5,126 research outputs found
Security of Continuous-variable quantum cryptography using coherent states: Decline of postselection advantage
We investigate the security of continuous-variable (CV) quantum key
distribution (QKD) using coherent states in the presence of quadrature excess
noise. We consider an eavesdropping attack which uses a linear amplifier and
beam splitter. This attack makes a link between beam-splitting attack and
intercept-resend attack (classical teleportation attack). We also show how
postselection loses its efficiency in a realistic channel.Comment: Revtex4, 4 pages, 2 figure
A practical limitation for continuous-variable quantum cryptography using coherent states
In this letter, first, we investigate the security of a continuous-variable
quantum cryptographic scheme with a postselection process against individual
beam splitting attack. It is shown that the scheme can be secure in the
presence of the transmission loss owing to the postselection. Second, we
provide a loss limit for continuous-variable quantum cryptography using
coherent states taking into account excess Gaussian noise on quadrature
distribution. Since the excess noise is reduced by the loss mechanism, a
realistic intercept-resend attack which makes a Gaussian mixture of coherent
states gives a loss limit in the presence of any excess Gaussian noise.Comment: RevTeX4, 4 pages, 5 figure
Emergence of a Wiener process as a result of the quantum mechanical interaction with a macroscopic medium
We analyze a modified version of the Coleman-Hepp model, that is able to take
into account energy-exchange processes between the incoming particle and the
linear array made up of spin-1/2 systems. We bring to light the presence of
a Wiener dissipative process in the weak-coupling, macroscopic () limit. In such a limit and in a restricted portion of the total
Hilbert space, the particle undergoes a sort of Brownian motion, while the free
Hamiltonian of the spin array serves as a Wiener process. No assumptions are
made on the spectrum of the Hamiltonian of the spin system, and no partial
trace is computed over its states. The mechanism of appearance of the
stochastic process is discussed and contrasted to other noteworthy examples in
the literature. The links with van Hove's `` limits are
emphasized.Comment: 20 pages, LaTeX, no figure
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