Quantum simulation with integrated photonics

The ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications [1]. The technology for handling polarization-encoded qubits, the most commonly adopted approach, was still missing in quantum optical circuits until the ultrafast laser writing (ULW) technique was adopted to realize integrated devices able to support polarization encoded qubits [2]. In the ULW technique a femtosecond laser is focused on a glass substrate inducing a variation of the glass refractive index in the region around the focus: by translating the substrate with respect to the laser beam it is possible to directly write wave-guides inside the chip. Thanks to this method, the maintenance of polarization entanglement was demonstrated in a balanced polarization independent integrated beam splitter [2] and an integrated CNOT gate for polarization qubits was realized [3].