2,326 research outputs found
What Makes a Computation Unconventional?
A coherent mathematical overview of computation and its generalisations is
described. This conceptual framework is sufficient to comfortably host a wide
range of contemporary thinking on embodied computation and its models.Comment: Based on an invited lecture for the 'Symposium on
Natural/Unconventional Computing and Its Philosophical Significance' at the
AISB/IACAP World Congress 2012, University of Birmingham, July 2-6, 201
Quantum phase transitions of the diluted O(3) rotor model
We study the phase diagram and the quantum phase transitions of a
site-diluted two-dimensional O(3) quantum rotor model by means of large-scale
Monte-Carlo simulations. This system has two quantum phase transitions, a
generic one for small dilutions, and a percolation transition across the
lattice percolation threshold. We determine the critical behavior for both
transitions and for the multicritical point that separates them. In contrast to
the exotic scaling scenarios found in other random quantum systems, all these
transitions are characterized by finite-disorder fixed points with power-law
scaling. We relate our findings to a recent classification of phase transitions
with quenched disorder according to the rare region dimensionality, and we
discuss experiments in disordered quantum magnets.Comment: 11 pages, 14 eps figures, final version as publishe
Can biological quantum networks solve NP-hard problems?
There is a widespread view that the human brain is so complex that it cannot
be efficiently simulated by universal Turing machines. During the last decades
the question has therefore been raised whether we need to consider quantum
effects to explain the imagined cognitive power of a conscious mind.
This paper presents a personal view of several fields of philosophy and
computational neurobiology in an attempt to suggest a realistic picture of how
the brain might work as a basis for perception, consciousness and cognition.
The purpose is to be able to identify and evaluate instances where quantum
effects might play a significant role in cognitive processes.
Not surprisingly, the conclusion is that quantum-enhanced cognition and
intelligence are very unlikely to be found in biological brains. Quantum
effects may certainly influence the functionality of various components and
signalling pathways at the molecular level in the brain network, like ion
ports, synapses, sensors, and enzymes. This might evidently influence the
functionality of some nodes and perhaps even the overall intelligence of the
brain network, but hardly give it any dramatically enhanced functionality. So,
the conclusion is that biological quantum networks can only approximately solve
small instances of NP-hard problems.
On the other hand, artificial intelligence and machine learning implemented
in complex dynamical systems based on genuine quantum networks can certainly be
expected to show enhanced performance and quantum advantage compared with
classical networks. Nevertheless, even quantum networks can only be expected to
efficiently solve NP-hard problems approximately. In the end it is a question
of precision - Nature is approximate.Comment: 38 page
Synthetic Frequency Protocol in the Ramsey Spectroscopy of Clock Transitions
We develop an universal method to significantly suppress probe-induced shifts
in any types of atomic clocks using the Ramsey spectroscopy. Our approach is
based on adaptation of the synthetic frequency concept [V. I. Yudin, et al.,
Phys. Rev. Lett. 107, 030801 (2011)] (previously developed for BBR shift
suppression) to the Ramsey spectroscopy with the use of interrogations for
different dark time intervals. Universality of the method consists in
arbitrariness of the possible Ramsey schemes. However, most extremal results
are obtained in combination with so-called hyper-Ramsey spectroscopy [V. I.
Yudin, et al., Phys. Rev. A 82, 011804(R) (2010)]. In the latter case, the
probe-induced frequency shifts can be suppressed considerably below a
fractional level of 10 practically for any optical atomic clocks, where
this shift previously was metrologically significant. The main advantage of our
method in comparison with other radical hyper-Ramsey approaches [R. Hobson, et
al., Phys. Rev. A 93, 010501(R) (2016); T. Zanon-Willette, et al., Phys. Rev. A
93, 042506 (2016)] consist in much greater efficiency and resistibility in the
presence of decoherentization.Comment: 9 pages, 7 figure
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