Thomas Aref, University of Illinois at Urbana-Champaign
My research focuses on probing superconducting quantum bits or qubits with acoustic radiation in the form of surface acoustic waves (SAWs). This allows the investigation of sound interacting with artificial atoms on a quantum mechanical level, i.e. quantum acoustics with traveling phonons. We can then reproduce findings from quantum optics with sound taking over the role of light, highlighting the similarities between phonons and photons. In addition, new opportunities arise from the low propagation speed of phonons, potentially enabling dynamic schemes for processing quantum information. The relatively short wavelength of SAWs also allows regimes of atomic physics to be explored that cannot be easily reached in photonic systems. One example of this is the frequency dependent coupling of the artificial atom to the phononic vacuum. This coupling results in a non-monotonic Lamb shift due to causality, via the Kramers-Kronig relation. We have observed a frequency dependent Lamb shift and corresponding coupling variation which agree well with theory. A particularly interesting feature of this phononic Lamb shift is the ability for the atom to react at multiple frequencies, for sufficiently strong coupling.