Sound Waves Nearly Triple Quantum Memory in Diamond Qubits

Physicists at Harvard’s John A. Paulson School of Engineering and Applied Sciences have demonstrated a new method for protecting fragile quantum bits, or qubits, from environmental noise. By applying a continuous stream of sound waves, the researchers nearly tripled the time that silicon-vacancy qubits in diamond could retain quantum information.

“One emerging type of quantum network uses the spins of electrons associated with impurities in diamond as quantum memory, while sound particles called phonons carry information between qubit nodes,” said Harvard University researcher Eliza Cornell and her colleagues.

Phonons offer several advantages over light-based quantum communication systems, particularly at the chip scale.

First, phonons have much shorter wavelengths than light at the same frequency. This allows researchers to build smaller, more tightly integrated quantum devices.

Second, phonons can readily interact with both solid-state spins and electromagnetic fields. This makes them promising components for hybrid quantum systems that combine different types of qubits.

However, phonon-based quantum technologies also create challenges, especially when it comes to quantum memory. Qubits must be shielded from environmental disturbances to preserve their coherence—their ability to retain quantum information over time.

Conventional techniques often use microwave pulses to isolate qubits from noise. These methods are less effective for qubits placed inside phononic cavities, which are structures designed to confine and control mechanical vibrations.

Cornell and her co-authors addressed this problem by demonstrating what they describe as complete mechanical coherence protection for silicon-vacancy spin qubits in diamond.

Instead of using intermittent microwave pulses, the researchers applied a continuous mechanical driving field made up of phonons. This process transforms the qubit into a new state known as a “dressed” qubit.

Dressed qubits are less sensitive to low-frequency environmental noise, helping them maintain quantum information for longer periods. In the experiment, the phonon-based protection nearly tripled the qubits’ coherence time.

Because the method relies on a continuous mechanical field that is compatible with phononic cavities, it could be integrated into the same devices used to connect stationary qubits in future quantum networks.

In this type of system, phonons serve two important functions: carrying quantum information between nodes and protecting that information from noise.

“We are solving two problems. We want the spins to have strong interactions with the phonons, and we want the spins to have long coherence times,” Dr. Cornell said.

“Our paper demonstrates a method for extending the coherence time of silicon-vacancy centers located within a phononic cavity.”

The team’s paper was published online on July 15, 2026, in Nature Physics.

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E. Cornell et al. Mechanical coherence protection and fast control of spin qubits. Nature Physics, published online July 15, 2026. doi: 10.1038/s41567-026-03369-2.