Quantum and topological phononics with ultrasound waves on a chip
Join us for a talk by quantum physicist Albert Schliesser (Niels Bohr Institute), who was recently awarded with the 2025 EliteForsk Prize. After the talk there will be time for questions as well as informal chat over tea, coffee and cake.
Title: Quantum and topological phononics with ultrasound waves on a chip
Abstract: Ultrasound waves in membrane resonators with engineered phononic modes can maintain quantum coherence as long as 100 milliseconds.1 Optical monitoring of their motion allows approaching2 and beating3 the standard quantum limit (SQL) for displacement and force measurements, and to verify a past quantum state of the mechanical system.4
Using radiation pressure, electrostatic or magnetic forces couple to optical, microwave and spin degrees of freedom. This allows quantum control of the phononic degrees of freedom, and enables new applications in quantum sensing and information processing, such as spin microscopy5,6 and mechanical memories for light7.
There has also been growing interest in using traveling phonons to transport, mediate, and process quantum signals by routing them in waveguides8,9. We have developed a new topological phononic waveguide that combines the concept of a valley-Hall topological insulator with the soft clamping technique in thin SiN membranes10.
We demonstrate that it achieves dissipation-induced propagation loss as low as 3 dB/km at megahertz frequencies – four orders of magnitude lower than existing chip-scale phononic systems at room temperature – and very low (~0.01%) backscattering at sharp bends. Such low-loss, low-backscattering phononic waveguides are a promising platform for interconnecting hybrid quantum systems when cooled to cryogenic temperatures.
1 Seis, Y. et al. Nat Commun 13, 1507 (2022)
2 Rossi, M. et al. Nature 563, 53–58 (2018)
3 Mason, D. et al. Nature Physics 15, 745 (2019)
4 Rossi, M. et al. Phys. Rev. Lett. 123, 163601 (2019)
5 Hälg, D. et al. Phys. Rev. Applied 15, L021001 (2021)
6 Gisler, T. et al. Phys. Rev. Appl. 22, 044001 (2024)
7 Kristensen, M. B. et al. Phys. Rev. Lett. 132, 100802 (2024)
8 Wang, Y. et al. Applied Physics Letters 124, 070502 (2024)
9 Shah, T. et al. Rev. Mod. Phys. 96, 021002 (2024)
10 Xi, X. et al. arXiv.org (2024)
contact: albert.schliesser@nbi.ku.dk
Find the venue
When you enter the building at Lyngbyvej 2, go to the end furthest away from Jagtvej.
At the end of the building you turn right and walk down the hallway until you reach the lift.
Go to the 4th floor and turn left when you leave the lift. You’ll find us at the end of the hallway.