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1.
S. Carlip 《General Relativity and Gravitation》2007,39(10):1519-1523
2.
M. Combescot O. Betbeder-Matibet 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):63-76
The purpose of this paper is to show how the diagrammatic expansion
in fermion exchanges of scalar products of N-composite-boson
(“coboson”) states can be obtained in a practical way. The hard
algebra on which this expansion is based, will be given in an independent publication.
Due to the composite nature of the particles, the scalar products
of N-coboson states do not reduce to a set of Kronecker symbols, as
for elementary bosons, but contain subtle exchange terms between two or
more cobosons. These terms originate from Pauli exclusion between the
fermionic components of the particles. While our many-body
theory for composite bosons leads to write these scalar products as
complicated sums of products of “Pauli scatterings” between
two cobosons, they in fact correspond to fermion exchanges
between any number P of quantum particles, with
2 ≤P≤N. These P-body exchanges are nicely represented by the
so-called “Shiva diagrams”, which are topologically different from
Feynman diagrams, due to the intrinsic many-body nature of the Pauli
exclusion from which they originate. These Shiva diagrams in fact
constitute the novel part of our composite-exciton many-body theory
which was up to now missing to get its full
diagrammatic representation. Using them, we can now “see” through
diagrams the physics of any quantity in which enters N interacting
excitons — or more generally N composite bosons —, with fermion
exchanges included in an
exact — and transparent — way. 相似文献
3.
In this continuation of an earlier paper we develop further the theme of quantum logical specification and derive from it
some apparently physically viable instantiations of potential quantum computing devices. Specifically, in the case of a one-parameter
set of terms (or labels)—read as instants of time—we find, emerging quite naturally from the algebraic setup, the paradigm
for a single qubit epitomized by the case of a two-state fermion interacting with an external single mode boson. This covers
the cases: cavity QED, trapped ions, and, when the qubits are multiplexed appropriately, NMR based systems. (This case degenerates
to one in which only bosons are relevant as in the case of pure bosonic harmonic oscillator models in the “dual rail” representation.
Such models fly in the face of the logic itself, thus clearly revealing even at this level their well-known shortcomings as
practical quantum computing devices. Here as elsewhere logical constraints apparently dominate physical ones.)
In a final section we indicate briefly how this process exactly generalizes, in the case of a manifold of terms more general
than the one-parameter case, to yield the notion of holonomic quantum computation.
In the course of this investigation we find an interpretation of path integrals as limits of sequences of logical CUTS, thus establishing a link—though still tenuous—between ensembles of acts of quantum computation and Lagrangians. 相似文献
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6.
U. Mohrhoff 《Foundations of Physics》2009,39(2):137-155
This paper offers a critique of the Bayesian interpretation of quantum mechanics with particular focus on a paper by Caves,
Fuchs, and Schack containing a critique of the “objective preparations view” or OPV. It also aims to carry the discussion
beyond the hardened positions of Bayesians and proponents of the OPV. Several claims made by Caves et al. are rebutted, including
the claim that different pure states may legitimately be assigned to the same system at the same time, and the claim that
the quantum nature of a preparation device cannot legitimately be ignored. Both Bayesians and proponents of the OPV regard
the time dependence of a quantum state as the continuous dependence on time of an evolving state of some kind. This leads
to a false dilemma: quantum states are either objective states of nature or subjective states of belief. In reality they are
neither. The present paper views the aforesaid dependence as a dependence on the time of the measurement to whose possible
outcomes the quantum state serves to assign probabilities. This makes it possible to recognize the full implications of the
only testable feature of the theory, viz., the probabilities it assigns to measurement outcomes. Most important among these
are the objective fuzziness of all relative positions and momenta and the consequent incomplete spatiotemporal differentiation
of the physical world. The latter makes it possible to draw a clear distinction between the macroscopic and the microscopic.
This in turn makes it possible to understand the special status of measurements in all standard formulations of the theory.
Whereas Bayesians have written contemptuously about the “folly” of conjoining “objective” to “probability,” there are various
reasons why quantum-mechanical probabilities can be considered objective, not least the fact that they are needed to quantify
an objective fuzziness. But this cannot be appreciated without giving thought to the makeup of the world, which Bayesians
refuse to do. Doing this on the basis of how quantum mechanics assigns probabilities, one finds that what constitutes the
macroworld is a single Ultimate Reality, about which we know nothing, except that it manifests the macroworld or manifests
itself as the macroworld. The so-called microworld is neither a world nor a part of any world but instead is instrumental
in the manifestation of the macroworld. Quantum mechanics affords us a glimpse “behind” the manifested world, at stages in
the process of manifestation, but it does not allow us to describe what lies “behind” the manifested world except in terms
of the finished product—the manifested world, for without the manifested world there is nothing in whose terms we could describe
its manifestation. 相似文献
7.
