926 research outputs found
Holographic Bound From Second Law of Thermodynamics
A necessary condition for the validity of the holographic principle is the
holographic bound: the entropy of a system is bounded from above by a quarter
of the area of a circumscribing surface measured in Planck areas. This bound
cannot be derived at present from consensus fundamental theory. We show with
suitable {\it gedanken} experiments that the holographic bound follows from the
generalized second law of thermodynamics for both generic weakly gravitating
isolated systems and for isolated, quiescent and nonrotating strongly
gravitating configurations well above Planck mass. These results justify
Susskind's early claim that the holographic bound can be gotten from the second
law.Comment: RevTeX, 8 pages, no figures, several typos correcte
On the capacities of bipartite Hamiltonians and unitary gates
We consider interactions as bidirectional channels. We investigate the
capacities for interaction Hamiltonians and nonlocal unitary gates to generate
entanglement and transmit classical information. We give analytic expressions
for the entanglement generating capacity and entanglement-assisted one-way
classical communication capacity of interactions, and show that these
quantities are additive, so that the asymptotic capacities equal the
corresponding 1-shot capacities. We give general bounds on other capacities,
discuss some examples, and conclude with some open questions.Comment: V3: extensively rewritten. V4: a mistaken reference to a conjecture
by Kraus and Cirac [quant-ph/0011050] removed and a mistake in the order of
authors in Ref. [53] correcte
Holographic Formulation of Quantum Supergravity
We show that supergravity with a cosmological constant can be
expressed as constrained topological field theory based on the supergroup
. The theory is then extended to include timelike boundaries with
finite spatial area. Consistent boundary conditions are found which induce a
boundary theory based on a supersymmetric Chern-Simons theory. The boundary
state space is constructed from states of the boundary supersymmetric
Chern-Simons theory on the punctured two sphere and naturally satisfies the
Bekenstein bound, where area is measured by the area operator of quantum
supergravity.Comment: 30 pages, no figur
Security Trade-offs in Ancilla-Free Quantum Bit Commitment in the Presence of Superselection Rules
Security trade-offs have been established for one-way bit commitment in
quant-ph/0106019. We study this trade-off in two superselection settings. We
show that for an `abelian' superselection rule (exemplified by particle
conservation) the standard trade-off between sealing and binding properties
still holds. For the non-abelian case (exemplified by angular momentum
conservation) the security trade-off can be more subtle, which we illustrate by
showing that if the bit-commitment is forced to be ancilla-free an
asymptotically secure quantum bit commitment is possible.Comment: 7 pages Latex; v2 has 8 pages and additional references and
clarifications, this paper is to appear in the New Journal of Physic
String-net condensation: A physical mechanism for topological phases
We show that quantum systems of extended objects naturally give rise to a
large class of exotic phases - namely topological phases. These phases occur
when the extended objects, called ``string-nets'', become highly fluctuating
and condense. We derive exactly soluble Hamiltonians for 2D local bosonic
models whose ground states are string-net condensed states. Those ground states
correspond to 2D parity invariant topological phases. These models reveal the
mathematical framework underlying topological phases: tensor category theory.
One of the Hamiltonians - a spin-1/2 system on the honeycomb lattice - is a
simple theoretical realization of a fault tolerant quantum computer. The higher
dimensional case also yields an interesting result: we find that 3D string-net
condensation naturally gives rise to both emergent gauge bosons and emergent
fermions. Thus, string-net condensation provides a mechanism for unifying gauge
bosons and fermions in 3 and higher dimensions.Comment: 21 pages, RevTeX4, 19 figures. Homepage http://dao.mit.edu/~we
Quantum symmetry, the cosmological constant and Planck scale phenomenology
We present a simple algebraic argument for the conclusion that the low energy
limit of a quantum theory of gravity must be a theory invariant, not under the
Poincare group, but under a deformation of it parameterized by a dimensional
parameter proportional to the Planck mass. Such deformations, called
kappa-Poincare algebras, imply modified energy-momentum relations of a type
that may be observable in near future experiments. Our argument applies in both
2+1 and 3+1 dimensions and assumes only 1) that the low energy limit of a
quantum theory of gravity must involve also a limit in which the cosmological
constant is taken very small with respect to the Planck scale and 2) that in
3+1 dimensions the physical energy and momenta of physical elementary particles
is related to symmetries of the full quantum gravity theory by appropriate
renormalization depending on Lambda l^2_{Planck}. The argument makes use of the
fact that the cosmological constant results in the symmetry algebra of quantum
gravity being quantum deformed, as a consequence when the limit \Lambda
l^2_{Planck} -> 0 is taken one finds a deformed Poincare invariance. We are
also able to isolate what information must be provided by the quantum theory in
order to determine which presentation of the kappa-Poincare algebra is relevant
for the physical symmetry generators and, hence, the exact form of the modified
energy-momentum relations. These arguments imply that Lorentz invariance is
modified as in proposals for doubly special relativity, rather than broken, in
theories of quantum gravity, so long as those theories behave smoothly in the
limit the cosmological constant is taken to be small.Comment: LaTex, 19 page
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