Tue, Oct. 04th 2016, 15:00-16:00
Bât. K, Salle R. Lemaire (K223), Institut Néel
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Recent advances in optomechanics have led to outstanding discoveries. For instance, a macroscopic object (a mechanical resonator) has been cooled and measured in its quantum ground state of motion [1-2]. This technological and scientific challenge uses mechanical elements to measure weak forces and explore the interface between classical and quantum worlds. In parallel, atomically thin  (ex: graphene, transition metal dichalcogenides (TMD) MoS2, WSe2) have been integrated in various electronic, optical and mechanical devices. These objects are fascinating for both fundamental (electronic properties, cristal-molecule interface…) and applied aspects (soft electrodes, photo-detectors…). By combining these two domains, we envision optomechanics experiments in which the low dimensionality of the mechanical element will be an advantage (high frequency, ultra-low mass, enhanced optomechanical coupling) and an originality (electronic confinement, tunable light-matter interaction).
In this talk I will first show how to detect motion and mechanical stress within a graphitic resonator using Raman spectroscopy . Such detection scheme, based on the increase of mechanical stress at resonance, link the mechanical motion of the resonator, to a shift in energy of Raman scattered photons, and represents an original scheme for optomechanical coupling.
Then, I will introduce a new type of hybrid system, consisting of an on-chip graphene NEMS suspended a few tens of nanometers above nitrogen-vacancy centres (NVCs), which are stable single-photon emitters embedded in nanodiamonds . The optomechanical coupling between the graphene displacement and the NVC emission is based on near-field dipole–dipole interaction, making it suitable for nanoscale devices. These achievements hold promise for selective control of emitter arrays on-chip, optical spectroscopy of individual nano-objects, integrated optomechanical information processing and open new avenues towards quantum optomechanics.
Finally, I will show how we recently use an ultrasensitive optical readout of monolayer TMD resonators to reveal their mechanical properties at cryogenic temperatures.
We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 47000 at 4K, thus surpassing quality factor of monolayer graphene resonators with similar surface areas . Optomechanics with atomically thin 2D semiconducting resonators remains an unexplored field of physics, which is interested in light-matter interactions in these systems and their nanomechanical response (ultra-cold resonators, weak forces probes). It is also a precious tool to better understand thermalization and mechanical damping processes within nano-objects. This type of experiments suggests the optical control of mechanical resonator vibrations and the calibration of optomechanical interaction at the single photon scale.
 Chan, J. et al. Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature 478, 89–92 (2011).
 Teufel, J. D. et al. Sideband Cooling Micromechanical Motion to the Quantum Ground State. Nature 475, 13 (2011).
 Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666–9 (2004).
 Reserbat-Plantey, A., Marty, L., Arcizet, O., Bendiab, N. & Bouchiat, V. A local optical probe for measuring motion and stress in a nanoelectromechanical system. Nature Nanotechnology. 7, 151–5 (2012).
 Reserbat-plantey, A. et al. Electro-mechanical control of an optical emitter using graphene. Nature Communications 7, 10218, (2016).
 Bunch, J. S. et al. Electromechanical resonators from graphene sheets. Science 315, 490–3 (2007).