1,205 research outputs found
Femtosecond Time-Bin Entangled Qubits for Quantum Communication
We create pairs of non-degenerate time-bin entangled photons at telecom
wavelengths with ultra-short pump pulses. Entanglement is shown by performing
Bell kind tests of the Franson type with visibilities of up to 91%. As
time-bin entanglement can easily be protected from decoherence as encountered
in optical fibers, this experiment opens the road for complex quantum
communication protocols over long distances. We also investigate the creation
of more than one photon pair in a laser pulse and present a simple tool to
quantify the probability of such events to happen.Comment: 6 pages, 7 figure
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
Two independent photon pairs versus four-photon entangled states in parametric down conversion
We study the physics of four-photon states generated in spontaneous
parametric down-conversion with a pulsed pump field. In the limit where the
coherence time of the photons t_c is much shorter than the duration of the pump
pulse Delta t, the four photons can be described as two independent pairs. In
the opposite limit, the four photons are in a four-particle entangled state.
Any intermediate case can be characterized by a single parameter chi, which is
a function of t_c/Delta t. We present a direct measurement of chi through a
simple experimental setup. The full theoretical analysis is also provided.Comment: 10 pages, 3 figures, submitte
Long distance quantum teleportation in a quantum relay configuration
A long distance quantum teleportation experiment with a fiber-delayed Bell
State Measurement (BSM) is reported. The source creating the qubits to be
teleported and the source creating the necessary entangled state are connected
to the beam splitter realizing the BSM by two 2 km long optical fibers. In
addition, the teleported qubits are analyzed after 2,2 km of optical fiber, in
another lab separated by 55 m. Time bin qubits carried by photons at 1310 nm
are teleported onto photons at 1550 nm. The fidelity is of 77%, above the
maximal value obtainable without entanglement. This is the first realization of
an elementary quantum relay over significant distances, which will allow an
increase in the range of quantum communication and quantum key distribution.Comment: 4 pages, submitte
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
An arbitrated quantum signature scheme
The general principle for a quantum signature scheme is proposed and
investigated based on ideas from classical signature schemes and quantum
cryptography. The suggested algorithm is implemented by a symmetrical quantum
key cryptosystem and Greenberger-Horne-Zeilinger (GHZ) triplet states and
relies on the availability of an arbitrator. We can guarantee the unconditional
security of the algorithm, mostly due to the correlation of the GHZ triplet
states and the use of quantum one-time pads.Comment: 10 pages, no figures. Phys. Rev. A 65, (In press
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