1,822 research outputs found
Research on the control strategy of Bus Voltage of DC-Micro-grids utilizing bidirectional AC/DC converters
AbstractDesign a small-family DC-Micro-grids system, analyzes its existence value and meaning. Regarding bus voltage of DC-Micro-grids, it has always been an important index of DC-Micro-grids, this paper puts forward a two-way AC/DC converter voltage current double closed loop control method. It is easier to control the voltage and current by using d-q shaft transformation decoupling. Build the system model with MATLAB/simulink software and simulate in the time domain cases in the Condition of Synchronization. The results prove that the method can very good control dc bus voltage stability, ensure system power safety
Minimal sets determining universal and phase-covariant quantum cloning
We study the minimal input sets which can determine completely the universal
and the phase-covariant quantum cloning machines. We find that the universal
quantum cloning machine, which can copy arbitrary input qubit equally well,
however can be determined completely by only four input states located at the
four vertices of a tetrahedron. The phase-covariant quantum cloning machine,
which can copy all qubits located on the equator of the Bloch sphere, can be
determined by three equatorial qubits with equal angular distance. These
results sharpen further the well-known results that BB84 states and six-states
used in quantum cryptography can determine completely the phase-covariant and
universal quantum cloning machines. This concludes the study of the power of
universal and phase-covariant quantum cloning, i.e., from minimal input sets
necessarily to full input sets by definition. This can simplify dramatically
the testing of whether the quantum clone machines are successful or not, we
only need to check that the minimal input sets can be cloned optimally.Comment: 7 pages, 4 figure
No-compressing of quantum phase information
We raise a general question of quantum information theory whether the quantum
phase information can be compressed and retrieved. A general qubit contains
both amplitude and phase information, while an equatorial qubit contains only a
phase information. We study whether it is possible to compress the phase
information of n equatorial qubits into m general qubits with m being less than
n, and still those information can be retrieved perfectly. We prove that this
process is not allowed by quantum mechanics.Comment: 4 pages, 1 figur
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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