196 research outputs found
Driven binary mixtures: Clustering and giant diffusion
We study noise-assisted transport in a binary mixture of overdamped interacting particles. As one species (termed “active”) is subject to a weak dc drive, the other one (termed “passive”) can be dragged along due to the clustering of particles of both species. On increasing the external drive, clusters of different size fragment at different thresholds that depend on the mixture temperature, the inter-particle interaction strength, and the densities of both species of particles. Moreover, normal self-diffusion of both species at the fragmentation thresholds undergoes a giant enhancement simultaneous with a markedly negative cross-diffusion coefficient.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58110/2/epl_73_4_513.pd
Quantum electrodynamics and photon-assisted tunnelling in long Josephson junctions
We describe the interaction between an electromagnetic field and a long
Josephson junction (JJ) driven by a dc current. We calculate the amplitudes of
emission and absorption of light via the creation and annihilation of quantized
Josephson plasma waves (JPWs). Both, the energies of JPW quanta and the
amplitudes of light absorption and emission, strongly depend on the junction's
length and can be tuned by an applied dc current. Moreover, photon-assisted
macroscopic quantum tunnelling in long Josephson junctions show resonances when
the frequency of the outside radiation coincides with the current-driven
eigenfrequencies of the quantized JPWs.Comment: 9 pages, 4 figure
Quasi-Superradiant Soliton State of Matter in Quantum Metamaterials
Strong interaction of a system of quantum emitters (e.g., two-level atoms)
with electromagnetic field induces specific correlations in the system
accompanied by a drastic insrease of emitted radiation (superradiation or
superfluorescence). Despite the fact that since its prediction this phenomenon
was subject to a vigorous experimental and theoretical research, there remain
open question, in particular, concerning the possibility of a first order phase
transition to the superradiant state from the vacuum state. In systems of
natural and charge-based artificial atome this transition is prohibited by
"no-go" theorems. Here we demonstrate numerically a similar transition in a
one-dimensional quantum metamaterial - a chain of artificial atoms (qubits)
strongly interacting with classical electromagnetic fields in a transmission
line. The system switches from vacuum state with zero classical electromagnetic
fields and all qubits being in the ground state to the quasi-superradiant (QS)
phase with one or several magnetic solitons and finite average occupation of
qubit excited states along the transmission line. A quantum metamaterial in the
QS phase circumvents the "no-go" restrictions by considerably decreasing its
total energy relative to the vacuum state by exciting nonlinear electromagnetic
solitons with many nonlinearly coupled electromagnetic modes in the presence of
external magnetic field.Comment: 6 pages, 4 figure
Quantum metamaterial without local control
A quantum metamaterial can be implemented as a quantum coherent 1D array of
qubits placed in a transmission line. The properties of quantum metamaterials
are determined by the local quantum state of the system. Here we show that a
spatially-periodic quantum state of such a system can be realized without
direct control of the constituent qubits, by their interaction with the
initializing ("priming") pulses sent through the system in opposite directions.
The properties of the resulting quantum photonic crystal are determined by the
choice of the priming pulses. This proposal can be readily generalized to other
implementations of quantum metamaterials.Comment: 6 pages, 5 figure
Modelling chemical reactions using semiconductor quantum dots
We propose using semiconductor quantum dots for a simulation of chemical
reactions as electrons are redistributed among such artificial atoms. We show
that it is possible to achieve various reaction regimes and obtain different
reaction products by varying the speed of voltage changes applied to the gates
forming quantum dots. Considering the simplest possible reaction, , we show how the necessary initial state can be obtained and what
voltage pulses should be applied to achieve a desirable final product. Our
calculations have been performed using the Pechukas gas approach, which can be
extended for more complicated reactions
Electronic properties of the armchair graphene nanoribbon
We investigate the electronic band structure of an undoped graphene armchair
nanoribbon. We demonstrate that such nanoribbon always has a gap in its
electronic spectrum. Indeed, even in the situations where simple
single-electron calculations predict a metallic dispersion, the system is
unstable with respect to the deformation of the carbon-carbon bonds dangling at
the edges of the armchair nanoribbon. The edge bonds' deformation couples
electron and hole states with equal momentum. This coupling opens a gap at the
Fermi level. In a realistic sample, however, it is unlikely that this
instability could be observed in its pure form. Namely, since chemical
properties of the dangling carbon atoms are different from chemical properties
of the atoms inside the sample (for example, the atoms at the edge have only
two neighbours, besides additional non-carbon atoms might be attached to
passivate unpaired covalent carbon bonds), it is very probable that the bonds
at the edge are deformed due to chemical interactions. This chemically-induced
modification of the nanoribbon's edges can be viewed as an effective field
biasing our predicted instability in a particular direction. Yet by disordering
this field (e.g., through random substitution of the radicals attached to the
edges) we may tune the system back to the critical regime and vary the
electronic properties of the system. For example, we show that electrical
transport through a nanoribbon is strongly affected by such disorder.Comment: 12 pages, 4 figur
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