EAGER: Wafer-scale manufacturing of long-lived rare-earth qubits

University Of Chicago, Chicago IL

Investigators

Abstract

Part 1: Scalable manufacturing of long-lived, fully controllable quantum bits (qubits) remains a central theme in quantum engineering, and is poised to revolutionize computing, data analytics, material and pharmaceutical discoveries. Current state-of-the-art superconducting quantum circuits triumph over other platforms because of their wafer-scale production where qubits are patterned lithographically with mature circuit fabrication technologies. On the other hand, atom-like solid-state spins constitute an appealing system that simultaneously possesses long coherence times and accessible optical transitions, while allowing for chip-scale integration with other quantum systems. In particular, rare-earth ions in solids feature numerous 4f- intra-shell transitions that are effectively shielded from their crystalline surroundings by closed outer shells, allowing for long spin coherence times (up to 6 hours in Eu:Y2SiO5) and narrow optical transitions (<100 Hz in Er:Y2SiO5). Yet, the lack of a wafer-scale synthesis technique for such high-performance qubits severely limits their prospects as a functional building block of quantum information processing. Here we propose a new technology of solid-state qubits based on rare-earth ions doped in epitaxial oxide thin films on silicon wafers. The thin film host matrix is synthesized by molecular beam epitaxy, offering the highest possible crystalline quality and ensuring consistent, long coherences of qubits throughout the wafer. This wafer architecture with embedded qubits can be processed with standard fabrication techniques into scalable quantum electronic and photonic devices. Beyond quantum science and engineering, this project will generate substantial knowledge and technical advancements to push the limits of wafer manufacturing and optoelectronic technologies by enabling a new class of thin film based electrical and optical devices including lasers, modulators, switches, and transducers. These technologies are poised to revolutionize the existing fields of communications, computing and sensing. The complex and highly interdisciplinary nature of this project will provide a unique opportunity for training graduate students and postdocs as new generation quantum scientists and engineers. The project will also highlight outreach efforts to engage undergraduate, women, and underrepresented minority students via sponsored summer research programs at the University of Chicago. Part 2: Qubits based on rare-earth ions possess long spin coherences and optical transitions in the telecom wavelength (erbium in particular), making them ideally suited for long-distance quantum network with existing fiber-optic telecommunication infrastructure. So far, the exceptional coherence of rare-earth ions has been routinely measured when they are doped in macroscopic bulk oxide crystals (e.g. Y2O3, Y2SiO5). These bulk materials, while having superior structural and optical quality, do not allow standard wafer processing to fabricate large-scale quantum devices as desired by state-of-the-art quantum technologies. In this EAGER proposal, we explore a new approach to epitaxially grow rare-earth qubits in oxide thin films as host matrix on industry-standard silicon wafers using molecular beam epitaxy (MBE). This concept is entirely new and exploratory given that there is little prior knowledge on the wafer-scale qubit manufacturing technique for long-lived rare-earth ions, which makes this research particularly fit for the NSF EAGER program. While the inherent risk is significant, the potential impact of this technology can be paradigm-shifting in the following aspects: 1) it vastly increases the packing factor of qubits (atomic length-scale) compared to the current superconducting circuit technology (micron scale). 2) high structural and optical quality of the epitaxial film enhances the rare-earth qubit coherence to ~1 second compared to ~100 microsecond in leading superconducting qubits; 3) qubits on silicon wafers enable seamless integration with silicon-based quantum electronics and photonics technology; 4) thin film topology enables large-scale top-down device fabrication using standard lithography and etching. 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.