2,196 research outputs found
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
Quantum Cloning of Mixed States in Symmetric Subspace
Quantum cloning machine for arbitrary mixed states in symmetric subspace is
proposed. This quantum cloning machine can be used to copy part of the output
state of another quantum cloning machine and is useful in quantum computation
and quantum information. The shrinking factor of this quantum cloning achieves
the well-known upper bound. When the input is identical pure states, two
different fidelities of this cloning machine are optimal.Comment: Revtex, 4 page
Universal quantum Controlled-NOT gate
An investigation of an optimal universal unitary Controlled-NOT gate that
performs a specific operation on two unknown states of qubits taken from a
great circle of the Bloch sphere is presented. The deep analogy between the
optimal universal C-NOT gate and the `equatorial' quantum cloning machine (QCM)
is shown. In addition, possible applications of the universal C-NOT gate are
briefly discussed.Comment: 18 reference
Cloning a Qutrit
We investigate several classes of state-dependent quantum cloners for
three-level systems. These cloners optimally duplicate some of the four
maximally-conjugate bases with an equal fidelity, thereby extending the
phase-covariant qubit cloner to qutrits. Three distinct classes of qutrit
cloners can be distinguished, depending on two, three, or four
maximally-conjugate bases are cloned as well (the latter case simply
corresponds to the universal qutrit cloner). These results apply to symmetric
as well as asymmetric cloners, so that the balance between the fidelity of the
two clones can also be analyzed.Comment: 14 pages LaTex. To appear in the Journal of Modern Optics for the
special issue on "Quantum Information: Theory, Experiment and Perspectives".
Proceedings of the ESF Conference, Gdansk, July 10-18, 200
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