超越具有自适应玻色采样的量子线性光学

摘要(中文译文)

通用光子量子计算需要光学非线性，这可以通过中间测量和自适应性来提供，以补充线性光学元件。在近期展望中，探究是否能在有限资源下获得超越线性光学的动力学至关重要。尽管近期结果显示了线性光学动力学如何对可生成的光子态集合施加限制，但用于研究非线性动力学涌现的定量方法在很大程度上仍然缺失。在此，我们分析了一种可以超越此类限制的情形。我们通过利用一种自适应玻色采样架构来实现这一点，其中光子器件中实现的光学演化通过基于测量的反馈逐步自适应。我们引入了实用方法来量化相对于线性光学出现差距的程度，并从线性光学演化的性质中推导出非线性见证量。然后，我们在最先进的光子平台上实现了复杂度递增的自适应玻色采样架构，验证了所开发的工具箱，既通过实现实时自适应性，也通过后选择对更复杂配置的自适应协议进行模拟。特别地，我们通过实验探测了一种情形，其中可以出现线性光学范式内无法获得的非线性动力学，从而展示了具有有限自适应性的光学架构是探索新情形的强大测试平台。

Abstract

Universal photon-based quantum computing requires optical nonlinearities, which can be induced by intermediate measurements and by adaptivity, to be supplied to linear-optical elements. In a near-term perspective, it is essential to probe whether dynamics going beyond linear optics can be accessed with a limited amount of resources. Although recent results show how linear-optical dynamics implies bounds on the set of photonic states that can be generated, quantitative methods for studying the emergence of nonlinear dynamics are largely missing. Here we analyse a regime in which such bounds can be surpassed. We do this by leveraging an adaptive boson sampling architecture in which the optical evolution implemented in a photonic device is progressively adapted via measurement-based feedback. We introduce practical methods to quantify the emergence of a gap with respect to linear optics and derive nonlinearity witnesses from the properties of linear-optical evolution. Then, we validate the toolbox developed within adaptive boson sampling architectures of increasing complexity implemented on a state-of-the-art photonic platform, both by realizing real-time adaptivity and by emulating adaptive protocols via post-selection for more complex configurations. In particular, we probe experimentally a regime in which nonlinear dynamics, unobtainable within a linear-optical paradigm, can arise, thus showing how optical architectures with limited adaptivity are a powerful testbed for exploring new regimes.

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