Bosonic encoding is an approach for quantum information processing, promising lower hardware overhead by encoding in the many levels of a harmonic-oscillator mode. Scaling to multiple modes requires weak interaction for independent control, yet strong interaction for fast control. Applying fast and efficient universal control on multiple modes remains an open problem. Surprisingly, we find that displacements conditioned on the state of a single-qubit ancilla coupled to multiple harmonic oscillators are sufficient for universal control. We present the conditional-no operation concept, which can be used to reduce the duration of entangling gates. Within this guiding concept, we develop the conditional-not displacement control method which enables fast generation and control of bosonic states in multimode systems weakly coupled to a single-ancilla qubit. Our method is fast despite the weak ancilla coupling. The weak coupling in turn allows for excellent separability and thus independent control. We demonstrate our control on a superconducting transmon qubit weakly coupled to a multimode superconducting cavity. We create both entangled and separable cat states in different modes of the multimode cavity, showing entangling operations at low crosstalk while maintaining independent control of the different modes. We show that the operation time is not limited by the inverse of the coupling rate, which is the typical timescale, and we exceed it by almost 2 orders of magnitude. We verify our results with an efficient method for measurement of the multimode characteristic function which employs our conditional-not displacement. Our results inspire a new approach toward general entangling operations and allow for fast and efficient multimode bosonic encoding and measurement.

中文翻译：

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条件非位移：使用单个量子位的快速多振荡器控制

玻色编码是一种量子信息处理方法，通过在谐波振荡器模式的多个级别进行编码，有望降低硬件开销。扩展到多种模式需要弱交互来实现独立控制，但需要强交互来实现快速控制。在多种模式上应用快速高效的通用控制仍然是一个悬而未决的问题。令人惊讶的是，我们发现以与多个谐振子耦合的单量子位辅助状态为条件的位移足以进行通用控制。我们提出了条件无操作的概念，它可以用来减少纠缠门的持续时间。在这一指导概念下，我们开发了条件非位移控制方法，该方法能够在与单辅助量子位弱耦合的多模系统中快速生成和控制玻色子态。尽管辅助耦合较弱，但我们的方法速度很快。弱耦合又允许出色的可分离性，从而实现独立控制。我们展示了对与多模超导腔弱耦合的超导传输量子位的控制。我们在多模腔的不同模式下创建纠缠和可分离猫状态，展示低串扰下的纠缠操作，同时保持对不同模式的独立控制。我们表明，操作时间不受耦合率倒数（这是典型的时间尺度）的限制，并且我们超过了它几乎 2 个数量级。我们通过一种有效的多模特征函数测量方法验证了我们的结果，该方法采用我们的条件非位移。我们的研究结果启发了一种通用纠缠操作的新方法，并允许快速高效的多模玻色子编码和测量。