Quantum acoustics with propagating phonons
Doctoral thesis, 2020

Surface acoustic waves (SAWs) are mechanical vibrations that propagate on the surface of solids while dissipating little power, consequently enabling them to propagate freely over long distances. The speed and wavelength of SAWs are reduced a five order of magnitude compared to when light is used as a carrier at gigahertz frequencies. The unique properties of SAWs combined with the possibility to let them interact with artificial atoms, discovered and shown for the very first time in appended Paper I of this thesis, open up for exploration of new regimes of quantum physics. The appended Paper II is a book chapter providing an overview of many of the new areas of research, as well as going into depth of the method and significance of the results ofthe appended Paper I.

The essential interaction between artificial atoms and SAWs was further investigated by using Autler-Townes splitting to achieve fast control of the interactions. The appended Paper IV, shows a transmitted field extinction of 80 %, and provides proof of concept for a SAW router in the quantum regime. In addition, due to the artificial atom's highly frequency dependent coupling to SAWs, electromagnetically induced transparency (EIT) could be observed in the appended Paper V. Furthermore, the EIT region was distinguished from the Autler-Townes splitting region by a threshold in the applied power. The results produce parallel findings to quantum optics, but are perhaps best described as part of a different field, quantum acoustics.

Among the many possible areas of research emerging as an outcome of this work, a variety of potential quantum experiments would benefit greatly from a higher conversion efficiency between electric signals and SAWs. Due to this, focus was put on improving this conversion efficiency by studying superconducting unidirectional transducers (UDTs), making use of advances in classical SAW devices. The appended Paper III shows that 99.4~\% of the acoustic power can be focused in a desired direction and that the conversion between electric signals and SAWs is greatly improved by using UDTs, thereby eliminating the largest source of loss of symmetric inter-digital transducers. There is, however, a trade-off between conversion efficiency and bandwidth. This finding allows tailoring of quantum experiments based on SAWs that may pave the way towards measuring quantum sound.

phonon router


quantum acoustics

interdigital transducer

Electromagnetically Induced Transparency

artificial atom

Surface acoustic wave

superconducting circuits


unidirectional transducer

Kollektorn, Kemivägen 9
Opponent: Professor Christopher Bäuerle, Department of Nanoscience, Néel Institute, CNRS Grenoble


Maria Ekström

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Technology

Propagating phonons coupled to an artificial atom

Science,; Vol. 346(2014)p. 207-211

Journal article

Surface acoustic wave unidirectional transducers for quantum applications

Applied Physics Letters,; Vol. 110(2017)

Journal article

Cavity-free vacuum-Rabi splitting in circuit quantum acoustodynamics

PHYSICAL REVIEW A,; Vol. 99(2019)

Journal article

Quantum Acoustics with Surface Acoustic Waves

Quantum Optics, Quantum Science and Technology,; (2016)

Book chapter

Gustav Andersson, Maria K. Ekström, Per Delsing - Electromagnetically induced transparency in a propagating mechanical mode, Accepted in Phys. Rev. Lett.

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)


Basic sciences

Driving Forces

Innovation and entrepreneurship

Subject Categories

Atom and Molecular Physics and Optics

Other Physics Topics

Nano Technology

Other Electrical Engineering, Electronic Engineering, Information Engineering


Nanofabrication Laboratory



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4797


Chalmers University of Technology

Kollektorn, Kemivägen 9

Opponent: Professor Christopher Bäuerle, Department of Nanoscience, Néel Institute, CNRS Grenoble

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