CAREER: Controlling noise in quantum devices with light and sound

Northern Arizona University, Flagstaff AZ

Investigators

Abstract

While the mastery of nascent quantum technologies promises new forms of high-performance computing, precision sensing, and unconditionally secure communications, noise inherent to these quantum devices degrades the very features that enable their remarkable properties. The most problematic source of noise for a wide variety of quantum devices is produced by so-called two-level tunneling states (TLSs). While not well understood, TLSs are ubiquitous—appearing in crystals, on surfaces, and within disordered materials—and the noise they produce is more acute at the low temperatures required for the operation of many quantum technologies. The proposed research aims to leverage the strong interaction between TLSs and sound waves to develop new techniques to control and reduce this vexing source of noise. Key objectives involve engineering devices: (1) to shape how sound impacts quantum device performance through device geometry, and (2) to show how noise in quantum devices can be controlled through the active transduction of mechanical waves. This project explores the ability to drastically reduce the noise produced by TLS and shed light on the—currently unknown—microscopic origin of TLSs, toward practical applications of quantum technology. Through paid undergraduate research opportunities, new curricula on light-matter interactions, and quantum science themed outreach, the proposed educational objectives aim to address the workforce needs of Arizona’s burgeoning technology sector. This project aims to demonstrate control of noise produced by two-level tunneling states (TLSs) through the manipulation of phononic degrees of freedom and to show how this control can be used to improve the performance of quantum devices. To achieve these objectives, electronic, phononic and photonic devices will be created: (1) from highly confined membranes, waveguides and resonators that alter and control the phonon density of states, predicted to drastically alter and reshape the spectrum of TLS noise, and (2) where light can be harnessed to transduce large amplitude mechanical waves, expected to reduce noise by “saturating” TLS losses. Pulse sequence measurements, microwave spectroscopy and a new form of pump-probe phonon spectroscopy will connect device performance with phonon manipulation. Whereas, detailed theory-experiment comparison will elucidate the impact of phonon confinement and transduction on various noise and dissipation mechanisms produced by TLS, e.g., in the form of the temperature dependence of the mechanical quality factor. This project will show (1) how TLS noise can be altered in an array of highly confined structures, (2) how phonons can be used to control TLS noise in the microwave domain, and (3) how phonons can be leveraged to improve quantum device performance for the first time. Together, these results are expected to establish that phonon manipulation can extend lifetimes of electromagnetic quantum states within superconducting qubits and may pave the way for practical forms of quantum computing and ultra-sensitive detectors of forces, rotation, magnetic fields and displacement. 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.