**The Photonic Forces group studies light-matter interactions, enhanced by confining photons to very small length scales for appreciable times. A strong focus is the coupling between light and motion in nano-optomechanical systems. Optical and acoustic degrees of freedom, both confined on the nanoscale in tiny optical cavities and vibrating mechanical structures, can strongly interact through radiation pressure forces. This allows extremely precise sensors, new photonic functionality, and control over the motional quantum state of a ‘macroscopic’ object.**

## Quantum measurement and control of mechanical motion

The intimate connection between precise measurements and control over the quantum state of a system is reflected in the notion that a strong measurement can directly affect a system by projecting it in an eigenstate. We study nanophotonic optomechanical systems that can serve as extremely sensitive and fast sensors of mechanical displacement. Using such displacement measurements, we aim to precisely control the quantum state of small mechanical objects.

- R. Leijssen and E. Verhagen,
*Strong optomechanical interactions in a sliced photonic crystal nanobeam*,**Sci. Rep. 5**, 15794, (SI), arXiv:1505.00324 (2015) - R. Leijssen, G. R. La Gala, L. Freisem, J. T. Muhonen, and E. Verhagen,
*Nonlinear cavity optomechanics with nanomechanical thermal fluctuations,***Nature Commun. 8**, 16024 (2017), (SI), arXiv:1612.08072 (2016)

## Optomechanical nonreciprocity

We study the breaking of Lorentz reciprocity, which stipulates that the transmission through a system is the same when the position of source and detector are interchanged. We exploit optomechanical interactions, which effectively break time-reversal symmetry for light. *Collaboration: Andrea Alù (UT Austin)*

- F. Ruesink, J. Mathew, M.-A. Miri, A. Alù, and E. Verhagen,
*Optical circulation in a multimode optomechanical resonator,***arXiv:1708.07792** - F. Ruesink, M. A. Miri, A. Alù, and E. Verhagen,
*Nonreciprocity and magnetic-free isolation based on optomechanical interactions,***Nature Commun. 7**, 13662 (2016), (SI) - M.-A. Miri, F. Ruesink, E. Verhagen, and A. Alù,
*Optical non-reciprocity based on optomechanical interactions,***Phys. Rev. Applied**, in press (2017), arXiv:1612.07375. - M.-A. Miri, E. Verhagen, and A. Alù,
*Optomechanically-induced spontaneous symmetry breaking,***Phys. Rev. A 95**, 053822 (2017)

## Plasmomechanics

The strength of radiation pressure forces scales inversely with the scale to which photons are confined. Ultimately strong optomechanical interactions are therefore enabled in plasmonic resonators, which allow squeezing light waves in deeply subwavelength dimensions. We investigate the use of such systems for broadband, practical nano-optomechanical sensors, reconfigurable photonic devices, and electro-optic conversion. *Collaborations: Albert Polman and Tobias Kippenberg (EPFL)*

- R. Thijssen, T. J. Kippenberg, A. Polman, and E. Verhagen,
*Plasmomechanical resonators based on dimer nanoantennas*,**Nano Lett. 15**, 3971 (2015), (SI) - A. Fratalocchi et al.,
*Nano-optics gets practical*,**Nature Nanotech. 10**, 11 (2015) - R. Thijssen, T. J. Kippenberg, A. Polman, and E. Verhagen,
*Parallel transduction of nanomechanical motion using plasmonic resonators*,**ACS Photon. 1**, 1181 (2014) - R. Thijssen, E. Verhagen, T. J. Kippenberg, and A. Polman,
*Plasmon nanomechanical coupling for nanoscale transduction*,**Nano Lett. 13**, 3293 (2013)

## Optical interactions in nanophotonic systems

We try to understand nanophotonic functionality such as emission enhancement, sensing, imaging, and polarization manipulation can be understood in terms of the system’s resonant eigenmodes. We study how concepts such as energy conservation, reciprocity, and dissipation put fundamental bounds on functionality. In this context, we study hybrid plasmonic-photonic resonators and strongly chiral structures. *Collaborations: Femius Koenderink, Kobus Kuipers*

