A sound advantage over light
A similar version of this experiment had already been done with light a decade ago, making this an “acoustic cover of an electronic hit,” Sletten joked. However, as sound is nearly a million times slower than light, the acoustic version can access new physics.
“This is not the race car of the superconducting qubit world,” Sletten said. “When you switch to sound, you lose a fair amount of things, but you also gain some cool stuff.”
Sound waves used in this experiment are a million times smaller than light because sound is a million times slower. Phonons are also usually much longer-lived than photons.
“The slowness of sound let us build a cavity for sound in an on-chip device which would be really, really long if you made it for light,” Sletten said.
Why build an effectively long cavity? It has to do with the amount of quantum information that a device can store. The echo chamber has certain frequencies that resonate, similarly to the pitches you can play on a wind instrument. The longer the instrument, the smaller the difference between adjacent notes. (As a tuba player, Sletten is keenly aware of how tightly spaced these notes become when the instrument becomes very long.) Each acoustic resonance can independently store information. Thus, more resonances means higher capacity.
And that’s good news for quantum computers, which need a way to expand the computing power by adding more qubits. Sound could give quantum computers an alternative way to go from one qubit to many.
“If you can control the quantum state of the sound in these modes, then you can use these as your qubits,” Sletten explained. “And you can make more of them just by taking the mirrors and moving them apart. So, this gives you a different path [to go from one] to many.”
This study was published in Physical Review X in June.