On-chip Parametric Amplification in a Double Quantum Dots Circuit

Abstract

In microwave-based quantum circuits, including double quantum dots (DQDs), superconducting qubits and spin qubits, parametric amplifiers are indispensable in achieving high-fidelity qubit readouts. Despite its importance, the application of parametric amplifiers is hampered by several challenges, such as high insertion losses, constrained tunability, and a pronounced vulnerability to magnetic fields. Here, we demonstrate an on-site single-atom parametric amplifier (SAPA) within a reconfigurable quantum circuit, which consists of a superconducting microwave cavity and two GaAs gate-defined DQDs. Leveraging the inherent nonlinearity of the DQD, a parametric gain exceeding 11 dB is achieved. This gain contributes to enhance the qubit readout, as evidenced by exceeding two times improvement in the signal-to-noise ratio (SNR) when employing the DQD-based amplifier for reading out another DQD. Our work not only presents a versatile experimental platform with enhanced readout capabilities in quantum computing, but also introduces alternative choices of parametric amplifiers for a variety of microwave-based quantum circuits.

Figures (4)

• Figure 1: (a) Illustration of the reconfigurable quantum system, where functions of DQDs are adaptable through control lines "Control Lx". (b) Sketch of parametric amplification and on-chip integrated readout in the hybrid system composed of DQDs and a cavity. (c) Optical micrograph of the experimental device, which comprises two DQDs coupled to a cavity. Inset: false-color scanning electron micrograph of the DQD. The plunger gate PL (orange) is connected to the cavity. (d) Normalized cavity transmission amplitude $A/A_0$ of DQD$_1$ as functions of gate voltages $V_{\mathrm{1BR}}$ and $V_{\mathrm{1BL}}$, where $A_0$ is the averaged cavity transmission amplitude with DQD$_1$ in the Coulomb blockade regime. The orange arrow indicates the detuning $\varepsilon$, which is adjusted by $V_{\mathrm{1BR}}$ with the lever arm 0.072 in this experiment. Inset: Energy diagram of the charge qubit defined in DQD.
• Figure 2: (a) Vacuum Rabi splitting pattern of DQD$_1$ without applying a pump tone. (b) Corresponding simulation result for (a). (c) Comparison of the maximum transmission spectrum with a pump tone applied (purple circles), at the same detuning without a pump tone (orange triangles), and for a large detuning without a pump tone (brown diamonds). The lines are theoretical calculations using independently determined parameters, rather than fitting of the experimental data (symbols). (d) Cavity transmission with the same parameters as in (a) but with a pump tone applied, where the pump-signal detuning $\Delta \omega=2\pi\times5\,\mathrm{kHz}$. (e) Corresponding simulation result for (d).
• Figure 3: Characterization of the SAPA. (a) Spectra of the parametric amplification as a function of the probe frequency detuning with respect to the input signal $\delta \omega$. The orange line shows the signal without applying a pump tone, centered at $\omega_{s}=\omega_{r}$. The purple line represents the scenario with the pump tone applied to DQD$_1$, centered at $\omega_{s}=\omega_{r}-2\pi\times 4~\rm MHz$. (b) The normalized transmission amplitude under pump, as functions of frequency difference $\Delta \omega=\omega_p-\omega_s$ and gate voltage $V_{\mathrm{1BR}}$. (c) The signal with detuning $\varepsilon=0$, as marked by the gray dashed line in (b). The red dashed line indicates $A/A_0=1$.
• Figure 4: On-site readout enhancement using the SAPA. (a) and (b), Charge stability diagrams of DQD$_2$, without and with a pump tone applied to DQD$_1$, respectively. (c) Average transmission spectra of DQD$_2$ as a function of the detuning $\varepsilon_{0,2}$, with (orange) and without (gray) a pump tune. The values of $V_{\mathrm{2BL}}$ are fixed as indicated by dashed lines in (a) and (b).