Discovery Early Career Researcher Award (DECRA) ’22-’25!

I was awarded a highly competitive Discovery Early Career Researcher Award (DECRA) by the Australian Research Council!

The project, set to begin in late 2022 and last for 3 years, will be focused on developing quantum acoustic devices and protocols for quantum communication, novel acoustic sources, and sensing.

Probing the optical response of nanoantennas by vortex electron beams

A new result from a long-standing collaboration with my colleagues from Donostia-San Sebastian: Andrea Konecna (now at Brno University of Technology in Czech Republic), Rainer Hillenbrand, and Javier Aizpurua: in arXiv:2111.08810 we looked at the possiblity of near-field probing of electric and magnetic resonant modes in high-refractive-index nanoantennas with focused electron beams.

Electron microscopy forms a versatile set of tools for interrogating the physical, and chemical properties of nanosystems. In particular, in Electron Energy Loss Spectroscopy (EELS), electron beams are used as broadband sources of electromagnetic waves to map out the optical response of the surroundings (see Fig. 1(a)) – specifically, the electric component of the Local Density of States (e-LDOS).

Over the last decade, the ultra-high spatial resolution offered by EELS was complemented by increasing its spectral resolution, and efficient coupling to electron‑beam‑forming optics [Phys. Rev. Lett. 126, 123901 (2021)]. Another recent innovation in electron microscopy was the introduction of Vortex Electron Beams (VEBs) made up of electrons with large Orbital Angular Momentum [Nature 467, 301 (2010); Rev. Mod. Phys. 89, 035004 (2017)]. In VEBs, the circulating electrons create an effective magnetic current Jm, which can probe the magnetic LDOS, complementing the capabilities of the standard EELS (see Fig. 1(b)).

In this work we introduce a full quantum‑mechanical description of the magnetic EELS. This treatment allows us to account for the considerable spatial extension of the electrons, or the interference between the electric and magnetic currents [Phys. Rev. Lett. 113, 066102 (2014); Opt. Express 20, 15024 (2012)]. We then identify the semi‑classical limit of this problem to build a complete analogy with the EELS technique. Finally, we show how the magnetic EELS can interrogate the magnetic response of several 2D and 3D systems of interest in nanophotonics: dielectric nanoantennas, waveguides, and simple chiral structures.

Addressing picosecond and noisy Brillouin scattering

A few students-led projects investigating the effects of noise and (very) short pulse lengths finally bore fruits, with 3 papers on SBS published:


In Noise and pulse dynamics in backward stimulated Brillouin scattering Optics Express 29 (3), 3132-3146 (2021), and Numerical simulation of noise in pulsed Brillouin scattering J. Opt. Soc. Am. B 38 (8), 2343-2352 (2021), we (in a collaboration led by the University of Technology Sydney) considered the general problem of thermal and laser phase noise in SBS, and devised analytical and numerical methods to calculate how they impact the resulting signal.


In Picosecond acoustic dynamics in stimulated Brillouin scattering Optics Letters 46 (12), 2972-2975 (2021), we (in a collaboration with the University of Technology Sydney and Max-Planck Institute for Light) analyzed the limits of SBS induced by optical pulses of length comparable to the period of acoustic oscillations. We found that when two short optical pulses collide in a waveguide, they can excite an acoustic wave with a well-defined momentum, but no frequency info i.e. no hint on which way to propagate!

Intensity correlations in optomechanics in Quantum Science and Technology

UPDATE (13/6/2021): The paper’s now published in Quantum Science and Technology 6, 034005 (2021) https://doi.org/10.1088/2058-9565/abe569.

Measuring intensity correlation (g(2)) of light emitted from a quantum system is Quantum Optics 101.

But what if you want to measure intensity correlations within a specific spectral window? Say, to consider correlations between particular transitions within your quantum system?

And what if that quantum system was a nontrivial and nonlinear one, like an optomechanical cavity, which can exhibit both optical Kerr nonlinearity and mutli-phonon transitions?

We try to answer, or at least approach all of this questions in the new manuscript: “Frequency-resolved photon correlations in cavity optomechanics”, arXiv:2009.06216 (2020), co-authored with people who taught me everything I know about classical and quantum nanooptics – Ruben Esteban, Javier Aizpurua, Geza Giedke and Alejandro Gonzalez-Tudela.

“Acoustic diamond resonators with ultra-small mode volumes” in Physical Review Research!

New manuscript on (deeply!) subwavelength acoustic GHz cavities for C>1 coupling with NVs with@magneticlemur and @cg_poulton is finally published by Physical Review Research (Phys. Rev. Research 2, 033153 (2020))! It is also available on arXiv arxiv.org/abs/2003.01834).

In this project we wanted to learn if one can acoustic mode into a subwavelength cavity, as we would in plasmonics. Or, recently, dielectric PC cavities – check these gems out here: advances.sciencemag.org/content/4/8/ea (Weiss group @VandyPhysics),journals.aps.org/prl/abstract/1 (@Dirk_Englund group). Inspired by these ideas, and the late-night reading of Landau&Lifschitz we played around with an acoustic analogue of the lightning rod effect. Wrapping it into a phononic crystal, we found modes with non-resonant reduction of mode volumes towards 1e-4 lambda^3!

