ERC Grant


Ewold was awarded a Starting Grant of 1.5 million euros from the European Research Council (ERC). The ERC uses the Starting Grants to support talented scientists in the early stages of their career in pursuing ground-breaking projects for a duration of five years.

We will use the grant to study how mechanical vibrations (‘sound’) can be transported along nanostructured surfaces. Light can control these mechanical vibrations through optical ‘radiation pressure’ forces. The prospective result is remarkable; the sound waves will start behaving in ways not found in nature. The force of light will make the sound waves move in only one direction, it will transport them unhindered around arbitrary corners, and let the waves interact with each other.

In particular, the project aims to study the unique behavior of mechanical motion that is normally associated only with electrons in so-called ‘topological insulators’: materials with remarkable electronic properties whose description was awarded the Nobel prize in physics last year. Creating analogous effects for sound at the nanoscale could lead to fundamentally new opportunities in technology, for example in sensing and information processing.

Professor appointment in Eindhoven

I’m very honoured to have been appointed as professor at Eindhoven University of Technology (TU/e) as of July 1. I’ve accepted a part-time position as professor of Nano-optomechanics within the Photonics and Semiconductor Nanophysics (PSN) group in the Department of Applied Physics. Of course I continue to lead the Photonic Forces group at AMTUE_benoeming_bloemenOLF. This appointment further boosts the very nice collaboration between my group and that of prof. Andrea Fiore, and strengthens the links between nanophotonics research at AMOLF and TU/e. Thank you very much to Andrea, as well as prof. Paul Koenraad (PSN), prof. Gerrit Kroesen (dean of Applied Physics), and the whole PSN group, for welcoming me so warmly! I’m looking forward to working with you. — Ewold

See announcements of TU/e

Nanobeams rock out

nonlinearbeam_smallIn a new paper in Nature Communications, we present photonic crystal nanobeams that exhibit extremely strong coupling between light and motion. As a result, the optomechanical interaction is no longer linear, even for the tiny thermal mechanical fluctuations of the beams. This has many important consequences, including the fact that the produced light signals are distorted, similar to how an overdriven guitar amplifier converts the clean motion of a guitar string into a screaming rock sound. See also our press release.

New light on eigenmodes and scattering. And on chirality and reciprocity, while we’re at it.

Eigenmodes are powerful things in physics – there’s a reason we learn so much about them early on in BSc studies. They tell us how a system likes to behave if it’s left alone, decoupled from the outside world. But physical systems are never decoupled fully from their surroundings. Optical systems (i.e., structured polarizable matter), for example, can be driven by light waves coming in from afar, and in turn radiate waves into the space surrounding them – a response that is captured in the scattering matrix of a system. That scattering matrix is a powerful thing too: For any given incoming field, it tells us what waves we could expect to come out of the system. For example, it can tell us how a chiral optical system can change the polarization of light transmitted through it.

It was in trying to understand the chiral response of a complex photonic crystal slab that we stumbled on a very general problem. We wondered if we could predict the full scattering matrix of a system, if we happened to know all of its eigenmodes? Even though in recent years it has become clear how we can talk about eigenmodes in systems that are not decoupled from the rest of the world (by talking about complex ‘quasi-normal modes’ instead), the answer to that question was not known, except for very special cases.

In a publication in Physical Review X, we now present the solution to that general problem, showing that one can accurately predict and understand the response of any optical system from the fields of its eigenmodes at some distance away from the structure. We think it’s a hugely powerful method, that can actually be much faster than brute-force alternatives to calculate scattering matrices of practically any nanophotonic system one can think of. And it allowed us to solve the problem that started it all: to understand just how ‘chiral’ a thin photonic crystal slab can be. In a paper in ACS Photonics, we show that such systems can show large asymmetric transmission of polarized light, that is connected to the polarization of its eigenmodes. And we reveal that there is a fundamental limit on asymmetric transmission, that is linked to the principle of reciprocity. Using our theory, we show how one can design chiral photonic crystals that have nearly ideal asymmetry: blocking light of a certain polarization in one direction, while allowing it through in the other.

Congratulations to Nikhil Parappurath and Filippo Alpeggiani for shedding so much new light!

How to make an atom emit sound?

With Michele Cotrufo and Andrea Fiore from TU Eindhoven, we published new theory work in Physical Review Letters. We present a new way to realize a strong and controllable interaction between a natural (or artificial) atom and a macroscopic mechanical resonator. This has been a long-sought aim in quantum physics, as it would allow using the nonlinearities of the atom to  create nonclassical states (e.g., superposition states) of a macroscopic object, which are of extreme interest for fundamental studies in quantum mechanics. We show how such an interaction can be readily obtained via an intermediate light field, an effect that we termed “mode field coupling”: if the mechanical displacement modulates the light amplitude at the atom’s position, a coherent interaction between the atom and the mechanical resonator is obtained. Importantly, the coupling rate scales with the light amplitude. Therefore, by simply modulating an external optical pumping, it is possible to control in time and to enhance at will the coupling between the atom and the mechanical resonator. Arbitrary mechanical states can be created with this method, by transferring the excitation from the atom to the resonator with properly timed optical pulses. Even accounting for realistic losses, the coupling rate of this interaction is strong enough to generate  several nonclassical mechanical states, including superposition states,  with large fidelities. The proposed optically-controlled atom-phonon interaction paves the way for future developments such as control of spontaneous phonon emission, creation of nonclassical states of motion and phonon lasing.

Coupling mechanical resonators and emitters

In our latest arXiv submission, we propose a new mechanism to create a coherent coupling between a macroscopic mechanical resonator to a two-level quantum emitter. The idea relies on a principle we term mode field coupling: mechanical deformation directly affects the Rabi rate with which an emitter couples to a cavity. This effect allows the emitter to emit phonons instead of photons, and can be surprisingly strong. This research is a direct collaboration with Michele Cotrufo and Andrea Fiore at TUE.