3,201 research outputs found
Spin correlations and consequences of quantum-mechanical coherence
The difference in the properties of the spin correlation tensor for
factorizable and nonfactorizable two-particle states is analyzed. The
inequalities for linear combinations of the components of this tensor are
obtained for the case of incoherent mixtures of factorizable two-particle spin
states. They include the well known Bell inequalities and can be violated for
coherent superpositions of two-particle spin states. The possibility to verify
the consequences of the quantum-mechanical coherence is discussed using the
angular correlations in the asymmetric (parity violating) decays of the pairs
of spin-1/2 particles (muons, top-quarks or lambda-hyperons), the coherence
arising either from the production dynamics or due to the effect of quantum
statistics.Comment: 11 pages, LaTe
Modal and Polarization Qubits in Ti:LiNbO Photonic Circuits for a Universal Quantum Logic Gate
Lithium niobate photonic circuits have the salutary property of permitting
the generation, transmission, and processing of photons to be accommodated on a
single chip. Compact photonic circuits such as these, with multiple components
integrated on a single chip, are crucial for efficiently implementing quantum
information processing schemes. We present a set of basic transformations that
are useful for manipulating modal qubits in Ti:LiNbO photonic quantum
circuits. These include the mode analyzer, a device that separates the even and
odd components of a state into two separate spatial paths; the mode rotator,
which rotates the state by an angle in mode space; and modal Pauli spin
operators that effect related operations. We also describe the design of a
deterministic, two-qubit, single-photon, CNOT gate, a key element in certain
sets of universal quantum logic gates. It is implemented as a Ti:LiNbO
photonic quantum circuit in which the polarization and mode number of a single
photon serve as the control and target qubits, respectively. It is shown that
the effects of dispersion in the CNOT circuit can be mitigated by augmenting it
with an additional path. The performance of all of these components are
confirmed by numerical simulations. The implementation of these transformations
relies on selective and controllable power coupling among single- and two-mode
waveguides, as well as the polarization sensitivity of the Pockels coefficients
in LiNbO
Interference contrast in multi-source few photon optics
Many recent experiments employ several parametric down conversion (PDC)
sources to get multiphoton interference. Such interference has applications in
quantum information. We study here how effects due to photon statistics,
misalignment, and partial distinguishability of the PDC pairs originating from
different sources may lower the interference contrast in the multiphoton
experiments.Comment: 23 pages, 9 figures, journal versio
Low-Energy Nondipole Effects in Molecular Nitrogen Valence-Shell Photoionization
Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3sigmag, 1piu, and 2sigmau shells of N2 exhibit spectral variations with incident photon energies from thresholds to ~200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)[direct-product](M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule
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