2,128 research outputs found
Low-cost error mitigation by symmetry verification
We investigate the performance of error mitigation via measurement of
conserved symmetries on near-term devices. We present two protocols to measure
conserved symmetries during the bulk of an experiment, and develop a zero-cost
post-processing protocol which is equivalent to a variant of the quantum
subspace expansion. We develop methods for inserting global and local symetries
into quantum algorithms, and for adjusting natural symmetries of the problem to
boost their mitigation against different error channels. We demonstrate these
techniques on two- and four-qubit simulations of the hydrogen molecule (using a
classical density-matrix simulator), finding up to an order of magnitude
reduction of the error in obtaining the ground state dissociation curve.Comment: Published versio
Possibly your rooms may have defects. Like men, few are perfect: comedores y género en el ámbito anglosajón
El interior doméstico del siglo XIX se adaptaba a las necesidades privadas y públicas de la clase burguesa. Las diversas estancias, su distribución y su ornamentación se sometían a los dictados de la moda, pero también a unas exigencias familiares y sociales cuidadosamente codificadas. En esta época, uno de los espacios más destacados dentro del hogar era el comedor. Este constituía una estancia de representación destacada, donde la familia podía exhibir su posición dentro de la sociedad y, asimismo, era un lugar en el que sus miembros podían reunirse en intimidad. Los manuales normativos y los libros sobre decoración otorgaron a esta habitación un carácter masculino y ello condicionó su diseño. Sin embargo, aunque el género está presente también en la vivienda del Ochocientos, los límites que se establecen entre lo femenino y lo masculino no siempre están tan claros. Ahí el interés, el valor y quizás también el misterio de un espacio creado para el devenir de lo cotidiano.Nineteenth Century domestic interiors were adapted to private and public needs of the bourgeois class. The different rooms, their distribution and ornamentation were subjected to the dictates of fashion, but also to the family and social expectations of that time. One of the most outstanding spaces within the home was the dining room. This was an area where the family could demonstrate their status in society and a place where its members could meet in privacy. The etiquette manuals and books on decorating gave this room a male character and this determined its design. However, while gender is also present in the housing of the
19th Century, the boundaries established between the feminine and masculine are not always so clear. Hence, the interest, value and perhaps also the mystery of a space created for the development of the everyda
STM and ab initio study of holmium nanowires on a Ge(111) Surface
A nanorod structure has been observed on the Ho/Ge(111) surface using
scanning tunneling microscopy (STM). The rods do not require patterning of the
surface or defects such as step edges in order to grow as is the case for
nanorods on Si(111). At low holmium coverage the nanorods exist as isolated
nanostructures while at high coverage they form a periodic 5x1 structure. We
propose a structural model for the 5x1 unit cell and show using an ab initio
calculation that the STM profile of our model structure compares favorably to
that obtained experimentally for both filled and empty states sampling. The
calculated local density of states shows that the nanorod is metallic in
character.Comment: 4 pages, 12 figures (inc. subfigures). Presented at the the APS March
meeting, Baltimore MD, 200
Acute effects of exercise on mood and HRV
El objetivo del estudio es analizar los efectos agudos del ejercicio físico sobre el estado de ánimo y la variabilidad de la frecuencia cardíaca (HRV), en personas activas y sedentarias. Para ello participaron 30 estudiantes clasificados en Activos y No activos. En una sola sesión realizaban una prueba de esfuerzo submáximo (UKK), cumplimentando el Perfil de Estados de Ánimo (POMS) y realizando un test en reposo de la HRV antes y después del ejercicio. Los resultados indican una mejora en el estado de ánimo, aumentando en los factores de Vigor y Fatiga y disminuyendo en Tensión y Depresión después del ejercicio. Se encontraron diferencias significativas en función del nivel de ejercicio físico de los participantes en el nivel de Depresión, al observarse una mayor disminución después del ejercicio en los Activos. La HRV también mostró diferencias entre Activos y No activos en los parámetros de dominio frecuencial, LFnu2 y HFnu2The aim of this study was to analyze the acute effects of exercise on mood and on heart rate variability (HRV), in active and sedentary people. This involved 30 undergraduates classified into Active and Non active participants. In a single session participants performed a submaximal exercise test (UKK), answered the Profile of Mood States (POMS) and performed before and after the exercise a test of HRV at rest. The participants improved their mood state, by increasing Vigor and Fatigue factors and decreased Tension and Depression after the exercise test. Moreover, Active participants presented a significant higher decrease in Depression after exercise than Non active. HRV analysis also showed differences between Active and Non active participants in the frequency domain parameters LFnu2 and HFnu
