Researchers in the Netherlands have unveiled a groundbreaking chip-based device that can split phonons, the fundamental units of mechanical vibrations. This innovative technology, known as a single-phonon directional coupler or phonon splitter, has the potential to facilitate communication between different quantum technologies, enhancing their interoperability.
The phonon splitter could enable the transfer of quantum information from spin-based systems, which excel in data storage, to superconducting circuits that are better suited for data processing. “One of the main advantages of phonons over photons is their ability to interact with various systems,” stated Simon Gröblacher, the team leader from the Kavli Institute of Nanoscience at the Delft University of Technology. “This makes interfacing with different technologies much more accessible.”
Despite the promising features of phononic circuits, certain essential components are still required. One such component is a reversible beam splitter capable of either merging two phonon channels or dividing one channel into two based on the device”s orientation. Previous research has primarily explored designs based on surface acoustic waves, which have been commercially utilized, such as in mobile phone filters. However, these unconfined mechanical excitations are prone to significant losses as phonons escape into the surrounding chip.
In contrast, Gröblacher and his team opted to emulate the design principles of beam splitters found in photonic chips. They crafted a strip of thin silicon to create a phonon waveguide that confines phonons in all but one dimension, which enhances control and minimizes losses. By placing two waveguides in contact, the researchers enabled one waveguide to sense the mechanical vibrations of the other, allowing phonon modes to couple between them. This coupling was demonstrated at the single-phonon level.
The team also discovered that they could adjust the coupling strength by modifying the length of the contact between the waveguides. Although this marks the first instance of single-mode phonon coupling in this type of waveguide, Gröblacher expressed confidence in the results based on preliminary simulations using the finite element method. “I”m not surprised that it worked. I”m always surprised at how challenging it is to achieve the desired results,” he remarked.
A T Charlie Johnson, a physicist from the University of Pennsylvania, commented on the significance of the findings, noting, “These very exciting new results further advance the prospects for phonon-based qubits in quantum technology. Integrated quantum phononics is now one significant step closer.” In addition to facilitating communication between varied quantum systems, the new single-phonon coupler could also be instrumental in frequency shifting. For instance, microwave frequencies are susceptible to thermal noise due to their proximity to ambient heat, which complicates signal clarity.
Gröblacher is also leading a company focused on developing transducers for converting quantum information from microwave to optical frequencies, addressing this thermal noise issue. He believes that a single-phonon coupler could be an essential tool in this endeavor.
Lastly, one of the challenges that remains is managing dispersion, which happens when phonon modes couple to undesired modes, often due to imperfections in the nanofabricated device. However, Gröblacher has further ambitions, stating, “I believe the missing component for achieving the same level of control over phonons as we currently have with photons is a phonon phase shifter.” This addition would enable on-chip interferometry to direct phonons to various parts of a chip, facilitating advanced quantum experiments.
The findings from this research are detailed in the journal Optica.
