A team of researchers from the University of Colorado Boulder has found one of the missing pieces of the hardware puzzle that allows quantum computers to function at scale.
The team, led by Jake Freedman, an incoming PhD student in the Department of Electrical, Computer & Energy Engineering; Matt Eichenfield, professor and the Karl Gustafson Endowed Chair in Quantum Engineering; and collaborators from Sandia National Laboratories, including co-senior author Nils Otterstrom, have built a very small and very efficient chip that can precisely control laser light using standard semiconductor manufacturing. The ability to precisely control laser light is essential in quantum technology.
How do lasers work in quantum?
Some quantum computers store information in individual atoms or ions. Each atom acts as a qubit.
To make those atoms do anything useful, researchers shine lasers at them. The laser’s frequency, timing, and phase have to be extremely precise. Even tiny errors can break the computation. However, to scale this up would require millions of frequencies. Generating those laser frequencies requires large, power-hungry, table-top equipment. Because many quantum computers are controlled entirely by lasers, the need to scale and miniaturise in tandem becomes an important inflection point if quantum is to progress beyond lab-based research.
What does the quantum optical modulator do?
Using microwave-frequency vibrations to “nudge” the laser light in a controlled way, a quantum optical modulator allows a single laser to generate multiple, precisely defined frequencies that retain a fixed phase relationship, which is essential for quantum operation.
Whilst optical phase modulators aren’t new to research labs, what is new is the size of the modulator – almost 100 times smaller than the diameter of a human hair, it is power efficient – using around 80 times less microwave power than a standard modulator, and it is manufactured using CMOS, making it highly scalable. This shows promise that the same function can be built using the same manufacturing approach that is used for mainstream electronics.
CMOS matters
CMOS (complementary metal-oxide semiconductor) fabrication is widely used, which is why modern electronics can scale. By using CMOS, the team were able to make thousands of identical optical devices at once and integrate them onto a single chip, all whilst reducing cost, power consumption, and heat output.
Removing the bottleneck
Though quantum processors are steadily improving, the optical control systems around them are not scaling fast enough. This device dramatically shrinks optical control hardware, allowing many laser channels to sit close together on a single chip and creating a pathway towards physically plausible control of tens, or even hundreds of thousands, of qubits.
By removing one of the key barriers to scalability, the work helps shift quantum systems from hand-built lab experiments towards manufacturable engineering platforms, which the researchers describe as “one of the final pieces of the puzzle” for scalable quantum technologies.
