7,862 research outputs found
Observation of Fast Evolution in Parity-Time-Symmetric System
To find and realize the optimal evolution between two states is significant
both in theory and application. In quantum mechanics, the minimal evolution is
bounded by the gap between the largest and smallest eigenvalue of the
Hamiltonian. In the parity-time-symmetric(PT-symmetric) Hamiltonian theory, it
was predicted that the optimized evolution time can be reduced drastically
comparing to the bound in the Hermitian case, and can become even zero. In this
Letter, we report the experimental observation of the fast evolution of a
PT-symmetric Hamiltonian in an nuclear magnetic resonance (NMR) quantum system.
The experimental results demonstrate that the PT-symmetric Hamiltonian can
indeed evolve much faster than that in a quantum system, and time it takes can
be arbitrary close to zero.Comment: 13 pages, 5 figure
On the Mutual Information in Conformal Field Theory
In this work, we study the universal behaviors in the mutual information of
two disjoint spheres in a conformal field theory(CFT). By using the operator
product expansion of the spherical twist operator in terms of the conformal
family, we show that the large distance expansion of the mutual information can
be cast in terms of the conformal blocks. We develop the prescription to
compute the coefficients before the conformal blocks. For a single conformal
family, the leading nonvanishing contribution to the mutual information comes
from the bilinear operators. We show that the coefficients of these operators
take universal forms and such universal behavior persists in the bilinear
operators with derivatives as well. Consequently the first few leading order
contributions to the mutual information in CFT take universal forms. To
illustrate our framework, we discuss the free scalars and free fermions in
various dimensions. For the free scalars, we compute the mutual information to
the next-to-leading order and find good agreement with the improved numerical
lattice result. For the free fermion, we compute the leading order result,
which is of universal form, and find the good match with the numerical study.
Our formalism could be applied to any CFT potentially.Comment: 27+14 pages, 8 figures; References adde
Godel Universe from String Theory
G\"odel universe is a direct product of a line and a three-dimensional
spacetime we call G. In this paper, we show that the G\"odel metrics
can arise as exact solutions in Einstein-Maxwell-Axion, Einstein-Proca-Axion,
or Freedman-Schwarz gauged supergravity theories. The last allows us to embed
G\"odel universe in string theory. The ten-dimensional spacetime is a direct
product of a line and the nine-dimensional one of an bundle
over G, and it can be interpreted as some decoupling limit of the
rotating D1/D5/D5 intersection. For some appropriate parameter choice, the
nine-dimensional metric becomes an AdS bundle over squashed
3-sphere. We also study the properties of the G\"odel black holes that are
constructed from the double Wick rotations of the G\"odel metrics.Comment: latex, 20 pages, discussion on null-energy condition included, typos
corrected and references adde
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