969 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
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
Super-harmonic injection locking of nano-contact spin-torque vortex oscillators
Super-harmonic injection locking of single nano-contact (NC) spin-torque
vortex oscillators (STVOs) subject to a small microwave current has been
explored. Frequency locking was observed up to the fourth harmonic of the STVO
fundamental frequency in microwave magneto-electronic measurements. The
large frequency tunability of the STVO with respect to allowed the
device to be locked to multiple sub-harmonics of the microwave frequency
, or to the same sub-harmonic over a wide range of by tuning
the DC current. In general, analysis of the locking range, linewidth, and
amplitude showed that the locking efficiency decreased as the harmonic number
increased, as expected for harmonic synchronization of a non-linear oscillator.
Time-resolved scanning Kerr microscopy (TRSKM) revealed significant differences
in the spatial character of the magnetization dynamics of states locked to the
fundamental and harmonic frequencies, suggesting significant differences in the
core trajectories within the same device. Super-harmonic injection locking of a
NC-STVO may open up possibilities for devices such as nanoscale frequency
dividers, while differences in the core trajectory may allow mutual
synchronisation to be achieved in multi-oscillator networks by tuning the
spatial character of the dynamics within shared magnetic layers.Comment: 21 pages, 8 figure
Hyperentanglement-enabled Direct Characterization of Quantum Dynamics
We use hyperentangled photons to experimentally implement an
entanglement-assisted quantum process tomography technique known as Direct
Characterization of Quantum Dynamics. Specifically, hyperentanglement-assisted
Bell-state analysis enabled us to characterize a variety of single-qubit
quantum processes using far fewer experimental configurations than are required
by Standard Quantum Process Tomography (SQPT). Furthermore, we demonstrate how
known errors in Bell-state measurement may be compensated for in the data
analysis. Using these techniques, we have obtained single-qubit process
fidelities as high as 98.2% but with one-third the number experimental
configurations required for SQPT. Extensions of these techniques to multi-qubit
quantum processes are discussed.Comment: This is part of a joint submission with an implementation with Ions:
"Experimental characterization of quantum dynamics through many-body
interactions" by Daniel Nigg, Julio T. Barreiro, Philipp Schindler, Masoud
Mohseni, Thomas Monz, Michael Chwalla, Markus Hennrich and Rainer Blat
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