Quantum computers hold immense potential, capable of tackling complex problems that would take classical supercomputers countless years to solve. However, building such powerful machines hinges on the ability to create and control millions of interconnected qubits, the fundamental building blocks of quantum information.
Researchers at MIT and MITRE have taken a significant stride toward this goal by demonstrating a modular hardware platform that integrates thousands of these interconnected qubits into a customized integrated circuit. This “quantum-system-on-chip” (QSoC) architecture allows for precise tuning and control of a dense array of qubits. Moreover, multiple chips can be linked using optical networking to form a large-scale quantum communication network.
“We will need a large number of qubits, and great control over them, to really leverage the power of a quantum system and make it useful. We are proposing a brand new architecture and a fabrication technology that can support the scalability requirements of a hardware system for a quantum computer,” explains Linsen Li, an electrical engineering and computer science (EECS) graduate student and lead author of the research paper published in Nature.
The team’s breakthrough lies in their use of diamond color centers as qubits. These “artificial atoms” offer scalability advantages due to their compatibility with modern semiconductor fabrication processes. Diamond color centers are compact, possess relatively long coherence times (the duration a qubit’s state remains stable), and have photonic interfaces enabling remote entanglement with other qubits.
Professor Dirk Englund, senior author of the paper, highlights the innovative approach: “The conventional assumption in the field is that the inhomogeneity of the diamond color center is a drawback. However, we turn this challenge into an advantage by embracing the diversity of the artificial atoms: Each atom has its own spectral frequency. This allows us to communicate with individual atoms by voltage tuning them into resonance with a laser, much like tuning the dial on a tiny radio.”
The researchers developed a novel “lock-and-release” fabrication process to transfer diamond color center “microchiplets” onto a CMOS backplane at scale. This intricate process involves fabricating an array of diamond microchiplets and nanoscale optical antennas, followed by meticulously aligning and bonding them to a specially prepared CMOS chip.
To assess the system’s performance, the team built a custom cryo-optical metrology setup and a digital twin simulation. They successfully demonstrated a chip with over 4,000 qubits tunable to the same frequency while preserving their quantum properties.
This research, supported by organizations including the MITRE Corporation and the U.S. National Science Foundation, represents a significant advancement in quantum computing hardware. Future work will focus on refining materials, enhancing control processes, and exploring the architecture’s applicability to other quantum systems.
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