Quantum Seminar: Generation, control and applications of photonic spatial qudits

Zoom: https://tau-ac-il.zoom.us/j/82245900781

Abstract:

Non classical states of light are required for many applications in quantum information, including secure quantum key distribution, quantum sensing and quantum computation. One of the main methods for generating non-classical light is spontaneous parametric down conversion (SPDC), a second-order nonlinear optical process in which one pump photon spontaneously splits into two sub-harmonic photons. The generated photons can be naturally entangled in many degrees of freedom, making SPDC useful as a bright source of entangled photons. 

The properties of the generated quantum light depend on the parameters of the pump beam and the nonlinear crystal, but it is not a trivial task to predict the outcome of the SPDC process or to tailor it in order to obtain a desired state.

Here I will present a systematic method to design and control SPDC processes. It is based on a classical simulator that we developed, that enables to precisely predict the first order and second order correlations between the generated single photons, and to reconstruct the density matrix of the quantum state. In order to obtain a desired state, we developed an inverse solver using machine learning methods. We use the forward process to train our solver, as a function of parameters such as the pump shape and crystal parameters. This enables to generate maximally entangled bi-photon states using the spatial degree of freedom of light. The Laguerre-Gauss and Hermite-Gauss family of modes are two bases that we use for realizing bi-photon spatial qubits, qutrits and quqarts. Furthermore, all-optical coherent control of the generated quantum state can be obtained by varying the profile of the pump beam.