Two-qubit parametric amplifier: large amplification of weak signals

TL;DR

This paper demonstrates through numerical simulations that two coupled qubits can serve as a robust parametric amplifier, significantly boosting weak signals by about hundredfold while also functioning as a frequency shifter.

Contribution

The study introduces a novel scheme for using coupled qubits as a combined parametric amplifier and frequency shifter, with detailed analysis of robustness and efficiency.

Findings

Amplification of weak signals by approximately hundredfold.

Robustness of amplification against noise levels.

Efficiency decreases when deviating from optimal parameters, but still provides significant enhancement.

Abstract

Using numerical simulations, we show that two coupled qubits can amplify a weak signal about hundredfold. This can be achieved if the two qubits are biased simultaneously by this weak signal and a strong pump signal, both of which having frequencies close to the inter-level 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 inter-level 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.