46,231 research outputs found
Attacking quantum key distribution with single-photon two-qubit quantum logic
The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual
attack on Bennett-Brassard 1984 quantum key distribution (BB84 QKD) by means of
a single controlled-NOT (CNOT) gate. This paper describes a complete physical
simulation of the FPB-probe attack on polarization-based BB84 QKD using a
deterministic CNOT constructed from single-photon two-qubit quantum logic.
Adding polarization-preserving quantum nondemolition measurements of photon
number to this configuration converts the physical simulation into a true
deterministic realization of the FPB attack.Comment: 8 pages, 9 figures; references added, 1 new figure, appendix
expanded; accepted for publication in Phys. Rev.
Spin-Seebeck effect in a strongly interacting Fermi gas
We study the spin-Seebeck effect in a strongly interacting, two-component
Fermi gas and propose an experiment to measure this effect by relatively
displacing spin up and spin down atomic clouds in a trap using spin-dependent
temperature gradients. We compute the spin-Seebeck coefficient and related
spin-heat transport coefficients as functions of temperature and interaction
strength. We find that when the inter-spin scattering length becomes larger
than the Fermi wavelength, the spin-Seebeck coefficient changes sign as a
function of temperature, and hence so does the direction of the
spin-separation. We compute this zero-crossing temperature as a function of
interaction strength and in particular in the unitary limit for the inter-spin
scattering
Linking Light Scalar Modes with A Small Positive Cosmological Constant in String Theory
Based on the studies in Type IIB string theory phenomenology, we conjecture
that a good fraction of the meta-stable de Sitter vacua in the cosmic stringy
landscape tend to have a very small cosmological constant when
compared to either the string scale or the Planck scale , i.e.,
. These low lying de Sitter vacua tend to be
accompanied by very light scalar bosons/axions. Here we illustrate this
phenomenon with the bosonic mass spectra in a set of Type IIB string theory
flux compactification models. We conjecture that small with light
bosons is generic among de Sitter solutions in string theory; that is, the
smallness of and the existence of very light bosons (may be even the
Higgs boson) are results of the statistical preference for such vacua in the
landscape. We also discuss a scalar field model to illustrate
how this statistical preference for a small remains when quantum loop
corrections are included, thus bypassing the radiative instability problem.Comment: 35 pages, 7 figures; added subsection: Finite Temperature and Phase
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