1,180 research outputs found
Quantum Key Distribution Using Quantum Faraday Rotators
We propose a new quantum key distribution (QKD) protocol based on the fully
quantum mechanical states of the Faraday rotators. The protocol is
unconditionally secure against collective attacks for multi-photon source up to
two photons on a noisy environment. It is also robust against impersonation
attacks. The protocol may be implemented experimentally with the current
spintronics technology on semiconductors.Comment: 7 pages, 7 EPS figure
Nonequilibrium plasmons and transport properties of a double--junction quantum wire
We study theoretically the current-voltage characteristics, shot noise, and
full counting statistics of a quantum wire double barrier structure. We model
each wire segment by a spinless Luttinger liquid. Within the sequential
tunneling approach, we describe the system's dynamics using a master equation.
We show that at finite bias the non-equilibrium distribution of plasmons in the
central wire segment leads to increased average current, enhanced shot noise,
and full counting statistics corresponding to a super-Poissonian process. These
effects are particularly pronounced in the strong interaction regime, while in
the non-interacting case we recover results obtained earlier using detailed
balance arguments.Comment: 22 pages, RevTex 2-column, 11 figure
Probing spin and orbital Kondo effects with a mesoscopic interferometer
We investigate theoretically the transport properties of a closed
Aharonov-Bohm interferometer containing two quantum dots in the strong coupling
regime. We find two distinct physical scenarios depending on the strength of
the interdot Coulomb interaction. When the interdot Coulomb interaction is
negligible only spin fluctuations are important and each dot develops a Kondo
resonance at the Fermi level independently of the applied magnetic flux. The
transport is characterized by the interference of these two independent Kondo
resonances. On the contrary, for large interdot interaction, only one electron
can be accommodated onto the double dot system. In this situation, not only the
spin can fluctuate but also the orbital degree of freedom (the pseudo-spin). As
a result, we find different ground states depending on the value of the applied
flux. When (mod ) (, where is
applied flux, and the flux quantum) the electronic transport can
take place via simultaneous correlations in the spin and pseudo-spin sectors,
leading to the highly symmetric SU(4) Kondo state. Nevertheless, we find
situations with (mod ) where the pseudo-spin quantum number is
not conserved during tunneling events, giving rise to the common SU(2) Kondo
state with an enhanced Kondo temperature. We investigate the crossover between
both ground states and discuss possible experimental signatures of this physics
as a function of the applied magnetic flux.Comment: 12 pages, 3 figures; extended discussions, improved presentatio
Ultrafast element-resolved magneto-optics using a fiber-laser-driven extreme ultraviolet light source
We present a novel setup to measure the transverse magneto-optical Kerr
effect in the extreme ultraviolet spectral range at exceptionally high
repetition rates based on a fiber laser amplifier system. This affords a very
high and stable flux of extreme ultraviolet light, which we use to measure
element-resolved demagnetization dynamics with unprecedented depth of
information. Furthermore, the setup is equipped with a strong electromagnet and
a cryostat, allowing measurements between 10 and 420 K using magnetic fields up
to 0.86 T. The performance of our setup is demonstrated by a set of
temperature- and time-dependent magnetization measurements showing distinct
element-dependent behavior
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