1,174 research outputs found
Dynamical Belyi maps
We study the dynamical properties of a large class of rational maps with
exactly three ramification points. By constructing families of such maps, we
obtain infinitely many conservative maps of degree ; this answers a question
of Silverman. Rather precise results on the reduction of these maps yield
strong information on the rational dynamics.Comment: 21 page
Long-lived driven solid-state quantum memory
We investigate the performance of inhomogeneously broadened spin ensembles as
quantum memories under continuous dynamical decoupling. The role of the
continuous driving field is two-fold: first, it decouples individual spins from
magnetic noise; second and more important, it suppresses and reshapes the
spectral inhomogeneity of spin ensembles. We show that a continuous driving
field, which itself may also be inhomogeneous over the ensemble, can enhance
the decay of the tails of the inhomogeneous broadening distribution
considerably. This fact enables a spin ensemble based quantum memory to exploit
the effect of cavity protection and achieve a much longer storage time. In
particular, for a spin ensemble with a Lorentzian spectral distribution, our
calculations demonstrate that continuous dynamical decoupling has the potential
to improve its storage time by orders of magnitude for the state-of-art
experimental parameters
Nanodiamonds carrying quantum emitters with almost lifetime-limited linewidths
Nanodiamonds (NDs) hosting optically active defects are an important
technical material for applications in quantum sensing, biological imaging, and
quantum optics. The negatively charged silicon vacancy (SiV) defect is known to
fluoresce in molecular sized NDs (1 to 6 nm) and its spectral properties depend
on the quality of the surrounding host lattice. This defect is therefore a good
probe to investigate the material properties of small NDs. Here we report
unprecedented narrow optical transitions for SiV colour centers hosted in
nanodiamonds produced using a novel high-pressure high-temperature (HPHT)
technique. The SiV zero-phonon lines were measured to have an inhomogeneous
distribution of 1.05 nm at 5 K across a sample of numerous NDs. Individual
spectral lines as narrow as 354 MHz were measured for SiV centres in
nanodiamonds smaller than 200 nm, which is four times narrower than the best
SiV line previously reported for nanodiamonds. Correcting for apparent spectral
diffusion yielded a homogeneous linewith of about 200 MHz, which is close to
the width limit imposed by the radiative lifetime. These results demonstrate
that the direct HPHT synthesis technique is capable of producing nanodiamonds
with high crystal lattice quality, which are therefore a valuable technical
material
Sensing remote nuclear spins
Sensing single nuclear spins is a central challenge in magnetic resonance
based imaging techniques. Although different methods and especially diamond
defect based sensing and imaging techniques in principle have shown sufficient
sensitivity, signals from single nuclear spins are usually too weak to be
distinguished from background noise. Here, we present the detection and
identification of remote single C-13 nuclear spins embedded in nuclear spin
baths surrounding a single electron spins of a nitrogen-vacancy centre in
diamond. With dynamical decoupling control of the centre electron spin, the
weak magnetic field ~10 nT from a single nuclear spin located ~3 nm from the
centre with hyperfine coupling as weak as ~500 Hz is amplified and detected.
The quantum nature of the coupling is confirmed and precise position and the
vector components of the nuclear field are determined. Given the distance over
which nuclear magnetic fields can be detected the technique marks a firm step
towards imaging, detecting and controlling nuclear spin species external to the
diamond sensor
Towards a large-scale quantum simulator on diamond surface at room temperature
Strongly-correlated quantum many-body systems exhibits a variety of exotic
phases with long-range quantum correlations, such as spin liquids and
supersolids. Despite the rapid increase in computational power of modern
computers, the numerical simulation of these complex systems becomes
intractable even for a few dozens of particles. Feynman's idea of quantum
simulators offers an innovative way to bypass this computational barrier.
However, the proposed realizations of such devices either require very low
temperatures (ultracold gases in optical lattices, trapped ions,
superconducting devices) and considerable technological effort, or are
extremely hard to scale in practice (NMR, linear optics). In this work, we
propose a new architecture for a scalable quantum simulator that can operate at
room temperature. It consists of strongly-interacting nuclear spins attached to
the diamond surface by its direct chemical treatment, or by means of a
functionalized graphene sheet. The initialization, control and read-out of this
quantum simulator can be accomplished with nitrogen-vacancy centers implanted
in diamond. The system can be engineered to simulate a wide variety of
interesting strongly-correlated models with long-range dipole-dipole
interactions. Due to the superior coherence time of nuclear spins and
nitrogen-vacancy centers in diamond, our proposal offers new opportunities
towards large-scale quantum simulation at room temperatures
Meaning and definition:Skepticism and semantics in twelfth-century Arabic Philosophy
The theory of essential definitions is a fundamental anti-sceptic element of the Aristotelian-Avicennian epistemology. In this theory, when we distinguish the genus and the specific differentia of a given essence we thereby acquire a scientific understanding of it. The aim of this article is to analyse systematically the sceptical reasons, arguments and conclusions against real definitions of three major authorities of twelfth-century Arabic philosophy: Fahr al-Din al-Razi, Sihab al-Din al-Suhrawardi and Abu l-Barakat al-Badadi. I focus on showing how their refutation of our capacity to provide essential definitions of things is rooted in their semantic theory: we only know things under certain descriptions which are identical to the meanings of the words that we use to refer to them, yet these descriptions do not capture the essences of things in themselves. The best result one can achieve with Aristotelian-Avicennian scientific definitions is a "nominal definition". With this, Razi, Suhrawardi and Abu l-Barakat will put some serious epistemic limitations on our capacity to attain scientific knowledge of things, at least as Aristotle and Avicenna would have it
Fermi-surface topologies and low-temperature phases of the filled skutterudite compounds CeOs
Grand unified theory constrained supersymmetry and neutrinoless double beta decay
We analyze the contributions to the neutrinoless double decay
(-decay) coming from the Grand Unified Theory (GUT) constrained
Minimal Supersymmetric Standard Model (MSSM) with trilinear R-parity breaking.
We discuss the importance of two-nucleon and pion-exchange realizations of the
quark-level -decay transitions. In this context, the questions
of reliability of the calculated relevant nuclear matrix elements within the
Renormalized Quasiparticle Random Phase Approximation (pn-RQRPA) for several
medium and heavy open-shell nuclei are addressed. The importance of gluino and
neutralino contributions to -decay is also analyzed. We review
the present experiments and deduce limits on the trilinear R-parity breaking
parameter from the non-observability of -decay
for different GUT constrained SUSY scenarios. In addition, a detailed study of
limits on the MSSM parameter space coming from the processes
by using the recent CLEO and OPAL results is performed. Some studies in respect
to the future -decay project GENIUS are also presented.Comment: 29 pages, 8 figure
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