Fundamental laws of quantum mechanics impose that arbitrary quantum states cannot be perfectly cloned
or amplified without introducing some unavoidable noise in the process. The quantum noise intrinsic to the
functioning of a linear phase-insensitive amplifier can however be avoided by relaxing the requirement of a deterministic
operation. Non-deterministic noiseless linear amplifiers that do not violate any fundamental quantum
law are therefore possible and here we present the first experimental realization of a scheme that allows noiseless
amplification of coherent states at the best level of effective gain and final state fidelity ever reached. This
scheme, based on a sequence of photon addition and subtraction, and characterized by a significant amplification
and low distortions, may become a useful tool for quantum communications and metrology, by enhancing the
discrimination between partially overlapping quantum states or by recovering the information transmitted over lossy channels.
One of the most important and sometimes controversial stages of the conservation process is surface cleaning:
decisions have to be made regarding partial or complete removal of varnish. Technical considerations include
selection of a method that allows a great deal of control in the cleaning process, so that undesired layers can be
removed without damage to the underlying ones. Traditional cleaning methods include mechanical or chemical
removal, and restorers and conservators work would be considerably helped by the knowledge of the varnish
thickness. Up to now thickness measurement has been performed in an invasive way by means of stratigraphy, a well
known painting structure investigation technique since half a century. In this work we present an application of
Optical Coherence Tomography (OCT), a well-established technique for biomedical applications, for non-destructive
measuring of the varnish film thickness during the cleaning process of an ancient painting, the <i>Ritratto Trivulzio</i> by
Antonello da Messina. OCT images of three differently cleaned areas on the painting surface were acquired and the
results were compared with a spectral characterization of the same areas.
We present a review of our recent studies concerning remotely prepared entangled bits (ebits) made of a single photon coherently delocalized between two well-separated temporal modes (or time bins). The preparation scheme represents a remotely tunable source for tailoring arbitrary ebits, whether maximally or non-maximally entangled, which is highly desirable for applications in quantum information technology. The remotely prepared ebit is analyzed by performing both single-mode and two-mode homodyne tomography with the ultra-fast balanced homodyne detection scheme recently developed in our lab. Beside the non-classical behavior typical of single-photon Fock states (negative values around the origin), the reconstructed two-mode Wigner function is found to be characterized by an intriguing phase and by correlations between the two distant time bins sharing the single photon.
We show the experimental observation of quantum states of light exhibiting nonclassical features obtained by single photon excitation of a thermal state. Such single-photon-added thermal states are the result of the single action of the creation operator on a mixed state that can be fully described classically. They show different degree of nonclassicality depending on the mean photon number of the original thermal state. The generated state is characterized by means of ultra-fast homodyne detection which allows us to reconstruct its density matrix and Wigner function by quantum tomography. We demonstrate the nonclassical behavior of single-photon added thermal states by an analysis of the negativity of the Wigner function.
A new class of non-classical light states has been experimentally generated and their complete phase-space characterization has been achieved by quantum homodyne tomography. Such states are produced by the action of the photon creation operator on a coherent light field and are thus the result of the elementary excitation process of a classical field by a single quantum. Being intermediate between a single-photon Fock state and a coherent one, they offer the unique opportunity to closely follow the smooth evolution between the particle-like and the wave-like behavior of the light field.
In the last few years many non-destructive techniques have entered the field of painting conservation, and most of them are routinely applied to study and monitoring the painting status. Among them optical techniques are by now widely diffused and extremely well received because of their effectiveness and safety, nevertheless none of them is suitable for a quantitative characterization of varnish. One of the most important and often controversial stages of painting restoration is the surface cleaning process up to now being carried out without any tool to measure the actual varnish thickness but microscope observation of micro-detach. In this work we present an application of Optical Coherence Tomography to non-destructive diagnostics of artwork: the potentiality of this technique is demonstrated by measuring the thickness of the varnish layer in a fragment of a nineteenth-century oil painting.
Non-destructive optical testing techniques are widely used in the field of painting diagnostics because of their effectiveness and safety. At present, many techniques for non-destructive investigations of paintings are available. Optical Coherence Tomography (OCT) is a non invasive technique allowing cross sectional imaging of partially transparent or scattering tissue which is now well-established for biomedical applications. Particularly, the OCT techniques allow evaluating multilayer tissues. Being applied to painting diagnostics, the OCT gives a possibility to measure the actual varnish thickness that is very important in painting restoration by the cleaning process. Because of complicated local structure of layers and light scattering, noise-immune signal processing methods should be used. In the paper, the Kalman filtering method involving random fringe model applied to the OCT signals is investigated and compared with conventional fringe amplitude demodulation method. Experimental results obtained when recovering OCT tomograms of paintings are presented and discussed.
We present the experimental generation of a new class of non-classical light states and their complete phase-space characterization by quantum homodyne tomography. These states are the result of the most elementary amplification process of classical light fields by a single quantum of excitation and can be generated by the process of stimulated emission of a single photon in the mode of a coherent state. Being intermediate between a single-photon Fock state and a coherent one, they offer the unique opportunity to closely follow the smooth evolution between the particle-like and the wave-like behavior of the light field and to witness the gradual change from the spontaneous to the stimulated regimes of light emission.