224 research outputs found
Conductance beyond the Landauer limit and charge pumping in quantum wires
Periodically driven systems, which can be described by Floquet theory, have
been proposed to show characteristic behavior that is distinct from static
Hamiltonians. Floquet theory proposes to describe such periodically driven
systems in terms of states that are indexed by a photon number in addition to
the usual Hilbert space of the system. We propose a way to measure directly
this additional Floquet degree of freedom by the measurement of the DC
conductance of a single channel quantum point contact. Specifically, we show
that a single channel wire augmented with a grating structure when irradiated
with microwave radiation can show a DC conductance above the limit of one
conductance quantum set by the Landauer formula. Another interesting feature of
the proposed system is that being non-adiabatic in character, it can be used to
pump a strong gate-voltage dependent photo-current even with linearly polarized
radiation.Comment: 9 pages; 3 figures: Final published version; includes minor revisions
from the last versio
Exploring Topological Phases With Quantum Walks
The quantum walk was originally proposed as a quantum mechanical analogue of
the classical random walk, and has since become a powerful tool in quantum
information science. In this paper, we show that discrete time quantum walks
provide a versatile platform for studying topological phases, which are
currently the subject of intense theoretical and experimental investigation. In
particular, we demonstrate that recent experimental realizations of quantum
walks simulate a non-trivial one dimensional topological phase. With simple
modifications, the quantum walk can be engineered to realize all of the
topological phases which have been classified in one and two dimensions. We
further discuss the existence of robust edge modes at phase boundaries, which
provide experimental signatures for the non-trivial topological character of
the system
Transport properties of non-equilibrium systems under the application of light: Photo-induced quantum Hall insulators without Landau levels
In this paper, we study transport properties of non-equilibrium systems under
the application of light in many-terminal measurements, using the Floquet
picture. We propose and demonstrate that the quantum transport properties can
be controlled in materials such as graphene and topological insulators, via the
application of light. Remarkably, under the application of off-resonant light,
topological transport properties can be induced; these systems exhibits quantum
Hall effects in the absence of a magnetic field with a near quantization of the
Hall conductance, realizing so-called quantum Hall systems without Landau
levels first proposed by Haldane.Comment: Updated to include the detailed explanation of formalism to study the
non-equilibrium transpor
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New phenomena in non-equilibrium quantum physics
From its beginning in the early 20th century, quantum theory has become progressively more important especially due to its contributions to the development of technologies. Quantum mechanics is crucial for current technology such as semiconductors, and also holds promise for future technologies such as superconductors and quantum computing. Despite of the success of quantum theory, its applications have been mostly limited to equilibrium or static systems due to 1. lack of experimental controllability of non-equilibrium quantum systems 2. lack of theoretical frameworks to understand non-equilibrium dynamics. Consequently, physicists have not yet discovered too many interesting phenomena in non-equilibrium quantum systems from both theoretical and experimental point of view and thus, non-equilibrium quantum physics did not attract too much attentions.Physic
Topological characterization of periodically-driven quantum systems
Topological properties of physical systems can lead to robust behaviors that
are insensitive to microscopic details. Such topologically robust phenomena are
not limited to static systems but can also appear in driven quantum systems. In
this paper, we show that the Floquet operators of periodically driven systems
can be divided into topologically distinct (homotopy) classes, and give a
simple physical interpretation of this classification in terms of the spectra
of Floquet operators. Using this picture, we provide an intuitive understanding
of the well-known phenomenon of quantized adiabatic pumping. Systems whose
Floquet operators belong to the trivial class simulate the dynamics generated
by time-independent Hamiltonians, which can be topologically classified
according to the schemes developed for static systems. We demonstrate these
principles through an example of a periodically driven two--dimensional
hexagonal lattice model which exhibits several topological phases. Remarkably,
one of these phases supports chiral edge modes even though the bulk is
topologically trivial.Comment: 9 Pages + Appendi
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