CAREER: Quantum silicon phononics: Harnessing long-lived phonons for memories and interconnects

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Over the last two decades, quantum technologies have progressed steadily, promising solutions to a wide range of applications in computation, communication, and sensing. The bulk of efforts in developing physical platforms for quantum technologies has so far focused on photons as carriers of quantum information and atomic and solid-state qubits for storing and processing quantum information. Phonons, the quanta of energy in vibrations in solid-state materials, have recently emerged as a viable resource for quantum technologies. Due to their ability to interact with a wide range of systems, phonons can serve as interconnects to pass quantum signals from the electrical domain, where quantum computers are likely to operate, to the optical domain, where optical fibers enable long-distance quantum communication. Additionally, phonons can be well isolated from their environments in nano-engineered devices, potentially providing memory elements for storing quantum states. Developing these physical properties into experimental capabilities and, subsequently, a technological advantage requires methods of interfacing mechanical devices with other quantum hardware platforms. This project aims to create scalable, chip-scale optical and electrical quantum interfaces to long-lived mechanical resonators. Furthermore, the project aims to assess the practical benefits of the developed interfaces by using them in experimental demonstrations that create quantum entanglement between electrical, optical, and mechanical quantum devices. GHz-frequency acoustic resonators made from single-crystal silicon offer the unique properties of exceptionally low loss (reaching 50-billion quality factors at low temperatures) and the ease of interfacing with telecom-band optical photons. However, while quantum manipulations of phonons have been previously demonstrated with piezoelectric coupling to superconducting qubits, the absence of piezoelectricity in silicon forbids direct integration with qubits. This project aims to overcome this challenge by developing new mechanisms for electromechanical coupling of GHz-frequency mechanical resonators with superconducting qubits and cavity optomechanical systems in a monolithic silicon-on-insulator platform. To achieve this goal, the project will develop electrostatic transducers based on phononic crystals and high-impedance microwave cavities based on kinetic inductance in disordered superconductors. Integrating these components, the PI aims to realize full quantum control of electromechanical resonators with transmon qubits and demonstrate electro-optomechanical conversion of microwave photons to optical photons. The absence of lossy piezoelectric materials and the reliance on light-resistant superconductors in this approach is expected to translate to exceptionally long mechanical lifetimes and orders-of-magnitude improvement in the efficiency of microwave-to-optical frequency conversion. The project aims to take benefit of these improvements for demonstrating quantum entangling operations in a lab-scale hybrid network made from transmon qubits (acting as processors), phononic crystal resonators (memory elements), and telecommunication band photons (interconnects). Demonstrating such a hybrid quantum network would be essential for future real-world applications in providing secure remote access to quantum computing clouds, distributed quantum computing, and quantum-enabled sensing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.