Two-qubit parametric amplifier: Large amplification of weak signals

摘要

Using numerical simulations, we show that two coupled qubits can amplify a weak signal about a hundredfold.nThis can be achieved if the two qubits are biased simultaneously by this weak signal and a strong pump signal,nboth having frequencies close to the interlevel transitions in the system. The weak signal strongly affects thenspectrum generated by the strong pumping drive by producing and controlling mixed harmonics with amplitudesnof the order of the main harmonic of the strong drive. We show that the amplification is robust with respect tonnoise, with an intensity of the order of the weak signal. When deviating from the optimal regime (correspondingnto strong qubit coupling and a weak signal frequency equal to the interlevel transition frequency), the proposednamplifier becomes less efficient, but it can still considerably enhance a weak signal (by several tens).We thereforenpropose to use coupled qubits as a combined parametric amplifier and frequency shifter.