As quantum information science approaches the goal of constructing quantum computers, understanding loss of information through
decoherence becomes increasingly important. The information about a system that can be obtained from its environment can facilitate
quantum control and error correction. Moreover, observers gain most of their information indirectly, by monitoring (primarily
photon) environments of the “objects of interest.” Exactly how this information is inscribed in the environment is essential
for the emergence of “the classical” from the quantum substrate. In this paper, we examine how many-qubit (or many-spin) environments
can store information about a single system. The information lost to the environment can be stored redundantly, or it can
be encoded in entangled modes of the environment. We go on to show that randomly chosen states of the environment almost always
encode the information so that an observer must capture a majority of the environment to deduce the system’s state. Conversely,
in the states produced by a typical decoherence process, information about a particular observable of the system is stored
redundantly. This selective proliferation of “the fittest information” (known as Quantum Darwinism) plays a key role in choosing
the preferred, effectively classical observables of macroscopic systems. The developing appreciation that the environment
functions not just as a garbage dump, but as a communication channel, is extending our understanding of the environment’s
role in the quantum-classical transition beyond the traditional paradigm of decoherence. 相似文献
9.
To make sense of quantum field theory in an arbitrary (globally hyperbolic) curved spacetime, the theory must be formulated
in a local and covariant manner in terms of locally measurable field observables. Since a generic curved spacetime does not
possess symmetries or a unique notion of a vacuum state, the theory also must be formulated in a manner that does not require
symmetries or a preferred notion of a “vacuum state” and “particles”. We propose such a formulation of quantum field theory,
wherein the operator product expansion (OPE) of the quantum fields is elevated to a fundamental status, and the quantum field
theory is viewed as being defined by its OPE. Since the OPE coefficients may be better behaved than any quantities having
to do with states, we suggest that it may be possible to perturbatively construct the OPE coefficients—and, thus, the quantum
field theory. By contrast, ground/vacuum states—in spacetimes, such as Minkowski spacetime, where they may be defined—cannot
vary analytically with the parameters of the theory. We argue that this implies that composite fields may acquire nonvanishing
vacuum state expectation values due to nonperturbative effects. We speculate that this could account for the existence of
a nonvanishing vacuum expectation value of the stress-energy tensor of a quantum field occurring at a scale much smaller than
the natural scales of the theory.
Fourth Award in the 2008 Essay Competition of the Gravity Research Foundation. 相似文献
10.
M. Combescot O. Betbeder-Matibet F. Dubin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):181-189
We have recently constructed a many-body theory for composite excitons, in
which the possible carrier exchanges between N excitons can be treated
exactly through a set of dimensionless “Pauli scatterings” between two
excitons. Many-body effects with free excitons turn out to be rather
simple because these excitons are the exact one-pair
eigenstates of the semiconductor Hamiltonian, in the absence of localized
traps. They consequently form a complete orthogonal basis for one-pair
states. As essentially all quantum particles known as bosons are
composite bosons, it is highly desirable to
extend this free exciton many-body theory to other kinds of
“cobosons” — a contraction for composite bosons — the physically
relevant ones being possibly not the exact one-pair eigenstates of
the system Hamiltonian. The purpose of this paper is
to derive the “Pauli scatterings” and the “interaction scatterings” of
these cobosons in terms of their wave functions and the interactions
which exist between the fermions from which they are
constructed. It is also explained how to calculate many-body effects in
such a very general composite boson system. 相似文献
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Thomas Filk 《International Journal of Theoretical Physics》2006,45(6):1166-1180
The famous “spooky action at a distance” in the EPR-scenario is shown to be a local interaction, once entanglement is interpreted as a kind of “nearest neighbor” relation among quantum systems. Furthermore, the wave function itself is interpreted as encoding the “nearest neighbor” relations between a quantum system and spatial points. This interpretation becomes natural, if we view space and distance in terms of relations among spatial points. Therefore, “position” becomes a purely relational concept. This relational picture leads to a new perspective onto the quantum mechanical formalism, where many of the “weird” aspects, like the particle-wave duality, the non-locality of entanglement, or the “mystery” of the double-slit experiment, disappear. Furthermore, this picture circumvents the restrictions set by Bell’s inequalities, i.e., a possible (realistic) hidden variable theory based on these concepts can be local and at the same time reproduce the results of quantum mechanics.
PACS: 03.65.Ud, 04.60.Nc 相似文献
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Hans-Thomas Elze 《International Journal of Theoretical Physics》2007,46(8):2063-2081
We explore how energy-parity, a protective symmetry for the cosmological constant [Kaplan and Sundrum, 2005], arises naturally
in the classical phase space dynamics of matter.We derive and generalize the Liouville operator of electrodynamics, incorporating
a “varying alpha” and diffusion.In this model, a one-parameter deformation connects classical ensemble and quantum field theory.
