88 research outputs found
Measurement-induced quantum operations on multiphoton states
We investigate how multiphoton quantum states obtained through optical
parametric amplification can be manipulated by performing a measurement on a
small portion of the output light field. We study in detail how the macroqubit
features are modified by varying the amount of extracted information and the
strategy adopted at the final measurement stage. At last the obtained results
are employed to investigate the possibility of performing a
microscopic-macroscopic non-locality test free from auxiliary assumptions.Comment: 13 pages, 13 figure
Entanglement criteria for microscopic-macroscopic systems
We discuss the conclusions that can be drawn on a recent experimental
micro-macro entanglement test [F. De Martini, F. Sciarrino, and C. Vitelli,
Phys. Rev. Lett. 100, 253601 (2008). The system under investigation is
generated through optical parametric amplification of one photon belonging to
an entangled pair. The adopted entanglement criterion makes it possible to
infer the presence of entanglement before losses, that occur on the macrostate,
under a specific assumption. In particular, an a priori knowledge of the system
that generates the micro-macro pair is necessary to exclude a class of
separable states that can reproduce the obtained experimental results. Finally,
we discuss the feasibility of a micro-macro "genuine" entanglement test on the
analyzed system by considering different strategies, which show that in
principle a fraction epsilon, proportional to the number of photons that
survive the lossy process, of the original entanglement persists in any losses
regime.Comment: 11 pages, 10 figure
Simulation of noise-assisted transport via optical cavity networks
Recently, the presence of noise has been found to play a key role in
assisting the transport of energy and information in complex quantum networks
and even in biomolecular systems. Here we propose an experimentally realizable
optical network scheme for the demonstration of the basic mechanisms underlying
noise-assisted transport. The proposed system consists of a network of coupled
quantum optical cavities, injected with a single photon, whose transmission
efficiency can be measured. Introducing dephasing in the photon path this
system exhibits a characteristic enhancement of the transport efficiency that
can be observed with presently available technology.Comment: 8 pages, 7 figures. New version with more detail
Coherent scattering of a Multiphoton Quantum Superposition by a Mirror-BEC
We present the proposition of an experiment in which the multiphoton quantum
superposition consisting of N= 10^5 particles generated by a quantum-injected
optical parametric amplifier (QI-OPA), seeded by a single-photon belonging to
an EPR entangled pair, is made to interact with a Mirror-BEC shaped as a Bragg
interference structure. The overall process will realize a Macroscopic Quantum
Superposition (MQS) involving a microscopic single-photon state of polarization
entangled with the coherent macroscopic transfer of momentum to the BEC
structure, acting in space-like separated distant places.Comment: 4 pages, 4 figure
Quantum-enhanced multiparameter estimation in multiarm interferometers
Quantum metrology is the state-of-the-art measurement technology. It uses
quantum resources to enhance the sensitivity of phase estimation beyond what
reachable within classical physics. While single parameter estimation theory
has been widely investigated, much less is known about the simultaneous
estimation of multiple phases, which finds key applications in imaging and
sensing. In this manuscript we provide conditions of useful entanglement (among
multimode particles, qudits) for multiphase estimation and adapt them to
multiarm Mach-Zehnder interferometry. We discuss benchmark multimode Fock
states containing useful qudit entanglement and overcoming the sensitivity of
separable qudit states in three and four arm Mach-Zehnder-like interferometers
- currently within the reach of integrated photonics technology.Comment: 7+3 pages, 4+2 figure
Phase estimation via quantum interferometry for noisy detectors
The sensitivity in optical interferometry is strongly affected by losses
during the signal propagation or at the detection stage. The optimal quantum
states of the probing signals in the presence of loss were recently found.
However, in many cases of practical interest, their associated accuracy is
worse than the one obtainable without employing quantum resources (e.g.
entanglement and squeezing) but neglecting the detector's loss. Here we detail
an experiment that can reach the latter even in the presence of imperfect
detectors: it employs a phase-sensitive amplification of the signals after the
phase sensing, before the detection. We experimentally demonstrated the
feasibility of a phase estimation experiment able to reach its optimal working
regime. Since our method uses coherent states as input signals, it is a
practical technique that can be used for high-sensitivity interferometry and,
in contrast to the optimal strategies, does not require one to have an exact
characterization of the loss beforehand.Comment: 4 pages + supplementary information (10 pages), 3 + 4 figure
Schroedinger Cat: Entanglement test in a Micro-Macroscopic system
A Macro-state consisting of N= 3.5 x 10^4 photons in a quantum superposition
and entangled with a far apart single-photon state (Micro-state) is generated.
Precisely, an entangled photon pair is created by a nonlinear optical process,
then one photon of the pair is injected into an optical parametric amplifier
(OPA) operating for any input polarization state, i.e. into a phase-covariant
cloning machine. Such transformation establishes a connection between the
single photon and the multi particle fields. We then demonstrate the
non-separability of the bipartite system by adopting a local filtering
technique within a positive operator valued measurement.Comment: 4 pages, 4 figure
Experimental sub-Rayleigh resolution by an unseeded high-gain optical parametric amplifier for quantum lithography
Quantum lithography proposes to adopt entangled quantum states in order to
increase resolution in interferometry. In the present paper we experimentally
demonstrate that the output of a high-gain optical parametric amplifier can be
intense yet exhibits quantum features, namely, sub-Rayleigh fringes, as
proposed by Agarwal et al. (Phys. Rev. Lett. 86, 1389 (2001)). We investigate
multiphoton states generated by a high-gain optical parametric amplifier
operating with a quantum vacuum input for a gain values up to 2.5. The
visibility has then been increased by means of three-photon absorption. The
present article opens interesting perspectives for the implementation of such
an advanced interferometrical setup.Comment: 5 pages, 7 figure
Experimental Scattershot Boson Sampling
Boson Sampling is a computational task strongly believed to be hard for
classical computers, but efficiently solvable by orchestrated bosonic
interference in a specialised quantum computer. Current experimental schemes,
however, are still insufficient for a convincing demonstration of the advantage
of quantum over classical computation. A new variation of this task,
Scattershot Boson Sampling, leads to an exponential increase in speed of the
quantum device, using a larger number of photon sources based on parametric
downconversion. This is achieved by having multiple heralded single photons
being sent, shot by shot, into different random input ports of the
interferometer. Here we report the first Scattershot Boson Sampling
experiments, where six different photon-pair sources are coupled to integrated
photonic circuits. We employ recently proposed statistical tools to analyse our
experimental data, providing strong evidence that our photonic quantum
simulator works as expected. This approach represents an important leap toward
a convincing experimental demonstration of the quantum computational supremacy.Comment: 8 pages, 5 figures (plus Supplementary Materials, 14 pages, 8
figures
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