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