1,902 research outputs found
Symmetry-enhanced supertransfer of delocalized quantum states
Coherent hopping of excitation rely on quantum coherence over physically
extended states. In this work, we consider simple models to examine the effect
of symmetries of delocalized multi-excitation states on the dynamical
timescales, including hopping rates, radiative decay, and environmental
interactions. While the decoherence (pure dephasing) rate of an extended state
over N sites is comparable to that of a non-extended state, superradiance leads
to a factor of N enhancement in decay and absorption rates. In addition to
superradiance, we illustrate how the multi-excitonic states exhibit
`supertransfer' in the far-field regime: hopping from a symmetrized state over
N sites to a symmetrized state over M sites at a rate proportional to MN. We
argue that such symmetries could play an operational role in physical systems
based on the competition between symmetry-enhanced interactions and localized
inhomogeneities and environmental interactions that destroy symmetry. As an
example, we propose that supertransfer and coherent hopping play a role in
recent observations of anomolously long diffusion lengths in nano-engineered
assembly of light-harvesting complexes.Comment: 6 page
Motion of pole-dipole and quadrupole particles in non-minimally coupled theories of gravity
We study theories of gravity with non-minimal coupling between polarized
media with pole-dipole and quadrupole moments and an arbitrary function of the
space-time curvature scalar and the squares of the Ricci and Riemann
curvature tensors. We obtain the general form of the equation of motion and
show that an induced quadrupole moment emerges as a result of the curvature
tensor dependence of the function coupled to the matter. We derive the explicit
forms of the equations of motion in the particular cases of coupling to a
function of the curvature scalar alone, coupling to an arbitrary function of
the square of the Riemann curvature tensor, and coupling to an arbitrary
function of the Gauss-Bonnet invariant. We show that in these cases the extra
force resulting from the non-minimal coupling can be expressed in terms of the
induced moments
Direct Characterization of Quantum Dynamics
The characterization of quantum dynamics is a fundamental and central task in
quantum mechanics. This task is typically addressed by quantum process
tomography (QPT). Here we present an alternative "direct characterization of
quantum dynamics" (DCQD) algorithm. In contrast to all known QPT methods, this
algorithm relies on error-detection techniques and does not require any quantum
state tomography. We illustrate that, by construction, the DCQD algorithm can
be applied to the task of obtaining partial information about quantum dynamics.
Furthermore, we argue that the DCQD algorithm is experimentally implementable
in a variety of prominent quantum information processing systems, and show how
it can be realized in photonic systems with present day technology.Comment: 4 pages, 2 figures, published versio
Minimising the heat dissipation of quantum information erasure
Quantum state engineering and quantum computation rely on information erasure
procedures that, up to some fidelity, prepare a quantum object in a pure state.
Such processes occur within Landauer's framework if they rely on an interaction
between the object and a thermal reservoir. Landauer's principle dictates that
this must dissipate a minimum quantity of heat, proportional to the entropy
reduction that is incurred by the object, to the thermal reservoir. However,
this lower bound is only reachable for some specific physical situations, and
it is not necessarily achievable for any given reservoir. The main task of our
work can be stated as the minimisation of heat dissipation given probabilistic
information erasure, i.e., minimising the amount of energy transferred to the
thermal reservoir as heat if we require that the probability of preparing the
object in a specific pure state be no smaller than
. Here is the maximum
probability of information erasure that is permissible by the physical context,
and the error. To determine the achievable minimal heat
dissipation of quantum information erasure within a given physical context, we
explicitly optimise over all possible unitary operators that act on the
composite system of object and reservoir. Specifically, we characterise the
equivalence class of such optimal unitary operators, using tools from
majorisation theory, when we are restricted to finite-dimensional Hilbert
spaces. Furthermore, we discuss how pure state preparation processes could be
achieved with a smaller heat cost than Landauer's limit, by operating outside
of Landauer's framework
Geometrical effects on energy transfer in disordered open quantum systems
We explore various design principles for efficient excitation energy
transport in complex quantum systems. We investigate energy transfer efficiency
in randomly disordered geometries consisting of up to 20 chromophores to
explore spatial and spectral properties of small natural/artificial
Light-Harvesting Complexes (LHC). We find significant statistical correlations
among highly efficient random structures with respect to ground state
properties, excitonic energy gaps, multichromophoric spatial connectivity, and
path strengths. These correlations can even exist beyond the optimal regime of
environment-assisted quantum transport. For random configurations embedded in
spatial dimensions of 30 A and 50 A, we observe that the transport efficiency
saturates to its maximum value if the systems contain 7 and 14 chromophores
respectively. Remarkably, these optimum values coincide with the number of
chlorophylls in (Fenna-Matthews-Olson) FMO protein complex and LHC II monomers,
respectively, suggesting a potential natural optimization with respect to
chromophoric density.Comment: 11 pages, 10 figures. Expanded from the former appendix to
arXiv:1104.481
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