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Scientific Report 2007-2009
Condensed matter physics and biophysics
C43. Optical technologies for quantum information processing
Quantum information (QI) is a new scientific field with
origins in the early 90s, introduced by the merging of
classical information and quantum physics. It is multidisciplinary
by nature, with scientists coming from diverse
areas in both theoretical and experimental physics
(atomic physics, quantum optics and laser physics, condensed
matter, etc.) and from other disciplines such as
computer science, mathematics, material science and engineering.
It has known a huge and rapid growing in the
last years, both on the theoretical and the experimental
side and has the potential to revolutionize many areas
of science and technology. The main goal is to understand
the quantum nature of information and to learn
how to formulate manipulate, and process it using physical
systems that operate on quantum mechanical principles,
more precisely on the control and manipulation of
individual quantum degrees of freedom. On this perspective
completely new schemes of information transfer and
processing, enabling new forms of communication and
enhancing the computational power, will be developed.
Within the framework of QI theory, quantum optics
represents an excellent experimental test bench for various
novel concepts introduced. Photons are the natural
candidate for QI transmission since they are practically
immune from decoherence and can be distributed over
long distances both in free-space and in low-loss optical
fibres. Photons are also important for future quantum
networks and are an obvious choice for optical sensing
and metrology and, finally, they are a promising candidate
for computing.
Figure 1: Schematic representation of the multiqubit source
based on multipath entanglement [2].
In the last few years, the Quantum Optics group of
Roma has contributed to develop different experimental
photonic platforms to carry out quantum information
processing based on different photon degrees of freedom
(DOFs).
In our laboratory, by starting from a hyperentangled
state, i.e. a two photon state built on two entangled
DOFs, such as the polarization and the linear k momentum,
we were able to generate four/six qubits cluster
states to realize some basic computation algorithms.
Cluster state are the fundamental resource for a new
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A ) B )
l
m = + 2 m = - 2
TqP
’
l’
R
L
l
q = 1
Figure 2: Schematic representation of the coupling between
polarization (spin) and orbital angular momentum (OAM).
model of Quantum Computation, the so called one-way
model. In this model the algorithms are simply realized
by a sequence of single qubit measurements and feedforward
operations. The aim of our research has been
to increase the dimensionality of the generated quantum
states by using more degrees of freedom of the photons
[1,2].
The standard encoding process of quantum information
adopting the methods of quantum optics is based
on the two-dimensional space of photon polarization
(“spin” angular momentum). Very recently the orbital
angular momentum (OAM) of light, associated to the
transverse amplitude profile, has been recognized as a
new promising resource, allowing the implementation
of a higher-dimensional quantum space, or a “qu-dit”,
encoded in a single photon. Our research topic is based
on the study of new optical devices able to couple the
orbital and spinorial components of the angular momentum
[3]. Such devices allow to manipulate efficiently
and deterministically the orbital angular momentum
degree of freedom, exploiting both the polarization and
the OAM advantages [4].
References
1. G. Vallone, et al., Phys. Rev. Lett. 100, 160502 (2008).
2. A. Rossi, et al., Phys. Rev. Lett. 102, 153902 (2009).
3. E. Nagali, et al., Phys. Rev. Lett. 103, 013601 (2009).
4. E. Nagali, et al., Nature Photonics 3, 720 (2009).
Authors
P. Mataloni, F. Sciarrino, F. De Martini, G. Vallone 4 , E.
Nagali, S. Giacomini, G. Milani
http://quantumoptics.phys.uniroma1.it/
Sapienza Università di Roma 96 Dipartimento di Fisica