Photo credit: phys.org
Breakthrough in Mechanical Crystals: Optically Programmable Defect Modes
Mechanical crystals, also referred to as phononic crystals, are specialized materials capable of manipulating the travel of vibrations or sound waves, similar to how photonic crystals manage the flow of light. By intentionally introducing defects into the periodic structure of these crystals, researchers can create mechanical modes within their band gaps. This opens up new avenues for confining mechanical waves, potentially leading to advancements in technology.
A recent development by researchers at McGill University has resulted in an innovative mechanical crystal featuring an optically programmable defect mode. Their findings, detailed in a paper published in Physical Review Letters, present a novel method for dynamically reprogramming these mechanical systems through the application of an optical spring. This setup allows the mechanical mode to be shifted into the band gap of the crystal.
Jack C. Sankey, the principal investigator and co-author of the study, mentioned that the team was inspired by previous advancements in mechanical devices utilizing the band gap of phononic crystals to shield mechanical systems from environmental noise. This prompted them to explore the interactions between light and mechanical resonances further.
The team’s exploration led them to hypothesize that they could manipulate the resonance frequency of a membrane—punctured with a periodic array of holes—by leveraging optical forces. This approach would enable them to attract vibrational energy into a select area, akin to a tractor beam, effectively decreasing the inertial mass of the resonance.
“We discovered that the number of photons can have a considerable effect on how light influences mechanical systems,” Sankey noted. “Calculations indicated that larger structures would show greater responsiveness to photon variations, suggesting that even a single photon could potentially influence the motion of a practical, centimeter-sized device.”
As a proof of concept, the research group, led by Ph.D. student Tommy Clark, created and released a patterned membrane using conventional photolithography methods. They successfully positioned a fiber cavity at the membrane’s center, allowing for precise alignment.
Sankey elaborated on the experimental setup, stating, “We mounted everything on a vibration-isolating platform within a high-vacuum environment and employed feedback mechanisms to stabilize cavity mirrors to picometer accuracy, which is essential for laser light to align correctly with the cavity’s natural resonance.”
Once assembled, the optical cavity resonated at a high level, generating a substantial optical field that applied a spring-like force to a small area of the membrane. This manipulation allowed the team to purposefully disrupt the membrane’s periodic structure, thus creating a defect that could be adjusted in real-time depending on the intensity of the applied laser.
Sankey expressed enthusiasm for the broader implications of this research, stating, “The ability to couple light with the geometry and mass of mechanical resonances presents various intriguing applications. These range from enhancing our understanding of mechanical dissipation to simulating complex condensed matter systems.”
He also highlighted the growing interest in leveraging mechanical systems for quantum information storage and transportation on a chip, as well as connecting different quantum systems through mechanical means. The research exemplifies a groundbreaking method to control motion via light, offering prospects for future technological applications.
The practical implications of this new technique could extend to developing reprogrammable mechanical systems using arrays of defects. Such systems could enhance waveguides or routes for mechanical information transfer.
“In the near future, we aim to delve deeper into how individual photons can simultaneously influence multiple similar mechanical resonances while interlinking them through radiation forces,” Sankey added. “This integration could create a complex web of interactions, amplifying each photon’s effect, which could allow us to produce more significant quantum states of motion.”
More information: Thomas J. Clark et al, Optically Defined Phononic Crystal Defect, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.226904
Source
phys.org