CAREER: Quantum Acoustic Information Processing with Phononic Crystal Devices

Stanford University, Stanford CA

Investigators

Abstract

We understand the quantum laws of nature well enough to write equations that describe the behavior of real-world systems such as complex molecules, exotic materials, and electronic devices. However, in the majority of cases, computing the solutions of these equations on a computer to make concrete predictions remains outside the realm of possibilities. Recently, physicists have developed a different approach to computation that could harness the enormous complexity inherent in the laws of quantum physics to make predictions about nature. Such quantum computers, if they can be built, would also execute powerful quantum algorithms that break cryptographic codes, solve optimization problems, and simulate currently intractable systems in quantum chemistry. Realizing a useful quantum machine remains an elusive dream. In the last decade, an approach involving microwave frequency circuits and systems made from superconducting materials has emerged as a leading candidate for realizing a quantum machine. These systems use the interactions between microwave frequency light, or photons, to encode, process, and store quantum information. We propose an enhancement of this approach that uses microwave-frequency sound, or phonons. If successful, our approach will significantly reduce the complexity of a quantum machine and enable rapid scaling to larger quantum computers. Improving the processing power of these quantum computers is expected to significantly impact science and technology in many application spaces ranging from basic science to drug discovery. For further impact, our proposed program includes a professional education outreach component that will develop and deliver a curriculum to engineers who hope to move into quantum science and engineering. The proposed program will deliver a targeted set of four courses tailored to practicing engineers that will build the theoretical and practical skills needed to become quantum scientists. Emerging quantum machines use the interactions between photons, single quanta of electromagnetic excitation, to encode, process, and store quantum information. We propose an enhancement of this approach that in addition to photons, uses phonons, the quanta of vibrations, to realize quantum functionality. The proposed phonon devices are many thousands of times smaller than the circuit elements used in current approaches to quantum computing because the speed of sound is considerably lower than the speed of light. Additionally, phonon devices can be remarkably coherent, with the coherence times many thousands of times longer than competing photonic systems. These properties enable new architectures that greatly facilitate scaling to larger system sizes. To investigate the feasibility of this approach, we will fabricate chips that contain superconducting transmon qubits and mechanical resonators, and we will perform quantum gates between these elements. We will also develop ways of using quantum acoustic devices as a means of efficiently multiplexing and routing quantum signals. Successful demonstration of the proposed architecture bringing together mechanical devices and superconducting qubits significantly accelerates the development of quantum machines. 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.