974 research outputs found
Pulsed energy-time entangled twin-photon source for quantum communication
A pulsed source of energy-time entangled photon pairs pumped by a standard
laser diode is proposed and demonstrated. The basic states can be distinguished
by their time of arrival. This greatly simplifies the realization of 2-photon
quantum cryptography, Bell state analyzers, quantum teleportation, dense
coding, entanglement swapping, GHZ-states sources, etc. Moreover the
entanglement is well protected during photon propagation in telecom optical
fibers, opening the door to few-photon applications of quantum communication
over long distances.Comment: 8 pages, 4 figure
Unjamming due to local perturbations in granular packings with and without gravity
We investigate the unjamming response of disordered packings of frictional
hard disks with the help of computer simulations. First, we generate jammed
configurations of the disks and then force them to move again by local
perturbations. We study the spatial distribution of the stress and displacement
response and find long range effects of the perturbation in both cases. We
record the penetration depth of the displacements and the critical force that
is needed to make the system yield. These quantities are tested in two types of
systems: in ideal homogeneous packings in zero gravity and in packings settled
under gravity. The penetration depth and the critical force are sensitive to
the interparticle friction coefficient. Qualitatively, the same nonmonotonic
friction dependence is found both with and without gravity, however the
location of the extrema are at different friction values. We discuss the role
of the connectivity of the contact network and of the pressure gradient in the
unjamming response.Comment: 12 pages, 13 figure
A Cryptographic Analysis of the WireGuard Protocol
WireGuard (Donenfeld, NDSS 2017) is a recently proposed secure network tunnel operating at layer 3. WireGuard aims to replace existing tunnelling solutions like IPsec and OpenVPN, while requiring less code, being more secure, more performant, and easier to use. The cryptographic design of WireGuard is based on the Noise framework. It makes use of a key exchange component which combines long-term and ephemeral Diffie-Hellman values (along with optional preshared keys). This is followed by the use of the established keys in an AEAD construction to encapsulate IP packets in UDP. To date, WireGuard has received no rigorous security analysis. In this paper, we, rectify this. We first observe that, in order to prevent Key Compromise Impersonation (KCI) attacks, any analysis of WireGuard\u27s key exchange component must take into account the first AEAD ciphertext from initiator to responder. This message effectively acts as a key confirmation and makes the key exchange component of WireGuard a 1.5 RTT protocol. However, the fact that this ciphertext is computed using the established session key rules out a proof of session key indistinguishability for WireGuard\u27s key exchange component, limiting the degree of modularity that is achievable when analysing the protocol\u27s security. To overcome this proof barrier, and as an alternative to performing a monolithic analysis of the entire WireGuard protocol, we add an extra message to the protocol. This is done in a minimally invasive way that does not increase the number of round trips needed by the overall WireGuard protocol. This change enables us to prove strong authentication and key indistinguishability properties for the key exchange component of WireGuard under standard cryptographic assumptions
Practical Quantum Bit Commitment Protocol
A quantum protocol for bit commitment the security of which is based on
technological limitations on nondemolition measurements and long-term quantum
memory is presented.Comment: Quantum Inf. Process. (2011
Violation of Bell inequalities by photons more than 10 km apart
A Franson-type test of Bell inequalities by photons 10.9 km apart is
presented. Energy-time entangled photon-pairs are measured using two-channel
analyzers, leading to a violation of the inequalities by 16 standard deviations
without subtracting accidental coincidences. Subtracting them, a 2-photon
interference visibility of 95.5% is observed, demonstrating that distances up
to 10 km have no significant effect on entanglement. This sets quantum
cryptography with photon pairs as a practical competitor to the schemes based
on weak pulses.Comment: 4 pages, REVTeX, 2 postscript figures include
Quantum Cryptography using entangled photons in energy-time Bell states
We present a setup for quantum cryptography based on photon pairs in
energy-time Bell states and show its feasability in a laboratory experiment.
Our scheme combines the advantages of using photon pairs instead of faint laser
pulses and the possibility to preserve energy-time entanglement over long
distances. Moreover, using 4-dimensional energy-time states, no fast random
change of bases is required in our setup : Nature itself decides whether to
measure in the energy or in the time base.Comment: 4 pages including 2 figure
Linear Optical CNOT Gate in the Coincidence Basis
We describe the operation and tolerances of a non-deterministic, coincidence
basis, quantum CNOT gate for photonic qubits. It is constructed solely from
linear optical elements and requires only a two-photon source for its
demonstration.Comment: Submitted to Physical Review
Long-distance Bell-type tests using energy-time entangled photons
Long-distance Bell-type experiments are presented. The different experimental
challenges and their solutions in order to maintain the strong quantum
correlations between energy-time entangled photons over more than 10 km are
reported and the results analyzed from the point of view of tests of
fundamental physics as well as from the more applied side of quantum
communication, specially quantum key distribution. Tests using more than one
analyzer on each side are also presented.Comment: 22 pages including 7 figures and 5 table
Experimental Test of Relativistic Quantum State Collapse with Moving Reference Frames
An experimental test of relativistic wave-packet collapse is presented. The
tested model assumes that the collapse takes place in the reference frame
determined by the massive measuring detectors. Entangled photons are measured
at 10 km distance within a time interval of less than 5 ps. The two apparatuses
are in relative motion so that both detectors, each in its own inertial
reference frame, are first to perform the measurement. The data always
reproduces the quantum correlations and thus rule out a class of collapse
models. The results also set a lower bound on the "speed of quantum
information" to 0.66 x 10^7 and 1.5 x 10^4 times the speed of light in the
Geneva and the background radiation reference frames, respectively. The very
difficult and deep question of where the collapse takes place - if it takes
place at all - is considered in a concrete experimental context.Comment: 4 pages + 2 ps figure
Elastic behavior in Contact Dynamics of rigid particles
The systematic errors due to the practical implementation of the Contact
Dynamics method for simulation of dense granular media are examined. It is
shown that, using the usual iterative solver to simulate a chain of rigid
particles, effective elasticity and sound propagation with a finite velocity
occur. The characteristics of these phenomena are investigated analytically and
numerically in order to assess the limits of applicability of this simulation
method and to compare it with soft particle molecular dynamics.Comment: submitted to PRE, 7 pages, 6 figure
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