9,723 research outputs found
Two-step orthogonal-state-based protocol of quantum secure direct communication with the help of order-rearrangement technique
The Goldenberg-Vaidman (GV) protocol for quantum key distribution (QKD) uses
orthogonal encoding states of a particle. Its security arises because
operations accessible to Eve are insufficient to distinguish the two states
encoding the secret bit. We propose a two-particle cryptographic protocol for
quantum secure direct communication, wherein orthogonal states encode the
secret, and security arises from restricting Eve from accessing any
two-particle operations. However, there is a non-trivial difference between the
two cases. While the encoding states are perfectly indistinguishable in GV,
they are partially distinguishable in the bi-partite case, leading to a
qualitatively different kind of information-vs-disturbance trade-off and also
options for Eve in the two cases.Comment: 9 pages, 4 figures, LaTex, Accepted for publication in Quantum
Information Processing (2014
Beyond the Goldenberg-Vaidman protocol: Secure and efficient quantum communication using arbitrary, orthogonal, multi-particle quantum states
It is shown that maximally efficient protocols for secure direct quantum
communications can be constructed using any arbitrary orthogonal basis. This
establishes that no set of quantum states (e.g. GHZ states, W states, Brown
states or Cluster states) has an advantage over the others, barring the
relative difficulty in physical implementation. The work provides a wide choice
of states for experimental realization of direct secure quantum communication
protocols. We have also shown that this protocol can be generalized to a
completely orthogonal state based protocol of Goldenberg-Vaidman (GV) type. The
security of these protocols essentially arises from duality and monogamy of
entanglement. This stands in contrast to protocols that employ non-orthogonal
states, like Bennett-Brassard 1984 (BB84), where the security essentially comes
from non-commutativity in the observable algebra.Comment: 7 pages, no figur
On the origin of nonclassicality in single systems
In the framework of certain general probability theories of single systems,
we identify various nonclassical features such as incompatibility, multiple
pure-state decomposability, measurement disturbance, no-cloning and the
impossibility of certain universal operations, with the non-simpliciality of
the state space. This is shown to naturally suggest an underlying simplex as an
ontological model. Contextuality turns out to be an independent nonclassical
feature, arising from the intransitivity of compatibility.Comment: Close to the published versio
Inhomogeneous Cooling of the Rough Granular Gas in Two Dimensions
We study the inhomogeneous clustered regime of a freely cooling granular gas
of rough particles in two dimensions using large-scale event driven simulations
and scaling arguments. During collisions, rough particles dissipate energy in
both the normal and tangential directions of collision. In the inhomogeneous
regime, translational kinetic energy and the rotational energy decay with time
as power-laws and . We numerically determine
and , independent of the
coefficients of restitution. The inhomogeneous regime of the granular gas has
been argued to be describable by the ballistic aggregation problem, where
particles coalesce on contact. Using scaling arguments, we predict
and for ballistic aggregation, being different from
that obtained for the rough granular gas. Simulations of ballistic aggregation
with rotational degrees of freedom are consistent with these exponents.Comment: 6 pages, 5 figure
Quantum cryptography: key distribution and beyond
Uniquely among the sciences, quantum cryptography has driven both
foundational research as well as practical real-life applications. We review
the progress of quantum cryptography in the last decade, covering quantum key
distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK
The dyadic diffraction coefficient for a curved edge
A compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edge formed by perfectly conducting curved or plane surfaces is obtained. This diffraction coefficent remains valid in the transition regions adjacent to shadow and reflection boundaries, where the diffraction coefficients of Keller's original theory fail. The method is on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by plane, cylindrical, conical, and spherical waves. When the proper ray fixed coordinate system is introduced, the dyadic diffraction coefficient for the wedge is found to be the sum of only two dyads, and it is shown that this is also true for the dyadic diffraction coefficients of higher order edges. One dyad contains the acoustic soft diffraction coefficient; the other dyad contains the acoustic hard diffraction coefficient. The expressions for the acoustic wedge diffraction coefficients contain Fresnel integrals, which ensure that the total field is continuous at shadow and reflection boundaries. The diffraction coefficients have the same form for the different types of edge illumination; only the arguments of the Fresnel integrals are different. Since diffraction is a local phenomenon, and locally the curved edge structure is wedge shaped, this result is readily extended to the curved edge
Analysis of the EM scattering from arbitrary open-ended waveguide cavities using axial Gaussian Beam tracking
The electromagnetic (EM) scattering from a planar termination located inside relatively arbitrarily shaped open-ended waveguide cavities with smoothly curved interior walls is analyzed using a Gaussian Beam (GB) expansion of the incident plane wave fields in the open end. The cavities under consideration may contain perfectly-conducting interior walls with or without a thin layer of material coating, or the walls may be characterized by an impedance boundary condition. In the present approach, the GB's are tracked only to the termination of the waveguide cavity via beam reflections from interior waveguide cavity walls. The Gaussian beams are tracked approximately only along their beam axes; this approximation which remains valid for relatively well focussed beams assumes that an incident GB gives rise to a reflected GB with parameters related to the incident beam and the radius of curvature of the wall. It is found that this approximation breaks down for GB's which come close to grazing a convex surface and when the width of the incident beam is comparable to the radius of curvature of the surface. The expansion of the fields at the open end depend on the incidence angle only through the expansion coefficients, so the GB's need to be tracked through the waveguide cavity only once for a wide range of incidence angles. At the termination, the sum of all the GB's are integrated using a result developed from a generalized reciprocity principle, to give the fields scattered from the interior of the cavity. The rim edge at the open end of the cavity is assumed to be sharp and the external scattering from the rim is added separately using Geometrical Theory of Diffraction. The results based on the present approach are compared with solutions based on the hybrid asymptotic modal method. The agreement is found to be very good for cavities made up of planar surfaces, and also for cavities with curved surfaces which are not too long with respect to their width
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