Very Cold Computing Is a Very Hot Topic
Cold computing's development has been slowed by the enormous difficulty of working with temperatures just a hair above absolute zero (0° Kelvin, or −273° Celsius).
Now, Milton Feng’s group has published a pair of papers that will push cryogenic computing forward by presenting a record-breaking optical data interconnect, which the team has already demonstrated in the context of a complete system. What’s the point of computing at such extreme temperatures? The classical computing architecture is reaching its performance limits, and cryogenic computing—in which extreme cold enables either superconductivity or maintenance of quantum state, depending on the kind of system—offers an opportunity to move beyond them.
“The goal is to have a high-speed, energy-efficient, and also low-thermal-conductivity data interconnect between a 4°K processor and a room-temperature memory and other circuits,”
explains Wenning Fu, who is an ECE Ph.D. student of Feng’s.
Unfortunately, cryogenic computing can’t work without an effective way to transmit data between the cold processor and much warmer system components—while limiting heat’s ability to pass through the data connection and disastrously warm up the processor.
“The goal is to have a high-speed, energy-efficient, and also low-thermal-conductivity data interconnect between a 4°K processor and a room-temperature memory and other circuits,” explains Wenning Fu, who is an ECE Ph.D. student of Feng’s. “Optical interconnects are perfect candidates.”
The first paper, which is the cover story of a recent issue of Applied Physics Letters, was lead-authored by ECE Ph.D. student Haonan Wu. To provide the high-speed data interconnect needed for cryogenic computing, the paper presents the world’s first demonstrated semiconductor laser, as an integrated optical transmitter, that functions below 4°K—the temperature at which helium becomes a liquid. Indeed, the researchers showed that it could work in temperatures as low as 2.6°K.
The second paper, a cover story in the IEEE Journal of Quantum Electronics, was lead-authored by Fu and takes some big steps beyond the contributions of the first paper. For one thing, it reports even higher data transfer rates: a semiconductor laser performance over 50 gigabits per second (Gb/s) near 4°K. But on top of that, it also incorporates a superconducting processor based on single quantum flux (SQF) technology together with the laser at 4°K, and describes a successful demonstration, in Feng’s HMNTL lab, of a full optical fiber data linkage system with a data transfer rate of up to 20 Gb/s.
Feng, who is the Nick Holonyak, Jr., Endowed Chair Emeritus in Electrical and Computer Engineering, says, “We are very proud of this work as the first demonstration of a full high-speed NRZ [non-return-to-zero] error-free data transmission optical link from 40K to room temperature. And we expect that cryogenic oxide-VCSEL [vertical-cavity surface-emitting laser] optical fiber links will be able to deliver greater than 200 gigabits per second NRZ for the most energy-efficient data transfer rate toward approximately one femtojoule per bit.”