Optical Back-action Research Articles

Optical back-action on the photothermal relaxation rate

Photothermal effects can alter the response of an optical cavity, for example, by inducing self-locking behavior or unstable anomalies. The consequences of these effects are often regarded as parasitic and generally cause limited operational performance of the cavity. Despite their importance, however, photothermal parameters are usually hard to characterize precisely. In this work, we use an optical cavity strongly coupled to photothermal effects to experimentally observe an optical back-action on the photothermal relaxation rate. This effect, reminiscent of the radiation-pressure-induced optical spring effect in cavity optomechanical systems, uses optical detuning as a fine control to change the photothermal relaxation process. The photothermal relaxation rate of the system can be accordingly modified by more than an order of magnitude. This approach offers an opportunity to obtain precise in situ estimations of the parameters of the cavity in a way that is compatible with a wide range of optical resonator platforms. Through this back-action effect, we are able to determine the natural photothermal relaxation rate and the effective thermal conductivity of cavity mirrors with unprecedented resolution.

Position and mode dependent optical detection back-action in cantilever beam resonators

Optical detection back-action in cantilever resonant or static detection presents a challenge when striving for state-of-the-art performance. The origin and possible routes for minimizing optical back-action have received little attention in literature. Here, we investigate the position and mode dependent optical back-action on cantilever beam resonators. A high power heating laser (100 µW) is scanned across a silicon nitride cantilever while its effect on the first three resonance modes is detected via a low-power readout laser (1 µW) positioned at the cantilever tip. We find that the measured effect of back-action is not only dependent on position but also the shape of the resonance mode. Relevant silicon nitride material parameters are extracted by fitting finite element (FE) simulations to the temperature-dependent frequency response of the first three modes. In a second round of simulations, using the extracted parameters, we successfully fit the FEM results with the measured mode and position dependent back-action. From the simulations, we can conclude that the observed frequency tuning is due to temperature induced changes in stress. Effects of changes in material properties and dimensions are negligible. Finally, different routes for minimizing the effect of this optical detection back-action are described, allowing further improvements of cantilever-based sensing in general.

Quantum feedback cooling of a mechanical oscillator using variational measurements: tweaking Heisenberg’s microscope

We revisit the problem of preparing a mechanical oscillator in the vicinity of its quantum-mechanical ground state by means of feedback cooling based on continuous optical detection of the oscillator position. In the parameter regime relevant to ground-state cooling, the optical back-action and imprecision noise set the bottleneck of achievable cooling and must be carefully balanced. This can be achieved by adapting the phase of the local oscillator in the homodyne detection realizing a so-called variational measurement. The trade-off between accurate position measurement and minimal disturbance can be understood in terms of Heisenberg’s microscope and becomes particularly relevant when the measurement and feedback processes happen to be fast within the quantum coherence time of the system to be cooled. This corresponds to the regime of large quantum cooperativity , which was achieved in recent experiments on feedback cooling. Our method provides a simple path to further pushing the limits of current state-of-the-art experiments in quantum optomechanics.

Photonic Cavity Synchronization of Nanomechanical Oscillators

Synchronization in oscillatory systems is a frequent natural phenomenon and is becoming an important concept in modern physics. Nanomechanical resonators are ideal systems for studying synchronization due to their controllable oscillation properties and engineerable nonlinearities. Here we demonstrate synchronization of two nanomechanical oscillators via a photonic resonator, enabling optomechanical synchronization between mechanically isolated nanomechanical resonators. Optical backaction gives rise to both reactive and dissipative coupling of the mechanical resonators, leading to coherent oscillation and mutual locking of resonators with dynamics beyond the widely accepted phase oscillator (Kuramoto) model. In addition to the phase difference between the oscillators, also their amplitudes are coupled, resulting in the emergence of sidebands around the synchronized carrier signal.

Optical back-action in silicon nanowire resonators: bolometric versus radiation pressure effects

We study optical back-action effects associated with confined electromagnetic modes in silicon nanowire resonators interacting with a laser beam used for interferometric read-out of the nanowire vibrations. Our analysis describes the resonance frequency shift produced in the nanowires by two different mechanisms: the temperature dependence of the nanowire's Young's modulus and the effect of radiation pressure. We find different regimes in which each effect dominates depending on the nanowire morphology and dimensions, resulting in either positive or negative frequency shifts. Our results also show that in some cases bolometric and radiation pressure effects can have opposite contributions so that their overall effect is greatly reduced. We conclude that Si nanowire resonators can be engineered for harnessing back-action effects for either optimizing frequency stability or exploiting dynamic phenomena such as parametric amplification.

Backaction limits on self-sustained optomechanical oscillations

The maximum amplitude of mechanical oscillators coupled to optical cavities is studied both analytically and numerically. The optical backaction on the resonator enables self-sustained oscillations whose limit cycle is set by the dynamic range of the cavity. The maximum attainable amplitude and the phonon generation quantum efficiency of the backaction process are studied for both unresolved and resolved cavities. Quantum efficiencies far exceeding one are found in the resolved sideband regime where the amplitude is low. On the other hand, the maximum amplitude is found in the unresolved system. Finally, the role of mechanical nonlinearities is addressed.

Optomechanics of deformable optical cavities

Resonant optical cavities such as Fabry–Perot resonators or whispering-gallery structures are subject to radiation pressure pushing their reflecting 'walls' apart. Deformable optical cavities yield to this pressure, but in doing so they in turn affect the stored optical energy, resulting in an optical back-action. For such cavities the optics and the mechanics become strongly coupled, making them fascinating systems in which to explore theories of measurements at the quantum limit. Here we provide a summary of the current state of optomechanics of deformable optical cavities, identifying some of the most important recent developments in the field.

Back-action-evading measurement via nondegenerate optical parametric down-conversion in a ring cavity

The optical back-action evading (BAE) measurement via nondegenerate parametric optical down conversion in a ring cavity has been analyzed. Two BAE schemes which are readily performed by experiments are presented and the dependences of BAE gains on the system parameters are discussed.

Generation of superpositions of classically distinguishable quantum states from optical back-action evasion.

We describe a method for generating superpositions of classically distinguishable quantum states in an optical-frequency mode. The method uses the optical back-action-evading apparatus demonstrated recently by La Porta, Slusher, and Yurke [Phys. Rev. Lett. 62, 28 (1989)].