2,452 research outputs found
Photonic realization of the relativistic Dirac oscillator
A photonic realization of the Dirac oscillator (DO), i.e. of the relativistic
extension of the quantum harmonic oscillator, is proposed for light propagation
in fiber Bragg gratings. Transmission spectra clearly show the existence of
electron and positron bound states of the DO, corresponding to resonance modes
above and below the Bragg frequency, as well as the asymmetry of the energy
spectrum for electron and positron branches
Dirac oscillator in an external magnetic field
We show that 2+1 dimensional Dirac oscillators in an external magnetic field
is mapped onto the same with reduced angular frequency in absence of magnetic
field. This can be used to study the atomic transitions in a radiation field.
Relativistic Landau levels are constructed explicitly. Several interesting
features of this system are discussed.Comment: Revised Version, Latex, 9 pages, No figs, To appear in Phys. Lett.
Edge states and topological orders in the spin liquid phases of star lattice
A group of novel materials can be mapped to the star lattice, which exhibits
some novel physical properties. We give the bulk-edge correspondence theory of
the star lattice and study the edge states and their topological orders in
different spin liquid phases. The bulk and edge-state energy structures and
Chern number depend on the spin liquid phases and hopping parameters because
the local spontaneous magnetic flux in the spin liquid phase breaks the time
reversal and space inversion symmetries. We give the characteristics of bulk
and edge energy structures and their corresponding Chern numbers in the
uniform, nematic and chiral spin liquids. In particular, we obtain analytically
the phase diagram of the topological orders for the chiral spin liquid states
SL[\phi,\phi,-2\phi], where \phi is the magnetic flux in two triangles and a
dodecagon in the unit cell. Moreover, we find the topological invariance for
the spin liquid phases, SL[\phi_{1},\phi_{2},-(\phi_{1}+\phi_{2})] and
SL[\phi_{2},\phi_{1},-(\phi_{1}+\phi_{2})]. The results reveal the relationship
between the energy-band and edge-state structures and their topological orders
of the star lattice.Comment: 7 pages, 8 figures, 1 tabl
Topological phase transitions between chiral and helical spin textures in a lattice with spin-orbit coupling and a magnetic field
We consider the combined effects of large spin-orbit couplings and a
perpendicular magnetic field in a 2D honeycomb fermionic lattice. This system
provides an elegant setup to generate versatile spin textures propagating along
the edge of a sample. The spin-orbit coupling is shown to induce topological
phase transitions between a helical quantum spin Hall phase and a chiral
spin-imbalanced quantum Hall state. Besides, we find that the spin orientation
of a single topological edge state can be tuned by a Rashba spin-orbit
coupling, opening an interesting route towards quantum spin manipulation. We
discuss the possible realization of our results using cold atoms trapped in
optical lattices, where large synthetic magnetic fields and spin-orbit
couplings can be engineered and finely tuned. In particular, this system would
lead to the observation of a time-reversal-symmetry-broken quantum spin Hall
phase.Comment: 8 pages, 3 figures, Accepted in Europhys. Lett. (Dec 2011
Dynamical delocalization of Majorana edge states by sweeping across a quantum critical point
We study the adiabatic dynamics of Majorana fermions across a quantum phase
transition. We show that the Kibble-Zurek scaling, which describes the density
of bulk defects produced during the critical point crossing, is not valid for
edge Majorana fermions. Therefore, the dynamics governing an edge state quench
is nonuniversal and depends on the topological features of the system. Besides,
we show that the localization of Majorana fermions is a necessary ingredient to
guaranty robustness against defect production.Comment: Submitted to the Special Issue on "Dynamics and Thermalization in
Isolated Quantum Many-Body Systems" in New Journal of Physics. Editors:M.