Putting an NV in the centre of the structure (check out this awesome review from A. Jayich group @UCSBPhysics: iopscience.iop.org/article/10.108), we arrived as > 1 MHz orbit-phonon couplings, and cooperativities > 1. We also compare our results to an awesome (and underplayed?) result on resonant localization in the flapping modes highlighted by Meesala et al. from @MeteAtature and Loncar lab @harvardphysics journals.aps.org/prb/abstract/1

What are the limits of this effect? Are there other, more efficient mechanisms for non-resonant localization? How does Veff scale against the Q of acoustic resonators? I’m eager to find out, and will keep you posted.

“ARRAW: Anti-resonant reflecting acoustic waveguides” in New Journal of Physics!

Our struggles with designing new optoacoustic waveguides continue! Our draft, previously published here arxiv:1909.01632, is now published in New Journal of Physics as an open-access publication (click here for the pdf). 

Fig1_2

After developing a blueprint for suspended mid-IR waveguide for forward Brillouin scattering, we look to we introduce a new type of optoacoustic waveguides, dubbed ARRAWs (Anti‑Resonant Reflecting Acoustic Waveguides), which implement acoustic guidance in multi-layer waveguides planar and cylindrical by engineering anti-reflective cladding layers that suppress the dissipation of acoustic waves.

This principle was previously embraced in the optical domain and led to the development of the Anti-Resonant Reflecting Optical Waveguides (ARROWs), which are now widely used in biomedical photonic devices.

This work is prepared in collaboration with Matthew O’Brien – brilliant student once at MQ, now at UNSW, Mike Steel at MQ and Chris Poulton at UTS.

Resonant Molecular Optomechanics in PRA!

An important development on the front of Molecular Optomechanics (MO)!

The initial proposals for MO coming from the groups of Kippenberg and Galland and Aizpurua were introduced to describe off-resonant Raman scattering from molecules in plasmonic cavities. The keyword here is off-resonant, meaning that these formalisms did not consider the effect of populating excited electronic levels. The natural extension of this formalism towards resonant Raman scattering (RRS) has now been put forward in the paper entitled “Quantum description of surface-enhanced resonant Raman scattering within a hybrid-optomechanical model” published in Physical Review A.

This work was led by the former PhD student from the group in San Sebastian, now a postdoc at Harvard – Tomas Neuman, and co-authored by Ikerbasque researchers Geza Giedke and Ruben Esteban, Theory of Nanophotonics Group leader Javier Aizpurua and me.

serrs

Suspended mid-IR waveguides for SBS in “Optics Express”

website_suspendedOur manuscript on novel design of mid-IR silicon waveguides for Brillouin scattering was just published in Optics Express (open access)! In this work we merge ideas from linear physics of mid-IR waveguides developed in the research groups of our co-authors – Profs. Goran Mashanovich and Graham Reed from The University of Southampton (click here for one of their reports), with the some phonon bandgap engineering to design novel waveguides operating in mid-IR (which is hard and attractive!), and exhibiting strong SBS gain.

I’m off to visit Southampton in a month, to figure out where to take this work next!

“Elastic Purcell Effect” in PRL (Editors’ Suggestion)!

In collaboration with Luke Helt, Chris Poulton and Michael Steel we have recently submitted our new manuscript on the elastic analogue of the electromagnetic Purcell factor for review. It has been finally published in Physical Review Letters, and highlighted as an Editors’ Suggestion. You can either read it on the PRL website, or access the arXiv version for free.

In this manuscript we explore a possiblewebsite3 analogue of the familiar electromagnetic concept – modification of the energy dissipation rate from a localized, dipolar source. In our study, the source in given by a localized harmonic force, and the modification of its radiation is governed by an elastic nanoantenna – a small spherical particle positioned near the emitter, and embedded in a different elastic material. We provide a theoretical framework for identifying the quasi-normal modes of the structure, demonstrate the effects in an exemplary system, and discuss the possibility of using this effect for engineering the rates of nonlinear, phonon-mediated optical effects.

New paper on Molecular Optomechanics in PRX!

Our paper Pulsed Molecular Optomechanics in Plasmonic Nanocavities: From Nonlinear Vibrational Instabilities to Bond-Breaking has just been published in Physical Review X (Open Access)!

It’s a part of our effort to verify the predictions of the optomechanical picture of Raman Scattering from molecules, which was first proposed by researchers from EPFL, and further developed in my former group, headed by Javier Aizpurua in San Sebastian in Basque Country, in collaboration with Geza Giedke and Alejandro Gonzalez-Tudela.

The paper reports and discusses nonlinearities observed in Raman scattering from molecules positioned in well-controlled plasmonic nanosystems, which have been extensively studied by the research groups of Jeremy Baumberg at Cambridge University. While these systems are rather easy to destroy by a strong continuous laser illumination, Anna Lombardi, the lead author of the paper, found that one can instead use picosecond pulses of a much more intense laser source to stimulate the vibrations of the molecules.

Furthermore, she observed that the amount of light scattered off the molecules in the Raman process does not scale linearly with the peak intensity of the lasers! Instead, in accordance with the predictions of the Molecular Optomechanical, the Raman scattering becomes superlinear after a certain threshold.

Upconverting nanocrystals coupled to plasmons in MDPI Materials!

Our manuscript “Spectral Selectivity of Plasmonic Interactions between Individual Up-Converting Nanocrystals and Spherical Gold Nanoparticles”, describing experimental and theoretical analysis of the effect of plasmonic nanoparticles on two independent relaxation channels of nanocrystals, has been published in MPDI Materials. The experiments were conducted in Optics of Hybrid Nanostructures labs at Nicolaus Copernicus University in Torun, Poland.