Controlling Mechanical Sensors with Light Research Program ● Optically-Controlled MEMS ● Force Sensing ● Quantum Transduction ● MEMS Materials Research McGill Optomechanics Lab Christoph Reinhardt, Simon Bernard Alexandre Bourassa, Xin Yuan Zhang Julian Self, Chris McNally Jack Sankey
Measuring Forces with Flexible Materials Grütter Lab: forces from individual atoms (McGill) Goal al: high-Q -Q & tunab able. Rugar Lab: non-contact forces from virus nuclei (IBM)
One Pursuit: Replace Mechanical Materials w/ Light Very weak restoring force from material Fabrication at McGill Very strong restoring force from light ● laser-tuned frequency ● laser-tuned damping ● optically supported disc predicted to ring for a month ~1 um 0.75 mm
Implications for Sensing High Mechanical Q = Better Force Sensor Grütter Lab: forces from individual atoms (McGill) Current technology ringdown wn ~ second nds Rugar Lab: non-contact forces from virus nuclei (IBM)
Quantum Properties of Massive Objects? ● Quantum state transfer and information transfer entanglement at a distance? ● Fundamental studies of quantum behavior in solid objects “superposition” photon Penrose: Gravity might ruin quantum superpositions of heavy objects. For me: For me: R. Penrose, Gen. Rel. Grav. 28 , 5, 581-600 (1996)
Encouraging Result: Optically Trapped Pendulum Kimble Group at Caltech: ● Optically trapped disc, Q ~ f 2 ● Mechanical modes mix, limiting Q ● Q x f ~ 10 11 (“low” initial Q) K.-K. Ni et. al. , PRL 108, 214302 (2012)
Solid Objects Controlled by Photons Most Devices: LIGO One goal: make solid objects kg behave quantum mechanically. ENS MIT g ENS Oregon cavity resonances Vienna Vienna μg Caltech UCSB (not photons) laser Laussane Frequency Yale (this talk) UMichigan NIST-JILA ng n ~ 0.4 Laussane-LMU n ~ 0.01 UCSB, Leiden Max Planck Mechanical Displacement Yale pg Caltech JILA, Caltech n ~ 0.9 nanotubes, NIST BEC's, atoms...
Optomechanical Systems Are Guitars: Same Physics Electric Field ~ Zero (i.e. “clamped”) Radiation Force Single Frequency: 200,000,000,000,000 Hz Speed of Light: 300,000,000 m/s String Motion ~ Zero (clamped) Single Frequency: 440 Hz Acoustic Force Speed of Sound: ~500 m/s
When the Input Frequency Matches the Cavity Frequency ~ micronewton ~ micronewton combined force of ~ weight of 10 grains of salt ~ weight of 10 grains of salt 1,000,000,000,000,000,000,000 ~ push a paper clip 1 mm in a few seconds (in space) ~ push a paper clip 1 mm in a few seconds (in space) photons striking the mirror each second ~milliwatt input (weak laser pointer) ~ 100 Watts circulating Energy Inside Cavity more light = more force a spring! (plus “wind”) less light = less force Mirror Position
Laser Engines Takes time for light to leak in and out (i.e. Radiation Force) Energy in the Cavity cavity light pumps mirror motion ∫ F dx work = Mirror Position
“Damping” for this Optical Spring Motion can be cooled to its quantum ground state Power takes time to ramp up and down Radiation Force mirror motion pumps cavity light “Laser Cooling” Mirror Position
Our Device: “Linear” and “Quadratic” Coupling quadratic ● Couple laser to TEM 00 cavity mode linear ● Cavity resonance frequencies vary antinode with membrane position optical node ● Can choose linear or quadratic optomechanical coupling ● Linear coupling within factor of 3 of maximum possible
At Yale: Laser Cooling in Cryogenic Environment free-space laser ● 50 nm thick membrane, 1.5 x 1.5 mm 2 , 261 kHz drumhead, Q = 5 Million ● System at 400 mK (~30,000 phonons) membrane 3 He fridge ● Free-space laser coupling ● Heterodyne readout of reflected light cavity motorized membrane mount
Test: Laser Cooling to Low Phonon Numbers ● “Raw” laser cooling from 30,000 to ~60- 80 phonons, limited by classical laser Unfiltered Cooling Laser ~30,000 phonons (i.e. 0.4K) with no lasers noise ● Filtered laser cooling to ~20 phonons sideband ratio ● Next: monolithic, vibration isolation, double-filtered laser, smaller membrane alternative fitting method (should achieve < 0.01 phonons*) Theory: Kjetil Børkje theory: unfiltered laser filter cavity laser theory: filtered laser now also commercially available
Quadratic Coupling: QND Phonon Readout ● Quadratic coupling: detuning measures quadratic displacement squared ● Enables nondemolition readout of phonon number state linear
Quadratic Coupling: QND Phonon Readout motionless Cavity Frequency average average average Membrane Position ● If cavity response is slow, it will time Wavefunction Membrane average the membrane's motion ● Each membrane quantum state has a different average cavity shift ground state two phonons one phonon ● Want: sharper curvature, more zero- point motion, ...
