Two independent research efforts have introduced fresh approaches to measuring and controlling phonons—discrete packets of vibrational energy that behave as quantum particles. These developments could provide a clearer window into how individual phonons behave within large-scale systems, potentially unlocking practical uses such as quantum information storage.
The first technique, demonstrated by a team led by Sungkun Hong, employs light to steer the state of single phonons. Until now, optical control of phonons was only possible when they were entangled with other quantum particles. Hong's group, however, first detected a lone phonon inside a nanomechanical resonator using a blue pulse of light. They then applied a red pulse to induce a state-swap interaction, effectively transferring the phonon's quantum state to a photon. The emitted photons were reflected back to single-photon detectors, allowing the team to infer the phonon's non-classical state from the photon's measured state.
This marks a significant step because it enables direct observation and manipulation of a phonon in its quantum ground state, a feat that had previously required coupling to other systems. The ability to probe phonons in isolation could aid in understanding how these particles interact within larger assemblies, which is crucial for developing quantum memory and transduction technologies.
In a parallel effort, Yiwen Chu and colleagues have engineered a new device that leverages electromechanical forces to achieve quantum-level control. Historically, achieving such control without resorting to bulky electromagnetic cavities or complex circuits has been a formidable challenge. While a single proof-of-principle device existed, it was impractical due to qubit loss and fabrication complexity.
Chu's team has overcome these hurdles with a simpler, more manufacturable design. The device consists of a piezoelectric resonator coupled to a qubit. When the resonator and qubit are strongly coupled, manipulating the qubit's state generates single phonons within the resonator. This setup allows for a wide range of quantum modes to be induced coherently and offers a high degree of control over the states of quantum particles.
The researchers believe their device can be further refined, potentially enabling the storage and transduction of quantum microwave signals—a key requirement for future quantum networks and computing systems.
Both studies, while still in the experimental stage, underscore the rapid progress in quantum control. By providing new tools to harness phonons, they pave the way for more robust quantum information processing, where sound-based particles could serve as reliable carriers of quantum information.
