Two-qubit parametric amplifier: Large amplification of weak signals
Sergey E. Savel'ev, Alexandre M. Zagoskin, Aleksandr L Rakhmanov, A. N. Omelyanchouk, Z. Washington, Franco Nori · Physical Review A · 2012
Using numerical simulations, we show that two coupled qubits can amplify a weak signal about a hundredfold. This can be achieved if the two qubits are biased simultaneously by this weak signal and a strong pump signal, both having frequencies close to the interlevel transitions in the system. The weak signal strongly affects the spectrum generated by the strong pumping drive by producing and controlling mixed harmonics with amplitudes of the order of the main harmonic of the strong drive. We show that the amplification is robust with respect to noise, with an intensity of the order of the weak signal. When deviating from the optimal regime (corresponding to strong qubit coupling and a weak signal frequency equal to the interlevel transition frequency), the proposed amplifier becomes less efficient, but it can still considerably enhance a weak signal (by several tens). We therefore propose to use coupled qubits as a combined parametric amplifier and frequency shifter.