PACS:03.65.Ta, 03.70+k, 05.20.-y 相似文献
15.
D. J. Miller 《Foundations of Physics Letters》2006,19(4):321-335
A qualification is suggested for the counterfactual reasoning involved in some aspects of time-symmetric quantum theory (which
involves ensembles selected by both the initial and final states). The qualification is that the counterfactual reasoning
should only apply to times when the quantum system has been subjected to physical interactions which place it in a “measurement-ready
condition” for the unperformed experiment on which the counterfactual reasoning is based. The defining characteristic of a
“measurement-ready condition” is that a quantum system could be found to have the counterfactually ascribed property without
direct physical interaction with the eigenstate corresponding to that property. 相似文献
16.
Fabio Gavarini 《Czechoslovak Journal of Physics》2001,51(12):1330-1335
The “quantum duality principle” states that a quantisation of a Lie bialgebra provides also a quantisation of the dual formal
Poisson group and, conversely, a quantisation of a formal Poisson group yields a quantisation of the dual Lie bialgebra as
well. We extend this to a much more general result: namely, for any principal ideal domainR and for each primepεR we establish an “inner” Galois’ correspondence on the categoryHA of torsionless Hopf algebras overR, using two functors (fromHA to itself) such that the image of the first and the second is the full subcategory of those Hopf algebras which are commutative
and cocommutative, modulop, respectively (i.e., they are“quantum function algebras” (=QFA) and“quantum universal enveloping algebras” (=QUEA), atp, respectively). In particular we provide a machine to get two quantum groups — a QFA and a QUEA — out of any Hopf algebraH over a fieldk: apply the functors tok[ν] ⊗k H forp=ν.
A relevant example occurring in quantum electro-dynamics is studied in some detail.
Presented at the 10th International Colloquium on Quantum Groups: “Quantum Groups and Integrable Systems”, Prague, 21–23 June
2001 相似文献
17.
The FRT quantum Euclidean spaces O
q
N
are formulated in terms of Cartesian generators. The quantum analogs of N-dimensional Cayley-Klein spaces are obtained by contractions and analytical continuations. Noncommutative constant-curvature
spaces are introduced as spheres in the quantum Cayley-Klein spaces. For N = 5 part of them is interpreted as the noncommutative analogs of (1+3) space-time models. As a result the quantum (anti)
de Sitter, Minkowski, Newton, Galilei kinematics with the fundamental length and the fundamental time are suggested.
Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005. 相似文献
18.
L. S. Schulman 《Foundations of Physics》1997,27(12):1623-1636
The quantum Zeno effect (QZE) is often associated with the ironic maxim, “a watched pot never boils”, although the notion
of “watching” suggests a continuous activity at odds with the usual (pulsed measurement) presentation of the QZE. We show
how continuous watching can provide the same halting of decay as the usual QZE, and, for incomplete hindrance, we provide
a precise connection between the interval between projections and the response time of the continuous observer. Thus, watching
closely, but not so closely as to halt the “boiling”, is equivalent to—gives the same degree of partial hindrance as—pulsed
measurements with a particular pulsing rate. Our demonstration is accomplished by treating the apparatus for the continuous
watching as a fully quantum object. This in turn allows us a second perspective on the QZE, in which it is the modified level
structure of the combined system/apparatus Hamiltonian that slows the decay. This and other considerations favor the characterization
“dominated time evolution” for the QZE. 相似文献
19.
Quantum theory has the property of “local tomography”: the state of any composite system can be reconstructed from the statistics
of measurements on the individual components. In this respect the holism of quantum theory is limited. We consider in this
paper a class of theories more holistic than quantum theory in that they are constrained only by “bilocal tomography”: the
state of any composite system is determined by the statistics of measurements on pairs of components. Under a few auxiliary assumptions, we derive certain general features of such theories. In particular, we
show how the number of state parameters can depend on the number of perfectly distinguishable states. We also show that real-vector-space
quantum theory, while not locally tomographic, is bilocally tomographic. 相似文献
20.
The Relational Blockworld (RBW) interpretation of non-relativistic quantum mechanics (NRQM) is introduced. Accordingly, the
spacetime of NRQM is a relational, non-separable blockworld whereby spatial distance is only defined between interacting trans-temporal
objects. RBW is shown to provide a novel statistical interpretation of the wavefunction that deflates the measurement problem,
as well as a geometric account of quantum entanglement and non-separability that satisfies locality per special relativity
and is free of interpretative mystery. We present RBW’s acausal and adynamical resolution of the so-called “quantum liar paradox,”
an experimental set-up alleged to be problematic for a spacetime conception of reality, and conclude by speculating on RBW’s
implications for quantum gravity. 相似文献