507 research outputs found
Discording power of quantum evolutions
We introduce the discording power of a unitary transformation, which assesses
its capability to produce quantum discord, and analyze in detail the generation
of discord by relevant classes of two-qubit gates. Our measure is based on the
Cartan decomposition of two-qubit unitaries and on evaluating the maximum
discord achievable by a unitary upon acting on classical-classical states at
fixed purity. We found that there exist gates which are perfect discorders for
any value of purity, and that they belong to a class of operators that includes
the $\sqrt{{SWAP}}. Other gates, even those universal for quantum computation,
do not posses the same property: the CNOT, for example, is a perfect discorder
only for states with low or unit purity, but not for intermediate values. The
discording power of a two-qubit unitary also provides a generalization of the
corresponding measure defined for entanglement to any value of the purity.Comment: accepted for publication in Physical Review Letter
Maximally discordant mixed states of two qubits
We study the relative strength of classical and quantum correlations, as
measured by discord, for two-qubit states. Quantum correlations appear only in
the presence of classical correlations, while the reverse is not always true.
We identify the family of states that maximize the discord for a given value of
the classical correlations and show that the largest attainable discord for
mixed states is greater than for pure states. The difference between discord
and entanglement is emphasized by the remarkable fact that these states do not
maximize entanglement and are, in some cases, even separable. Finally, by
random generation of density matrices uniformly distributed over the whole
Hilbert space, we quantify the frequency of the appearance of quantum and
classical correlations for different ranks
Innovative Design and Evaluation of a Transmission Lifter
This study focuses on the design, fabrication, and evaluation of the Transmission Lifter, a specialized device tailored for the convenient, stable, and durable servicing of vehicle transmission assemblies. The research aims to address the prevalent challenges faced by automotive technicians and mechanics during transmission servicing, offering an innovative solution that meets the high-performance requirements of the automotive industry.The study meticulously follows industry standards and leverages expert feedback to ensure the Transmission Lifter's quality, performance, and safety. It goes through comprehensive testing, meticulous analysis, and critical evaluation to gauge the device's effectiveness. The results of the study lead to several key conclusions: The Transmission Lifter successfully meets industry standards and the expectations of automotive experts, ensuring that it aligns with the highest quality requirements. The device exhibits high performance efficiency as affirmed by expert evaluations, highlighting its superior capabilities. It boasts an impressive load capacity, accommodating medium to heavy-duty transmissions with ease. The device is adaptable to the diverse configurations of automobile transmissions. It maintains stability even during extended use and can handle a substantial load. The Transmission Lifter performs exceptionally well, earning an overall "Excellent" rating based on expert evaluations. This study's findings inform a set of valuable recommendations, including patent protection, material enhancements for portability, improved finishing and adherence to industry standards, instructional manuals for users, and a call for continued research in the field. The Transmission Lifter presents a significant advancement in the field of automotive technology, contributing to the safety, efficiency, and quality of transmission servicing. Its innovation serves as a testament to the commitment of the researcher and his desire to support fellow technicians and automotive enthusiasts. By addressing the critical needs of the automotive industry, the Transmission Lifter embodies innovation, safety, and a commitment to excellence, setting a benchmark for future developments in the field.As
Development of a data-driven model for spatial and temporal shallow landslide probability of occurrence at catchment scale
Open access funding provided by Universita degli Studi di Pavia within the CRUI-CARE Agreement. This work has been in the frame of the ANDROMEDA project, which has been supported by Fondazione Cariplo, grant no. 2017-0677.We thank the anonymous reviewers for their contributions in
improving the paper. We thank Beatrice Corradini for the help in
