602 research outputs found
Optically detected spin-mechanical resonance in silicon carbide membranes
Hybrid spin-mechanical systems are a promising platform for future quantum
technologies. Usually they require application of additional microwave fields
to project integer spin to a readable state. We develop a theory of optically
detected spin-mechanical resonance associated with half-integer spin defects in
silicon carbide (SiC) membranes. It occurs when a spin resonance frequency
matches a resonance frequency of a mechanical mode, resulting in a shortening
of the spin relaxation time through resonantly enhanced spin-phonon coupling.
The effect can be detected as an abrupt reduction of the photoluminescence
intensity under optical pumping without application of microwave fields. We
propose all-optical protocols based on such spin-mechanical resonance to detect
external magnetic fields and mass with ultra-high sensitivity. We also discuss
room-temperature nonlinear effects under strong optical pumping, including
spin-mediated cooling and heating of mechanical modes. Our approach suggests a
new concept for quantum sensing using spin-optomechanics.Comment: 9 pages, 4 figure
Continuum of consciousness: Mind uploading and resurrection of human consciousness. Is there a place for physics, neuroscience and computers?
In this paper, I perform mental experiment to analyze hypothetical process of
mind uploading. That process suggested as a way to achieve resurrection of
human consciousness. Mind uploading can be seen as a migration process of the
core mental functions, which migrate from a human brain to an artificial
environment. To simulate the process, I suggest a topological approach which is
based on a formalism of information geometry. Geometrical formalism lets us
simulate the toy mind as geometrical structures as well as gives us powerful
geometrical and topological methods for analysis of the information system.
This approach leads to the insight about using holographic model as an analogy
for the mind migration to an artificial environment. This model represents the
toy mind functionality in terms of information geometry (as a geometrical
shape) on information manifold. Such shape can have distributed holographic
representation. This representation gives us delocalized representation of the
system. At the same time, the process of creating the holographic
representation gives us a strategy to migrate from original to an artificial
environment and back. The interface between brain and an environment is modeled
as an entropy flow which is defined as a geometrical flow on information
manifold. Such flow is an analogy of holography recording for the toy mind. The
opposite process of holography reconstruction is modeled by none-local
Hamiltonians defined on the information manifold.Comment: 8 figures, submitted to conference Toward a Science of Consciousness
2008 April 8-12, 200
Advances in the theory and methods of computational vibronic spectroscopy
We discuss semiempirical approaches and parametric methods developed for
modeling molecular vibronic spectra. These methods, together with databases of
molecular fragments, have proved efficient and flexible for solving various
problems ranging from detailed interpretation of conventional vibronic spectra
and calculation of radiative transition probabilities to direct simulations of
dynamical (time-resolved) spectra and spectrochemical analysis of individual
substances and mixtures. A number of specific examples and applications
presented here show the potential of the semiempirical approach for predictive
calculations of spectra and solution of inverse spectral problems. It is
noteworthy that these advances provide computational insights into developing
theories of photoinduced isomer transformations and nonradiative transitions in
polyatomic molecules and molecular ensembles, theory of new methods for
standardless quantitative spectral analysis.Comment: to appear in "Advances in Laser and Optics Research", Nova Science
Publishers, 200
Anisotropic Spin-Acoustic Resonance in Silicon Carbide at Room Temperature
We report on acoustically driven spin resonances in atomic-scale centers in
silicon carbide at room temperature. Specifically, we use a surface acoustic
wave cavity to selectively address spin transitions with magnetic quantum
number differences of 1 and 2 in the absence of external microwave
electromagnetic fields. These spin-acoustic resonances reveal a non-trivial
dependence on the static magnetic field orientation, which is attributed to the
intrinsic symmetry of the acoustic fields combined with the peculiar properties
of a half-integer spin system. We develop a microscopic model of the
spin-acoustic interaction, which describes our experimental data without
fitting parameters. Furthermore, we predict that traveling surface waves lead
to a chiral spin-acoustic resonance, which changes upon magnetic field
inversion. These results establish silicon carbide as a highly-promising hybrid
platform for on-chip spin-optomechanical quantum control enabling engineered
interactions at room temperature.Comment: 6 pages, 3 figures, Supplemental Informatio
Engineering near infrared single photon emitters in ultrapure silicon carbide
Quantum emitters hosted in crystalline lattices are highly attractive
candidates for quantum information processing, secure networks and nanosensing.
For many of these applications it is necessary to have control over single
emitters with long spin coherence times. Such single quantum systems have been
realized using quantum dots, colour centres in diamond, dopants in
nanostructures and molecules . More recently, ensemble emitters with spin
dephasing times on the order of microseconds and room-temperature optically
detectable magnetic resonance have been identified in silicon carbide (SiC), a
compound being highly compatible to up-to-date semiconductor device technology.
