Two-qubit parametric amplifier: Large amplification of weak signals

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.

Harmonic mixing in two coupled qubits: Quantum synchronization via ac drives

“…As we have recently shown, this results in a quite unusual spectra of a,b and in particular X 1 and Z 1 with many harmonic peaks Fig. 1 and driving frequency ω 1 = 2 + g 2 − g (a) equal to an energy level transition frequency [11] and for ω 1 = 2.113( 2 + g 2 − g) (b), which is away from the energy-level transition. Simulations with a ten-times-denser point mesh for a frequency ratio from 0.01 to 1 [see inset in (a)] uncovered some extra commensurate frequency ratio where peaks in X 1 occurs.…”

“…We simulated the set (5) by using the standard Euler method which has been proved to converge well for low-noise drives [10,11] and analyzed the time-averaged diagonal element of density matrix…”

“…This set of ordinary differential equations is an ideal starting point for numerical analysis of the dynamics of two driven and dissipative qubits as it has been proved before [10,11]. We simulate these differential equations for two differently driven qubits and study quantum harmonic mixing.…”

“…Following this direction of research, several quantum amplifiers have been recently proposed for one- [9] and two-qubit [10,11] systems. The idea [9,10] was to extend the stochastic resonance phenomenon (amplification by certain amount of noise) for one or two ac-driven qubits to enhance quantum coherence.…”

“…The idea [9,10] was to extend the stochastic resonance phenomenon (amplification by certain amount of noise) for one or two ac-driven qubits to enhance quantum coherence. Further analogy [11][12][13] between two-qubit systems, a Brownian particle driven in periodic substrate and a parametric amplifier, has resulted in a proposal to use two coupled qubits as an amplifier of quantum oscillations.…”