the collection of rainfall data and of shallow landslide events.A combined method was developed to forecast the spatial and the temporal probability of occurrence of rainfall-induced shallow landslides over large areas. The method also allowed to estimate the dynamic change of this probability during a rainfall event. The model, developed through a data-driven approach basing on Multivariate Adaptive Regression Splines technique, was based on a joint probability between the spatial probability of occurrence (susceptibility) and the temporal one. The former was estimated on the basis of geological, geomorphological, and hydrological predictors. The latter was assessed considering short-term cumulative rainfall, antecedent rainfall, soil hydrological conditions, expressed as soil saturation degree, and bedrock geology. The predictive capability of the methodology was tested for past triggering events of shallow landslides occurred in representative catchments of Oltrepò Pavese, in northern Italian Apennines. The method provided excellently to outstanding performance for both the really unstable hillslopes (area under ROC curve until 0.92, true positives until 98.8%, true negatives higher than 80%) and the identification of the triggering time (area under ROC curve of 0.98, true positives of 96.2%, true negatives of 94.6%). The developed methodology allowed us to obtain feasible results using satellite-based rainfall products and data acquired by field rain gauges. Advantages and weak points of the method, in comparison also with traditional approaches for the forecast of shallow landslides, were also provided.Universita degli Studi di Pavia within the CRUI-CARE AgreementFondazione Cariplo
2017-067
Orthogonal measurements are {\it almost} sufficient for quantum discord of two qubits
The common use in literature of orthogonal measurements in obtaining quantum
discord for two-qubit states is discussed and compared with more general
measurements. We prove the optimality of orthogonal measurements for rank 2
states. While for rank 3 and 4 mixed states they are not optimal, we present
strong numerical evidence showing that they give the correct quantum discord up
to minimal corrections. Based on the connection, through purification with an
ancilla, between discord and entanglement of formation (EoF), we give a tight
upper bound for the EoF of a mixed state of rank 2, given by an
optimal decomposition of 2 elements. We also provide an alternative way to
compute the quantum discord for two qubits based on the Bloch vectors of the
state.Comment: EPL 96, 40005 (2011
Robustness of different indicators of quantumness in the presence of dissipation
The dynamics of a pair of coupled harmonic oscillators in separate or common
thermal environments is studied, focusing on different indicators of
quantumness, such as entanglement, twin oscillators correlations and quantum
discord. We compare their decay under the effect of dissipation and show,
through a phase diagram, that entanglement is more likely to survive
asymptotically than twin oscillators correlations
Monogamy properties of quantum and classical correlations
In contrast with entanglement, as measured by concurrence, in general,
quantum discord does not possess the property of monogamy, that is, there is no
tradeoff between the quantum discord shared by a pair of subsystems and the
quantum discord that both of them can share with a third party. Here, we show
that, as far as monogamy is considered, quantum discord of pure states is
equivalent to the entanglement of formation. This result allows one to
analytically prove that none of the pure three-qubit states belonging to the
subclass of W states is monogamous. A suitable physical interpretation of the
meaning of the correlation information as a quantifier of monogamy for the
total information is also given. Finally, we prove that, for rank 2 two-qubit
states, discord and classical correlations are bounded from above by
single-qubit von Neumann entropies
Propagation properties and limitations on the attainable entanglement in a driven harmonic chain
The limitations on the production and profitability of entanglement in a
harmonic chain under strong driving are considered. We report on the limits of
attainable entanglement for a given set of squeezings of the eigenmodes,
showing that the higher the entanglement the more oscillatory and thus less
easy to profit from. We also comment on propagation properties of entanglement,
discussing the role of fast rotating terms and illustrating several issues with
the example of a sudden switch of the coupling.Comment: 9 pages, 5 figure
Entanglement dynamics in presence of diversity under decohering environments
We study the evolution of entanglement of a pair of coupled, non-resonant
harmonic oscillators in contact with an environment. For both the cases of a
common bath and of two separate baths for each of the oscillators, a full
master equation is provided without rotating wave approximation. This allows us
to characterize the entanglement dynamics as a function of the diversity
between the oscillators frequencies and their mutual coupling. Also the
correlation between the occupation numbers is considered to explore the degree
of quantumness of the system. The singular effect of the resonance condition
(identical oscillators) and its relationship with the possibility of preserving
asymptotic entanglement are discussed. The importance of the bath's memory
properties is investigated by comparing Markovian and non-Markovian evolutions
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