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