2,822 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
Fitting magnetic field gradient with Heisenberg-scaling accuracy
We propose a quantum fitting scheme to estimate the magnetic field gradient
with -atom spins preparing in W state, which attains the Heisenberg-scaling
accuracy. Our scheme combines the quantum multi-parameter estimation and the
least square linear fitting method to achieve the quantum Cram\'{e}r-Rao bound
(QCRB). We show that the estimated quantity achieves the Heisenberg-scaling
accuracy. In single parameter estimation with assumption that the magnetic
field is strictly linear, two optimal measurements can achieve the identical
Heisenberg-scaling accuracy. Proper interpretation of the
super-Heisenberg-scaling accuracy is presented. The scheme of quantum metrology
combined with data fitting provides a new method in fast high precision
measurements.Comment: 7 pages, 2 figure
Effect of resultant velocity of sandy water on interactive erosion and cavitation wears
Based on the computational fluid dynamics (CFD) method, this paper simulated the working conditions of hydraulic turbine under various sandy water resultant velocities. The vapor, liquid and solid phase flow fields and their characteristics on the turntable surface are numerically analyzed. The results show that the interactive wear regions mainly appeared on the regions with higher volume fractions of vapor phase and higher pressure gradients. When the resultant velocity increased, the interactive wears were heavier since the interactive wear regions increased along the edge of the hole in the tangential direction. The relationship curve between time and interactive wear weight loss was obtained in the test of four different resultant velocities. The results proved the theoretical analysis was reasonable. The overlay area of total pressure contours and vapor phase volume fraction contours were in good correlation with the shape of interactive wear surface in the test specimens
Quantum Cloning Machines and the Applications
No-cloning theorem is fundamental for quantum mechanics and for quantum
information science that states an unknown quantum state cannot be cloned
perfectly. However, we can try to clone a quantum state approximately with the
optimal fidelity, or instead, we can try to clone it perfectly with the largest
probability. Thus various quantum cloning machines have been designed for
different quantum information protocols. Specifically, quantum cloning machines
can be designed to analyze the security of quantum key distribution protocols
such as BB84 protocol, six-state protocol, B92 protocol and their
generalizations. Some well-known quantum cloning machines include universal
quantum cloning machine, phase-covariant cloning machine, the asymmetric
quantum cloning machine and the probabilistic quantum cloning machine etc. In
the past years, much progress has been made in studying quantum cloning
machines and their applications and implementations, both theoretically and
experimentally. In this review, we will give a complete description of those
important developments about quantum cloning and some related topics. On the
other hand, this review is self-consistent, and in particular, we try to
present some detailed formulations so that further study can be taken based on
those results.Comment: 98 pages, 12 figures, 400+ references. Physics Reports (published
online
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