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تسجيل مستخدم جديدNanocavity optomechanical torque magnetometry and radiofrequency susceptometry
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Nanophotonic optomechanical devices allow observation of nanoscale vibrations with sensitivity that has dramatically advanced metrology of nanomechanical structures [1-9] and has the potential to impact studies of nanoscale physical systems in a similar manner [10, 11]. Here we demonstrate this potential with a nanophotonic optomechanical torque magnetometer and radiofrequency (RF) magnetic susceptometer. Exquisite readout sensitivity provided by a nanocavity integrated within a torsional nanomechanical resonator enables observations of the unique net magnetization and RF-driven responses of single mesoscopic magnetic structures in ambient conditions. The magnetic moment resolution is sufficient for observation of Barkhausen steps in the magnetic hysteresis of a lithographically patterned permalloy island [12]. In addition, significantly enhanced RF susceptibility is found over narrow field ranges and attributed to thermally assisted driven hopping of a magnetic vortex core between neighboring pinning sites [13]. The on-chip magneto-susceptometer scheme offers a promising path to powerful integrated cavity optomechanical devices for quantitative characterization of magnetic micro- and nanosystems in science and technology.
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Dissipative and dispersive optomechanical couplings are experimentally observed in a photonic crystal split-beam nanocavity optimized for detecting nanoscale sources of torque. Dissipative coupling of up to approximately $500$ MHz/nm and dispersive c
oupling of $2$ GHz/nm enable measurements of sub-pg torsional and cantilever-like mechanical resonances with a thermally-limited torque detection sensitivity of 1.2$times 10^{-20} text{N} , text{m}/sqrt{text{Hz}}$ in ambient conditions and 1.3$times 10^{-21} text{N} , text{m}/sqrt{text{Hz}}$ in low vacuum. Interference between optomechanical coupling mechanisms is observed to enhance detection sensitivity and generate a mechanical-mode-dependent optomechanical wavelength response.
Tunable evanescent coupling is used to modify the optomechanical interactions within a split-beam photonic crystal nanocavity. An optical fiber taper probe is used to renormalize the optical nanocavity field and introduce a dissipative optomechanical
coupling channel, reconfiguring and enhancing coupling between the optical and mechanical resonances of the device. Positioning of the fiber taper allows preferential coupling to specific mechanical modes and provides a mechanism for tuning the optomechanical interaction between dissipative and dispersive coupling regimes.
Magnetic torque is used to actuate nano-torsional resonators, which are fabricated by focused-ion-beam milling of permalloy coated silicon nitride membranes. Optical interferometry is used to measure the mechanical response of two torsion modes at re
sonance, which is proportional to the magnetization vector of the nanomagnetic volume. By varying the bias magnetic field, the magnetic behavior can be measured with excellent sensitivity ($approx 10^8 mu_B$) for single magnetic elements.
Recent progress in optomechanical systems may soon allow the realization of optomechanical arrays, i.e. periodic arrangements of interacting optical and vibrational modes. We show that photons and phonons on a honeycomb lattice will produce an optica
lly tunable Dirac-type band structure. Transport in such a system can exhibit transmission through an optically created barrier, similar to Klein tunneling, but with interconversion between light and sound. In addition, edge states at the sample boundaries are dispersive and enable controlled propagation of photon-phonon polaritons.
We demonstrate the integration of a mesoscopic ferromagnetic needle with a cavity optomechanical torsional resonator, and its use for quantitative determination of the needles magnetic properties, as well as amplification and cooling of the resonator
motion. With this system we measure torques as small as 32 zNm, corresponding to sensing an external magnetic field of 0.12 A/m (150 nT). Furthermore, we are able to extract the magnetization (1710 kA/m) of the magnetic sample, not known a priori, demonstrating this systems potential for studies of nanomagnetism. Finally, we show that we can magnetically drive the torsional resonator into regenerative oscillations, and dampen its mechanical mode temperature from room temperature to 11.6 K, without sacrificing torque sensitivity.
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