The quantum interference represents an essential resource for the quantum simulation, the characterization of the quantumness of a system, and the achievement of the quantum advantage. The peculiar characteristics of quantum interference are due to quantum superposition and bosonic coalescence, which can be explained only by using the rules of quantum mechanics. The quantum superposition is particularly exploited in Quantum Walks (QWs) experiments. The QWs can be performed in several photonic architectures to simulate quantum phenomena like decoherence in presence of disorder, quantum transport, the evolution of bosonic and fermionic particles. The bosonic coalescence is the core of the Boson Sampling problem, which is the best candidate to prove the quantum advantage over classical computation. Indeed, the calculation of Boson Sampling distribution is a hard computational task for a classical computer, which can be accomplished by a rudimental quantum computer.
This project's aim is to create an innovative platform feasible for the realization of two-dimensional QW and multimode Boson Sampling experiments. The novelty of the platform is given by a new device, the G-plate, designed by Lorenzo Marrucci's research group of the University of Naples "Federico II". Such a device allows one to obtain quantum interference in the transverse momentum of light on a scalable platform. In order to improve the precision of the apparatus, we need to reduce the photon losses in the detection. This could be achieved by coupling the photon in the 2D fiber array using a coated microlens array mounted on high precision support. We strongly believe that endowing our experimental setup with such a device would significantly improve our current and future results.
The innovative platform we purpose will significantly improve in quantum interference experiments. In particular, the implementation of G-plate technology lets the system overcome the limitations affecting older platforms working with bulk interferometers and photonic chips. Indeed, a photonic chip is not easily scalable because it is designed for a fixed number of modes and consequently also the maximal number of input photons will be. On the other hand, the G-plate technology introduces no limits on the number of injected photons and modes, because it works on transverse momentum space. The best feature of this technology is its great versatility. The G-plates depend on a great number of parameters that can be easily controlled, for instance, the grating direction, the delay retardation, and the grating pitch. Moreover, different G-plates can be combined with waveplates to easily obtain a plethora of configuration. In this way, we are able to realize different unitary transformation, with a suitable tuning in the parameters and disposition of the devices. These features make this platform particularly suitable for the Boson Sampling experiment. Our platform is also able to entangle the interfering photons with an external degree of freedom like Orbital Angular Momentum. Notice that this not possible in a photonic chip because the waveguides allow only the propagation of Gaussian Mode. Our platform is very compact in comparison with the other bulk platforms, making it a great resource for the realization of more complex interferometers. All these advantages are achievable if we reduced the losses of our platform by improving the photon coupling with the microlens array.
As an immediate application, our apparatus can be implemented to investigate the dynamics of two dimensional Quantum Walks with one and two photons. It is the first experimental realization of two particle quantum walk dynamics on a two dimensional lattice. In particular, we aim to study the dynamics of two particles in different initial positions on the lattice. We want to investigate the walker evolution in the distinguishable as well as indistinguishable particle regimes. We also want to study the changing of the final photon distribution among the transition between these regimes. As a future perspective, we want to test the platform in more complex applications, as the realization of a multimode Boson Sampling, by increasing the number of input photons. Our platform is particularly suitable for many of the Boson Sampling experiment variants like the Scattershot and the Gaussian Bosons Sampling.