C. E. R. Souza

Topological phase for spin-orbit transformations on a laser beam

We investigate the topological phase associated with the SO(3) representation in terms of maximally entangled states. An experimental demonstration of this topological phase is provided for polarization and spatial mode transformations of a laser beam.

Vector vortex implementation of a quantum game

The concept of nonseparability between spin and orbital degrees of freedom of laser modes is applied in the implementation of the quantum prisoners dilemma. The quantum version of the game brings novel features with a richer universe of strategies and is one of the basic examples to illustrate the concepts of game theory. Exploiting the classical paraxial spin–orbit modes, we implemented the most important strategies that can be achieved in the quantum version of the game.

Topological phase structure of vector vortex beams.

The topological phase acquired by vector vortex optical beams is investigated. Under local unitary operations on their polarization and transverse degrees of freedom, the vector vortices can only acquire discrete geometric phase values, 0 or π, associated with closed paths belonging to different homotopy classes on the SO(3) manifold. These discrete values are demonstrated through interferometric measurements, and the spin-orbit mode separability is associated to the visibility of the interference patterns. The local unitary operations performed on the vector vortices involved both polarization and transverse mode transformations with birefringent wave plates and astigmatic mode converters. The experimental results agree with our theoretical simulations and generalize our previous results obtained with polarization transformations only.

Arbitrary orbital angular momentum addition in second harmonic generation

We demonstrate second harmonic generation performed with optical vortices with different topological charges imprinted on orthogonal polarizations. Besides the intuitive charge doubling, we implement arbitrary topological charge addition on the second harmonic field using polarization as an auxiliary parameter.

Quantum information processing with spin-orbit laser modes

Optical vortices are employed for quantum information encoding, where the wave front structure combined to the polarization vector of an optical beam can be regarded as a spin-orbit realization of a two-qubit system. We will discuss quantum information protocols that can be implemented in these degrees of freedom.

Playing a quantum game on polarization vortices

The quantum mechanical approach to the well known prisoners dilemma, one of the basic examples to illustrate the concepts of Game Theory, is implemented with a classical optical resource, nonquantum entanglement between spin and orbital degrees of freedom of laser modes. The concept of entanglement is crucial in the quantum version of the game, which brings novel features with a richer universe of strategies. As we show, this richness can be achieved in a quite unexpected context, namely that of paraxial spin-orbit modes in classical optics.

A Michelson controlled-not gate with a single-lens astigmatic mode converter

Using a single lens design for a paraxial mode converter, we implement a controlled-not gate based on a Michelson interferometer in which the photon polarization acts as the control bit and the first order transverse mode as the target. We also build a parity sorter which can be useful for quantum information processing.

Topological Phase for Spin-Orbit Transformations on a Laser Beam

We investigate the topological phase associated with the SO(3) representation in terms of maximally entangled states. An experimental demonstration of this topological phase is provided for polarization and spatial mode transformations of a laser beam.

Experimental Demonstration of the Topological Phase for Entangled Qubits

We investigate the topological phase associated with the SO(3) representation in terms of maximally entangled states. An experimental demonstration of this topological phase is provided for polarization and spatial mode transformations of a laser beam.

Orbital Angular Momentum and Geometric Phase Conjugation in an Optical Parametric Oscillator

We discuss the spatial mode dynamics of an optical parametric oscillator under injection of orbital angular momentum. By considering the adiabatic mode conversion of the injected signal, we predict a geometric phase conjugation effect.