195,661 research outputs found
Environmental engineering for quantum energy transport
Transport phenomena are ubiquitous throughout the science, engineering and
technology disciplines as it concerns energy, mass, charge and information
exchange between systems. In particular, energy transport in the nanoscale
regime has attracted significant attention within the physical science
community due to its potential to explain complex phenomena like the electronic
energy transfer in molecular crystals or the Fenna-Matthews-Olson / light
harvesting complexes in photosynthetic bacteria with long time coherences.
Energy transport in these systems is highly affected by environmental noise but
surprisingly not always in a detrimental way. It was recently found that
situations exist where noise actually enhances the transport phenomena. Such
noise can take many forms, but can be characterised in three basic behaviours:
quantum, coloured or nonlocal. All have been shown potential to offer an energy
transport enhancement. The focus of this work is on quantum transport caused by
stochastic environment with spatio-temporal correlation. We consider a
multi-site nearest neighbour interaction model with pure dephasing
environmental noise with coloured and nonlocal character and show how an
accelerated rate for the energy transfer results especially under
anti-correlation. Negative spatial correlations provide another control
parameter to help one establish the most efficient transfer of energy and may
provide new insights into the working of exciton transport in photosynthetic
complexes. Further the usage of spatio-temporal correlated noise may be a
beneficial resource for efficient transport in large scale quantum networks.Comment: 11 pages 5 figure
Efficient robust routing for single commodity network flows
We study single commodity network flows with suitable robustness and efficiency specs. An original use of a maximum entropy problem for distributions on the paths of the graph turns this problem into a steering problem for Markov chains with prescribed initial and final marginals. From a computational standpoint, viewing scheduling this way is especially attractive in light of the existence of an iterative algorithm to compute the solution. The present paper builds on [13] by introducing an index of efficiency of a transportation plan and points, accordingly, to efficient-robust transport policies. In developing the theory, we establish two new invariance properties of the solution (called bridge) \u2013 an iterated bridge invariance property and the invariance of the most probable paths. These properties, which were tangentially mentioned in our previous work, are fully developed here. We also show that the distribution on paths of the optimal transport policy, which depends on a \u201ctemperature\u201d parameter, tends to the solution of the \u201cmost economical\u201d but possibly less robust optimal mass transport problem as the temperature goes to zero. The relevance of all of these properties for transport over networks is illustrated in an example
Efficient quantum state transfer in spin chains via adiabatic passage
We propose a method for quantum state transfer in spin chains using an
adiabatic passage technique. Modifying even and odd nearest-neighbour couplings
in time allows to achieve transfer fidelities arbitrarily close to one, without
the need for a precise control of coupling strengths and timing. We study in
detail transfer by adiabatic passage in a spin-1 chain governed by a
generalized Heisenberg Hamiltonian. We consider optimization of the transfer
process applying optimal control techniques. We discuss a realistic
experimental implementation using cold atomic gases confined in deep optical
lattices.Comment: 14 pages, 6 figures, to be published in New J. Phy
Recommended from our members
Advances in global optimization of high brightness beams
High brightness electron beams play an important role in accelerator-based applications such as driving X-ray free electron laser (FEL) radiation. In this paper, we report on advances in global beam dynamics optimization of an accelerator design using start-to-end simulations and a new parallel multi-objective differential evolution optimization method. The global optimization results in significant improvement of the final electron beam brightness
Functional optimization of the arterial network
We build an evolutionary scenario that explains how some crucial
physiological constraints in the arterial network of mammals - i.e. hematocrit,
vessels diameters and arterial pressure drops - could have been selected by
evolution. We propose that the arterial network evolved while being constrained
by its function as an organ. To support this hypothesis, we focus our study on
one of the main function of blood network: oxygen supply to the organs. We
consider an idealized organ with a given oxygen need and we optimize blood
network geometry and hematocrit with the constraint that it must fulfill the
organ oxygen need. Our model accounts for the non-Newtonian behavior of blood,
its maintenance cost and F\aa hr\ae us effects (decrease in average
concentration of red blood cells as the vessel diameters decrease). We show
that the mean shear rates (relative velocities of fluid layers) in the tree
vessels follow a scaling law related to the multi-scale property of the tree
network, and we show that this scaling law drives the behavior of the optimal
hematocrit in the tree. We apply our scenario to physiological data and reach
results fully compatible with the physiology: we found an optimal hematocrit of
0.43 and an optimal ratio for diameter decrease of about 0.79. Moreover our
results show that pressure drops in the arterial network should be regulated in
order for oxygen supply to remain optimal, suggesting that the amplitude of the
arterial pressure drop may have co-evolved with oxygen needs.Comment: Shorter version, misspelling correctio
Quantum Ratchets for Quantum Communication with Optical Superlattices
We propose to use a quantum ratchet to transport quantum information in a
chain of atoms trapped in an optical superlattice. The quantum ratchet is
created by a continuous modulation of the optical superlattice which is
periodic in time and in space. Though there is zero average force acting on the
atoms, we show that indeed the ratchet effect permits atoms on even and odd
sites to move along opposite directions. By loading the optical lattice with
two-level bosonic atoms, this scheme permits to perfectly transport a qubit or
entangled state imprinted in one or more atoms to any desired position in the
lattice. From the quantum computation point of view, the transport is achieved
by a smooth concatenation of perfect swap gates. We analyze setups with
noninteracting and interacting particles and in the latter case we use the
tools of optimal control to design optimal modulations. We also discuss the
feasibility of this method in current experiments.Comment: Published version, 9 pages, 5 figure
- …