9 research outputs found
Preparation of entangled states of two photons in several spatial modes
We describe a protocol capable of preparing an arbitrary state of two photons
in several spatial modes using pairs of photons generated by spontaneous
parametric down-conversion, linear optical elements and single-photon detectors
or post-selection. The protocol involves unitary and non-unitary
transformations realizable by beam splitters and phase shifters. Non-unitary
transformations are implemented by attenuation filters. The protocol contains
several optimization capabilities with the goal of improving overall
probability of its success. We also show how entangled two-photon states
required for quantum computing with linear optics can be prepared using a very
simple and feasible scheme.Comment: 9 pages, 9 figures, REVTeX
Classical Teleportation of a Quantum Bit
Classical teleportation is defined as a scenario where the sender is given
the classical description of an arbitrary quantum state while the receiver
simulates any measurement on it. This scenario is shown to be achievable by
transmitting only a few classical bits if the sender and receiver initially
share local hidden variables. Specifically, a communication of 2.19 bits is
sufficient on average for the classical teleportation of a qubit, when
restricted to von Neumann measurements. The generalization to
positive-operator-valued measurements is also discussed.Comment: 4 pages, RevTe
Preparation of Knill-Laflamme-Milburn states using tunable controlled phase gate
A specific class of partially entangled states known as
Knill-Laflamme-Milburn states (or KLM states) has been proved to be useful in
relation to quantum information processing [Knill et al., Nature 409, 46
(2001)]. Although the usage of such states is widely investigated, considerably
less effort has been invested into experimentally accessible preparation
schemes. This paper discusses the possibility to employ a tunable controlled
phase gate to generate an arbitrary Knill-Laflamme-Milburn state. In the first
part, the idea of using the controlled phase gate is explained on the case of
two-qubit KLM states. Optimization of the proposed scheme is then discussed for
the framework of linear optics. Subsequent generalization of the scheme to
arbitrary n-qubit KLM state is derived in the second part of this paper.Comment: 5 pages, 4 figures, accepted in Journal of Physics
Entanglement, local measurements, and symmetry
A definition of entanglement in terms of local measurements is discussed.
Viz, the maximum entanglement corresponds to the states that cause the highest
level of quantum fluctuations in all local measurements determined by the
dynamic symmetry group of the system. A number of examples illustrating this
definition is considered.Comment: 10 pages. to be published in Journal of Optics
Tunneling Violates Special Relativity
Experiments with evanescent modes and tunneling particles have shown that i)
their signal velocity may be faster than light, ii) they are described by
virtual particles, iii) they are nonlocal and act at a distance, iv)
experimental tunneling data of phonons, photons, and electrons display a
universal scattering time at the tunneling barrier front, and v) the properties
of evanescent, i.e. tunneling modes is not compatible with the special theory
of relativity