Abstract
Orbital angular momentum is a discrete degree of freedom that can access an infinite dimensional Hilbert space, thus enhancing the information capacity of a single optical beam. Continuous variables field quadratures allow achieving some quantum tasks in a more advantageous way with respect to the use of photon-number states. Here, we use a hybrid approach realizing bipartite continuous-variable Gaussian entangled state made up of two electromagnetic modes carrying orbital angular momentum. A q-plate is used for endowing a pair of entangled beams with such a degree of freedom. This quantum state is then completely characterized thanks to a novel design of a homodyne detector in which also the local oscillator is an orbital angular momentum-carrying beams so allowing the direct detection of vortex modes quadratures.
Highlights
Quantum entanglement, from simple bipartite systems up to complex multipartite ones, is a prominent resource in quantum information allowing to accomplish tasks not achievable with classical tools
In ref. [7] we presented the generation of a Gaussian bipartite Continuous Variable (CV) entangled state carrying OAM
Afterwards, the state is completely characterized by means of a reconfigurable Homodyne Detector (HD) capable of measuring quadratures relative to helical modes
Summary
From simple bipartite systems up to complex multipartite ones, is a prominent resource in quantum information allowing to accomplish tasks not achievable with classical tools. Angular Momentum (OAM) represents, with no doubt, an easy to handle candidate It characterizes a class of transverse optical modes that carry non-zero OAM so that many modes can co-propagate preserving their distinguishability. Beams carrying OAM are paraxial beams characterized by the presence of an azimuthal angle phase dependence eimφ These beams have helical wavefronts and an optical vortex on the axis, i.e., a phase singularity in which the field vanishes. Afterwards, the state is completely characterized by means of a reconfigurable Homodyne Detector (HD) capable of measuring quadratures relative to helical modes. In this way, we have provided a complete characterization of a multi-distinguishable polarization-OAM CV entangled state
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