A quantum computer is like an orchestra that has to tune its instruments before every piece. Tuning takes time and requires quiet — in our case, deep cold. For silicon chips with boron atoms, this tuning is usually done with microwaves, slowly and only at temperatures below 2 kelvin (minus 271 degrees Celsius).
A group of researchers proposed a different tool: short flashes of light with a frequency of about 10 terahertz. This is the far-infrared range, invisible to the eye, but capable of giving the electron shell of a boron atom a sharp jolt. A light pulse lasting 9 picoseconds (trillionths of a second) flips the atom into the desired spin state, like a snap of the fingers making a top spin in a given direction. A second pulse reads out the result, checking which way the spin is pointing.
The experiment showed that at a temperature of 3 kelvin, where conventional microwave technology already falls behind, light pulses prepare 99% of the spins in 250 picoseconds. That is more than a thousand times faster than previous methods. Fast tuning means a quantum computer can perform more operations in the same time and rely less on expensive refrigerators.
So light from the far-infrared edge of the spectrum becomes the conductor of the quantum orchestra. It not only speeds up tuning but also allows playing at slightly higher temperatures, where chaos used to reign. Perhaps terahertz pulses will help quantum chips leave the lab and enter the everyday world.
Terahertz radiation sits between microwaves and infrared light. It passes through clothing, paper, and plastic, but not through metal — which is why it's used in airport security scanners.
In the series 'Star Trek,' the quantum computers of the starship Enterprise run at room temperature — without bulky cryostats. Terahertz qubit tuning brings that fantasy closer to reality.