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F De Martini

Publications and source records attributed to F De Martini.

11 recordsLinked to original sources
PubMed2006

Realization of a minimal disturbance quantum measurement.

We report the first experimental realization of an "optimal" quantum device able to perform a minimal disturbance measurement on polarization encoded qubits saturating the theoretical boundary established between the classical knowledge acquired of any input state, i.e., a "classical guess," and the fidelity of the same state after disturbance due to measurement. The device has been physically realized by means of a linear optical qubit manipulation, postselection measurement, and a classical feed-forward process.

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PubMed2005

All-versus-nothing nonlocality test of quantum mechanics by two-photon hyperentanglement.

We report the experimental realization and the characterization of polarization and momentum hyperentangled two-photon states, generated by a new parametric source of correlated photon pairs. By adoption of these states an "all-versus-nothing" test of quantum mechanics was performed. The two-photon hyperentangled states are expected to find at an increasing rate a widespread application in state engineering and quantum information.

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PubMed2005

Separating the classical and quantum information via quantum cloning.

An application of quantum cloning to optimally interface a quantum system with a classical observer is presented; in particular, we describe a procedure to perform a minimal disturbance measurement on a single qubit by adopting a 1-->2 cloning machine followed by a generalized measurement on a single clone and the anticlone or on the two clones. Such a scheme can be applied to enhance the transmission fidelity over a lossy quantum channel.

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PubMed2004

Experimental purification of single qubits.

We report the experimental realization of the purification protocol for single qubits sent through a depolarizing channel. The qubits are associated with polarization states of single photons and the protocol is achieved by means of passive linear optical elements. The present approach may represent a convenient alternative to the distillation and error correction protocols of quantum information.

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PubMed2004

Generation and characterization of Werner states and maximally entangled mixed states by a universal source of entanglement.

We present a novel technique for generating two-photon polarization mixed states of any structure, which is based on the peculiar spatial characteristics of a high brilliance source of entangled pairs. Werner states and maximally entangled mixed states, two well-known families of mixed states important for quantum information, have been created and fully characterized by this technique. We have also investigated and tested the nonlocal properties of these states.

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PubMed2004

Teleportation scheme implementing the universal optimal quantum cloning machine and the universal NOT gate.

By a significant modification of the standard protocol of quantum state teleportation, two processes "forbidden" by quantum mechanics in their exact form, the universal NOT gate and the universal optimal quantum cloning machine, have been implemented contextually and optimally by a fully linear method. In particular, the first experimental demonstration of the tele-UNOT gate, a novel quantum information protocol, has been reported. The experimental results are found in full agreement with theory.

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PubMed2003

Detection of entanglement with polarized photons: experimental realization of an entanglement witness.

We report on the first experimental realization of an entanglement witness, a method to detect entanglement with few local measurements. The present demonstration has been performed with polarized photons in Werner states, a well-known family of mixed states that can be either separable or nonseparable. The Werner states are generated by a novel high brilliance source of bipartite entangled states by which the state mixedness can be easily adjusted.

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PubMed2003

Frequency hopping in quantum interferometry: efficient up-down conversion for qubits and ebits.

A novel Mach-Zehnder interferometer terminated at two different frequencies realizes in a quantum regime the nonlinear frequency conversion of optical quantum superposition states. The information-preserving character of the relevant unitary transformation has been experimentally demonstrated for input qubits and ebits. Besides its own intrinsic fundamental interest, the new scheme is expected to find important applications in modern quantum information technology.

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PubMed2002

Experimental realization of the quantum universal NOT gate.

In classical computation, a 'bit' of information can be flipped (that is, changed in value from zero to one and vice versa) using a logical NOT gate; but the quantum analogue of this process is much more complicated. A quantum bit (qubit) can exist simultaneously in a superposition of two logical states with complex amplitudes, and it is impossible to find a universal transformation that would flip the original superposed state into a perpendicular state for all values of the amplitudes. But although perfect flipping of a qubit prepared in an arbitrary state (a universal NOT operation) is prohibited by the rules of quantum mechanics, there exists an optimal approximation to this procedure. Here we report the experimental realization of a universal quantum machine that performs the best possible approximation to the universal NOT transformation. The system adopted was an optical parametric amplifier of entangled photon states, which also enabled us to investigate universal quantum cloning.

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PubMed2001

Multiparticle quantum superposition and stimulated entanglement by parity selective amplification of entangled states.

We report the creation of an entangled multiphoton quantum superposition by quantum injection of entangled 2-photon states into a parity selective parametric amplifier. The information preserving property of the state transformation suggests for these macrostates the name of large qubits. They are ideal objects for investigating the emergence of the classical world in complex quantum systems and have relevant new applications in quantum information.

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