5,311 research outputs found
The Fidelity of Measurement-Based Quantum Computation under a Boson Environment
We investigate the fidelity of the measurement-based quantum computation
(MBQC) when it is coupled with boson environment, by measuring cluster state
fidelity and gate fidelity. Two different schemes of cluster state preparation
are studied. In the Controlled-Z (CZ) creation scheme, cluster states are
prepared by entangling all qubits in state with CZ gates on all
neighboring sites. The fidelity shows an oscillation pattern over time
evolution. The influence of environment temperature is evaluated, and
suggestions are given to enhance the performance of MBQC realized in this way.
In the Hamiltonian creation scheme, cluster states are made by cooling a system
with cluster Hamiltonians, of which ground states are cluster states. The
fidelity sudden drop phenomenon is discovered. When the coupling is below a
threshold, MBQC systems are highly robust against the noise. Our main
environment model is the one with a single collective bosonic mode.Comment: 13 pages, 16 figure
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
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
- …