Matteo Menotti

Energy correlations of photon pairs generated by a silicon microring resonator probed by Stimulated Four Wave Mixing

Compact silicon integrated devices, such as micro-ring resonators, have recently been demonstrated as efficient sources of quantum correlated photon pairs. The mass production of integrated devices demands the implementation of fast and reliable techniques to monitor the device performances. In the case of time-energy correlations, this is particularly challenging, as it requires high spectral resolution that is not currently achievable in coincidence measurements. Here we reconstruct the joint spectral density of photons pairs generated by spontaneous four-wave mixing in a silicon ring resonator by studying the corresponding stimulated process, namely stimulated four wave mixing. We show that this approach, featuring high spectral resolution and short measurement times, allows one to discriminate between nearly-uncorrelated and highly-correlated photon pairs.

Optical resonators based on Bloch surface waves

A few recent works suggest the possibility of controlling light propagation at the interface of periodic multilayers supporting Bloch surface waves (BSWs), but optical resonators based on BSWs are yet to be demonstrated. Here we discuss the feasibility of exploiting guided BSWs in a ring resonator configuration. In particular, we investigate the main issues related to the design of these structures, and we discuss their limitations in terms of quality factors and dimensions. We believe these results might be useful for the development of a complete BSW-based platform for applications ranging from optical sensing to the study of the light–matter interaction in micro and nano structures.

Truly unentangled photon pairs without spectral filtering

We demonstrate that an integrated silicon microring resonator is capable of efficiently producing photon pairs that are completely unentangled; such pairs are a key component of heralded single-photon sources. A dual-channel interferometric coupling scheme can be used to independently tune the quality factors associated with the pump and signal and idler modes, yielding a biphoton wavefunction with a Schmidt number arbitrarily close to unity. This will permit the generation of heralded single-photon states with unit purity.

Low-power four-wave mixing in porous silicon microring resonators

We report the measurement of low-power continuous-wave four-wave mixing in porous silicon microring resonators operating in the 1550 nm telecom band. Resonantly enhanced stimulated four-wave mixing has been measured in rings with 25 μm radius and quality factor around 5000 for pump powers as low as a few hundreds of microwatts. A waveguide nonlinear parameter γ = 20 W–1 m−1 has been determined. These results suggest further research on porous silicon for low-power nonlinear optics, possibly taking advantage of its tunable porosity.

Generation of energy-entangled W states

Tripartite entangled states, such as Greenberger-Horne-Zeilinger (GHZ) and W states, are appealing for tests of fundamental aspects of quantum mechanics, as well as for implementations of quantum communication protocols. While the information is typically encoded in the polarization or path of the photons, we propose a feasible scheme to generate W states that are entangled in the energy degree of freedom. This is achieved by propagating photon pairs generated by parametric fluorescence in a linear optical circuit and post-selecting on the output channels. Such source can be easily integrated, profiting from high stability and a compact footprint. We also present a simple protocol to characterize the generated tripartite state, which is based on the reduced density matrix approach. Unexpectedly, although we rely on the energy degree of freedom, the full state tomography does not require any frequency conversion.

Guided bloch long-range surface plasmon polaritons

A few years ago, Konopsky showed that a one dimensional photonic crystal structure can be used on one side of a thin metal layer to mimic the optical properties of the material on the other side. Inspired by this approach and motivated by using LRSPP waveguides for biosensing, we propose and realized a thin metal stripe on a truncated SiO2/Ta2O5 multilayer stack to support a fully guided LRSPPs. These results further the attraction of metal stripe waveguides and LRSPPs for biosensing applications and more in general for LRSPP integrated optics.

Generation and characterization of energy-entangled W states

We demonstrate the generation of W states entangled in the energy degree of freedom. Using a reduced density matrix approach, these states are characterized without the need for frequency conversion.