9,569 research outputs found
On the Minimal Uncompletable Word Problem
Let S be a finite set of words over an alphabet Sigma. The set S is said to
be complete if every word w over the alphabet Sigma is a factor of some element
of S*, i.e. w belongs to Fact(S*). Otherwise if S is not complete, we are
interested in finding bounds on the minimal length of words in Sigma* which are
not elements of Fact(S*) in terms of the maximal length of words in S.Comment: 5 pages; added references, corrected typo
Coherent population trapping of a single nuclear spin under ambient conditions
Coherent control of quantum systems has far-reaching implications in quantum
engineering. In this context, coherent population trapping (CPT) involving dark
resonances has played a prominent role, leading to a wealth of major
applications including laser cooling of atoms and molecules, optical
magnetometry, light storage and highly precise atomic clocks. Extending CPT
methods to individual solid-state quantum systems has been only achieved in
cryogenic environments for electron spin impurities and superconducting
circuits. Here, we demonstrate efficient CPT of a single nuclear spin in a room
temperature solid. To this end, we make use of a three-level system with a
-configuration in the microwave domain, which consists of nuclear spin
states addressed through their hyperfine coupling to the electron spin of a
single nitrogen-vacancy defect in diamond. Dark state pumping requires a
relaxation mechanism which, in atomic systems, is simply provided by
spontaneous emission. In this work, the relaxation process is externally
controlled through incoherent optical pumping and separated in time from
consecutive coherent microwave excitations of the nuclear spin
-system. Such a pumping scheme with controlled relaxation allows us
(i) to monitor the sequential accumulation of population into the dark state
and (ii) to reach a new regime of CPT dynamics for which periodic arrays of
dark resonances can be observed, owing to multiple constructive interferences.
This work offers new prospects for quantum state preparation, information
storage in hybrid quantum systems and metrology.Comment: 13 pages including supplementary information, links to figures
correcte
Coherent population trapping of a single nuclear spin under ambient conditions
Coherent control of quantum systems has far-reaching implications in quantum
engineering. In this context, coherent population trapping (CPT) involving dark
resonances has played a prominent role, leading to a wealth of major
applications including laser cooling of atoms and molecules, optical
magnetometry, light storage and highly precise atomic clocks. Extending CPT
methods to individual solid-state quantum systems has been only achieved in
cryogenic environments for electron spin impurities and superconducting
circuits. Here, we demonstrate efficient CPT of a single nuclear spin in a room
temperature solid. To this end, we make use of a three-level system with a
-configuration in the microwave domain, which consists of nuclear spin
states addressed through their hyperfine coupling to the electron spin of a
single nitrogen-vacancy defect in diamond. Dark state pumping requires a
relaxation mechanism which, in atomic systems, is simply provided by
spontaneous emission. In this work, the relaxation process is externally
controlled through incoherent optical pumping and separated in time from
consecutive coherent microwave excitations of the nuclear spin
-system. Such a pumping scheme with controlled relaxation allows us
(i) to monitor the sequential accumulation of population into the dark state
and (ii) to reach a new regime of CPT dynamics for which periodic arrays of
dark resonances can be observed, owing to multiple constructive interferences.
This work offers new prospects for quantum state preparation, information
storage in hybrid quantum systems and metrology.Comment: 13 pages including supplementary information, links to figures
correcte
Multiscale Finite Element Modeling of Nonlinear Magnetoquasistatic Problems Using Magnetic Induction Conforming Formulations
In this paper we develop magnetic induction conforming multiscale
formulations for magnetoquasistatic problems involving periodic materials. The
formulations are derived using the periodic homogenization theory and applied
within a heterogeneous multiscale approach. Therefore the fine-scale problem is
replaced by a macroscale problem defined on a coarse mesh that covers the
entire domain and many mesoscale problems defined on finely-meshed small areas
around some points of interest of the macroscale mesh (e.g. numerical
quadrature points). The exchange of information between these macro and meso
problems is thoroughly explained in this paper. For the sake of validation, we
consider a two-dimensional geometry of an idealized periodic soft magnetic
composite.Comment: Paper accepted for publication in the SIAM MMS journa
Efficient single photon emission from a high-purity hexagonal boron nitride crystal
Among a variety of layered materials used as building blocks in van der Waals
heterostructures, hexagonal boron nitride (hBN) appears as an ideal platform
for hosting optically-active defects owing to its large bandgap ( eV).
Here we study the optical response of a high-purity hBN crystal under green
laser illumination. By means of photon correlation measurements, we identify
individual defects emitting a highly photostable fluorescence under ambient
conditions. A detailed analysis of the photophysical properties reveals a high
quantum efficiency of the radiative transition, leading to a single photon
source with very high brightness. These results illustrate how the wide range
of applications offered by hBN could be further extended to photonic-based
quantum information science and metrology.Comment: 5 pages, 4 figure
Perfect preferential orientation of nitrogen-vacancy defects in a synthetic diamond sample
We show that the orientation of nitrogen-vacancy (NV) defects in diamond can
be efficiently controlled through chemical vapor deposition (CVD) growth on a
(111)-oriented diamond substrate. More precisely, we demonstrate that
spontaneously generated NV defects are oriented with a ~ 97 % probability along
the [111] axis, corresponding to the most appealing orientation among the four
possible crystallographic axes. Such a nearly perfect preferential orientation
is explained by analyzing the diamond growth mechanism on a (111)-oriented
substrate and could be extended to other types of defects. This work is a
significant step towards the design of optimized diamond samples for quantum
information and sensing applications.Comment: 6 pages, 4 figure
Current non-conservation effects in DIS diffraction
In the neutrino DIS diffraction the charged current non-conservation gives
rise to sizable corrections to the longitudinal structure function, .
These corrections is a higher twist effect enhanced at small- by the rapidly
growing gluon density. The phenomenon manifests itself in abundant production
of charm and strangeness by longitudinally polarized W bosons of moderate
virtualities Q^2\lsim m_c^2.Comment: Prepared for the Int. Workshop on Diffraction in High-Energy Physics,
Diffraction 2008, La Londe-les-Maures, France, Sept. 9-14, 200
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