This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have demonstrated a promising new way to protect fragile quantum information using nothing but mechanical vibrations—essentially extremely small sound waves.
The breakthrough, which comes from the lab of Marko Lončar, Tiantsai Lin Professor of Electrical Engineering, paves a path toward compact, sound-based quantum networks on chips, as well as hybrid quantum systems that combine many different types of quantum bits, or qubits. The research is published in Nature Physics. Experiments were led by Eliza Cornell, a recent Ph.D. graduate from the Lončar lab and current postdoctoral researcher at Boston University, and Zhujing Xu, a former postdoctoral scholar in Lončar's group.
One emerging type of quantum network uses the spin of an electron associated with an impurity in diamond as quantum memory and sound waves—or more precisely, sound particles called phonons—as information carriers between qubit nodes. The Lončar lab has been a leader in demonstrating the potential of this kind of system, in part by developing a qubit housing called a phononic cavity that traps the vibrations to make them interact with the electron spin. Phonons offer several advantages over more traditional approaches to quantum networking that use light as information carriers at the chip scale.
First, phonon wavelengths at a given frequency are much shorter than light wavelengths, enabling devices with far smaller footprints and tighter integration. Second, phonons couple easily to both solid-state spins and electromagnetic fields, making them attractive components in hybrid quantum systems that employ more than one type of qubit. But working with phonons has unique challenges—mainly related to memory.
Quantum memories need to be protected from their environment to extend their coherence, or ability to retain memory for a sufficiently long time. But existing approaches that rely on microwave pulses to decouple memories from their environment do not work well on qubits housed in phononic cavities. SEAS researchers solved this bottleneck by demonstrating all-mechanical coherence protection of a silicon-vacancy spin in diamond.
Rather than traditional microwave pulses, the team applied a continuous mechanical driving field made of phonons to change the qubit into a different state, called a "dressed" qubit. These states, called "dressed" because they are "wearing" a continuous acoustic field, are less sensitive to low-frequency noise in the environment. Because spin coherence is protected by a continuous mechanical field compatible with phononic cavities, the approach is designed to work within the same structures that would eventually be used to connect stationary nodes in a quantum network.
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