Andrea Marini
University of L'Aquila
Dr Marini achieved his PhD in Photonics in November 2011 at The University of Bath, United Kingdom. He led postdoctoral research at the Max Planck Institute for the Science of Light (2011-2014) in Erlangen, Germany, and at ICFO - The Institute of Photonic Sciences (2014-2017) in Castelldefels, Spain. In his career he has been awarded two Marie Curie Postdoctoral Fellowships and a ''Rita Levi Montalcini'' Assistant Professorship funded by the Italian Ministry of Education and Research. Since December 2017 he is Assistant Professor in Physics of Condensed Matter at The University of L'Aquila, Italy.
Parametric down-conversion (PDC) furnishes tunable sources of coherent radiation and generators of entangled photons and squeezed states of light. In traditional configurations, a nonlinear crystal with broken centrosymmetry and second-order nonlinearity sustains PDC. Since three-wave parametric coupling is intrinsically weak, one can achieve low oscillation thresholds only by doubly or triply resonant optical cavities. In addition, parametric effects are severely hampered by the destructive interference among the three waves propagating with different wavenumbers in the dispersive nonlinear medium because the momentum mismatch does not generally vanish. To avoid this highly detrimental effect, the use of phase-matching (PM) strategies is imperative.
Here, we show that emerging two-dimensional (2D) materials with high quadratic nonlinearity open unprecedented possibilities for tunable parametric micro-sources. Very remarkably, when illuminated with different visible and infrared waves, these novel 2D materials provide a negligible dispersive dephasing owing to their atomic-scale thickness. Due to the lack of destructive interference, 2D materials support PDC without any need of satisfying a PM condition. The most famous 2D material, graphene, is not the best candidate for PDC owing to the centrosymmetric structure. Recent years have witnessed the rise of transition metal dichalcogenides (TMDs) as promising photonic 2D materials. Bulk TMDs are semiconductors with an indirect bandgap, but the optical properties of their monolayer (ML) counterpart are characterized by a direct bandgap ranging from 1.55 eV to 1.9 eV. In addition, ML-TMDs have broken centrosymmetry and thus undergo second-order nonlinear processes.
We investigate PDC in microcavities embedding ML-TMDs; we find that the cavity design is extremely flexible if compared to standard parametric oscillators thanks to their phase-matching-free operation. We demonstrate that, at conventional infrared pump intensity, parametric oscillation occurs in wavelength-sized micro-cavities with ML-TMDs. We show that the output signal and idler frequencies can be engineered, tuned by the pump incidence angle, and modulated electrically by an external gate voltage.
Our results pave the way for new ultrafast tunable micron-sized sources of entangled photons, a key device underpinning any quantum protocol. Highly-miniaturized optical parametric oscillators may also be employed in lab-on-chip technologies for biophysics, environmental pollution detection and security.
Optics and transport on 2D materials , Nonlinear nano-optics , Strong light-matter interactions at the nanoscale
