21,248 research outputs found
Criterion on remote clocks synchronization within a Heisenberg scaling accuracy
We propose a quantum method to judge whether two spatially separated clocks
have been synchronized within a specific accuracy . If the measurement
result of the experiment is obviously a nonzero value, the time difference
between two clocks is smaller than ; otherwise the difference is beyond
. On sharing the 2-qubit bipartite maximally entangled state in this
scheme, the accuracy of judgement can be enhanced to
. This criterion is consistent with Heisenberg
scaling that can be considered as beating standard quantum limit, moreover, the
unbiased estimation condition is not necessary.Comment: 5 pages, 1 figur
Entanglement R\'enyi -entropy
We study the entanglement R\'{e}nyi -entropy (ERE) as the
measure of entanglement. Instead of a single quantity in standard entanglement
quantification for a quantum state by using the von Neumann entropy for the
well-accepted entanglement of formation (EoF), the ERE gives a
continuous spectrum parametrized by variable as the entanglement
measure, and it reduces to the standard EoF in the special case . The ERE provides more information in entanglement
quantification, and can be used such as in determining the convertibility of
entangled states by local operations and classical communication. A series of
new results are obtained: (i) we can show that ERE of two states,
which can be mixed or pure, may be incomparable, in contrast to the fact that
there always exists an order for EoF of two states; (ii) similar as the case of
EoF, we study in a fully analytical way the ERE for arbitrary
two-qubit states, the Werner states and isotropic states in general
d-dimension; (iii) we provide a proof of the previous conjecture for the
analytical functional form of EoF of isotropic states in arbitrary d-dimension.Comment: 11 pages, 4 figure
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