Wide-band, tunable and high-efficiency microwave-to-acoustics transduction on lithium niobate

Acoustic waves play an essential role in a wide variety of quantum systems such as microwave-to-optics transducers, quantum acoustics devices or devices using strain to couple to spin defects. For surface acoustic waves and Lamb waves, control and detection are commonly achieved using interdigital transducers (IDTs) on piezoelectric materials. However, due their frequency dependent impedance, IDTs can only be efficient over narrow bandwidths.



We propose a wide-band high-efficiency transducer to perform microwave-to-acoustics transduction where an interdigital transducer (IDT) is used to couple to Lamb waves in suspended Lithium Niobate. By using a SQUID array, we design a magnetic flux tunable impedance matching network that optimizes power conversion at the IDT despite its frequency dependent impedance.

Measurements at cryogenic temperatures show that this bi-directional transducer can reach high efficiencies over large bandwidths (typically 400 MHz) and can be tuned over a wide frequency band (4-8GHz). This device is a building block for quantum acoustics experiments and could be used to perform the acoustic spectroscopy of quantum objects or couple superconducting qubits to mechanical degrees of freedom.