Using numerical simulations, we show that two coupled qubits can amplify aweak signal about hundredfold. This can be achieved if the two qubits arebiased simultaneously by this weak signal and a strong pump signal, both ofwhich having frequencies close to the inter-level transitions in the system.The weak signal strongly affects the spectrum generated by the strong pumpingdrive by producing and controlling mixed harmonics with amplitudes of the orderof the main harmonic of the strong drive. We show that the amplification isrobust with respect to noise, with an intensity of the order of the weaksignal. When deviating from the optimal regime (corresponding to strong qubitcoupling and a weak-signal frequency equal to the inter-level transitionfrequency) the proposed amplifier becomes less efficient, but it can stillconsiderably enhance a weak signal (by several tens). We therefore propose touse coupled qubits as a combined parametric amplifier and frequency shifter.
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