Researchers from Delft University of Technology and the University of Vienna have demonstrated the first 4-port directional coupler for quantum mechanical excitations, a key building block for phononic circuits. The research, published in Optica Quantum, presents a device that functions as a phononic beam splitter for single phonons, which are quantized mechanical vibrations that can carry information in quantum systems.
The integrated phononic directional coupler is built on a silicon-on-insulator wafer and uses highly confined, gigahertz-frequency phonons traveling in phononic-crystal waveguides. The device’s design is intended to allow for a small footprint and a millisecond-long phononic lifetime, which are key advantages over other platforms. The researchers validated the device’s quantum-level performance by sending a single-phonon Fock state through it, confirming that it can be used with quantized excitations.
This work represents a foundational advancement toward scalable, integrated phononic platforms for both classical and quantum applications. The device is intended to help connect various quantum systems via phonons, which could enable hybrid quantum networks, on-chip quantum routers, and ultra-sensitive mechanical sensors. The research was funded by the European Research Council and the Netherlands Organization for Scientific Research.
Read the full announcement in Optica Quantum here.
October 7, 2025
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