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.
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.
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.