Tunable superconducting transmissionline resonator for qubit coupling
Licentiate thesis, 2008

In this licentiate thesis design, fabrication, and measurements of tunable superconducting microwave transmission line resonators are described. The resonators are of quarter wavelength type were the tuning is achieved by changing one of the boundary conditions of the resonator through a tunable impedance. As tunable impedance the Josephson inductance in form of SQUIDs is used. The Josephson inductance can then be tuned by applying a magnetic field to the SQUID loop. A tuning range of 750 MHz for a 5 GHz resonator is achieved, and as a figure of merit it can be tuned over 200 line widths. The purpose of the tunable resonators is to use them for dynamic coupling of superconducting quantum bits, this requires that the resonators can be tuned fast on the timescale of the resonator-qubit coupling. To measure tuning speeds faster then the ring up time of the resonators a method that measures the leakage of energy out of a detuned resonator was developed. With this method a frequency shift of the energy stored in the resonator can be measured. A detuning of 330 MHz in less than 10 ns is demonstrated for a 4.5 GHz resonator with a quality factor of 10$^4$. Working in the few photon limit indicates that the devices can be used to change the frequency of individual photons, this is however still to be demonstrated. As a part of this work the dressed states of a superconducting charge qubit was also studied.

fast tuning

superconductivity

transmission line

SCB

Josephson inductance.

Frequency tunable resonator

SQUID

CPW

aluminium

FB-salen
Opponent: Prof. Mikael Fogelström, Department of Microtechnology and Nanosicence, Chalmers.

Author

Martin Sandberg

Chalmers, Microtechnology and Nanoscience (MC2)

Subject Categories

Condensed Matter Physics

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 119

FB-salen

Opponent: Prof. Mikael Fogelström, Department of Microtechnology and Nanosicence, Chalmers.

More information

Created

10/6/2017