QDev Seminar: Pasquale Scarlino – University of Copenhagen

QDev Seminar: Pasquale Scarlino

ETH Zurich

Microwave Cavity Quantum Electro/Acousto-dynamics with superconductor-semiconductor hybrid technology

Semiconductor qubits rely on the control of charge and spin degrees of freedom of electrons or holes confined in quantum dots (QDs). Typically, semiconductor qubit-qubit coupling is short range, effectively limiting qubit distance to the spatial extent of the wavefunction of the confined particle (a few 100 nanometers). This is a significant constraint towards scaling of the QD-based architectures to reach dense 1D or 2D arrays of QDs.  Inspired by the success of circuit QED (cQED), I will demonstrate the strong coupling limit of individual electron charges [1] and an exchange only spins system [2], realized in GaAs quantum dots, by using the enhancement of the electric component of the vacuum fluctuations of a resonator with impedance beyond the typical 50 Ohm of standard coplanar waveguide technology.

By making use of this hybrid technology, I recently realized a proof of concept experiment, where the coupling between a transmon qubit and a double QD (DQD) is mediated by virtual microwave photon excitations in a high impedance SQUID array resonator, which acts as a quantum bus enabling long-range coupling between dissimilar qubits [3]. Furthermore, a similar solution can be implemented also to achieve a coherent coupling between two double quantum dot charge qubits placed ~50 um far away [4].

Electron charge and spin embedded in a solid-state environment experience also a strong interaction with the crystal lattice vibrations, which are the main responsible of the energy relaxation process. Among those phononic vibrations, surface acoustic waves (SAW) have attracted much interest as an alternative quantum mode localized at the surface of a material. I will explore a new innovative cQED architecture in which the electric field of the photon is replaced by the electric field of SAW phonons, confined in a SAW cavity. It is possible to envision a hybrid architecture where artificial atoms (superconducting qubits, QDs charge and spin qubits) are strongly coupled simultaneously to a microwave-superconducting resonator (photonic modes) and to a piezomachanical cavity (phononic modes). This will allow to explore light/matter hybridization in a class of solid-state systems and regimes, which are new in the context of cavity QED, and to make use of those phonons as a new computational resource.

[1] A. Stockklauser*, P. Scarlino*, et al. "Strong coupling cavity QED with gate-defined double quantum dots enabled by a high impedance resonator." Physical Review X (2017).

[2] A. Landig*, J. Koski*, et al. "Coherent spin-qubit photon coupling", arXiv:1806.09902 (accepted in Nature).

[3] P. Scarlino*, D. J. van Woerkom*, et al. "Coherent microwave photon mediated coupling between a semiconductor and a superconductor qubit", arXiv:1806.10039.

[4] D. J. van Woerkom*, P. Scarlino*, et al. "Microwave photon-mediated interactions between semiconductor qubits", arXiv:1806.09902.