Efficient bidirectional piezo-optomechanical transduction between microwave and optical frequency (1909.04627v1)

Abstract: Efficient interconversion of both classical and quantum information between microwave and optical frequency is an important engineering challenge. The optomechanical approach with gigahertz-frequency mechanical devices has the potential to be extremely efficient due to the large optomechanical response of common materials, and the ability to localize mechanical energy into a micron-scale volume. However, existing demonstrations suffer from some combination of low optical quality factor, low electrical-to-mechanical transduction efficiency, and low optomechanical interaction rate. Here we demonstrate an on-chip piezo-optomechanical transducer that systematically addresses all these challenges to achieve nearly three orders of magnitude improvement in conversion efficiency over previous work. Our modulator demonstrates acousto-optic modulation with $V_{\pi} = {0.02}$ V. We show bidirectional conversion efficiency of $10^{-5}$ with ${3.3}$ microwatts red-detuned optical pump, and $5.5\%$ with $323$ microwatts blue-detuned pump. Further study of quantum transduction at millikelvin temperatures is required to understand how the efficiency and added noise are affected by reduced mechanical dissipation, thermal conductivity, and thermal capacity.

• The paper reports nearly three orders of magnitude improvement in conversion efficiency using red- and blue-detuned optical pumps.
• It employs an on-chip piezo-optomechanical device integrating an optomechanical crystal on an X-cut lithium niobate platform to enhance photon-mechanical interactions.
• The research demonstrates effective microwave-to-mechanical coupling with interdigitated transducers, paving the way for advanced quantum transduction in low-power applications.

Overview of Piezo-Optomechanical Transduction Paper

The paper "Efficient bidirectional piezo-optomechanical transduction between microwave and optical frequency" presents significant advancements in the field of optomechanical systems, focusing on efficient transduction from microwaves to optical frequencies. The paper addresses a long-standing challenge in converting information between microwave and optical domains, particularly relevant for both classical and quantum information processing. This paper achieves a notable milestone by significantly increasing the conversion efficiency through an on-chip integrated piezo-optomechanical device.

The research conducted by Wentao Jiang et al. at Stanford University systematically tackles the problems faced in previous demonstrations that suffered from low optical quality factors and limited transduction efficiencies. The key achievement reported is a nearly three orders of magnitude improvement in conversion efficiency compared to earlier benchmarks. Particularly, the demonstration of acousto-optic modulation with a very low $V_{\pi} = 0.02 \text{~V}$ underscores the efficiency achieved.

Key Findings

1. Conversion Efficiency: The authors report bidirectional conversion efficiencies of $10^{-5}$ with a red-detuned optical pump and $5.5\%$ with a blue-detuned optical pump. These figures represent a significant leap over previous efforts, suggesting a pathway to practical implementation in quantum networks.
2. Optical and Mechanical Co-localization: Utilizing an optomechanical crystal (OMC), the research achieves high optomechanical interaction rates by effectively localizing optical and mechanical energies. This design is crucial for minimizing energy consumption while facilitating efficient conversion.
3. Device Performance: The modulation index and efficiencies were thoroughly characterized, revealing coherence in interaction between optical photons and mechanical motion. The integration on an $X$-cut thin-film lithium niobate platform is particularly noteworthy for its potential compatibility with superconducting circuits.
4. Mechanical Mode and Microwave Coupling: A novel use of interdigitated transducers (IDT) and a wavelength-scale mechanical waveguide enhanced the microwave-to-mechanical conversion. This integration significantly improved the efficiency while isolating optical quality from the deleterious effects of metal absorption.

Implications

The practical implications of this work are extensive. In creating a device capable of efficient bidirectional conversion, the authors pave the way for future quantum transduction technologies that could integrate into quantum computers or sensors requiring low thermal dissipation and high conversion rates. These advances could transform microwave photons and optical photons' interaction within superconducting qubits, aiding in distributed quantum computing and sensing network applications.

Theoretically, this development is a robust demonstration of integrating various technologies—optoelectronic, mechanical, microwave—into a cohesive system, providing a template for future research in hybrid quantum systems and nanomechanical devices.

Future Directions

The paper identifies a future need to investigate quantum transduction dynamics at cryogenic temperatures to reduce losses further and enhance efficiency. Reducing these parameters would be pivotal in harnessing these systems' full potential for quantum networks. Furthermore, integrating these systems with superconducting circuits presents enticing challenges and opportunities, particularly for enhancing quantum communication efficiency over larger networks.

Conclusion

This paper highlights the intricacies of designing efficient piezo-optomechanical systems within integrated platforms. The improvements in bidirectional conversion set a new standard and vision for such transducers' development, providing a comprehensive analysis of achieving high-performance levels without significant power consumption, hence making a notable contribution within its domain.