641 research outputs found
Review of studies about quantum communication and foundations of quantum mechanics at IENGF
In this proceeding I review the main experimental results obtained at IENGF
(Turin, Italy) by using a source of entangled photons realised superposing, by
means of an optical condenser, type I PDC produced in two crystals. More in
details, after having described how this source is built, I will report on a
Bell inequalities test obtained with it. Then I describe a recent innovative
double slit experiment realised with a similar scheme. Finally, I hint about
future developments of this activity at IENGF and in particular about a quantum
cryptographic scheme in d=4.Comment: to appear as invited talk in: SPIE Proceedings on Quantum
Communications and Quantum Imaging (2003
Real applications of quantum imaging
In the last years the possibility of creating and manipulating quantum states
of light has paved the way to the development of new technologies exploiting
peculiar properties of quantum states, as quantum information, quantum
metrology & sensing, quantum imaging ...
In particular Quantum Imaging addresses the possibility of overcoming limits
of classical optics by using quantum resources as entanglement or
sub-poissonian statistics. Albeit quantum imaging is a more recent field than
other quantum technologies, e.g. quantum information, it is now substantially
mature for application. Several different protocols have been proposed, some of
them only theoretically, others with an experimental implementation and a few
of them pointing to a clear application. Here we present a few of the most
mature protocols ranging from ghost imaging to sub shot noise imaging and sub
Rayleigh imaging.Comment: REVIEW PAPE
Quantum Correlations and Quantum Non-Locality: A Review and a Few New Ideas
In this paper we make an extensive description of quantum non-locality, one
of the most intriguing and fascinating facets of quantum mechanics. After a
general presentation of several studies on this subject, we consider if quantum
non-locality, and the friction it carries with special relativity, can
eventually find a "solution" by considering higher dimensional spaces.Comment: 1
Bipartite entanglement of quantum states in a pair basis
The unambiguous detection and quantification of entanglement is a hot topic
of scientific research, though it is limited to low dimensions or specific
classes of states. Here we identify an additional class of quantum states, for
which bipartite entanglement measures can be efficiently computed, providing
new rigorous results. Such states are written in arbitrary
dimensions, where each basis state in the subsystem A is paired with only one
state in B. This new class, that we refer to as pair basis states, is
remarkably relevant in many physical situations, including quantum optics. We
find that negativity is a necessary and sufficient measure of entanglement for
mixtures of states written in the same pair basis. We also provide analytical
expressions for a tight lower-bound estimation of the entanglement of
formation, a central quantity in quantum information.Comment: 8 pages, 10 figure
Review on qudits production and their application to Quantum Communication and Studies on Local Realism
The codification in higher dimensional Hilbert Spaces (whose logical basis
states are dubbed qudits in analogy with bidimensional qubits) presents various
advantages both for Quantum Information applications and for studies on
Foundations of Quantum Mechanics.
Purpose of this review is to introduce qudits, to summarize their application
to Quantum Communication and researches on Local Realism and, finally, to
describe some recent experiment for realizing them.
A Little more in details: after a short introduction, we will consider the
advantages of testing local realism with qudits, discussing both the 3-4
dimensional case (both for maximally and non-maximally entanglement) and then
the extension to an arbitrary dimension. Afterwards, we will discuss the
theoretical results on using qudits for quantum communication, epitomizing the
outcomes on a larger security in Quantum Key Distribution protocols (again
considering separately qutrits, ququats and generalization to arbitrary
dimension). Finally, we will present the experiments performed up to now for
producing quantum optical qudits and their applications. In particular, we will
mention schemes based on interferometric set-ups, orbital angular momentum
entanglement and biphoton polarization. Finally, we will summarize what
hyperentanglement is and its applications
Experimental realization of a measurement conditional unitary operation at single photon level and application to detector characterization
Our last experimental results on the realization of a measurement-conditional
unitary operation at single photon level are presented. This gate operates by
rotating by the polarization of a photon produced by means of Type-II
Parametric Down Conversion conditional to a polarization measurement on the
correlated photon. We then propose a new scheme for measuring the quantum
efficiency of a single photon detection apparatus by using this set-up. We
present experimental results obtained with this scheme compared with {\it
traditional} biphoton calibration. Our results show the interesting
potentiality of the suggested scheme.Comment: to appear in Proc. of SPIE meeting, Denver august 200
Quantum Time: experimental multi-time correlations
In this paper we provide an experimental illustration of Page and Wootters'
quantum time mechanism that is able to describe two-time quantum correlation
functions. This allows us to test a Leggett-Garg inequality, showing a
violation from the "internal" observer point of view. The "external" observer
sees a time-independent global state. Indeed, the scheme is implemented using a
narrow-band single photon where the clock degree of freedom is encoded in the
photon's position. Hence, the internal observer that measures the position can
track the flow of time, while the external observer sees a delocalized photon
that has no time evolution in the experiment time-scale.Comment: 5 pages, 4 figure
Cosmology and entanglement
In this paper we present the problem of quantum to classical transition of
quantum fluctuations during inflation and in particular the question of
evolution of entanglement. After a general introduction, three specific very
recent works are discussed in some more detail drawing some conclusion about
the present status of these researches
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