As superconducting quantum circuits are scaling up rapidly towards the noisy intermediate-scale quantum (NISQ) era, the demand for electronic control equipment has increased significantly. To fully control a quantum chip of N qubits, the common method based on up-conversion technology costs at least 2 × N digital-to-analog converters (DACs) and N IQ mixers. The expenses and complicate mixer calibration have become a hinderance for intermediate-scale quantum control. Here we propose a universal control scheme for superconducting circuits, fully based on parametric modulation. To control N qubits on a chip, our scheme only requires N DACs and no IQ mixer, which significantly reduces the expenses. One key idea in the control scheme is to introduce a global pump signal for single-qubit gates. We theoretically explain how the universal gates are constructed using parametric modulation. The fidelity analysis shows that parametric single-qubit (two-qubit) gates in the proposed scheme can achieve low error rates of 10−4, with a gate time of about 60 ns (100 ns).
The quantum gate, as the foundation of quantum computation, depends on the architecture of the quantum chip, especially in superconducting systems. The parametric modulation to the flux bias is an important protocol to realize the multi‐qubit gate, which has some intrinsic advantages. Similar to other two‐qubit operations, parametric gates leave the extra phase in single‐qubit space, which is required to be corrected. In this article, the relation between the phases of the modulated pulse and the applied microwaves is experimentally characterized. By adjusting the envelope shape and phase of the applied pulses, the extra phase of the one qubit generated by the two‐qubit gate is suppressed via a simple and fast Ramsey‐like experiment. The tomography results demonstrate that this protocol is an effective calibrating method for future large‐scale quantum circuit manipulation.
High-fidelity parametric gates have been demonstrated with superconducting qubits via rf flux modulation of the qubit frequency. The modulation however leads to renormalization of the bare qubit-qubit coupling, thereby reducing the gate speed. Here, we realize a parametric-resonance gate, which is activated by bringing the average frequency of the modulated qubit in resonance with a static-frequency qubit while approximately retaining the bare qubit-qubit coupling. The activation of parametric-resonance gates does not depend on the frequency of modulation, allowing us to choose the modulation frequencies and avoid frequency collisions. Moreover, we show that this approach is compatible with tunable coupler architectures, which reduce always-on residual couplings. Using these techniques, we demonstrate iswap and controlled-
Z gates between two qubits coupled via a tunable coupler with average process fidelities as high as $99.3\mathrm{%}$ and $97.9\mathrm{%}$, respectively. The flexibility in activating parametric-resonance gates combined with a tunable coupler architecture provides a pathway for building large-scale quantum computers.