标题： 超越旋转波近似的强非谐低频单量子比特门 显示英文标题

标题： Single-Qubit Gates Beyond the Rotating-Wave Approximation for Strongly Anharmonic Low-Frequency Qubits

摘要： 单量子比特门在许多量子平台上通过与量子比特跃迁频率线性驱动共振来实现，这通常在旋转波近似（RWA）的理论框架下进行描述。 然而，对于低频量子比特的快速门操作，RWA可能不成立，我们需要考虑反向旋转项对量子比特动力学的贡献。 将反向旋转项纳入理论描述会带来两个挑战。 首先，由于哈密顿量不再自交换，解析计算时间演化变得具有挑战性。 此外，时间演化现在依赖于载波相位，因此在一般情况下，门序列中的每个操作都是不同的。 在本工作中，我们推导并验证了对驱动脉冲的修正，以最小化两能级系统中这些反向旋转项的影响。 随后，我们推导了一个第二修正项，该修正项来源于强非简谐系统中的非计算能级。 我们在一个通量子超导量子比特上实验实现了这些修正项，通量子是一个强非简谐、低频量子比特的示例，其RWA可能不成立，并展示了如何在不需要额外硬件复杂性的前提下实现快速且高保真度的单量子比特门。 显示英文摘要

摘要： Single-qubit gates are in many quantum platforms applied using a linear drive resonant with the qubit transition frequency which is often theoretically described within the rotating-wave approximation (RWA). However, for fast gates on low-frequency qubits, the RWA may not hold and we need to consider the contribution from counter-rotating terms to the qubit dynamics. The inclusion of counter-rotating terms into the theoretical description gives rise to two challenges. Firstly, it becomes challenging to analytically calculate the time evolution as the Hamiltonian is no longer self-commuting. Moreover, the time evolution now depends on the carrier phase such that, in general, every operation in a sequence of gates is different. In this work, we derive and verify a correction to the drive pulses that minimizes the effect of these counter-rotating terms in a two-level system. We then derive a second correction term that arises from non-computational levels for a strongly anharmonic system. We experimentally implement these correction terms on a fluxonium superconducting qubit, which is an example of a strongly anharmonic, low-frequency qubit for which the RWA may not hold, and demonstrate how fast, high-fidelity single-qubit gates can be achieved without the need for additional hardware complexities.