  We analyze the transfer of a quantum state between two resonators connected
by a superconducting transmission line. Nearly perfect state-transfer
efficiency can be achieved by using adjustable couplers and destructive
interference to cancel the back-reflection into the transmission line at the
receiving coupler. We show that the transfer protocol is robust to parameter
variations affecting the transmission amplitudes of the couplers. We also show
that the effects of Gaussian filtering, pulse-shape noise, and multiple
reflections on the transfer efficiency are insignificant. However, the transfer
protocol is very sensitive to frequency mismatch between the two resonators.
Moreover, the tunable coupler we considered produces time-varying frequency
detuning caused by the changing coupling. This detuning requires an active
frequency compensation with an accuracy better than 90% to yield the transfer
efficiency above 99%.
