In-situ tuning of optomechanical crystals with nano-oxidation (2312.02123v1)

Abstract: Optomechanical crystals are a promising device platform for quantum transduction and sensing. Precise targeting of the optical and acoustic resonance frequencies of these devices is crucial for future advances on these fronts. However, fabrication disorder in these wavelength-scale nanoscale devices typically leads to inhomogeneous resonance frequencies. Here we achieve in-situ, selective frequency tuning of optical and acoustic resonances in silicon optomechanical crystals via electric field-induced nano-oxidation using an atomic-force microscope. Our method can achieve a tuning range >2 nm (0.13%) for the optical resonance wavelength in the telecom C-band, and >60 MHz (1.2%) for the acoustic resonance frequency at 5 GHz. The tuning resolution of 1.1 nm for the optical wavelength, and $150$ kHz for the acoustic frequency allows us to spectrally align multiple optomechanical crystal resonators using optimal oxidation patterns determined via an inverse design protocol. Our results establish a method for precise post-fabrication tuning of optomechancical crystals. This technique can enable coupled optomechanical resonator arrays, scalable resonant optomechanical circuits, and frequency matching of microwave-optical quantum transducers.

• The paper introduces a technique using AFM-controlled nano-oxidation to in-situ tune the resonant frequencies of optomechanical crystals.
• It demonstrates fine-tuning with over 2 nm optical resonance shift and 150 kHz acoustic frequency change through an inverse design protocol.
• The method enhances scalability and uniformity in quantum systems while opening research avenues for topological phases and atomic defects in materials.

Optomechanical crystals (OMCs) have shown significant promise in the fields of quantum transduction and sensing. These devices, which act as intermediaries between light (photons) and vibration (phonons), have become pivotal for applications such as quantum computing, where they can serve as links between superconducting processors and optical communication channels. Ensuring that these crystals operate at the same resonant frequencies is critical for efficient information transfer.

Unfortunately, the precision required to manufacture these nanoscale devices is so high that even slight discrepancies in the fabrication process can lead to variations in their resonance frequencies. Overcoming this variability is a challenge that has hampered the scalability and interconnectivity of optomechanical systems.

A solution comes from a technique developed using electric field-induced nano-oxidation controlled by an atomic force microscope (AFM). This paper describes how the researchers were able to selectively and precisely tune the resonant frequencies of the OMCs in-situ—that is, directly on the chip where the devices are situated. By applying a strong electric field via the AFM tip, a controlled oxidation reaction occurs on the silicon surface of the OMCs, altering both their optical and acoustic properties.

The tuning approach was impressively precise, achieving more than 2 nm change in optical resonance (corresponding to a 0.13% frequency shift) and 150 kHz change in acoustic frequency. Researchers demonstrated that they could align multiple crystals by iteratively adjusting them with this novel method.

Moreover, the research introduced an "inverse design protocol." This technique guides the placement and size of the oxidized regions on the OMCs to achieve the desired frequency shifts. The protocol calculates the optimal pattern needed for the oxidation process and is capable of simultaneous fine-tuning of both optical and acoustic frequencies, offering nanometer precision for optical and hundred-kilohertz precision for acoustic tuning. This level of control solves a significant problem of uniformity and is crucial for OMCs' proper function in quantum networks and circuits.

The impressive contribution of this research extends beyond immediate practical applications. It opens the possibility of studying topological phases of photons and phonons in coupled optomechanical resonators. Additionally, it provides a method that could be applied to other material systems, such as silicon nitride, which is significant since different materials may be used depending on the application.

It also suggests potential for a new avenue of exploration regarding atomic-scale defects in materials, which have implications for the paper of quantum information science and could further our understanding of two-level systems that play a crucial role in quantum technology.

In summary, this paper outlines a significant step forward in optomechanical crystal technology, introducing a targeted tuning method that could be key to the widespread application of OMCs in quantum systems, potentially leading to more robust and scalable quantum networks.