  Simulating a system of two driven coupled qubits, we show that the
time-averaged probability to find one driven qubit in its ground or excited
state can be controlled by an ac drive in the second qubit. Moreover,
off-diagonal elements of the density matrix responsible for quantum coherence
can also be controlled via driving the second qubit, i.e., quantum coherence
can be enhanced by appropriate choice of the bi-harmonic signal. Such a dynamic
synchronization of two differently driven qubits has an analogy with harmonic
mixing of Brownian particles forced by two signals through a substrate.
Nevertheless, the quantum synchronization in two qubits occurs due to
multiplicative coupling of signals in the qubits rather than via a nonlinear
harmonic mixing for a classical nano-particle.
