Bell states generation on a III-V semiconductor chip at room temperature

Summary form only given. In these last years, a great deal of effort has been devoted to the miniaturization of quantum information technology on semiconductor chips. In the context of photon pair sources, the bi-exciton cascade of a quantum dot and the four-wave mixing in Silicon waveguides have been used to demonstrate the generation of entangled states. Spontaneous parametric down-conversion in III-V semiconductor waveguides combines the advantages of room temperature and telecom wavelength operation, while keeping open the possibility of electrically pumping of the device. Here we present a source consisting of a multilayer AlGaAs waveguide grown on a GaAs substrate and then chemically etched to achieve lateral confinement in a ridge. The structure design is such that a pump beam (around 775 nm), impinging on the surface of the waveguide with an incidence angle θ, generates two counterpropagating orthogonally polarized beams (around 1550 nm). The waveguide core is surrounded by distributed Bragg reflectors to enhance the pump field. We demonstrate the direct emission of polarization entangled photons by pumping the device with two symmetric angles of incidence corresponding to frequency degeneracy and performing a quantum tomography measurement. Most common entanglement witnesses are satisfied and a raw fidelity of 0.8 to the Bell state ( Hν +eiφ vx ) is obtained. A theoretical model, taking into account the experimental parameters, provides ways to understand and control the amount of entanglement.These results open the route to the demonstration of other interesting features of our device such as the generation of hyper-entangled states via the control of the frequency correlation degree through the spatial and spectral pump beam profile, leading to a new generation of completely integrated devices for quantum information.