1,013 research outputs found
Quantum Technology: The Second Quantum Revolution
We are currently in the midst of a second quantum revolution. The first
quantum revolution gave us new rules that govern physical reality. The second
quantum revolution will take these rules and use them to develop new
technologies. In this review we discuss the principles upon which quantum
technology is based and the tools required to develop it. We discuss a number
of examples of research programs that could deliver quantum technologies in
coming decades including; quantum information technology, quantum
electromechanical systems, coherent quantum electronics, quantum optics and
coherent matter technology.Comment: 24 pages and 6 figure
Antiferro-quadrupolar correlations in the quantum spin ice candidate Pr2Zr2O7
We present an experimental study of the quantum spin ice candidate pyrochlore
coumpound \przr\ by means of magnetization measurements, specific heat and
neutron scattering up to 12 T and down to 60 mK. When the field is applied
along the and directions, field induced
structures settle in. We find that the ordered moment rises slowly, even at
very low temperature, in agreement with macroscopic magnetization.
Interestingly, for , the ordered moment appears on the
so called chains only. The spin excitation spectrum is essentially
{\it inelastic} and consists in a broad flat mode centered at about 0.4 meV
with a magnetic structure factor which resembles the spin ice pattern. For (at least up to 2.5 T), we find that a well defined mode
forms from this broad response, whose energy increases with , in the same
way as the temperature of the specific heat anomaly. We finally discuss these
results in the light of mean field calculations and propose a new
interpretation where quadrupolar interactions play a major role, overcoming the
magnetic exchange. In this picture, the spin ice pattern appears shifted up to
finite energy because of those new interactions. We then propose a range of
acceptable parameters for \przr\, that allow to reproduce several experimental
features observed under field. With these parameters, the actual ground state
of this material would be an antiferroquadrupolar liquid with spin-ice like
excitations
When resources collide: Towards a theory of coincidence in information spaces
This paper is an attempt to lay out foundations for a general theory of coincidence in information spaces such as the World Wide Web, expanding on existing work on bursty structures in document streams and information cascades. We elaborate on the hypothesis that every resource that is published in an information space, enters a temporary interaction with another resource once a unique explicit or implicit reference between the two is found. This thought is motivated by Erwin Shroedingers notion of entanglement between quantum systems. We present a generic information cascade model that exploits only the temporal order of information sharing activities, combined with inherent properties of the shared information resources. The approach was applied to data from the world's largest online citizen science platform Zooniverse and we report about findings of this case study
A Non-critical String (Liouville) Approach to Brain Microtubules: State Vector reduction, Memory coding and Capacity
Microtubule (MT) networks, subneural paracrystalline cytosceletal structures,
seem to play a fundamental role in the neurons. We cast here the complicated MT
dynamics in the form of a -dimensional non-critical string theory, thus
enabling us to provide a consistent quantum treatment of MTs, including
enviromental {\em friction} effects. Quantum space-time effects, as described
by non-critical string theory, trigger then an {\em organized collapse} of the
coherent states down to a specific or {\em conscious state}. The whole process
we estimate to take . The {\em microscopic arrow of
time}, endemic in non-critical string theory, and apparent here in the
self-collapse process, provides a satisfactory and simple resolution to the
age-old problem of how the, central to our feelings of awareness, sensation of
the progression of time is generated. In addition, the complete integrability
of the stringy model for MT we advocate in this work proves sufficient in
providing a satisfactory solution to memory coding and capacity. Such features
might turn out to be important for a model of the brain as a quantum computer.Comment: 70 pages Latex, 4 figures (not included), minor corrections, no
effect on conclusion
Is the Cell Really a Machine?
It has become customary to conceptualize the living cell as an intricate piece of machinery, different to a man-made machine only in terms of its superior complexity. This familiar understanding grounds the conviction that a cell's organization can be explained reductionistically, as well as the idea that its molecular pathways can be construed as deterministic circuits. The machine conception of the cell owes a great deal of its success to the methods traditionally used in molecular biology. However, the recent introduction of novel experimental techniques capable of tracking individual molecules within cells in real time is leading to the rapid accumulation of data that are inconsistent with an engineering view of the cell. This paper examines four major domains of current research in which the challenges to the machine conception of the cell are particularly pronounced: cellular architecture, protein complexes, intracellular transport, and cellular behaviour. It argues that a new theoretical understanding of the cell is emerging from the study of these phenomena which emphasizes the dynamic, self-organizing nature of its constitution, the fluidity and plasticity of its components, and the stochasticity and non-linearity of its underlying processes
Fermionic reaction coordinates and their application to an autonomous Maxwell demon in the strong coupling regime
We establish a theoretical method which goes beyond the weak coupling and
Markovian approximations while remaining intuitive, using a quantum master
equation in a larger Hilbert space. The method is applicable to all impurity
Hamiltonians tunnel-coupled to one (or multiple) baths of free fermions. The
accuracy of the method is in principle not limited by the system-bath coupling
strength, but rather by the shape of the spectral density and it is especially
suited to study situations far away from the wide-band limit. In analogy to the
bosonic case, we call it the fermionic reaction coordinate mapping. As an
application we consider a thermoelectric device made of two Coulomb-coupled
quantum dots. We pay particular attention to the regime where this device
operates as an autonomous Maxwell demon shoveling electrons against the voltage
bias thanks to information. Contrary to previous studies we do not rely on a
Markovian weak coupling description. Our numerical findings reveal that in the
regime of strong coupling and non-Markovianity, the Maxwell demon is often
doomed to disappear except in a narrow parameter regime of small power output.Comment: 18 pages incl. references, appendix and 10 figures; accepted versio
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