1,015 research outputs found
Information locking in black holes
The black hole information loss paradox has plagued physicists since
Hawking's discovery that black holes evaporate thermally in contradiction to
the unitarity expected by quantum mechanics. Here we show that one of the
central presumptions of the debate is incorrect. Ensuring that information not
escape during the semi-classical evaporation process does not require that all
the information remain in the black hole until the final stages of evaporation.
Using recent results in quantum information theory, we find that the amount of
information that must remain in the black hole until the final stages of
evaporation can be very small, even though the amount already radiated away is
negligible. Quantum effects mean that information need not be additive: a small
number of quanta can lock a large amount of information, making it
inaccessible. When this small number of locking quanta are finally emitted, the
full information (and unitarity) is restored. Only if the number of initial
states is restricted will the locking mechanism leak out information early.Comment: 5 pages, to appear in PRL. Presented at the Newton Institute's
workshop on Quantum gravity and quantum information, Dec. 17th, 200
Mixmaster quantum cosmology in terms of physical dynamics
An approach to quantum cosmology, relying on strengths of both canonical and path integral formalisms, is applied to the cosmological model, Bianchi type IX. Physical quantum states are constructed on the maximal slice of the cosmological history. A path integral is derived which evolves observables off the maximal slice. This result is compared a path integral propagator derived earlier with conventional Faddeev-Poppov gauge fixing
Can closed timelike curves or nonlinear quantum mechanics improve quantum state discrimination or help solve hard problems?
We study the power of closed timelike curves (CTCs) and other nonlinear
extensions of quantum mechanics for distinguishing nonorthogonal states and
speeding up hard computations. If a CTC-assisted computer is presented with a
labeled mixture of states to be distinguished--the most natural formulation--we
show that the CTC is of no use. The apparent contradiction with recent claims
that CTC-assisted computers can perfectly distinguish nonorthogonal states is
resolved by noting that CTC-assisted evolution is nonlinear, so the output of
such a computer on a mixture of inputs is not a convex combination of its
output on the mixture's pure components. Similarly, it is not clear that CTC
assistance or nonlinear evolution help solve hard problems if computation is
defined as we recommend, as correctly evaluating a function on a labeled
mixture of orthogonal inputs.Comment: 4 pages, 3 figures. Final version. Added several references, updated
discussion and introduction. Figure 1(b) very much enhance
Can non-private channels transmit quantum information?
We study the power of quantum channels with little or no capacity for private
communication. Because privacy is a necessary condition for quantum
communication, one might expect that such channels would be of little use for
transmitting quantum states. Nevertheless, we find strong evidence that there
are pairs of such channels that, when used together, can transmit far more
quantum information than the sum of their individual private capacities.
Because quantum transmissions are necessarily private, this would imply a large
violation of additivity for the private capacity. Specifically, we present
channels which display either (1) A large joint quantum capacity but very small
individual private capacities or (2) a severe violation of additivity for the
Holevo information.Comment: We both think so. 4 pages and 3 figures explain wh
Relative Locality in -Poincar\'e
We show that the -Poincar\'e Hopf algebra can be interpreted in the
framework of curved momentum space leading to the relativity of locality
\cite{AFKS}. We study the geometric properties of the momentum space described
by -Poincar\'e, and derive the consequences for particles propagation
and energy-momentum conservation laws in interaction vertices, obtaining for
the first time a coherent and fully workable model of the deformed relativistic
kinematics implied by -Poincar\'e. We describe the action of boost
transformations on multi-particles systems, showing that in order to keep
covariant the composed momenta it is necessary to introduce a dependence of the
rapidity parameter on the particles momenta themselves. Finally, we show that
this particular form of the boost transformations keeps the validity of the
relativity principle, demonstrating the invariance of the equations of motion
under boost transformations.Comment: 24 pages, 4 figures, 1 table. v2 matches accepted CQG versio
The linearization of the Kodama state
We study the question of whether the linearization of the Kodama state around
classical deSitter spacetime is normalizable in the inner product of the theory
of linearized gravitons on deSitter spacetime. We find the answer is no in the
Lorentzian theory. However, in the Euclidean theory the corresponding
linearized Kodama state is delta-functional normalizable. We discuss whether
this result invalidates the conjecture that the full Kodama state is a good
physical state for quantum gravity with positive cosmological constant.Comment: 14 pages, statement on the corresponding Yang-Mills case correcte
Constraints on the quantum gravity scale from kappa - Minkowski spacetime
We compare two versions of deformed dispersion relations (energy vs momenta
and momenta vs energy) and the corresponding time delay up to the second order
accuracy in the quantum gravity scale (deformation parameter). A general
framework describing modified dispersion relations and time delay with respect
to different noncommutative kappa -Minkowski spacetime realizations is firstly
proposed here and it covers all the cases introduced in the literature. It is
shown that some of the realizations provide certain bounds on quadratic
corrections, i.e. on quantum gravity scale, but it is not excluded in our
framework that quantum gravity scale is the Planck scale. We also show how the
coefficients in the dispersion relations can be obtained through a
multiparameter fit of the gamma ray burst (GRB) data.Comment: 9 pages, final published version, revised abstract, introduction and
conclusion, to make it clear to general reade
Unification of gravity, gauge fields, and Higgs bosons
We consider a diffeomorphism invariant theory of a gauge field valued in a
Lie algebra that breaks spontaneously to the direct sum of the spacetime
Lorentz algebra, a Yang-Mills algebra, and their complement. Beginning with a
fully gauge invariant action -- an extension of the Plebanski action for
general relativity -- we recover the action for gravity, Yang-Mills, and Higgs
fields. The low-energy coupling constants, obtained after symmetry breaking,
are all functions of the single parameter present in the initial action and the
vacuum expectation value of the Higgs.Comment: 12 pages, no figures. v2 minor correction
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