6,139 research outputs found
Paramagnetic Materials and Practical Algorithmic Cooling for NMR Quantum Computing
Algorithmic Cooling is a method that uses novel data compression techniques
and simplecquantum computing devices to improve NMR spectroscopy, and to offer
scalable NMR quantum computers. The algorithm recursively employs two steps. A
reversible entropy compression of the computation quantum-bits (qubits) of the
system and an irreversible heat transfer from the system to the environment
through a set of reset qubits that reach thermal relaxation rapidly.
Is it possible to experimentally demonstrate algorithmic cooling using
existing technology? To allow experimental algorithmic cooling, the
thermalization time of the reset qubits must be much shorter than the
thermalization time of the computation qubits. However such
thermalization-times ratios have yet to be reported.
We investigate here the effect of a paramagnetic salt on the
thermalization-times ratio of computation qubits (carbons) and a reset qubit
(hydrogen). We show that the thermalization-times ratio is improved by
approximately three-fold. Based on this result, an experimental demonstration
of algorithmic cooling by thermalization and magnetic ions is currently
performed by our group and collaborators.Comment: 5 pages, A conference version of this paper appeared in SPIE, volume
5105, pages 185-194 (2003
New, Highly Accurate Propagator for the Linear and Nonlinear Schr\"odinger Equation
A propagation method for the time dependent Schr\"odinger equation was
studied leading to a general scheme of solving ode type equations. Standard
space discretization of time-dependent pde's usually results in system of ode's
of the form u_t -Gu = s where G is a operator (matrix) and u is a
time-dependent solution vector. Highly accurate methods, based on polynomial
approximation of a modified exponential evolution operator, had been developed
already for this type of problems where G is a linear, time independent matrix
and s is a constant vector. In this paper we will describe a new algorithm for
the more general case where s is a time-dependent r.h.s vector. An iterative
version of the new algorithm can be applied to the general case where G depends
on t or u. Numerical results for Schr\"odinger equation with time-dependent
potential and to non-linear Schr\"odinger equation will be presented.Comment: 14 page
Chaotic Quivering of Micron-Scaled On-Chip Resonators Excited by Centrifugal Optical Pressure
Opto-mechanical chaotic oscillation of an on-chip resonator is excited by the radiation-pressure nonlinearity. Continuous optical input, with no external feedback or modulation, excites chaotic vibrations in very different geometries of the cavity (both tori and spheres) and shows that opto-mechanical chaotic oscillations are an intrinsic property of optical microcavities. Measured phenomena include period doubling, a spectral continuum, aperiodic oscillations, and complex trajectories. The rate of exponential divergence from a perturbed initial condition (Lyapunov exponent) is calculated. Continuous improvements in cavities mean that such chaotic oscillations can be expected in the future with many other platforms, geometries, and frequency spans
Pinpointing the massive black hole in the Galactic Center with gravitationally lensed stars
A new statistical method for pinpointing the massive black hole (BH) in the
Galactic Center on the IR grid is presented and applied to astrometric IR
observations of stars close to the BH. This is of interest for measuring the IR
emission from the BH, in order to constrain accretion models; for solving the
orbits of stars near the BH, in order to measure the BH mass and to search for
general relativistic effects; and for detecting the fluctuations of the BH away
from the dynamical center of the stellar cluster, in order to study the stellar
potential. The BH lies on the line connecting the two images of any background
source it gravitationally lenses, and so the intersection of these lines fixes
its position. A combined search for a lensing signal and for the BH shows that
the most likely point of intersection coincides with the center of acceleration
of stars orbiting the BH. This statistical detection of lensing by the BH has a
random probability of ~0.01. It can be verified by deep IR stellar
spectroscopy, which will determine whether the most likely lensed image pair
candidates (listed here) have identical spectra.Comment: 4 pages, 2 figures, submitted to ApJ
Algorithmic Cooling of Spins: A Practicable Method for Increasing Polarization
An efficient technique to generate ensembles of spins that are highly
polarized by external magnetic fields is the Holy Grail in Nuclear Magnetic
Resonance (NMR) spectroscopy. Since spin-half nuclei have steady-state
polarization biases that increase inversely with temperature, spins exhibiting
high polarization biases are considered cool, even when their environment is
warm. Existing spin-cooling techniques are highly limited in their efficiency
and usefulness. Algorithmic cooling is a promising new spin-cooling approach
that employs data compression methods in open systems. It reduces the entropy
of spins on long molecules to a point far beyond Shannon's bound on reversible
entropy manipulations (an information-theoretic version of the 2nd Law of
Thermodynamics), thus increasing their polarization. Here we present an
efficient and experimentally feasible algorithmic cooling technique that cools
spins to very low temperatures even on short molecules. This practicable
algorithmic cooling could lead to breakthroughs in high-sensitivity NMR
spectroscopy in the near future, and to the development of scalable NMR quantum
computers in the far future. Moreover, while the cooling algorithm itself is
classical, it uses quantum gates in its implementation, thus representing the
first short-term application of quantum computing devices.Comment: 24 pages (with annexes), 3 figures (PS). This version contains no
major content changes: fixed bibliography & figures, modified
acknowledgement
Deep Functional Maps: Structured Prediction for Dense Shape Correspondence
We introduce a new framework for learning dense correspondence between
deformable 3D shapes. Existing learning based approaches model shape
correspondence as a labelling problem, where each point of a query shape
receives a label identifying a point on some reference domain; the
correspondence is then constructed a posteriori by composing the label
predictions of two input shapes. We propose a paradigm shift and design a
structured prediction model in the space of functional maps, linear operators
that provide a compact representation of the correspondence. We model the
learning process via a deep residual network which takes dense descriptor
fields defined on two shapes as input, and outputs a soft map between the two
given objects. The resulting correspondence is shown to be accurate on several
challenging benchmarks comprising multiple categories, synthetic models, real
scans with acquisition artifacts, topological noise, and partiality.Comment: Accepted for publication at ICCV 201
Hidden Convexity in Partially Separable Optimization
The paper identifies classes of nonconvex optimization problems whose convex relaxations have optimal solutions which at the same time are global optimal solutions of the original nonconvex problems. Such a hidden convexity property was so far limited to quadratically constrained quadratic problems with one or two constraints. We extend it here to problems with some partial separable structure. Among other things, the new hidden convexity results open up the possibility to solve multi-stage robust optimization problems using certain nonlinear decision rules.convex relaxation of nonconvex problems;hidden convexity;partially separable functions;robust optimization
Erbium-doped and Raman microlasers on a silicon chip fabricated by the solâgel process
We report high-Q solâgel microresonators on silicon chips, fabricated directly from a solâgel layer deposited onto a silicon substrate. Quality factors as high as 2.5Ă10^7 at 1561 nm were obtained in toroidal microcavities formed of silica solâgel, which allowed Raman lasing at absorbed pump powers below 1 mW. Additionally, Er3+-doped microlasers were fabricated from Er3+-doped solâgel layers with control of the laser dynamics possible by varying the erbium concentration of the starting solâgel material. Continuous lasing with a threshold of 660 nW for erbium-doped microlaser was also obtained
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