Conditional addition of photons represents a crucial tool for optical quantum state engineering and it forms a fundamental building block of advanced quantum photonic devices. Here we report on experimental implementation of the conditional addition of several photons. We demonstrate the addition of one, two, and three photons to input coherent states with various amplitudes. The resulting highly nonclassical photon-added states are completely characterized with time-domain homodyne tomography, and the nonclassicality of the prepared states is witnessed by the negativity of their Wigner functions. We experimentally demonstrate that the conditional addition of photons realizes approximate noiseless quantum amplification of coherent states with sufficiently large amplitude. We also investigate certification of the stellar rank of the generated multiphoton-added coherent states, which quantifies the non-Gaussian resources required for their preparation. Our results pave the way towards the experimental realization of complex optical quantum operations based on combination of multiple photon additions and subtractions.

光子的条件相加是光学量子态工程的重要工具，它构成了先进量子光子器件的基本构建模块。在这里，我们报告了几个光子的条件相加的实验实施。我们演示了添加一个、两个和三个光子来输入具有不同幅度的相干态。由此产生的高度非经典的光子添加态完全可以通过时域零差断层扫描来表征，并且所制备的态的非经典性可以通过其维格纳函数的负性来证明。我们通过实验证明，光子的条件相加实现了具有足够大振幅的相干态的近似无噪声量子放大。我们还研究了生成的多光子相干态的恒星等级认证，这量化了其制备所需的非高斯资源。我们的结果为基于多光子加法和减法组合的复杂光学量子操作的实验实现铺平了道路。