7,614 research outputs found
How to Suppress Dark States in Quantum Networks and Bio-Engineered Structures
Transport across quantum networks underlies many problems, from state
transfer on a spin network to energy transport in photosynthetic complexes.
However, networks can contain dark subspaces that block the transportation, and
various methods used to enhance transfer on quantum networks can be viewed as
equivalently avoiding, modifying, or destroying the dark subspace. Here, we
exploit graph theoretical tools to identify the dark subspaces and show that
asymptotically almost surely they do not exist for large networks, while for
small ones they can be suppressed by properly perturbing the coupling rates
between the network nodes. More specifically, we apply these results to
describe the recently experimentally observed and robust transport behaviour of
the electronic excitation travelling on a genetically-engineered
light-harvesting cylinder (M13 virus) structure. We believe that these mainly
topological tools may allow us to better infer which network structures and
dynamics are more favourable to enhance transfer of energy and information
towards novel quantum technologies.Comment: 9 pages, 6 figure
Scenario-based Economic Dispatch with Uncertain Demand Response
This paper introduces a new computational framework to account for
uncertainties in day-ahead electricity market clearing process in the presence
of demand response providers. A central challenge when dealing with many demand
response providers is the uncertainty of its realization. In this paper, a new
economic dispatch framework that is based on the recent theoretical development
of the scenario approach is introduced. By removing samples from a finite
uncertainty set, this approach improves dispatch performance while guaranteeing
a quantifiable risk level with respect to the probability of violating the
constraints. The theoretical bound on the level of risk is shown to be a
function of the number of scenarios removed. This is appealing to the system
operator for the following reasons: (1) the improvement of performance comes at
the cost of a quantifiable level of violation probability in the constraints;
(2) the violation upper bound does not depend on the probability distribution
assumption of the uncertainty in demand response. Numerical simulations on (1)
3-bus and (2) IEEE 14-bus system (3) IEEE 118-bus system suggest that this
approach could be a promising alternative in future electricity markets with
multiple demand response providers
Universal spectral features of ultrastrongly coupled systems
We identify universal properties of the low-energy subspace of a wide class of quantum optical models in the ultrastrong coupling limit, where the coupling strength dominates over all other energy scales in the system. We show that the symmetry of the light-matter interaction is at the origin of a twofold degeneracy in the spectrum. We prove analytically this result for bounded Hamiltonians and extend it to a class of models with unbounded operators. As a consequence, we show that the emergence of superradiant phases previously investigated in the context of critical phenomena, is a general property of the ultrastrong coupling limit. The set of models we consider encompasses different scenarios of possible interplay between critical behavior and superradianceS. F. acknowledges support from the European Research Council (ERC-2016-STG-714870
Ultrastrong coupling regime of non-dipolar light-matter interactions
We present a circuit-QED scheme which allows to reach the ultrastrong
coupling regime of a nondipolar interaction between a single qubit and a
quantum resonator. We show that the system Hamiltonian is well approximated by
a two-photon quantum Rabi model and propose a simple scattering experiment to
probe its fundamental properties. In particular, we identify a driving scheme
that reveals the change in selection rules characterizing the breakdown of the
rotating-wave approximation and the transition from strong to ultrastrong
two-photon interactions. Finally, we show that a frequency crowding in a narrow
spectral region is observable in the output fluoresce spectrum as the coupling
strength approaches the collapse point, paving the way to the direct
observation of the onset of the spectral collapse in a solid-state device.Comment: 5+6 pages, 2 figure
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