- N. Parappurath, F. Alpeggiani, L. Kuipers, and E. Verhagen,
*The origin and limit of asymmetric transmission in chiral resonators*,**ACS Photonics 4**, 884 (2017) - F. Alpeggiani, P. Nikhil, E. Verhagen, and L. Kuipers,
*Quasinormal-mode expansion of the scattering matrix,***Phys Rev. X 7**, 0214035 (2017)*,*arXiv:1609.03902 (2016) - H. M. Doeleman, E. Verhagen, and A. F. Koenderink,
*Antenna-cavity hybrids: matching polar opposites for Purcell enhancements at any linewidth*,**ACS Photonics 3**, 1943 (2016), arXiv:1605.04181 (2016) - F. Ruesink, H. M. Doeleman, R. Hendrikx, A. F. Koenderink, and E. Verhagen,
*Perturbing open cavities: Anomalous resonance frequency shifts in a hybrid cavity-nanoantenna system*,**Phys. Rev. Lett. 115**, 203904 (2015), (SI), arXiv:1508.02638 (2015)

## Active optomechanics

We investigate the advanced control over light, matter, and motion that can be achieved in tripartite systems where optical and mechanical modes are coupled to quantum emitters. *Collaboration: Andrea Fiore (TU/e)*

- M. Cotrufo, A. Fiore, and E. Verhagen,
*Coherent Atom-Phonon Interaction through Mode Field Coupling in Hybrid Optomechanical Systems*,**Phys. Rev. Lett. 118**, 133603 (2017),**arXiv:1610.05153**(2016)

# Past research projects

## Optical cooling and control of mechanical resonators in the quantum regime

*Laboratory of Photonics and Quantum Measurement, EPFL*

- E. Verhagen, S. Deléglise, S. Weis, A. Schliesser, and T. J. Kippenberg,
*Quantum-coherent coupling of a mechanical oscillator to an optical cavity mode*, (SI),**Nature 482**, 63 (2012)

## Negative-index metamaterials based on plasmonic waveguides

*AMOLF (www.erbium.nl)*

- R. Maas, E. Verhagen, J. Parsons, and A. Polman,
*Negative refractive index and higher-order harmonics in layered metallodielectric optical metamaterial**,***ACS Photon. 1**, 670 (2014) - E. Verhagen, R. de Waele, L. Kuipers, and A. Polman,
*Three-dimensional negative index of refraction at optical frequencies by coupling plasmonic waveguides*,**Phys. Rev. Lett. 105**, 223901 (2010) - J. A. Dionne, E. Verhagen, A. Polman, and H. A. Atwater,
*Are negative index materials achievable with surface plasmon waveguides? A case study of three plasmonic geometries*,**Opt. Express 16**, 21793 (2008)

## Subwavelength nanofocusing of light with surface plasmons

*AMOLF (www.erbium.nl)*

- E. Verhagen, L. Kuipers, and A. Polman,
*Plasmonic nanofocusing in a dielectric wedge*,**Nano Lett. 10**, 3665 (2010) - E. Verhagen, M. Spasenović, A. Polman, and L. Kuipers,
*Nanowire plasmon excitation by adiabatic mode transformation*,**Phys. Rev. Lett. 102**, 203904 (2009) - E. Verhagen, A. Polman, and L. Kuipers,
*Nanofocusing in laterally tapered plasmonic waveguides*,**Opt. Express 16**, 45 (2008) - E. Verhagen, J. A. Dionne, L. Kuipers, H. A. Atwater, and A. Polman,
*Near-field visualization of strongly confined surface plasmon polaritons in metal-insulator-metal waveguides*,**Nano Lett. 8**, 2925 (2008)

**Enhancing absorption and emission with plasmonic resonators**

*AMOLF (www.erbium.nl)*

- E. J. A. Kroekenstoel, E. Verhagen, R. J. Walters, L. Kuipers, and A. Polman,
*Enhanced spontaneous emission rate in annular plasmonic nanocavities*,**Appl. Phys. Lett. 95**, 263106 (2009) - E. Verhagen, L. Kuipers, and A. Polman,
*Field enhancement in metallic subwavelength aperture arrays probed by erbium upconversion luminescence*,**Opt. Express 17**, 14586 (2009) - E. Verhagen, L. Kuipers, and A. Polman,
*Enhanced nonlinear optical effects with a tapered plasmonic waveguide*,**Nano Lett. 7**, 334 (2007)