  Frequency tunable qubit plays a significant role for scalable superconducting
quantum processors. The state-of-the-art room-temperature electronics for
tuning qubit frequency suffers from unscalable limit, such as heating problem,
linear growth of control cables, etc. Here we propose a scalable scheme to tune
the qubit frequency by using in situ superconducting circuit, which is based on
radio frequency superconducting quantum interference device (rf-SQUID). We
demonstrate both theoretically and experimentally that the qubit frequency
could be modulated by inputting several single pulses into rf-SQUID. Compared
with the traditional scheme, our scheme not only solves the heating problem,
but also provides the potential to exponentially reduce the number of cables
inside the dilute refrigerator and the room-temperature electronics resource
for tuning qubit frequency, which is achieved by a time-division-multiplex
(TDM) scheme combining rf-SQUID with switch arrays. With such TDM scheme, the
number of cables could be reduced from the usual $\sim 3n$ to $\sim
\log_2{(3n)} + 1$ for two-dimensional quantum processors comprising $n$ qubits
and $\sim 2n$ couplers. Our work paves the way for large-scale control of
superconducting quantum processor.
