MEMS News: From 5G Roots to Quantum Refrigerators
Mems News Researchers have confirmed a novel method for managing millions of quantum bits (qubits) without overheating their extremely cold environments, a major step toward large-scale quantum computing.
Commercial microelectromechanical system (MEMS) switches, originally designed for 5G and aerospace, work better at quantum computing temperatures than at ambient temperature. This discovery may enable the next generation of “interconnect architectures” needed to grow quantum computers from hundreds of qubits to millions for real-world applications. The Wiring Horror The state of superconducting quantum computing is a delicate temperature ballet. Electronics that run the quantum processor are usually at ambient temperature, but the processor is in a dilution cooler at 10 mK. A massive wide-band network links these worlds. Researchers seeking larger systems face a physical hurdle. They note that limited mK temperature starting area and cooling power make connections difficult when scaling those systems to a million qubits. Simply put, the refrigerator cannot resist the cables' heat, which could damage the qubits' quantum states. The answer is cryogenic multiplexing, where a few wires carry signals to numerous qubits in the cold zone. It has been impossible to design a switch that works at these temperatures and uses almost no power until now. Surprise performer MEMS Sunil A. Bhave of Purdue University and Menlo Microsystems, Inc. led the work using a Single-Pole Four-Throw (SP4T) MEMS switch. These switches electrostatically transport a small cantilever beam to an electrode, unlike transistors. The team found stunning results at 5.8 K: Improved Efficiency: Freezing temperatures reduced “phonon scattering” in metal components, lowering switches' “on-resistance” by 15.3%. Lower Power: The switch's voltage dropped 3.1% to 3.5%, requiring less energy to flip. Superior Signal Integrity: The switches maintained a “ultra-low insertion loss” of less than 0.5 dB to protect delicate quantum communications. The low static power consumption of MEMS switches is a key property for quantum applications. No power should escape through a quantum system's 20-microwatt cooling budget since the top and bottom electrodes are physically separated by an air gap while off. A “Bouncing” Problem Solution Despite promising results, the researchers encountered a cryogenic difficulty. The gases' phase shift inside the switches' hermetically sealed packaging generated a quasi-vacuum environment. In the lack of air to provide "damping," the small cantilever beams bounced wildly upon collision for up to 150 microseconds, threatening switch instability. To solve this, researchers constructed a “dual-pulse” waveform. By starting with a high-voltage “kick” and reducing the voltage before impact, they were able to land the beam with nearly little velocity. This stopped bouncing and allowed it to run for over 100 million cycles without a reduction in performance. Foundation for Future Logic The team demonstrated that these MEMS devices could switch and perform NAND and NOR gates at 5.8 K. In the future, the switches may manage complex signal routing and logic tasks inside the dilution refrigerator, eliminating the need for external wiring. The authors say the study is a big success for the profession, but there are still challenges. In "dielectric charging," switches may cling due to continuous high-speed use (stiction). New materials that reduce this effect will be the focus of future research. The confirmation of commercial MEMS technology is groundbreaking. By using proven semiconductor production methods that assure yield and quality, building a computer with over one million qubits is now possible.