13,661 research outputs found
Spatial correlations in parametric down-conversion
The transverse spatial effects observed in photon pairs produced by
parametric down-conversion provide a robust and fertile testing ground for
studies of quantum mechanics, non-classical states of light, correlated imaging
and quantum information. Over the last 20 years there has been much progress in
this area, ranging from technical advances and applications such as quantum
imaging to investigations of fundamental aspects of quantum physics such as
complementarity relations, Bell's inequality violation and entanglement. The
field has grown immensely: a quick search shows that there are hundreds of
papers published in this field. The objective of this article is to review the
building blocks and major theoretical and experimental advances in the field,
along with some possible technical applications and connections to other
research areas.Comment: 116 pages, 35 figures. To appear in Physics Report
Experimental determination of multipartite entanglement with incomplete information
Multipartite entanglement is very poorly understood despite all the
theoretical and experimental advances of the last decades. Preparation,
manipulation and identification of this resource is crucial for both practical
and fundamental reasons. However, the difficulty in the practical manipulation
and the complexity of the data generated by measurements on these systems
increase rapidly with the number of parties. Therefore, we would like to
experimentally address the problem of how much information about multipartite
entanglement we can access with incomplete measurements. In particular, it was
shown that some types of pure multipartite entangled states can be witnessed
without measuring the correlations [M. Walter et al., Science 340, 1205 (2013)]
between parties, which is strongly demanding experimentally. We explore this
method using an optical setup that permits the preparation and the complete
tomographic reconstruction of many inequivalent classes of three- and
four-partite entangled states, and compare complete versus incomplete
information. We show that the method is useful in practice, even for non-pure
states or non ideal measurement conditions.Comment: 12 pages, 7 figures. Close to published versio
Image and Coherence Transfer in the Stimulated Down-conversion Process
The intensity transverse profile of the light produced in the process of
stimulated down-conversion is derived. A quantum-mechanical treatment is used.
We show that the angular spectrum of the pump laser can be transferred to the
stimulated down-converted beam, so that images can also be transferred from the
pump to the down-converted beam. We also show that the transfer can occur from
the stimulating beam to the down-converted one. Finally, we study the process
of diffraction through an arbitrarily shaped screen. For the special case of a
double-slit, the interference pattern is explicitly obtained. The visibility
for the spontaneous emitted light is in accordance with the van Cittert -
Zernike theorem for incoherent light, while the visibility for the stimulated
emitted light is unity. The overall visibility is in accordance with previous
experimental results
Quantum key distribution with higher-order alphabets using spatially-encoded qudits
We propose and demonstrate a quantum key distribution scheme in higher-order
-dimensional alphabets using spatial degrees of freedom of photons. Our
implementation allows for the transmission of 4.56 bits per sifted photon,
while providing improved security: an intercept-resend attack on all photons
would induce an error rate of 0.47. Using our system, it should be possible to
send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio
Experimental investigation of quantum key distribution with position and momentum of photon pairs
We investigate the utility of Einstein-Podolsky-Rosen correlations of the
position and momentum of photon pairs from parametric down-conversion in the
implementation of a secure quantum key distribution protocol. We show that
security is guaranteed by the entanglement between downconverted pairs, and can
be checked by either direct comparison of Alice and Bob's measurement results
or evaluation of an inequality of the sort proposed by Mancini et al. (Phys.
Rev. Lett. 88, 120401 (2002)).Comment: 6 pages, 6 figures, subimitted for publicatio
- …