Newly fabricated crystals control interactions between high-frequency phonons and single quantum systems

Phonons, the quantum mechanical vibrations of atoms in solids, are often sources of noise in solid-state quantum systems, including quantum technologies, which can lead to decoherence and thus adversely impact their performance.

Strategies to reliably control phonons and their interactions with quantum systems could help to mitigate the adverse effects of these vibrations on the systems.

Researchers at Harvard University and other institutes have introduced a new approach to control the interactions between high-frequency phonons and single solid-state quantum systems. Their proposed method, outlined in a paper published in Nature Physics, relies on new diamond phononic crystals that they designed and fabricated, which can be used to engineer the local density of states in a host material.

“The ability to control phonons in solids is key since they often act as a source of noise and decoherence for solid-state quantum systems,” Kazuhiro Kuruma, first author of the paper, told Phys.org.

“The primary objective of our study was to demonstrate the control of the phononic local density of states of the host matrix using phononic crystals to suppress spontaneous single-phonon processes that induce the decoherence in individual quantum systems.”

Kuruma and his colleagues were able to design and fabricate diamond-based phononic crystals with nanoscale precision, embedding silicon-vacancy color centers within them. Using their newly fabricated crystals, the team observed an 18-fold reduction in the phonon-induced orbital relaxation rate, suggesting that these crystals suppress single-photon processes in the color centers.

“One of the most difficult parts of this study was the fabrication of phononic crystals in diamond,” explained Kuruma. “We carefully optimized a diamond etching process to fabricate these crystals with very small features down to 20 nm into single crystal diamond.”

The new diamond phononic crystals designed by the researchers were successfully used to control the interactions between the high-frequency phonons and color centers. Specifically, Kuruma and his colleagues found that these crystals could suppress interactions between single phonons and a quantum emitter at temperatures up to 20K.

“We demonstrated phononic crystals that can suppress high-frequency phonons from 50 to 70 GHz,” said Kuruma. “In addition, we demonstrated that spontaneous single-phonon processes in single quantum systems are suppressed by the phononic crystals even when increasing temperatures up to 20 K.”

In the future, the approach employed by this team of researchers and the phononic crystals they fabricated could contribute to the development of advanced quantum technologies that can benefit from the reliable control of phonon interactions, such as quantum phononic networks and quantum acoustic systems.

In addition, this recent study could inform future research rooted in acoustodynamics, an emerging field that focuses on quantum phenomena involving acoustic waves.

“Our results not only open the possibility of efficiently controlling specific high-frequency phonons for applications in radio-frequency signal processing, optomechanics, nonlinear phononics and thermoelectrics, but also could improve the properties of solid-state quantum systems at higher temperatures.”

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