How Sound Manipulates Quantum Electron Orbits

Researchers from Cornell University have shown that acoustic sound waves can be used to manipulate the movement of an electron orbiting a lattice defect in a diamond. This technique could enhance the sensitivity of quantum sensors and be applicable in other quantum devices.

As advancements in quantum information technology continue, finding new methods to control electrons and other tiny particles becomes crucial. In a study titled "Coherent Acoustic Control of Defect Orbital States in the Strong-Driving Limit," Gregory Fuchs, a professor of applied and engineering physics, and his postdoctoral associate, Brendan McCullian, worked with Erich Mueller, a professor of physics in the College of Arts and Sciences, and his doctoral student, Vaibhav Sharma. They created a setup where sound waves can induce quantum jumps between electron orbits.

This research, published in PRX Quantum, involves McCullian constructing a microscopic speaker on a diamond chip. This speaker operated at a frequency that matched an electronic transition, allowing him to demonstrate precise control of a single electron within the diamond.

In quantum computing, qubits—the quantum counterparts of classical bits—need to remain coherent to be effective. This coherence is delicate and can easily be disrupted by environmental fluctuations, such as when an adjacent electron shifts positions. For years, scientists have used spin resonance, which relies on microwaves and magnetic fields, to extend qubit coherence times. Fuchs and his team extended this approach to the acoustic domain to enhance the coherence of orbital states.

Fuchs explained, "We used acoustic methods to drive the orbital states in a manner similar to spin resonance, and then applied established spin resonance techniques to examine the coherence of these orbital states. It was fascinating to apply spin resonance tools—like coherent control and Rabi oscillations—to orbital states using a gigahertz acoustic resonator and find that these techniques were still effective."

Fuchs's research contributes to understanding the nitrogen-vacancy (NV) center, a defect in diamond crystal lattices critical for quantum sensing and quantum networking. It also aids in developing new tools to address spectral diffusion, which can pose significant challenges in quantum networking by disrupting the consistency of emitted photon frequencies.

Fuchs noted, "By exploring how the NV center interacts with noise sources and adjusting this interaction using tools typically used for spins, we’ve developed a method to apply these tools to orbital states. This is a significant scientific advancement."

Mueller added, "The collaboration was immensely rewarding. The acoustic waves excited the electrons similarly to how one pushes a swing on a playground. When the vibrations align with the electron’s motion, they can transfer energy effectively. It’s remarkable to control electron movement using essentially a loudspeaker."