41,244 research outputs found
Floquet theorem for open systems and its applications
For a closed system with periodic driving, Floquet theorem tells that the
time evolution operator can be written as with , and is Hermitian and
time-independent called Floquet Hamiltonian. In this work, we extend the
Floquet theorem from closed systems to open systems described by a Lindblad
master equation that is periodic in time. Lindbladian expansion in powers of
is derived, where is the driving frequency. Two
examples are presented to illustrate the theory. We find that appropriate trace
preserving time-independent Lindbladian of such a periodically driven system
can be constructed by the application of open system Floquet theory, and it
agrees well with the exact dynamics in the high frequency limit.Comment: 5 pages, 4 figure
Reply to Comment on: "Radiation-Induced 'Zero-Resistance State' and the Photon Assisted Transport"
We show that the comment by A.F. Volkov ignores a delicate issue in the
conductance measurement for a hall bar system. In such system, while , as
correctly pointed out in Ref.3. We clarify that the so called "zero resistance
state" is actually a "zero conductance state". A discussion concerning the
phase transition induced by the negative conductance is presented.Comment: 1 pag
The influence of localization transition on dynamical properties for an extended Aubry-Andr\'e-Harper model
We show the localization transition and its effect on two dynamical processes
for an extended Aubry-Andr\'e-Harper model with incommensurate on-site and
hopping potentials. After specifying an extended Aubry-Andr\'e-Harper model, we
check the localization transition for all the eigenstates and eigenenergy band
splitting behavior versus a system parameter. To examine the effect of
localization transition on dynamical processes, firstly, the slowly pumping of
the edge states are examined. In the dynamical processes, the system acts as
conductor for the excitation in the nonlocal region and insulator in the
localized region. Then by quantum Lyapunov control method with different
control Hamiltonians, we prepare an edge localized state which exists in the
nonlocal region. Compared to that in the nonlocal region, the control effect is
suppressed in the localized region. Then we employ the entropy and occupation
imbalance between even and odd sites to indicate the localization transition
further. Finally, the experimental schemes based on cold atoms trapped
quasiperiodic optical lattice and coupled optical waveguide arrays are
suggested
Population transfer driven by far-off-resonant fields
For a two-level system, it is believed that a far-off-resonant driving can
not help coherent population transfer between the states. In this work, we
propose a scheme to implement the coherent transfer with far-off-resonant
driving. The scheme works well with both constant driving and Gaussian driving.
The total time to finish population transfer is also minimized by optimizing
the detuning and coupling constants. We find that the scheme is sensitive to
spontaneous emission much more than dephasing. It might find potential
applications in X-ray quantum optics and population transfer in Rydberg atoms
as well.Comment: arXiv admin note: text overlap with arXiv:1011.4423 by other author
Preparation of edge states by shaking boundaries
Preparing topological states of quantum matter, such as edge states, is one
of the most important directions in condensed matter physics. In this work, we
present a proposal to prepare edge states in
Aubry-Andr-Harper (AAH) model with open boundaries, which
takes advantage of Lyapunov control to design operations. We show that edge
states can be obtained with almost arbitrary initial states. A numerical
optimalization for the control is performed and the dependence of control
process on the system size is discussed. The merit of this proposal is that the
shaking exerts only on the boundaries of the model. As a by-product, a
topological entangled state is achieved by elaborately designing the shaking
scheme.Comment: 11 pages, 11 figure
Hall conductance of two-band systems in a quantized field
Kubo formula gives a linear response of a quantum system to external fields,
which are classical and weak with respect to the energy of the system. In this
work, we take the quantum nature of the external field into account, and define
a Hall conductance to characterize the linear response of a two-band system to
the quantized field. The theory is then applied to topological insulators.
Comparisons with the traditional Hall conductance are presented and discussed.Comment: 6 pages, 7 figure
Engineering the coupling between Majorana bound states
We study the coupling between Majorana bound states (CMBS), which is mediated
by a topologically trivial chain in the presence of pairing coupling and
long-range coupling. The results show that CMBS can be enhanced by the pairing
coupling and long-range coupling of the trivial chain. When driving the trivial
chain by periodic driving field, we deduce the analytical expressions of CMBS
in the high-frequency limit, and demonstrate that CMBS can be modulated by the
frequency and amplitude of driving field. Finally we exhibit the application of
tunable CMBS in realizing quantum logic gates.Comment: 8 pages, 8 figure
Meta-Percolation and Metal-Insulator Transition in Two Dimensions
According to the scaling theory of localization, all quantum electronic
states are localized in two-dimensional (2D) systems. One consequence of the
theory is that there is no quantum percolation transition in 2D. However, in a
real system at a finite temperature, electron phase coherent length is finite
and the system is between quantum and classical. We find, in such a 2D system,
a metal-insulator transition (MIT) caused by a novel type of percolation,
meta-percolation. The relevance to recently observed 2D MIT is also discussed.Comment: 4 pages, 5 figure
Quantum computation with surface-state electrons by rapid population passages
Quantum computation requires coherently controlling the evolutions of qubits.
Usually, these manipulations are implemented by precisely designing the
durations (such as the -pulses) of the Rabi oscillations and tunable
interbit coupling. Relaxing this requirement, here we show that the desired
population transfers between the logic states can be deterministically realized
(and thus quantum computation could be implemented) both adiabatically and
non-adiabatically, by performing the duration-insensitive quantum
manipulations. Our proposal is specifically demonstrated with the surface-state
of electrons floating on the liquid helium, but could also be applied to the
other artificially controllable systems for quantum computing
Anti-Resonance and the 0.7 Anomaly in Conductance through a Quantum Point Contact
We investigate the transmission of electrons through a quantum point contact
by using a quasi-one-dimensional model with a local bound state below the band
bottom. While the complete transmission in lower channels gives rise to
plateaus of conductance at multiples of , the electrons in the lowest
channel are scattered by the local bound state when it is singly occupied. This
scattering produces a wide zero-transmittance (anti-resonance) for a singlet
formed by tunneling and local electrons, and has no effect on triplets, leading
to an exact shoulder prior to the first plateau.
Formation of a Kondo singlet from electrons in the Fermi sea screens the local
moment and reduces the effects of anti-resonance, complementing the shoulder
from 0.75 to 1 at low temperatures.Comment: 4 pages, 3 figure
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