1,644 research outputs found
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
Impulsive gravitational waves of massless particles in extended theories of gravity
We investigate the vacuum pp-wave and Aichelburg-Sexl-type solutions in f(R)
and the modified Gauss-Bonnet theories of gravity with both minimal and
nonminimal couplings between matter and geometry. In each case, we obtain the
necessary condition for the theory to admit the solution and examine it for
several specific models. We show that the wave profiles are the same or
proportional to the general relativistic one
Multicomponent solution in modified theory of gravity in the early universe
We study the modified theory of gravity in Friedmann Robertson Walker
universe composed of several perfect fluids. We consider the power law
inflation and determine the equation of state parameters in terms of the
parameters of modified gravity's Lagrangian in the early universe. We also
discuss briefly the gravitational baryogenesis in this model.Comment: 9 pages, accepted for publication in Physical Review
Numerical Evidence for Robustness of Environment-Assisted Quantum Transport
Recent theoretical studies show that decoherence process can enhance
transport efficiency in quantum systems. This effect is known as
environment-assisted quantum transport (ENAQT). The role of ENAQT in optimal
quantum transport is well investigated, however, it is less known how robust
ENAQT is with respect to variations in the system or its environment
characteristic. Toward answering this question, we simulated excitonic energy
transfer in Fenna-Matthews-Olson (FMO) photosynthetic complex. We found that
ENAQT is robust with respect to many relevant parameters of environmental
interactions and Frenkel-exciton Hamiltonian including reorganization energy,
bath frequency cutoff, temperature, and initial excitations, dissipation rate,
trapping rate, disorders, and dipole moments orientations. Our study suggests
that the ENAQT phenomenon can be exploited in robust design of highly efficient
quantum transport systems.Comment: arXiv admin note: substantial text overlap with arXiv:1104.481
A Note on Gravitational Baryogenesis
The coupling between Ricci scalar curvature and the baryon number current
dynamically breaks CPT in an expanding universe and leads to baryon asymmetry.
We study the effect of time dependence of equation of state parameter of the
FRW universe on this asymmetry.Comment: 10 pages, accepted for publication in Physical Review
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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