8,615 research outputs found
Quantum states representing perfectly secure bits are always distillable
It is proven that recently introduced states with perfectly secure bits of
cryptographic key (private states representing secure bit) [K. Horodecki et
al., Phys. Rev. Lett. 94, 160502 (2005)] as well as its multipartite and higher
dimension generalizations always represent distillable entanglement. The
corresponding lower bounds on distillable entanglement are provided. We also
present a simple alternative proof that for any bipartite quantum state
entanglement cost is an upper bound on distillable cryptographic key in
bipartite scenario.Comment: RevTeX, 5 pages, published versio
Entropy and Entanglement in Quantum Ground States
We consider the relationship between correlations and entanglement in gapped
quantum systems, with application to matrix product state representations. We
prove that there exist gapped one-dimensional local Hamiltonians such that the
entropy is exponentially large in the correlation length, and we present strong
evidence supporting a conjecture that there exist such systems with arbitrarily
large entropy. However, we then show that, under an assumption on the density
of states which is believed to be satisfied by many physical systems such as
the fractional quantum Hall effect, that an efficient matrix product state
representation of the ground state exists in any dimension. Finally, we comment
on the implications for numerical simulation.Comment: 7 pages, no figure
Quantum Phase Transitions in the Itinerant Ferromagnet ZrZn
We report a study of the ferromagnetism of ZrZn, the most promising
material to exhibit ferromagnetic quantum criticality, at low temperatures
as function of pressure . We find that the ordered ferromagnetic moment
disappears discontinuously at =16.5 kbar. Thus a tricritical point
separates a line of first order ferromagnetic transitions from second order
(continuous) transitions at higher temperature. We also identify two lines of
transitions of the magnetisation isotherms up to 12 T in the plane where
the derivative of the magnetization changes rapidly. These quantum phase
transitions (QPT) establish a high sensitivity to local minima in the free
energy in ZrZn, thus strongly suggesting that QPT in itinerant
ferromagnets are always first order
The Cult of Efficiency in Corporate Law
This paper challenges a fundamental assumption of corporate law scholarship. Corporate law is heavily influenced by economics, and by normative economics in particular. Economic efficiency, for example, is seen as the primary goal of good corporate governance. But this dependence on standard notions of economic efficiency is unfortunate, as those notions are highly problematic. In economic theory, efficiency is spelled out in terms of individual preference satisfaction, which is an inadequate foundation for any sort of normative analysis. We argue that on any account of the good, people will sometimes prefer things that aren’t good for them on that account. Giving people what they want, then, isn’t necessarily an accomplishment, and thus the normative assessment of economic outcomes is much more complicated than economists recognize. This fact is something that should be reflected in corporate law scholarship, and would greatly expand the range of possible considerations when restructuring corporate law
On black hole thermalization, D0 brane dynamics, and emergent spacetime
When matter falls past the horizon of a large black hole, the expectation
from string theory is that the configuration thermalizes and the information in
the probe is rather quickly scrambled away. The traditional view of a classical
unique spacetime near a black hole horizon conflicts with this picture. The
question then arises as to what spacetime does the probe actually see as it
crosses a horizon, and how does the background geometry imprint its signature
onto the thermal properties of the probe. In this work, we explore these
questions through an extensive series of numerical simulations of D0 branes. We
determine that the D0 branes quickly settle into an incompressible symmetric
state -- thermalized within a few oscillations through a process driven
entirely by internal non-linear dynamics. Surprisingly, thermal background
fluctuations play no role in this mechanism. Signatures of the background
fields in this thermal state arise either through fluxes, i.e. black hole hair;
or if the probe expands to the size of the horizon -- which we see evidence of.
We determine simple scaling relations for the D0 branes' equilibrium size, time
to thermalize, lifetime, and temperature in terms of their number, initial
energy, and the background fields. Our results are consistent with the
conjecture that black holes are the fastest scramblers as seen by Matrix
theory.Comment: 43 pages, 12 figures; v2: added analysis showing that results are
consistent with and confirm Susskind conjecture on black hole thermalization.
Added clarification about strong coupling regime. Citation adde
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