So far however, the engineering of such spin centres in SiC on single-emitter
level has remained elusive. Here, we demonstrate the control of spin centre
density in ultrapure SiC over 8 orders of magnitude, from below to
above cm using neutron irradiation. For a low irradiation
dose, a fully photostable, room-temperature, near infrared (NIR) single photon
emitter can clearly be isolated, demonstrating no bleaching even after
excitation cycles. Based on their spectroscopic fingerprints, these
centres are identified as silicon vacancies, which can potentially be used as
qubits, spin sensors and maser amplifiers.Comment: 5 pages, 4 figure
Locking of electron spin coherence over fifty milliseconds in natural silicon carbide
We demonstrate that silicon carbide (SiC) with natural isotope abundance can
preserve a coherent spin superposition in silicon vacancies over unexpectedly
long time approaching 0.1 seconds. The spin-locked subspace with drastically
reduced decoherence rate is attained through the suppression of heteronuclear
spin cross-talking by applying a moderate magnetic field in combination with
dynamic decoupling from the nuclear spin baths. We identify several
phonon-assisted mechanisms of spin-lattice relaxation, ultimately limiting
quantum coherence, and find that it can be extremely long at cryogenic
temperature, equal or even longer than 8 seconds. Our approach may be extended
to other polyatomic compounds and open a path towards improved qubit memory for
wafer-scale quantum techmologies.Comment: Added extended data analysis based on quantum process tomography,
discussion of spin-lattice relaxation mechanism
Highly efficient optical pumping of spin defects in silicon carbide for stimulated microwave emission
We investigate the pump efficiency of silicon vacancy-related spins in
silicon carbide. For a crystal inserted into a microwave cavity with a
resonance frequency of 9.4 GHz, the spin population inversion factor of 75 with
the saturation optical pump power of about 350 mW is achieved at room
temperature. At cryogenic temperature, the pump efficiency drastically
increases, owing to an exceptionally long spin-lattice relaxation time
exceeding one minute. Based on the experimental results, we find realistic
conditions under which a silicon carbide maser can operate in continuous-wave
mode and serve as a quantum microwave amplifier.Comment: 8 pages, 6 figure
Bound magnetic polarons in the very dilute regime
We study bound magnetic polarons (BMP) in a very diluted magnetic
semiconductor CdMnTe by means of site selective spectroscopy. In zero magnetic
field we detect a broad and asymmetric band with a characteristic spectral
width of about 5 meV. When external magnetic fields are applied a new line
appears in the emission spectrum. Remarkably, the spectral width of this line
is reduced greatly down to 0.24 meV. We attribute such unusual behavior to the
formation of BMP, effected by sizable fluctuations of local magnetic moments.
The modifications of the optical spectra have been simulated by the Monte-Carlo
method and calculated within an approach considering the nearest Mn ion. A
quantitative agreement with the experiment is achieved without use of fitting
parameters. It is demonstrated that the low-energy part of the emission spectra
originates from the energetic relaxation of a complex consisting of a hole and
its nearest Mn ion. It is also shown that the contribution to the narrow line
arises from the remote Mn ions.Comment: 5 pages, 5 figure
Excitation and recombination dynamics of vacancy-related spin centers in silicon carbide
We generate silicon vacancy related defects in high-quality epitaxial silicon
carbide layers by means of electron irradiation. By controlling the irradiation
fluence, the defect concentration is varied over several orders of magnitude.
We establish the excitation profile for optical pumping of these defects and
evaluate the optimum excitation wavelength of 770 nm. We also measure the
photoluminescence dynamics at room temperature and find a monoexponential decay
with a characteristic lifetime of 6.1 ns. The integrated photoluminescence
intensity depends linear on the excitation power density up to 20 kW/cm,
indicating a relatively small absorption cross section of these defects.Comment: 4 pages, 4 figure
Modeling of the time-resolved vibronic spectra of polyatomic molecules: the formulation of the problem and analysis of kinetic equations
A semiempirical parametric method is proposed for modeling three-dimensional
(time-resolved) vibronic spectra of polyatomic molecules. The method is based
on the use of the fragment approach in the formation of molecular models for
excited electronic states and parametrization of these molecular fragments by
modeling conventional (one-dimensional) absorption and fluorescence spectra of
polyatomic molecules. All matrix elements that are required for calculation of
the spectra can be found by the methods developed. The time dependencies of the
populations of a great number (>10^3) of vibronic levels can be most
conveniently found by using the iterative numerical method of integration of
kinetic equations. Convenient numerical algorithms and specialized software for
PC are developed. Computer experiments showed the possibility of the real-time
modeling of three-dimensional spectra of polyatomic molecules containing
several tens of atoms
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