4,739 research outputs found
Geometric phases for mixed states in interferometry
We provide a physical prescription based on interferometry for introducing
the total phase of a mixed state undergoing unitary evolution, which has been
an elusive concept in the past. We define the parallel transport condition that
provides a connection-form for obtaining the geometric phase for mixed states.
The expression for the geometric phase for mixed state reduces to well known
formulas in the pure state case when a system undergoes noncyclic and unitary
quantum evolution.Comment: Two column, 4 pages, Latex file, No figures, Few change
Reply to `Singularities of the mixed state phase'
The only difference between Bhandari's viewpoint [quant-ph/0108058] and ours
[Phys. Rev. Lett. 85, 2845 (2000)] is that our phase is defined modulo ,
whereas Bhandari argues that two phases that differ by , integer,
may be distinguished experimentally in a history-dependent manner.Comment: 2 page
Geometric local invariants and pure three-qubit states
We explore a geometric approach to generating local SU(2) and
invariants for a collection of qubits inspired by lattice
gauge theory. Each local invariant or 'gauge' invariant is associated to a
distinct closed path (or plaquette) joining some or all of the qubits. In
lattice gauge theory, the lattice points are the discrete space-time points,
the transformations between the points of the lattice are defined by parallel
transporters and the gauge invariant observable associated to a particular
closed path is given by the Wilson loop. In our approach the points of the
lattice are qubits, the link-transformations between the qubits are defined by
the correlations between them and the gauge invariant observable, the local
invariants associated to a particular closed path are also given by a Wilson
loop-like construction. The link transformations share many of the properties
of parallel transporters although they are not undone when one retraces one's
steps through the lattice. This feature is used to generate many of the
invariants. We consider a pure three qubit state as a test case and find we can
generate a complete set of algebraically independent local invariants in this
way, however the framework given here is applicable to mixed states composed of
any number of level quantum systems. We give an operational interpretation
of these invariants in terms of observables.Comment: 9 pages, 3 figure
Towards a Theory of Software Development Expertise
Software development includes diverse tasks such as implementing new
features, analyzing requirements, and fixing bugs. Being an expert in those
tasks requires a certain set of skills, knowledge, and experience. Several
studies investigated individual aspects of software development expertise, but
what is missing is a comprehensive theory. We present a first conceptual theory
of software development expertise that is grounded in data from a mixed-methods
survey with 335 software developers and in literature on expertise and expert
performance. Our theory currently focuses on programming, but already provides
valuable insights for researchers, developers, and employers. The theory
describes important properties of software development expertise and which
factors foster or hinder its formation, including how developers' performance
may decline over time. Moreover, our quantitative results show that developers'
expertise self-assessments are context-dependent and that experience is not
necessarily related to expertise.Comment: 14 pages, 5 figures, 26th ACM Joint European Software Engineering
Conference and Symposium on the Foundations of Software Engineering (ESEC/FSE
2018), ACM, 201
Multi-Layer Cyber-Physical Security and Resilience for Smart Grid
The smart grid is a large-scale complex system that integrates communication
technologies with the physical layer operation of the energy systems. Security
and resilience mechanisms by design are important to provide guarantee
operations for the system. This chapter provides a layered perspective of the
smart grid security and discusses game and decision theory as a tool to model
the interactions among system components and the interaction between attackers
and the system. We discuss game-theoretic applications and challenges in the
design of cross-layer robust and resilient controller, secure network routing
protocol at the data communication and networking layers, and the challenges of
the information security at the management layer of the grid. The chapter will
discuss the future directions of using game-theoretic tools in addressing
multi-layer security issues in the smart grid.Comment: 16 page
Instructional Design for Advanced Learners: Establishing Connections between the Theoretical Frameworks of Cognitive Load and Deliberate Practice
Cognitive load theory (CLT) has been successful in identifying instructional formats that are more effective and efficient than conventional problem solving in the initial, novice phase of skill acquisition. However, recent findings regarding the “expertise reversal effect” have begun to stimulate cognitive load theorists to broaden their horizon to the question of how instructional design should be altered as a learner's knowledge increases. To answer this question, it is important to understand how expertise is acquired and what fosters its development. Expert performance research, and, in particular, the theoretical framework of deliberate practice have given us a better understanding of the principles and activities that are essential in order to excel in a domain. This article explores how these activities and principles can be used to design instructional formats based on CLT for higher levels of skills mastery. The value of these formats for e-learning environments in which learning tasks can be adaptively selected on the basis of online assessments of the learner's level of expertise is discussed
Geometric Quantum Computation
We describe in detail a general strategy for implementing a conditional
geometric phase between two spins. Combined with single-spin operations, this
simple operation is a universal gate for quantum computation, in that any
unitary transformation can be implemented with arbitrary precision using only
single-spin operations and conditional phase shifts. Thus quantum geometrical
phases can form the basis of any quantum computation. Moreover, as the induced
conditional phase depends only on the geometry of the paths executed by the
spins it is resilient to certain types of errors and offers the potential of a
naturally fault-tolerant way of performing quantum computation.Comment: 15 pages, LaTeX, uses cite, eepic, epsfig, graphicx and amsfonts.
Accepted by J. Mod. Op
Mixed state geometric phases, entangled systems, and local unitary transformations
The geometric phase for a pure quantal state undergoing an arbitrary
evolution is a ``memory'' of the geometry of the path in the projective Hilbert
space of the system. We find that Uhlmann's geometric phase for a mixed quantal
state undergoing unitary evolution not only depends on the geometry of the path
of the system alone but also on a constrained bi-local unitary evolution of the
purified entangled state. We analyze this in general, illustrate it for the
qubit case, and propose an experiment to test this effect. We also show that
the mixed state geometric phase proposed recently in the context of
interferometry requires uni-local transformations and is therefore essentially
a property of the system alone.Comment: minor changes, journal reference adde
Geometric Phases for Mixed States during Cyclic Evolutions
The geometric phases of cyclic evolutions for mixed states are discussed in
the framework of unitary evolution. A canonical one-form is defined whose line
integral gives the geometric phase which is gauge invariant. It reduces to the
Aharonov and Anandan phase in the pure state case. Our definition is consistent
with the phase shift in the proposed experiment [Phys. Rev. Lett. \textbf{85},
2845 (2000)] for a cyclic evolution if the unitary transformation satisfies the
parallel transport condition. A comprehensive geometric interpretation is also
given. It shows that the geometric phases for mixed states share the same
geometric sense with the pure states.Comment: 9 pages, 1 figur
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