1,822 research outputs found
Robust Multi-Partite Multi-Level Quantum Protocols
We present a tripartite three-level state that allows a secret sharing
protocol among the three parties, or a quantum key distribution protocol
between any two parties. The state used in this scheme contains entanglement
even after one system is traced out. We show how to utilize this residual
entanglement for quantum key distribution purposes, and propose a realization
of the scheme using entanglement of orbital angular momentum states of photons.Comment: 9 pages, 2 figure
Plasmon assisted transmission of high dimensional orbital angular momentum entangled state
We present an experimental evidence that high dimensional orbital angular
momentum entanglement of a pair of photons can be survived after a
photon-plasmon-photon conversion. The information of spatial modes can be
coherently transmitted by surface plasmons. This experiment primarily studies
the high dimensional entangled systems based on surface plasmon with
subwavelength structures. It maybe useful in the investigation of spatial mode
properties of surface plasmon assisted transmission through subwavelength hole
arrays.Comment: 7 pages,6 figure
Experimental Quantum Cryptography with Qutrits
We produce two identical keys using, for the first time, entangled trinary
quantum systems (qutrits) for quantum key distribution. The advantage of
qutrits over the normally used binary quantum systems is an increased coding
density and a higher security margin. The qutrits are encoded into the orbital
angular momentum of photons, namely Laguerre-Gaussian modes with azimuthal
index l +1, 0 and -1, respectively. The orbital angular momentum is controlled
with phase holograms. In an Ekert-type protocol the violation of a
three-dimensional Bell inequality verifies the security of the generated keys.
A key is obtained with a qutrit error rate of approximately 10 %.Comment: New version includes additional references and a few minor changes to
the manuscrip
Triggered qutrits for Quantum Communication protocols
A general protocol in Quantum Information and Communication relies in the
ability of producing, transmitting and reconstructing, in general, qunits. In
this letter we show for the first time the experimental implementation of these
three basic steps on a pure state in a three dimensional space, by means of the
orbital angular momentum of the photons. The reconstruction of the qutrit is
performed with tomographic techniques and a Maximum-Likelihood estimation
method. In this way we also demonstrate that we can perform any transformation
in the three dimensional space
A Graphene-based Hot Electron Transistor
We experimentally demonstrate DC functionality of graphene-based hot electron
transistors, which we call Graphene Base Transistors (GBT). The fabrication
scheme is potentially compatible with silicon technology and can be carried out
at the wafer scale with standard silicon technology. The state of the GBTs can
be switched by a potential applied to the transistor base, which is made of
graphene. Transfer characteristics of the GBTs show ON/OFF current ratios
exceeding 50.000.Comment: 18 pages, 6 figure
Electromechanical Piezoresistive Sensing in Suspended Graphene Membranes
Monolayer graphene exhibits exceptional electronic and mechanical properties,
making it a very promising material for nanoelectromechanical (NEMS) devices.
Here, we conclusively demonstrate the piezoresistive effect in graphene in a
nano-electromechanical membrane configuration that provides direct electrical
readout of pressure to strain transduction. This makes it highly relevant for
an important class of nano-electromechanical system (NEMS) transducers. This
demonstration is consistent with our simulations and previously reported gauge
factors and simulation values. The membrane in our experiment acts as a strain
gauge independent of crystallographic orientation and allows for aggressive
size scalability. When compared with conventional pressure sensors, the sensors
have orders of magnitude higher sensitivity per unit area.Comment: 20 pages, 3 figure
Experimental Quantum Coin Tossing
In this letter we present the first implementation of a quantum coin tossing
protocol. This protocol belongs to a class of ``two-party'' cryptographic
problems, where the communication partners distrust each other. As with a
number of such two-party protocols, the best implementation of the quantum coin
tossing requires qutrits. In this way, we have also performed the first
complete quantum communication protocol with qutrits. In our experiment the two
partners succeeded to remotely toss a row of coins using photons entangled in
the orbital angular momentum. We also show the experimental bounds of a
possible cheater and the ways of detecting him
Thermal Transport Across Graphene Step Junctions
Step junctions are often present in layered materials, i.e. where
single-layer regions meet multi-layer regions, yet their effect on thermal
transport is not understood to date. Here, we measure heat flow across graphene
junctions (GJs) from monolayer to bilayer graphene, as well as bilayer to
four-layer graphene for the first time, in both heat flow directions. The
thermal conductance of the monolayer-bilayer GJ device ranges from ~0.5 to
9.1x10^8 Wm-2K-1 between 50 K to 300 K. Atomistic simulations of such GJ device
reveal that graphene layers are relatively decoupled, and the low thermal
conductance of the device is determined by the resistance between the two
dis-tinct graphene layers. In these conditions the junction plays a negligible
effect. To prove that the decoupling between layers controls thermal transport
in the junction, the heat flow in both directions was measured, showing no
evidence of thermal asymmetry or rectification (within experimental error
bars). For large-area graphene applications, this signifies that small bilayer
(or multilayer) islands have little or no contribution to overall thermal
transport
A Simple Route towards High-Concentration Surfactant-Free Graphene Dispersions
A simple solvent exchange method is introduced to prepare high-concentration
and surfactant-free graphene liquid dispersion. Natural graphite flakes are
first exfoliated into graphene in dimethylformamide (DMF). DMF is then
exchanged by terpineol through distillation, relying on their large difference
in boiling points. Graphene can then be concentrated thanks to the volume
difference between DMF and terpineol. The concentrated graphene dispersions are
used to fabricate transparent conductive thin films, which possess comparable
properties to those prepared by more complex methods.Comment: 9 pages, 3 figure
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