512 research outputs found
Realization of Universal Optimal Quantum Machines by Projective Operators and Stochastic Maps
Optimal quantum machines can be implemented by linear projective operations.
In the present work a general qubit symmetrization theory is presented by
investigating the close links to the qubit purification process and to the
programmable teleportation of any generic optimal anti-unitary map. In
addition, the contextual realization of the N ->M cloning map and of the
teleportation of the N->(M-N) universal NOT gate is analyzed by a novel and
very general angular momentum theory. An extended set of experimental
realizations by state symmetrization linear optical procedures is reported.
These include the 1->2 cloning process, the UNOT gate and the quantum
tomographic characterization of the optimal partial transpose map of
polarization encoded qubits.Comment: 11 pages, 7 figure
Contextual Realization of the Universal Quantum Cloning Machine and of the Universal-NOT gate by Quantum Injected Optical Parametric Amplification
A simultaneous, contextual experimental demonstration of the two processes of
cloning an input qubit and of flipping it into the orthogonal qubit is
reported. The adopted experimental apparatus, a Quantum-Injected Optical
Parametric Amplifier (QIOPA) is transformed simultaneously into a Universal
Optimal Quantum Cloning Machine (UOQCM) and into a Universal NOT
quantum-information gate. The two processes, indeed forbidden in their exact
form for fundamental quantum limitations, will be found to be universal and
optimal, i.e. the measured fidelity of both processes F<1 will be found close
to the limit values evaluated by quantum theory. A contextual theoretical and
experimental investigation of these processes, which may represent the basic
difference between the classical and the quantum worlds, can reveal in a
unifying manner the detailed structure of quantum information. It may also
enlighten the yet little explored interconnections of fundamental axiomatic
properties within the deep structure of quantum mechanics. PACS numbers:
03.67.-a, 03.65.Ta, 03.65.UdComment: 27 pages, 7 figure
Enhanced Resolution of Lossy Interferometry by Coherent Amplification of Single Photons
In the quantum sensing context most of the efforts to design novel quantum
techniques of sensing have been constrained to idealized, noise-free scenarios,
in which effects of environmental disturbances could be neglected. In this
work, we propose to exploit optical parametric amplification to boost
interferometry sensitivity in the presence of losses in a minimally invasive
scenario. By performing the amplification process on the 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.Comment: 4 + 3 pages, 3 + 5 figure
Entanglement, EPR correlations and mesoscopic quantum superposition by the high-gain quantum injected parametric amplification
We investigate the multiparticle quantum superposition and the persistence of
multipartite entanglement of the quantum superposition generated by the quantum
injected high-gain optical parametric amplification of a single photon. The
physical configuration based on the optimal universal quantum cloning has been
adopted to investigate how the entanglement and the quantum coherence of the
system persists for large values of the nonlinear parametric gain g.Comment: 9 pages, 5 figure
Quantum to classical transition via fuzzy measurements on high gain spontaneous parametric down-conversion
We consider the high gain spontaneous parametric down-conversion in a non
collinear geometry as a paradigmatic scenario to investigate the
quantum-to-classical transition by increasing the pump power, that is, the
average number of generated photons. The possibility of observing quantum
correlations in such macroscopic quantum system through dichotomic measurement
will be analyzed by addressing two different measurement schemes, based on
different dichotomization processes. More specifically, we will investigate the
persistence of non-locality in an increasing size n/2-spin singlet state by
studying the change in the correlations form as increases, both in the
ideal case and in presence of losses. We observe a fast decrease in the amount
of Bell's inequality violation for increasing system size. This theoretical
analysis is supported by the experimental observation of macro-macro
correlations with an average number of photons of about 10^3. Our results
enlighten the practical extreme difficulty of observing non-locality by
performing such a dichotomic fuzzy measurement.Comment: 15 pages, 18 figure
Teleportation scheme implementing contextually the Universal Optimal Quantum Cloning Machine and the Universal Not Gate. Complete experimental realization
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 (cfr. quant-ph/0304070). A
complete experimental realization of the protocol is presented here.Comment: 11 pages, 3 figure
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 anti-clone or on the two clones. Such scheme has been applied to
enhance the transmission fidelity over a lossy quantum channel.Comment: 4 pages, 2figure
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