Researchers at Yale University, led by Boxuan Tian, Jiacheng Xie, and Hong X. Tang in the Department of Electrical Engineering, have demonstrated the ability to excite mechanical vibrations at 110 GHz within a bulk lithium niobate crystal, with cooperativity up to 16.6 at 110 GHz. This enables efficient, non-contact excitation of centimeter-scale, milligram-mass vibrational modes across 7.0, 110 GHz, and establishes a versatile platform for precision tests of mechanical quantum physics at elevated temperatures and potentially enables new hybrid quantum technologies. Mechanical quality factors reach up to 30,000 at W band frequencies.
Bulk Lithium Niobate for Sub-Terahertz Mechanical Modes
A milligram-scale lithium niobate crystal has been made to vibrate at 110 gigahertz, a feat previously confined to far smaller, intricately manufactured devices. This approach bypasses the need for the complex microfabrication traditionally required for high-frequency mechanical resonators, utilizing instead a three-dimensional microwave cavity. The team, led by Boxuan Tian, Jiacheng Xie, and Hong X. Tang in the Department of Electrical Engineering, achieved mechanical quality factors up to 30,000 at W band frequencies, exciting milligram-mass crystals spanning 7.0, 110 GHz. This is accomplished by concentrating the microwave field within the crystal using a high-quality cavity, mitigating limitations seen in nanoscale thin-film devices. The researchers emphasize that the large volume-to-surface ratio of bulk lithium niobate supports low-loss propagation of acoustic waves, reducing damping and eliminating contact-induced loss. The Yale group demonstrated cooperativity up to 16.6 at 110 GHz.
The system relies on piezoelectric coupling, where the crystal’s response to an electric field generates mechanical motion. This non-contact excitation method, utilizing a frequency-tunable superconducting niobium cavity cooled to 4 Kelvin, establishes a versatile platform for accessing massive high-frequency mechanical modes and for precision tests of mechanical quantum physics at elevated temperatures. The ability to access these high-frequency mechanical modes in bulk crystals could enable hybrid quantum technologies, frequency conversion, and precision quantum metrology, all without the constraints of nanoscale fabrication and direct electrical contact.
Three-Dimensional Cavity Enables Non-Contact Excitation
Controlling mechanical motion at the sub-terahertz regime has traditionally relied on intricate microfabrication techniques, limiting the scalability and performance of high-frequency resonators. Researchers have largely overlooked bulk crystals due to their inherent inertia and the challenges of efficiently transducing energy at such high frequencies. However, a team at Yale University, Boxuan Tian, Jiacheng Xie, and Hong X. Tang, has demonstrated a novel approach utilizing a three-dimensional microwave cavity to non-contact excite milligram-mass lithium niobate crystals, achieving mechanical modes up to 110 GHz. This bypasses the need for complex microfabrication, opening new avenues for exploring macroscopic quantum mechanics. This new method centers on maximizing the overlap between the microwave field and high-order acoustic modes within the bulk lithium niobate crystal.
By employing a 3D cavity, the team observed mechanical modes with effective vibrational masses ranging from 0.21 to 5.0 mg, and remarkably high mechanical quality factors up to 30,000 across a broad frequency range of 7.0, 110 GHz. This achievement is particularly significant given the ultrashort phonon wavelength at 100 GHz, which typically leads to increased surface defects and electrode loading, limiting quality factors in traditional designs. The researchers explain that the crystal supports low-loss propagation of acoustic waves, mitigating these limitations. This allowed them to demonstrate strong coupling between microwave photons and mechanical phonons, with cooperativity up to 16.6 at 110 GHz. These results establish a versatile platform for accessing massive high-frequency mechanical modes and for precision tests of mechanical quantum physics at elevated temperatures.
Researchers at Yale University are developing a new approach to high-frequency mechanical resonators, moving beyond the limitations of traditional microfabrication techniques. Boxuan Tian, Jiacheng Xie, and Hong X. Tang have demonstrated the excitation of mechanical modes in bulk lithium niobate crystals across 7.0, 110 GHz, a frequency previously difficult to achieve without intricate nanoscale structures. Mechanical quality factors up to 30,000 were observed at W band frequencies. The team’s innovation bypasses the need for direct electrode contact, a common source of energy loss in conventional high-frequency resonators. At 110 GHz, cooperativity up to 16.6 was observed, indicating a robust and efficient exchange of energy between these two realms. The observed mechanical modes exhibited effective vibrational masses of 0.21, 5.0 mg, further highlighting the system’s ability to manipulate relatively large objects at extremely high frequencies.
The ability to manipulate mechanical motion at frequencies nearing the sub-terahertz range promises advancements in quantum technologies, and researchers are now demonstrating control over macroscopic objects at unprecedented speeds. This achievement bypasses the need for complex microfabrication by utilizing a three-dimensional microwave cavity to efficiently drive milligram-mass crystals spanning 7.0, 110 GHz. The team, led by Boxuan Tian, Jiacheng Xie, and Hong X. Tang in the Department of Electrical Engineering, designed a system that concentrates the microwave field within the crystal, maximizing interaction with the acoustic modes. By measuring the microwave reflection spectra using a vector network analyzer, the researchers were able to observe and characterize these high-frequency vibrations. Crucially, the Yale group didn’t just achieve high frequencies; they demonstrated strong coupling between the microwave photons and mechanical phonons. At 110 GHz, cooperativity up to 16.6 was observed. Measurements reveal mechanical quality factors up to 30,000 at W band frequencies. The implications extend to a range of applications, from quantum information processing and frequency conversion to precision metrology.
7.0, 110 GHz is not simply about reaching a higher frequency; it’s about doing so with a material that inherently minimizes energy loss. Cooperativity up to 16.6 was observed at 110 GHz, demonstrating strong coupling using a frequency-tunable superconducting niobium cavity at 4 K, enabling coherent energy exchange.
Milligram-mass crystals of lithium niobate are now resonating at frequencies previously confined to meticulously fabricated microstructures, a development enabled by a novel approach to electromechanical coupling. This achievement hinges on a three-dimensional microwave cavity that efficiently couples to the crystal’s vibrational modes without physical contact, a critical factor in minimizing energy loss. The conventional path to high-frequency mechanical resonators relies on intricate microfabrication techniques, creating complex structures susceptible to damping from surface defects and electrode loading. These limitations typically restrict quality factors to the hundreds. Measurements reveal mechanical quality factors up to 30,000 at W band frequencies, a significant improvement over existing sub-terahertz resonators. Cooperativity up to 16.6 is observed at 110 GHz. This platform potentially enables compact and broadband architectures for both classical and quantum information processing.
Source: https://arxiv.org/abs/2607.10737
See today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals.
