5,233 research outputs found
Sensitivity optimization in quantum parameter estimation
We present a general framework for sensitivity optimization in quantum
parameter estimation schemes based on continuous (indirect) observation of a
dynamical system. As an illustrative example, we analyze the canonical scenario
of monitoring the position of a free mass or harmonic oscillator to detect weak
classical forces. We show that our framework allows the consideration of
sensitivity scheduling as well as estimation strategies for non-stationary
signals, leading us to propose corresponding generalizations of the Standard
Quantum Limit for force detection.Comment: 15 pages, RevTe
Circuit QED with a Nonlinear Resonator : ac-Stark Shift and Dephasing
We have performed spectroscopic measurements of a superconducting qubit
dispersively coupled to a nonlinear resonator driven by a pump microwave field.
Measurements of the qubit frequency shift provide a sensitive probe of the
intracavity field, yielding a precise characterization of the resonator
nonlinearity. The qubit linewidth has a complex dependence on the pump
frequency and amplitude, which is correlated with the gain of the nonlinear
resonator operated as a small-signal amplifier. The corresponding dephasing
rate is found to be close to the quantum limit in the low-gain limit of the
amplifier.Comment: Paper : 4 pages, 3 figures; Supplementary material : 1 page, 1 figur
Tasas de dispersión y supervivencia de adultos y juveniles del rabijunco colirrojo (Phaethon rubricauda) expuestas a contaminantes potenciales
Annual survival and dispersal rates of adult and juvenile red–tailed tropicbirds were examined in connection with exposure to heavy metals. From 1990–2000 the incineration of a U.S. stockpile of chemical weapons stored at Johnston Atoll exposed nesting tropicbirds to increased levels of human disturbance, smoke stack emissions and potential leaks. Using a multi–state mark–recapture modeling approach, birds nesting in this site (downwind of the plant) were compared to those nesting in a reference site (upwind of the plant) with less human disturbance, no exposure to smoke stack emissions or other potential incineration emissions. We did not find any difference in survival of adults or juveniles when comparing the two sites. Adult breeding dispersal rates did not differ between the sites but we did find differences in the age–specific natal dispersal rates. Birds fledged from downwind areas were less likely to return to their natal area to nest and more likely to immigrate to the upwind area than vice–versa. This asymmetry in emigration rates is believed to be due to differing vegetation densities and has implications for vegetation management in relation to tropicbird nest success and population size.Se examinaron las tasas de dispersión y de supervivencia anual de adultos y jóvenes de los rabijuncos colirrojos en relación a la exposición a metales pesados. Entre los años 1990 y 2000, la incineración de un arsenal de armas quÃmicas del ejército de Estados Unidos almacenadas en Johnston Atoll expuso a las aves del trópico que anidaban en la zona a niveles más elevados de perturbaciones antrópicas/contaminación humana, emisiones procedentes de chimeneas y fugas potenciales. Se comparó las aves nidificantes en este lugar (a favor del viento de la planta) mediante modelos de captura–recaptura de multiestados, con las que anidaban en un emplazamiento de referencia (en cuyo caso la planta quedaba situada en contra del viento), caracterizado por menos perturbaciones antrópicas y ninguna exposición a emisiones procedentes de chimeneas ni a ningún otro tipo de emisiones potenciales de incineración. Al comparar ambos emplazamientos, no se halló ninguna diferencia en cuanto a la supervivencia de las aves adultas o jóvenes. Las tasas de dispersión reproductiva de los adultos no difirieron entre los emplazamientos; en cambio, sà que se observaron diferencias en las tasas de dispersión natal por edades. Las aves jóvenes que abandonaron las áreas situadas a favor del viento era menos probable que regresaran a su área natal para anidar y más probable que inmigraran al área situada en contra del viento. Se considera que esta asimetrÃa en las tasas de emigración obedece a las diferentes densidades de vegetación, repercutiendo en la gestión de la vegetación con respecto al éxito de los nidos de las aves del trópico y el tamaño poblacional
Quantum control on entangled bipartite qubits
Ising interaction between qubits could produce distortion in entangled pairs
generated for engineering purposes (as in quantum computation) in presence of
parasite magnetic fields, destroying or altering the expected behavior of
process in which is projected to be used. Quantum control could be used to
correct that situation in several ways. Sometimes the user should be make some
measurement upon the system to decide which is the best control scheme; other
posibility is try to reconstruct the system using similar procedures without
perturbate it. In the complete pictures both schemes are present. We will work
first with pure systems studying advantages of different procedures. After, we
will extend these operations when time of distortion is uncertain, generating a
mixed state, which needs to be corrected by suposing the most probably time of
distortion.Comment: 10 pages, 5 figure
The negatively charged nitrogen-vacancy centre in diamond: the electronic solution
The negatively charged nitrogen-vacancy centre is a unique defect in diamond
that possesses properties highly suited to many applications, including quantum
information processing, quantum metrology, and biolabelling. Although the
unique properties of the centre have been extensively documented and utilised,
a detailed understanding of the physics of the centre has not yet been
achieved. Indeed there persists a number of points of contention regarding the
electronic structure of the centre, such as the ordering of the dark
intermediate singlet states. Without a sound model of the centre's electronic
structure, the understanding of the system's unique dynamical properties can
not effectively progress. In this work, the molecular model of the defect
centre is fully developed to provide a self consistent model of the complete
electronic structure of the centre. The application of the model to describe
the effects of electric, magnetic and strain interactions, as well as the
variation of the centre's fine structure with temperature, provides an
invaluable tool to those studying the centre and a means to design future
empirical and ab initio studies of this important defect.Comment: 24 pages, 6 figures, 10 table
Deception and self-awareness
This paper presents a study conducted for the Shades of Grey EPSRC research project (EP/H02302X/1), which aims to develop a suite of interventions for identifying terrorist activities. The study investigated the body movements demonstrated by participants while waiting to be interviewed, in one of two conditions: preparing to lie or preparing to tell the truth. The effect of self-awareness was also investigated, with half of the participants sitting in front of a full length mirror during the waiting period. The other half faced a blank wall. A significant interaction was found for the duration of hand/arm movements between the deception and self-awareness conditions (F=4.335, df=1;76, p<0.05). Without a mirror, participants expecting to lie spent less time moving their hands than those expecting to tell the truth; the opposite was seen in the presence of a mirror. This finding indicates a new research area worth further investigation
Measuring the defect structure orientation of a single NV- centre in diamond
The negatively charged nitrogen-vacancy (NV-) centre in diamond has many exciting applications in quantum nano-metrology, including magnetometry, electrometry, thermometry and piezometry. Indeed, it is possible for a single NV- centre to measure the complete three-dimensional vector of the local electric field or the position of a single fundamental charge in ambient conditions. However, in order to achieve such vector measurements, near complete knowledge of the orientation of the centres defect structure is required. Here, we demonstrate an optically detected magnetic resonance (ODMR) technique employing rotations of static electric and magnetic fields that precisely determines the orientation of the centres major and minor trigonal symmetry axes. Thus, our technique is an enabler of the centres existing vector sensing applications and also motivates new applications in multi-axis rotation sensing, NV growth characterization and diamond crystallography
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