Metamaterials

*Metamaterials*
are artificially engineered materials that can alter the properties of
both wave-based and diffusion-based phenomena in a desired fashion. Such materials promise formidable advances
in a variety of fields, including optics, acoustics, elastodynamics, and heat transmission,
thanks to their ability to induce unconventional responses that cannot be replicated in nature (“invisibility cloaking,”
for instance).

Our research activities are focused on phenomenological aspects, modeling, design and possible applications to defense,
communications, and chemical and biological sensing.

Aperiodic order

The simplest conceivable form of “order” in nature is that associated with

*periodicity*.
However, the discovery of

“quasicrystals”
in solid-state physics has triggered a growing interest in the study of

*aperiodically ordered* structures in many branches of physics and engineering. Particularly inspiring in this context is the theory of

*aperiodic tilings*, i.e,
arrangements of polygonal shapes devoid of any translational symmetry and capable of covering a plane without overlaps or gaps.
Though aperiodic, these geometries can still exhibit long-range order and high-order
rotational symmetry not bound by the conventional crystallographic restrictions.

Our research activities encompass the theoretical understanding of aperiodic-order-induced wave phenomena (e.g., bandgap, resonances,
nonlocality), as well as the modeling, engineering and experimental characterization of aperiodically ordered structures and devices of interest
in a variety of applications, ranging from antenna arrays to particle accelerators.

Ray chaos

*Deterministic chaos*
is a multidisciplinary theory that studies
complex systems whose evolution is extremely sensitive to slight changes in initial conditions,
so that they exhibit apparently random or unpredictable behaviors.
This is nowadays recognized as a pervasive natural phenomenon of relevance in many fields of applied science and engineering, including electromagnetics. Under high-frequency/short-pulse conditions, the electromagnetic energy flow can be effectively described in terms of

*ray optics*. In certain deterministic environments, ray trajectories may become

*chaotic*, i.e., exponentially sensitive to tiny changes in the launch conditions.
Besides the inherent theoretical interest, ray chaos has strong impact in the design of reverberating enclosures, laser cavities, absorbers, and radar countermeasures.

Our research activities are focused on the study of ray-chaotic electromagnetic structures, both in

*closed* (“billiard” enclosures) and

*open* (“pinball” scatterers) configurations.

Gravitational interferometry

*Gravitational waves* are “ripples” of the space-time fabric generated by massive accelerating objects (e.g., neutron stars, black holes). Their existence, predicted by Einsten's theory of general relativity, was indirectly proved in 1974 by Hulse and Taylor by studying the decrease of the orbital period of a binary pulsar system (PSR 1913+16). However, their

*direct detection* has remained elusive for a long time, due to the extremely weak signal amplitude.
In 2016, the

Laser Intereferometer Gravitational wave Observatory
(LIGO)
announced the first

*direct detection* of a gravitational wave signal from the binary black hole coalescence, known as GW150914. This represents one of the most important discoveries in modern physics, and has opened a new window to understanding our universe.

Our research activities, within the framework of the

LIGO Scientific Collaboration, are focused on the reduction of the internal (mirror) thermal noise in the Fabry-Perot cavities of an interferometric detector, via the optimized design of the mirror coatings and of the laser-beam profile.