Integrated photonic circuits with many input and output modes are essential in applications ranging from conventional optical telecommunication networks, to the elaboration of photonic qubits in the integrated quantum information framework. In particular, the latter field has been object in the recent years of an increasing interest: the compactness and phase stability of integrated waveguide circuits are enabling experiments unconceivable with bulk-optics set-ups. Linear photonic devices for quantum information are based on quantum and classical interference effects: the desired circuit operation can be achieved only with tight fabrication control on both power repartition in splitting elements and phase retardance in the various paths. Here we report on a novel three-dimensional circuit architecture, made possible by the unique capabilities of femtosecond laser waveguide writing, which enables us to realize integrated multimode devices implementing arbitrary linear transformations. Networks of cascaded directional couplers can be built with independent control on the splitting ratios and the phase shifts in each branch. In detail, we show an arbitrarily designed 5×5 integrated interferometer: characterization with one- and two-photon experiments confirms the accuracy of our fabrication technique. We exploit the fabricated circuit to implement a small instance of the boson-sampling experiments with up to three photons, which is one of the most promising approaches to realize phenomena hard to simulate with classical computers. We will further show how, by studying classical and quantum interference in many random multimode circuits, we may gain deeper insight into the bosonic coalescence phenomenon.
In the optical sensing context one of the main challenge is to design and implement novel techniques of sensing optimized
to work in a lossy scenario, in which effects of environmental disturbances can destroy the benefits deriving from the
adoption of quantum resources. Here we describe the experimental implementation of a protocol based on the process
of optical parametric amplification to boost interferometry sensitivity in the presence of losses in a minimally invasive
scenario. By performing the amplification process on a microscopic probe after the interaction with the sample, we can
beat the losses detrimental effect on the phase measurement which affects the single photon state after its interaction with
the sample, and thus improve the achievable sensitivity.
In this work we present the realization of multiphoton quantum states, obtained by optical parametric amplification,
and we investigate their perspectives and possible applications. The multiphoton quantum states are
generated by a quantum-injected optical parametric amplifier (QI-OPA) seeded by a single-photon belonging
to an EPR entangled pair. The entanglement between the micro-macroscopic photon system is experimentally
demonstrated, and the possible applications of the macro-qubits states are presented and discussed.
In the present work we propose to realize a macroscopic light-matter entangled state, obtained by the interaction
of a multiphoton quantum superposition with a BEC system. The multiphoton quantum state is generated
by a quantum-injected optical parametric amplifier (QI-OPA) seeded by a single-photon belonging to an EPR
entangled pair and interacts with a <i>Mirror-BEC</i> shaped as a Bragg interference structure. The overall process
will realize an entangled macroscopic quantum superposition involving a "microscopic" single-photon state of
polarization and the coherent "macroscopic" displacement of the BEC structure acting in space-like separated
distant places. This hybrid photonic-atomic system could open new perspectives on the possibility of coupling
the amplified radiation with an atomic ensemble, a Bose-Einstein condensate, in order to implement innovative
quantum interface between light and matter.