10,672 research outputs found
Topological Phases for Fermionic Cold Atoms on the Lieb Lattice
We investigate the properties of the Lieb lattice, i.e a face-centered square
lattice, subjected to external gauge fields. We show that an Abelian gauge
field leads to a peculiar quantum Hall effect, which is a consequence of the
single Dirac cone and the flat band characterizing the energy spectrum. Then we
explore the effects of an intrinsic spin-orbit term - a non-Abelian gauge field
- and demonstrate the occurrence of the quantum spin Hall effect in this model.
Besides, we obtain the relativistic Hamiltonian describing the Lieb lattice at
low energy and derive the Landau levels in the presence of external Abelian and
non-Abelian gauge fields. Finally, we describe concrete schemes for realizing
these gauge fields with cold fermionic atoms trapped in an optical Lieb
lattice. In particular, we provide a very efficient method to reproduce the
intrinsic (Kane-Mele) spin-orbit term with assisted-tunneling schemes.
Consequently, our model could be implemented in order to produce a variety of
topological states with cold-atoms.Comment: 12 pages, 9 figure
Solar radio emission
Active areas of both observational and theoretical research in which rapid progress is being made are discussed. These include: (1) the dynamic spectrum or frequency versus time plot; (2) physical mechanisms in the development of various types of bursts; (3) microwave type 1, 2, 3, and moving type 4 bursts; (4) bursts caused by trapped electrons; (5) physics of type 3bursts; (6) the physics of type 2 bursts and their related shocks; (7) the physics of both stationary and moving traps and associated type 1 and moving type 4 bursts; and (8) the status of the field of solar radio emission
Laboratory studies of infrared absorption by NO2 and HNO3
Data concerning the quantitative absorption in the 11 and 22 micron region by HNO3 were obtained. Results are presented indicating the temperature dependence of these bands of HNO3 vapor. The 21.8 micron absorption bands of HNO3 vapor at 40 C are discussed along with the integrated intensity and line parameters for the 6.2 micron band of NO2
Electron interferometry in quantum Hall regime: Aharonov-Bohm effect of interacting electrons
An apparent h/fe Aharonov-Bohm flux period, where f is an integer, has been
reported in coherent quantum Hall devices. Such sub-period is not expected for
non-interacting electrons and thus is thought to result from interelectron
Coulomb interaction. Here we report experiments in a Fabry-Perot interferometer
comprised of two wide constrictions enclosing an electron island. By carefully
tuning the constriction front gates, we find a regime where interference
oscillations with period h/2e persist throughout the transition between the
integer quantum Hall plateaus 2 and 3, including half-filling. In a large
quantum Hall sample, a transition between integer plateaus occurs near
half-filling, where the bulk of the sample becomes delocalized and thus
dissipative bulk current flows between the counterpropagating edges
("backscattering"). In a quantum Hall constriction, where conductance is due to
electron tunneling, a transition between forward- and back-scattering is
expected near the half-filling. In our experiment, neither period nor amplitude
of the oscillations show a discontinuity at half-filling, indicating that only
one interference path exists throughout the transition. We also present
experiments and an analysis of the front-gate dependence of the phase of the
oscillations. The results point to a single physical mechanism of the observed
conductance oscillations: Aharonov-Bohm interference of interacting electrons
in quantum Hall regime.Comment: 10 pages, 4 Fig
Measuring topology in a laser-coupled honeycomb lattice: From Chern insulators to topological semi-metals
Ultracold fermions trapped in a honeycomb optical lattice constitute a
versatile setup to experimentally realize the Haldane model [Phys. Rev. Lett.
61, 2015 (1988)]. In this system, a non-uniform synthetic magnetic flux can be
engineered through laser-induced methods, explicitly breaking time-reversal
symmetry. This potentially opens a bulk gap in the energy spectrum, which is
associated with a non-trivial topological order, i.e., a non-zero Chern number.
In this work, we consider the possibility of producing and identifying such a
robust Chern insulator in the laser-coupled honeycomb lattice. We explore a
large parameter space spanned by experimentally controllable parameters and
obtain a variety of phase diagrams, clearly identifying the accessible
topologically non-trivial regimes. We discuss the signatures of Chern
insulators in cold-atom systems, considering available detection methods. We
also highlight the existence of topological semi-metals in this system, which
are gapless phases characterized by non-zero winding numbers, not present in
Haldane's original model.Comment: 30 pages, 12 figures, 4 Appendice
Primary-Filling e/3 Quasiparticle Interferometer
We report experimental realization of a quasiparticle interferometer where
the entire system is in 1/3 primary fractional quantum Hall state. The
interferometer consists of chiral edge channels coupled by quantum-coherent
tunneling in two constrictions, thus enclosing an Aharonov-Bohm area. We
observe magnetic flux and charge periods h/e and e/3, equivalent to creation of
one quasielectron in the island. Quantum theory predicts a 3h/e flux period for
charge e/3, integer statistics particles. Accordingly, the observed periods
demonstrate the anyonic statistics of Laughlin quasiparticles
Transport in the Laughlin quasiparticle interferometer: Evidence for topological protection in an anyonic qubit
We report experiments on temperature and Hall voltage bias dependence of the
superperiodic conductance oscillations in the novel Laughlin quasiparticle
interferometer, where quasiparticles of the 1/3 fractional quantum Hall fluid
execute a closed path around an island of the 2/5 fluid. The amplitude of the
oscillations fits well the quantum-coherent thermal dephasing dependence
predicted for a two point-contact chiral edge channel interferometer in the
full experimental temperature range 10.2<T<141 mK. The temperature dependence
observed in the interferometer is clearly distinct from the behavior in
single-particle resonant tunneling and Coulomb blockade devices. The 5h/e flux
superperiod, originating in the anyonic statistical interaction of Laughlin
quasiparticles, persists to a relatively high T~140 mK. This temperature is
only an order of magnitude less than the 2/5 quantum Hall gap. Such protection
of quantum logic by the topological order of fractional quantum Hall fluids is
expected to facilitate fault-tolerant quantum computation with anyons.Comment: 13 pages, 10 figure
Energetics of Quantum Antidot States in Quantum Hall Regime
We report experiments on the energy structure of antidot-bound states. By
measuring resonant tunneling line widths as function of temperature, we
determine the coupling to the remote global gate voltage and find that the
effects of interelectron interaction dominate. Within a simple model, we also
determine the energy spacing of the antidot bound states, self consistent edge
electric field, and edge excitation drift velocity.Comment: 4 pages, RevTex, 5 Postscript figure
Realization of a Laughlin quasiparticle interferometer: Observation of fractional statistics
In two dimensions, the laws of physics permit existence of anyons, particles
with fractional statistics which is neither Fermi nor Bose. That is, upon
exchange of two such particles, the quantum state of a system acquires a phase
which is neither 0 nor \pi, but can be any value. The elementary excitations
(Laughlin quasiparticles) of a fractional quantum Hall fluid have fractional
electric charge and are expected to obey fractional statistics. Here we report
experimental realization of a novel Laughlin quasiparticle interferometer,
where quasiparticles of the 1/3 fluid execute a closed path around an island of
the 2/5 fluid and thus acquire statistical phase. Interference fringes are
observed as conductance oscillations as a function of magnetic flux, similar to
the Aharonov-Bohm effect. We observe the interference shift by one fringe upon
introduction of five magnetic flux quanta (5h/e) into the island. The
corresponding 2e charge period is confirmed directly in calibrated gate
experiments. These results constitute direct observation of fractional
statistics of Laughlin quasiparticles.Comment: manuscript of the long version published in Phys. Rev.
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