9,729 research outputs found
The Minimal Modal Interpretation of Quantum Theory
We introduce a realist, unextravagant interpretation of quantum theory that
builds on the existing physical structure of the theory and allows experiments
to have definite outcomes, but leaves the theory's basic dynamical content
essentially intact. Much as classical systems have specific states that evolve
along definite trajectories through configuration spaces, the traditional
formulation of quantum theory asserts that closed quantum systems have specific
states that evolve unitarily along definite trajectories through Hilbert
spaces, and our interpretation extends this intuitive picture of states and
Hilbert-space trajectories to the case of open quantum systems as well. We
provide independent justification for the partial-trace operation for density
matrices, reformulate wave-function collapse in terms of an underlying
interpolating dynamics, derive the Born rule from deeper principles, resolve
several open questions regarding ontological stability and dynamics, address a
number of familiar no-go theorems, and argue that our interpretation is
ultimately compatible with Lorentz invariance. Along the way, we also
investigate a number of unexplored features of quantum theory, including an
interesting geometrical structure---which we call subsystem space---that we
believe merits further study. We include an appendix that briefly reviews the
traditional Copenhagen interpretation and the measurement problem of quantum
theory, as well as the instrumentalist approach and a collection of
foundational theorems not otherwise discussed in the main text.Comment: 73 pages + references, 9 figures; cosmetic changes, added figure,
updated references, generalized conditional probabilities with attendant
changes to the sections on the EPR-Bohm thought experiment and Lorentz
invariance; for a concise summary, see the companion letter at
arXiv:1405.675
Creation of macroscopic superpositions of flow states with Bose-Einstein condensates
We present a straightforward scheme for creating macroscopic superpositions
of different superfluid flow states of Bose-Einstein condensates trapped in
optical lattices. This scheme has the great advantage that all the techniques
required are achievable with current experiments. Furthermore, the relative
difficulty of creating cats scales favorably with the size of the cat. This
means that this scheme may be well-suited to creating superpositions involving
large numbers of particles. Such states may have interesting technological
applications such as making quantum-limited measurements of angular momentum.Comment: 9 pages, 7 figure
Orbital eigenchannel analysis for ab-initio quantum transport calculations
We show how to extract the orbital contribution to the transport
eigenchannels from a first-principles quantum transport calculation in a
nanoscopic conductor. This is achieved by calculating and diagonalizing the
first-principles transmission matrix reduced to selected scattering
cross-sections. As an example, the orbital nature of the eigenchannels in the
case of Ni nanocontacts is explored, stressing the difficulties inherent to the
use of non-orthogonal basis sets and first-principles Hamiltonians.Comment: 5 pages, 5 figurs; replaced with final version, introduction revised;
to be published in PR
A mathematical model of tumor self-seeding reveals secondary metastatic deposits as drivers of primary tumor growth
Two models of circulating tumor cell (CTC) dynamics have been proposed to
explain the phenomenon of tumor 'self-seeding', whereby CTCs repopulate the
primary tumor and accelerate growth: Primary Seeding, where cells from a
primary tumor shed into the vasculature and return back to the primary
themselves; and Secondary Seeding, where cells from the primary first
metastasize in a secondary tissue and form microscopic secondary deposits,
which then shed cells into the vasculature returning to the primary. These two
models are difficult to distinguish experimentally, yet the differences between
them is of great importance to both our understanding of the metastatic process
and also for designing methods of intervention. Therefore we developed a
mathematical model to test the relative likelihood of these two phenomena in
the subset of tumours whose shed CTCs first encounter the lung capillary bed,
and show that Secondary Seeding is several orders of magnitude more likely than
Primary seeding. We suggest how this difference could affect tumour evolution,
progression and therapy, and propose several possible methods of experimental
validation.Comment: 20 pages, 4 figure
Pension funds. asset allocation and participant age: a test of the life-cycle model
This paper examines the impact of participants. age distribution on the asset allocation of Dutch pension funds, using a unique data set of pension fund investment plans for 2007. Theory predicts a negative effect of age on (strategic) equity exposures. We observe that pension funds do indeed take the average age of their participants into account. However, the average age of active participants has been incorporated much more strongly in investment behaviour than the average ages of retired or dormant participants. This suggests that both employers and employees, who dominate pension fund boards, tend to show more interest in active participants. A one-year higher average age in active participants leads to a significant and robust reduction in the strategic equity exposure by around 0.5 percentage point. Larger pension funds show a stronger age-equity exposure effect than smaller pension funds. This age-dependent asset allocation of pension funds aligns with the original life-cycle model by which young workers should invest more in equity than older workers because of their larger human capital. Other factors, viz. fund size, funding ratio, and average pension wealth of participants, influence equity exposure positively and significantly, in line with theory. Pension plan type and pension fund type have no significant impact.Pension funds, strategic equity allocation, lifecycle saving and investing
The Birth-Death-Mutation process: a new paradigm for fat tailed distributions
Fat tailed statistics and power-laws are ubiquitous in many complex systems.
Usually the appearance of of a few anomalously successful individuals
(bio-species, investors, websites) is interpreted as reflecting some inherent
"quality" (fitness, talent, giftedness) as in Darwin's theory of natural
selection. Here we adopt the opposite, "neutral", outlook, suggesting that the
main factor explaining success is merely luck. The statistics emerging from the
neutral birth-death-mutation (BDM) process is shown to fit marvelously many
empirical distributions. While previous neutral theories have focused on the
power-law tail, our theory economically and accurately explains the entire
distribution. We thus suggest the BDM distribution as a standard neutral model:
effects of fitness and selection are to be identified by substantial deviations
from it
Measurement and Quantum Dynamics in the Minimal Modal Interpretation of Quantum Theory
Any realist interpretation of quantum theory must grapple with the measurement problem and the status of state-vector collapse. In a no-collapse approach, measurement is typically modeled as a dynamical process involving decoherence. We describe how the minimal modal interpretation closes a gap in this dynamical description, leading to a complete and consistent resolution to the measurement problem and an effective form of state collapse. Our interpretation also provides insight into the indivisible nature of measurement—the fact that you can't stop a measurement part-way through and uncover the underlying 'ontic' dynamics of the system in question. Having discussed the hidden dynamics of a system's ontic state during measurement, we turn to more general forms of open-system dynamics and explore the extent to which the details of the underlying ontic behavior of a system can be described. We construct a space of ontic trajectories and describe obstructions to defining a probability measure on this space
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