Quadratic Coupling: QND Phonon Readout ● Quadratic coupling: detuning measures quadratic displacement squared ● Enables nondemolition readout of phonon number state ● This coupling is too weak to measure mechanical energy quantization. (ground state motion ~ fm) cavity photons membrane phonons Totally symmetric coupling: ● cavity shift per phonon ● me mechan anical shift per photon (enh nhanc anced optical al trap ap)
Increasing Quadratic Readout Sensitivity ● Cavity supports many transverse quadratic optical modes ● Transverse modes cross each other
Avoided Crossings Generate Stronger Quadratic Coupling ● Membrane lifts degeneracies, couples modes membrane aligned ● Quadratic coupling > 100 x stronger ● Strong enough to resolve phonon shot noise of a 30 kHz/nm 2 driven membrane ● Coupling is highly tunable in situ QND 4.5 MHz/nm 2 membrane tilted 0.4 mrad Strong cav St avity laser cooling optical al trap ap!
Optomechanics Lab at McGill 6 mo months 12 mo months right now 200 Hz linewidth!? Tables here, please.
New Types of Devices and Theory SiN Fabrication (varied shapes, sizes, tethers, ...) Transfer matrix formalism Christoph Reinhardt
UHV Interferometer ● 2” platter ● 1.5” travel ● UHV ● Bakeable Technology stolen from Peter Grütter's lab (inside job): Yoichi Miyahara, Will Paul, Jeff Bates Design & Fabrication Alexandre Bourassa
Additional Directions Cryogenic System ● 100x fewer thermal phonons ● Higher mechanical quality (generally) Fiber Cavities ● compact, monolithic optomechanics ● no laser alignment required ● stronger coupling to smaller MEMS cleaved, coated optical fiber 250-micron membrane death ray Harris Lab
One Goal at McGill: Improved Mechanics COMSOL Mechanical Simulation Materials and Geometry ● improve untrapped Q x f ● Decrease optically-mediated mode coupling ● Create geometries useful for AFM Xinyuan Zhang
Another Goal: Stronger Per-Photon Impact MEEP Simulation (cross-section of 3D model) 99% reflective Solgaard group Incident light holey dielectric Normalized Transmission 99% reflective = 10 x more restoring force Julian Self Normalized Laser Frequency
Summary Optomechanics with a SiN Membrane ● laser cooling to ~20 phonons in a He-3 cryostat ● Strong, tunable nonlinear coupling for QND readout and trapping Building Stuff at McGill: ● Optically-Supported MEMS ● Force Sensing ● Hybrid quantum systems
McGill Optomechanics Group Graduate Students Christoph Reinhardt Simon Bernard Undergrads Alexandre Bourassa Xin Yuan Zhang Julian Self Perry Philippopoulos Chris McNally
Acknowledgments (Yale) Experiment Jack Harris (P.I.) Andrew Jayich Benjamin Zwickl Cheng Yang Donghun Lee Nathan Flowers-Jacobs Scott Hoch Woody Underwood Lily Childress Anna Kashkanova Andrei Petrenko Theory Steve Girvin (P.I.) Kjetil Børkje Andreas Nunnenkamp
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