noninteracting integrable systems with translation invariance. Our generalized ETH states that any pair of energy eigenstates with similar values of local conserved quantities looks similar with respect to local observables. This result tells us that an integrable system relaxes to a GGE for any initial state that has subextensive fluctuations of macroscopic local conserved quantities. Contrary to the previous derivations of the GGE, it is not necessary to assume the cluster decomposition property for an initial state.

5. arXiv:1810.00120 (cross-list from physics.atom-ph) [pdf, other]

Energy-dependent 3-body loss in 1D Bose gases

Laura A. Zundel, Joshua M. Wilson, Neel Malvania, Lin Xia, Jean-Felix Riou, David S. Weiss

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

We study the loss of atoms in quantum Newton's cradles (QNCs) with a range of average energies and transverse confinements. We find that the three-body collision rate in one-dimension is strongly energy dependent, as predicted by a strictly 1D theory. We adapt the theory to atoms in waveguides, then using detailed momentum measurements to infer all the collisions that occur, we compare the observed loss to the adapted theory and find that they agree well.

Oct. 1

1. arXiv:1809.11071 [pdf, ps, other]

Phonon-mediated Casimir interaction between finite mass impurities

Andrei I. Pavlov, Jeroen van den Brink, Dmitri V. Efremov

Comments: 5+7 pages, 5+6 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Other Condensed Matter (cond-mat.other)

The Casimir effect, a two-body interaction via vacuum fluctuations, is a fundamental property of quantum systems. In solid state physics it emerges as a long-range interaction between two impurity atoms via virtual phonons. In the classical limit for the impurity atoms in D dimensions the interaction is known to follow the universal power-law U(r)∼r−D. However, for finite masses of the impurity atoms on a lattice, it was predicted to be U(r)∼r−2D−1 at large distances. We examine how one power-law can change into another with increase of the impurity mass and in presence of an external potential. We provide the exact solution for the system in one-dimension. At large distances indeed U(r)∼r−3 for finite impurity masses, while for the infinite impurity masses or in an external potential it crosses over to U(r)∼r−1 . At short distances the Casimir interaction is not universal and depends on the impurity mass and the external potential.

2. arXiv:1809.10927 [pdf, other]

Universal Hall Response in Synthetic Dimensions

Sebastian Greschner, Michele Filippone, Thierry Giamarchi

Comments: 13 pages, 9 figures

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

We theoretically study the Hall effect on interacting M-leg ladder systems, comparing different measures and properties of the zero temperature Hall response in the limit of weak magnetic fields. Focusing on SU(M) symmetric interacting bosons and fermions, as relevant for e.g. typical synthetic dimensional quantum gas experiments, we identify an extensive regime in which the Hall imbalance ΔH is universal and corresponds to a classical Hall resistivity RH=−1/n for a large class of quantum phases. Away from this high symmetry point we observe interaction driven phenomena such as sign reversal and divergence of the Hall response.

3. arXiv:1805.01190 (cross-list from cond-mat.mes-hall) [pdf, other]

Floquet Perturbation Theory: Formalism and Application to Low-Frequency Limit

M. Rodriguez-Vega (IUB, MPI-PKS), M. Lentz (Syracuse), B. Seradjeh (IUB, MPI-PKS)

Comments: v2: 28 single-column pages, 5 figures; various typos fixed; some notation and connection to other perturbation schemes clarified; new, more descriptive title and abstract. Published version

Journal-ref: New J. Phys. 20, 093022 (2018)

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

We develop a low-frequency perturbation theory in the extended Floquet Hilbert space of a periodically driven quantum systems, which puts the high- and low-frequency approximations to the Floquet theory on the same footing. It captures adiabatic perturbation theories recently discussed in the literature as well as diabatic deviation due to Floquet resonances. For illustration, we apply our Floquet perturbation theory to a driven two-level system as in the Schwinger-Rabi and the Landau-Zener-St\"uckelberg-Majorana models. We reproduce some known expressions for transition probabilities in a simple and systematic way and clarify and extend their regime of applicability. We then apply the theory to a periodically-driven system of fermions on the lattice and obtain the spectral properties and the low-frequency dynamics of the system.