20,641 research outputs found
Arbitrary phase rotation of the marked state can not be used for Grover's quantum search algorithm
A misunderstanding that an arbitrary phase rotation of the marked state
together with the inversion about average operation in Grover's search
algorithm can be used to construct a (less efficient) quantum search algorithm
is cleared. The rotation of the phase of the marked state is not only the
choice for efficiency, but also vital in Grover's quantum search algorithm. The
results also show that Grover's quantum search algorithm is robust.Comment: 5 pages, 5 figure
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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