Nanocavities for measuring torque-actuated motion Marcelo Wu A. Hryciw, B. Khanaliloo, M. Freeman, J. Davis Supervisor: Paul Barclay University of Calgary/NRC-NINT CLEO 2012 – CW1M.7 - May 9, 12:15pm

Optomechanical coupling Yale: M. Bagheri et al., Nature Nanotechnology (2011) Parameters: g om : optomechanical coupling rate [Hz/nm] Mechanical properties: Q m, f m, m eff Optical properties: Q o, f o, V o

Optomechanical coupling 1) Lausanne/Max-Plack-Institut: E. Gavartin et al., arXiv: v1(2011) 2) Max-Plack-Institut/CeNS/Lausanne: G. Anetsberger et al., Nature Physics (2009) 3) NIST/Maryland: K. Srinivasan et al., Nano Letters (2011) 4) Yale/Columbia: Z. Sun et al., Nano Letters (2012) 5) Caltech: M. Eichenfield et al., Nature Letters 462 (2009) 6) Caltech: M. Eichenfield et al., Nature Letters 459 (2009) 7) Caltech: A. Safavi-Naeini et al., APL (2010) 8) Columbia: Y. Li et al., Optics Express (2010) 9) Tokyo: M. Nomura, Optics Express (2012) m eff = fg~pg g om → 1THz/nm

Torsional actuation Interaction between magnetic moments and fields at the nanoscale: constant magnetic field: no force, only torque!

Torsional actuation UofA: J. Davis et al., APL (2010) Yale: A. C. Bleszynski-Jayich et al., Science (2009) Example systems: Nanomagnetic fluctuations Persistent current measurements

Torsional actuation Queensland: S. Forstner et al., PRL (2012) Optical readout

Torsional actuation Our proposal Sensitive readout of torque Monolithic integration

Photonic crystal nanobeam cavity 1D photonic crystal cavity See also: Harvard: M.W. McCutcheon and M. Lončar, Optics Express (2008) Caltech: J. Chan et al., Optics Express (2009) Caltech: M. Eichenfield et al., Optics Express (2009) Caltech: A. H. Safavi-Naeini et al., PRL (2012) Harvard: P. Deotare et al., APL (2009) HP Labs: P.E. Barlcay, Optics Express (2009) Small V o Small mass Overlaps mechanical and optical modes

Photonic crystal nanobeam cavity Small form factor Acceptor mode optical cavity High Q-factor ~ 10 6 Small mode volume < (λ/n Si ) 3

Near-field mechanical resonator Trade-off: g om vs Q o

Floating paddle cavity Overlap mechanical and optical modes

Floating paddle cavity See also: Yale and LMU: J.C. Sankey et al., Nature Physics (2010) Vienna: Vanner, Physical Review X (2011) No optomechanical coupling in linear regime Membrane in the middle: Second order coupling Odd mechanical modes

Optomechanical design Still want large linear g om Want large Q o and maintain small m eff Natural mechanical modes are odd Caltech: M. Eichenfield et al., Optics Express (2009) Linear g om Quadratic g om Quadratic g om Linear g om

Split-beam cavity Donor mode cavity with gap at the centre E o1 E o2 For a gap size, find the dimensions of first ellipse

Split-beam cavity Optimization of ellipses: maximizing mirror strength 1 γ by varying (R x,R y ) 1 Q. Quan and M. Lončar Opt. Express (2011) A. Yariv and P. Yeh, Oxford University Press (2006)  at E o1 band edge  at E o2 band edge Mid-gap   at E o1 band edge at cavity centre

Split-beam cavity Optical properties Q total : 1.1 x 10 6 Q x : 2.3 x 10 8 Q y : 5.9 x 10 6 Q z : 1.3 x 10 6

Split-beam cavity Mechanical modes m eff = 0.5~1.1 pg g om = 5~17 GHz/nm Flexible design

Summary Optimized optical cavity High Q ~ 10 6 Mechanical modes suitable for torsional actuation Low m eff (0.5~1.1 pg) Flexible designs Large linear g om (5~17 GHz/nm)

Future work Optomechanical design Analysis of torsional actuation Actuation to readout: sensitivity and noise analysis Fabrication and measurement