Complete experimental toolbox for alignment-free quantum communication

D’Ambrosio, Vincenzo; Nagali, Eleonora; Walborn, S. P.; Aolita, Leandro; Slussarenko, Sergei; Marrucci, Lorenzo; Sciarrino, Fabio

doi:10.1038/ncomms1951

Cited by 289 publications

(201 citation statements)

References 50 publications

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“…Recently, it has attracted a growing interest due both to the fundamental aspects involved, but also for potential applications to classical optical information processing [13][14][15][16][17][18][19][20]. Nonseparable structures have also proved their utility in the quantum optical domain [22][23][24][25][26][27][28][29][30][31][32][33]. Analogously to its quantum counterpart, classical entanglement has been characterized via the violation of Bell-like inequalities [34][35][36].…”

Section: Pacs Numbersmentioning

confidence: 99%

Tripartite nonseparability in classical optics

et al. 2016

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It is possible to prepare classical optical beams which cannot be characterized by a tensor product of vectors describing each of their degrees of freedom. Here we report the experimental creation of such a non-separable, tripartite GHZ-like state of path, polarization and transverse modes of a classical laser beam. We use a Mach-Zehnder interferometer with an additional mirror and other optical elements to perform measurements that violate Mermin's inequality. This demonstration of a classical optical analogue of tripartite entanglement paves the path to novel optical applications inspired by multipartite quantum information protocols. PACS numbers:A composite quantum system is said to be entangled when it is not fully described by the state of its components [1]. Besides indicating a departure from classical physics, entangled states represent an important resource for a number of quantum information protocols [2]. In classical optics, the mode structure associated with different degrees of freedom of the wave field can also be described by complex vector spaces. As examples, an arbitrary polarization can be written as a complex superposition of circularly polarized beams, and the spatial configuration of a paraxial beam can be decomposed in terms of Laguerre-Gaussian beams. These degrees of freedom can be represented on two independent Poincaré spheres [3], in complete analogy with the Bloch sphere used to represent qubit states [2]. Intriguingly, also in classical optics there are field configurations which cannot be described as a tensor product of definite modes of each individual degree of freedom of the system [4]. These non-separable structures display a classical analogue of quantum entanglement [5][6][7][8]. One example are vector vortex beams, which are non-separable superpositions of transverse modes and polarization states of a laser beam [9][10][11]. This analogy was used to demonstrate the topological phase acquired by entangled states evolving under local unitary operations [12]. Recently, it has attracted a growing interest due both to the fundamental aspects involved, but also for potential applications to classical optical information processing [13][14][15][16][17][18][19][20]. Nonseparable structures have also proved their utility in the quantum optical domain [22][23][24][25][26][27][28][29][30][31][32][33]. Analogously to its quantum counterpart, classical entanglement has been characterized via the violation of Bell-like inequalities [34][35][36].Composite quantum systems may have more than two parts. For tripartite systems, Mermin [37] simplified an earlier argument by Greenberger, Horne and Zeilinger * Corresponding author.[38], to show that any local hidden-variable theory for tripartite systems must satisfy (1) where Z, Y, Z represent the Pauli operators. This inequality is violated by the so-called GHZ-Mermin state:for which ZZZ = +1 and ZXX = XZX = XXZ = −1, resulting in M = 4, the maximum algebraic violation of Mermin's inequality (1). In [39], Spreeuw proposed a scheme in which t...

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Section: Pacs Numbersmentioning

confidence: 99%

Tripartite nonseparability in classical optics

et al. 2016

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“…Many works have been devoted to schemes for implementing and applying this spin-orbit coupling [2][3][4][5][6][7][8][9][10][11]. Beyond the intrinsic beauty of this subject, one may find interesting applications to quantum information tasks like optical communication [12,13], teleportation schemes [14][15][16][17][18][19][20], alignment free quantum cryptography [21][22][23], controlled gates for quantum computation [24,25], quantum simulations [26,27] and metrology [28][29][30]. Quite curiously, the presence of spin-orbit structures in an optical beam can be characterized by inequality criteria similar to those used to witness entanglement in quantum mechanics [31][32][33][34][35][36][37].…”

Section: Introductionmentioning

confidence: 99%

Orbital-angular-momentum mixing in type-II second-harmonic generation

Pereira¹,

Buono²,

Tasca³

et al. 2017

Phys. Rev. A

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We investigate the non linear mixing of orbital angular momentum in type II second harmonic generation with arbitrary topological charges imprinted on two orthogonally polarized beams. Starting from the basic nonlinear equations for the interacting fields, we derive the selection rules determining the set of paraxial modes taking part in the interaction. Conservation of orbital angular momentum naturally appears as the topological charge selection rule. However, a less intuitive rule applies to the radial orders when modes carrying opposite helicities are combined in the nonlinear crystal, an intriguing feature confirmed by experimental measurements.

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“…Spatially coherent light beams containing phase singularities are used within optical physics, where their angular momentum and/or their annular intensity cross-section lead to interesting effects (1)(2)(3)(4). Of particular prominence are those beams with helical phase-fronts described by a term exp(i φ), where φ is the azimuthal angle within the beam and , the topological charge, is an integer describing the number of intertwined helical phase surfaces, i.e.…”

Section: Introductionmentioning

confidence: 99%

The transition from a coherent optical vortex to a Rankine vortex: beam contrast dependence on topological charge

Toninelli

Aspden

Phillips

et al. 2016

Journal of Modern Optics

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Spatially coherent helically phased light beams carry orbital angular momentum (OAM) and contain phase singularities at their centre. Destructive interference at the position of the phase singularity means the intensity at this point is necessarily zero, which results in a high contrast between the centre and the surrounding annular intensity distribution. Beams of reduced spatial coherence yet still carrying OAM have previously been referred to as Rankine vortices. Such beams no longer possess zero intensity at their centre, exhibiting a contrast that decreases as their spatial coherence is reduced. In this work, we study the contrast of a vortex beam as a function of its spatial coherence and topological charge. We show that beams carrying higher values of topological charge display a radial intensity contrast that is more resilient to a reduction in spatial coherence of the source.

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Complete experimental toolbox for alignment-free quantum communication

Cited by 289 publications

References 50 publications

Tripartite nonseparability in classical optics

Tripartite nonseparability in classical optics

Orbital-angular-momentum mixing in type-II second-harmonic generation

The transition from a coherent optical vortex to a Rankine vortex: beam contrast dependence on topological charge

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