In the optical sensing context one of the main challenge is to design and implement novel techniques of sensing optimized
to work in a lossy scenario, in which effects of environmental disturbances can destroy the benefits deriving from the
adoption of quantum resources. Here we describe the experimental implementation of a protocol based on the process
of optical parametric amplification to boost interferometry sensitivity in the presence of losses in a minimally invasive
scenario. By performing the amplification process on a microscopic probe after the interaction with the sample, we can
beat the losses detrimental effect on the phase measurement which affects the single photon state after its interaction with
the sample, and thus improve the achievable sensitivity.
In this work we present the realization of multiphoton quantum states, obtained by optical parametric amplification,
and we investigate their perspectives and possible applications. The multiphoton quantum states are
generated by a quantum-injected optical parametric amplifier (QI-OPA) seeded by a single-photon belonging
to an EPR entangled pair. The entanglement between the micro-macroscopic photon system is experimentally
demonstrated, and the possible applications of the macro-qubits states are presented and discussed.
The orbital angular momentum carried by single photons represents a promising resource in the quantum information
field. In this paper we report the characterization in the quantum regime of a recently introduced
optical device, known as <i>q-plate</i>. Exploiting the spin-orbit coupling that takes place in the q-plate, it is possible
to transfer coherently the information from the polarization to the orbital angular momentum degree of freedom,
and viceversa. Hence the q-plate provides a reliable bi-directional interface between polarization and orbital
angular momentum. As a first paradigmatic demonstration of the q-plate properties, we have carried out the
first experimental Hong-Ou-mandel effect purely observed in the orbital angular momentum degree of freedom.
In the present work we propose to realize a macroscopic light-matter entangled state, obtained by the interaction
of a multiphoton quantum superposition with a BEC system. The multiphoton quantum state is generated
by a quantum-injected optical parametric amplifier (QI-OPA) seeded by a single-photon belonging to an EPR
entangled pair and interacts with a <i>Mirror-BEC</i> shaped as a Bragg interference structure. The overall process
will realize an entangled macroscopic quantum superposition involving a "microscopic" single-photon state of
polarization and the coherent "macroscopic" displacement of the BEC structure acting in space-like separated
distant places. This hybrid photonic-atomic system could open new perspectives on the possibility of coupling
the amplified radiation with an atomic ensemble, a Bose-Einstein condensate, in order to implement innovative
quantum interface between light and matter.
We investigate the multiphoton states generated by high-gain optical parametric amplification of a single injected
photon, polarization encoded as a "qubit". The experiment configuration exploits the optimal phase-covariant
cloning in the high gain regime. The interference fringe pattern showing the non local transfer of coherence
between the injected qubit and the mesoscopic amplified output field involving up to 4000 photons has been
investigated. A probabilistic new method to extract full information about the multiparticle output wavefunction
has been implemented. This technique can be adopted to test the entanglement between a microscopic system
and a macro one.
Quantum states of two photons simultaneously entangled in polarization and linear momentum, namely hyper-entangled
or cluster states, allow to operate in a larger Hilbert space, since we can associate four qubits to two
photons. We describe how these states are generated, characterized and manipulated by linear optics technique.
Some recent results verifying that the ratio between the quantum and classical prediction grows with the size of
the Hilbert space are also presented in this work. Finally, we show the efficient realization of a C-NOT gate by
using two photon cluster states operating in the one-way model of quantum computation.
Two photon states entangled in polarization and momentum, hyper-entangled, have been generated by using linear optics and a single Type I nonlinear crystal. These states have been completely characterized and their nonlocal behaviour have been verified by independent Bell's inequalities tests performed in the two degrees of freedom of entanglement and by an "all versus nothing" test of local realism. The manipulation of these states may represent a useful control in quantum state engineering and Bell state measurements and, more in general, in Quantum Information applications.
Maximally entangled states, Werner state and maximally entangled mixed states (MEMS) have been created and fully characterized by a novel high brilliance universal source of entangled photon pairs with striking spatial characteristics. Mixed states of any structure, spanning a 2 x 2 Hilbert space may be created by this source. The non local properties of the generated entanglement have been tested by standard Bell measurements. Tunable Werner states and Maximally Entangled Mixed States (MEMS) have been created by an original patchwork technique and investigated by quantum tomography. The entropic and nonlocal properties of these states have been also undertaken.
A novel Mach-Zehnder interferometer terminated at two different frequencies which realizes for a single photon quantum state (<i>qubit</i>) the nonlinear frequency conversion has been realized. The <i>information-preserving</i> character of the nonlinear process allows to transfer the coherence of the input to the output state. The results of this experiment can have relevant applications in quantum information technology.
The process of two-dipole superradiance has been investigated by femtosecond excitation of two ensembles of dye molecules, located at a mutual distance R on the symmetry plane of a microcavity. In these conditions, superradiant coupling between the two objects can be established, giving rise to emission correlation effects, which have been investigated in the space-time domain.
Some ultrafast phenomena occurring in an active microcavity have been investigated. This device can behave as an efficient source of non-classical light, when a small number of molecules inside are excited by a femtosecond laser.In this way single photon n > states are generated with anon-classical sub-Poissonian distribution. Multiple excitations of a larger number of molecules can give rise to collective phenomena because of the strong super-radiant ultrafast coupling within the transverse region of the microcavity electromagnetic field. This process has been experimentally studied by means of a high efficiency, single photon, femtosecond non-linear optical gate.
The process of the spontaneous emission (SpE) from an active microscopic cavity (microcavity) is shown with emphasis on mirror separation of the order of the optical wavelength. The relevant effects of SpE enhancement and inhibition, non-exponential decay, and emission anisotropy are outlined for a cavity terminated by mirrors bearing either metal -- or semiconductor -- multilayered coatings. Finally, an experiment regarding the possibility of detecting the field distribution within the cavity of the emission wavelength is shown.