Cazalilla, M. Rigol. New references and some typos correcte
Projected shell model study of odd-odd f-p-g shell proton-rich nuclei
A systematic study of 2-quasiparticle bands of the proton-rich odd-odd nuclei
in the mass A ~ 70-80 region is performed using the projected shell model
approach. The study includes Br-, Rb-, and Y-isotopes with N = Z+2, and Z+4. We
describe the energy spectra and electromagnetic transition strengths in terms
of the configuration mixing of the angular-momentum projected
multi-quasiparticle states. Signature splitting and signature inversion in the
rotational bands are discussed and are shown to be well described. A
preliminary study of the odd-odd N = Z nucleus, 74Rb using the concept of
spontaneous symmetry breaking is also presented.Comment: 14 pages, 7 figures, final version accepted by Phys. Rev.
Topological phases of shaken quantum Ising lattices
The quantum compass model consists of a two-dimensional square spin lattice where the orientation of the spin-spin interactions depends on the spatial direction of the bonds. It has remarkable symmetry properties and the ground state shows topological degeneracy. The implementation of the quantum compass model in quantum simulation setups like ultracold atoms and trapped ions is far from trivial, since spin interactions in those systems typically are independent of the spatial direction. Ising spin interactions, on the contrary, can be induced and controlled in atomic setups with state-of-the art experimental techniques. In this work, we show how the quantum compass model on a rectangular lattice can be simulated by the use of the photon-assisted tunneling induced by periodic drivings on a quantum Ising spin model. We describe a procedure to adiabatically prepare one of the doubly-degenerate ground states of this model by adiabatically ramping down a transverse magnetic field, with surprising differences depending on the parity of the lattice size. Exact diagonalizations confirm the validity of this approach for small lattices. Specific implementations of this scheme are presented with ultracold atoms in optical lattices in the Mott insulator regime, as well as with Rydberg atoms
Discovery of HC4NC in TMC-1: A study of the isomers of HC3N, HC5N, and HC7N
We present a study of the isocyano isomers of the cyanopolyynes HC3N, HC5N,
and HC7N in TMC-1 and IRC+10216 carried out with the Yebes 40m radio telescope.
This study has enabled us to report the detection, for the first time in space,
of HCCCCNC in TMC-1 and to give upper limits for HC6NC in the same source. In
addition, the deuterated isotopologues of HCCNC and HNCCC were detected, along
with all 13C substitutions of HCCNC, also for the first time in space. The
abundance ratios of HC3N and HC5N, with their isomers, are very different in
TMC-1 and IRC+10216, namely, N(HC5N)/N(HC4NC) is 300 and >2100, respectively.
We discuss the chemistry of the metastable isomers of cyanopolyynes in terms of
the most likely formation pathways and by comparing observational abundance
ratios between different sources.Comment: This article was submitted to A&A on 27/08/2020 and accepted for
publication on 11/09/202
Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1
Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of
harmonically related lines with a rotational constant B0=4460.590 +/- 0.001 MHz
and a distortion constant D0=0.511 +/- 0.005 kHz towards the cold dense core
TMC-1. High-level-of-theory ab initio calculations indicate that the best
possible candidate is protonated tricarbon monoxide, HC3O+. We have succeeded
in producing this species in the laboratory and observed its J = 2-1 and 3-2
rotational transitions. Hence, we report the discovery of HC3O+ in space based
on our observations, theoretical calculations, and laboratory experiments. We
derive an abundance ratio N(C3O)/N(HC3O+) = 7. The high abundance of the
protonated form of C3O is due to the high proton affinity of the neutral
species. The chemistry of O-bearing species is modelled, and predictions are
compared to the derived abundances from our data for the most prominent
O-bearing species in TMC-1.Comment: Accepted for publication in A&A Letter
Noncommutative Dirac oscillator in an external magnetic field
We show that (2+1) dimensional noncommutative Dirac oscillator in an external
magnetic field is mapped onto the same but with reduced angular frequency in
absence of magnetic field. We construct the relativistic Landau levels by
solving corresponding Dirac equation in (2+1) dimensional noncommutative phase
space. We observe that lowest Landau levels are exactly same as in commutative
space and independent of non-commutative parameter. All the Landau levels
become independent of noncommutative parameter for a critical value of the
magnetic field. Several other interesting features along with the relevance of
such models in the study of atomic transitions in a radiation field have been
discussed.Comment: 10 pages, Np figs, communicated to journal. arXiv admin note: text
overlap with arXiv:0907.454
- …