Physicists at the Harvard John A. Paulson School of Engineering and Applied Sciences have found a new way to protect quantum information: shield it with sound. A steady stream of sound waves can keep a fragile quantum bit, or qubit, safe from the noise around it, nearly tripling how long it holds its data.
Why qubits lose their memory
Qubits are the building blocks of future quantum computers. They store information in delicate quantum states that are easy to disturb. Heat, stray electromagnetic fields and everyday vibrations all cause qubits to lose their data quickly — a problem known as decoherence. Keeping a qubit stable long enough to run calculations is one of the hardest challenges in the field.
A sound shield for fragile quantum states
The Harvard team took a different approach. Instead of trying to block out noise, they used mechanical vibrations — sound waves — to "dress" the qubit and protect it from its surroundings. In experiments reported in Nature Physics, the sound shield nearly tripled how long the qubit held information.
In a related demonstration, a group at Cornell applied all-mechanical coherence protection to a silicon-vacancy spin in diamond. Because the protection is mechanical rather than electrical, it avoids the electromagnetic interference that often disturbs quantum systems. Sound waves can also be routed on chip, which makes the method practical for real devices.
What comes next
The results point toward sound-based quantum networks built on chips, and toward hybrid systems that combine several types of quantum technology in one device. Researchers say the method is simpler than many existing protection schemes and could be combined with them. Building reliable quantum computers will still take years, but sound-shielded qubits remove one more obstacle on the road.
Sound-based protection also has a practical advantage: acoustic signals can be guided along tiny channels on a chip, so the same manufacturing technology used for today's microelectronics can be adapted for quantum devices. The Harvard and Cornell teams say the next step is to test the approach in larger arrays of qubits, where noise and interference multiply.
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