Evidence of photospheric vortex flows at supergranular junctions observed by FG/SOT (Hinode)
Twisting motions of different nature are observed in several layers of the
solar atmosphere. Chromospheric sunspot whorls and rotation of sunspots or even
higher up in the lower corona sigmoids are examples of the large scale twisted
topology of many solar features. Nevertheless, their occurrence at large scale
in the quiet photosphere has not been investigated. The present study reveals
the existence of vortex flows located at the supergranular junctions of the
quiet Sun. We use a 1-hour and a 5-hour time series of the granulation in Blue
continuum and G-band images from FG/SOT to derive the photospheric flows. A
feature tracking technique called Balltracking is performed to track the
granules and reveal the underlying flow fields. In both time series we identify
long-lasting vortex flow located at supergranular junctions. The first vortex
flow lasts at least 1 hour and is ~20-arcsec-wide (~15.5 Mm). The second vortex
flow lasts more than 2 hours and is ~27-arcsec-wide (~21 Mm).Comment: 4 pages, 10 figure
Calculating energy derivatives for quantum chemistry on a quantum computer
Modeling chemical reactions and complicated molecular systems has been
proposed as the `killer application' of a future quantum computer. Accurate
calculations of derivatives of molecular eigenenergies are essential towards
this end, allowing for geometry optimization, transition state searches,
predictions of the response to an applied electric or magnetic field, and
molecular dynamics simulations. In this work, we survey methods to calculate
energy derivatives, and present two new methods: one based on quantum phase
estimation, the other on a low-order response approximation. We calculate
asymptotic error bounds and approximate computational scalings for the methods
presented. Implementing these methods, we perform the world's first geometry
optimization on an experimental quantum processor, estimating the equilibrium
bond length of the dihydrogen molecule to within 0.014 Angstrom of the full
configuration interaction value. Within the same experiment, we estimate the
polarizability of the H2 molecule, finding agreement at the equilibrium bond
length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added
example to appendice
Formation of molecular oxygen in ultracold O + OH reaction
We discuss the formation of molecular oxygen in ultracold collisions between
hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based
on hyperspherical coordinates is employed for the calculations. Elastic,
inelastic and reactive cross sections as well as the vibrational and rotational
populations of the product O2 molecules are reported. A J-shifting
approximation is used to compute the rate coefficients. At temperatures T = 10
- 100 mK for which the OH molecules have been cooled and trapped
experimentally, the elastic and reactive rate coefficients are of comparable
magnitude, while at colder temperatures, T < 1 mK, the formation of molecular
oxygen becomes the dominant pathway. The validity of a classical capture model
to describe cold collisions of OH and O is also discussed. While very good
agreement is found between classical and quantum results at T=0.3 K, at higher
temperatures, the quantum calculations predict a larger rate coefficient than
the classical model, in agreement with experimental data for the O + OH
reaction. The zero-temperature limiting value of the rate coefficient is
predicted to be about 6.10^{-12} cm^3 molecule^{-1} s^{-1}, a value comparable
to that of barrierless alkali-metal atom - dimer systems and about a factor of
five larger than that of the tunneling dominated F + H2 reaction.Comment: 9 pages, 8 figure
Holography and Variable Cosmological Constant
An effective local quantum field theory with UV and IR cutoffs correlated in
accordance with holographic entropy bounds is capable of rendering the
cosmological constant (CC) stable against quantum corrections. By setting an IR
cutoff to length scales relevant to cosmology, one easily obtains the currently
observed rho_Lambda ~ 10^{-47} GeV^4, thus alleviating the CC problem. It is
argued that scaling behavior of the CC in these scenarios implies an
interaction of the CC with matter sector or a time-dependent gravitational
constant, to accommodate the observational data.Comment: 7 pages, final version accepted by PR
Kinetics of Particles Adsorption Processes Driven by Diffusion
The kinetics of the deposition of colloidal particles onto a solid surface is
analytically studied. We take into account both the diffusion of particles from
the bulk as well as the geometrical aspects of the layer of adsorbed particles.
We derive the first kinetic equation for the coverage of the surface (a
generalized Langmuir equation) whose predictions are in agreement with recent
simulation results where diffusion of particles from the bulk is explicitly
considered.Comment: 4 page
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