We propose methods to perform intensity interferometry of photons having two different wavelengths. Distinguishable particles typically cannot interfere with each other, but we overcome that obstacle by processing the particles via entanglement and projection so that they lead to the same final state at the detection apparatus. Specifically, we discuss how quasi-phase-matched nonlinear crystals can be used to convert a quantum superposition of light of different wavelengths onto a common wavelength, while preserving the phase information essential for their meaningful interference. We thereby gain access to a host of new observables, which can probe subtle frequency correlations and entanglement. Further, we generalize the van Cittert-Zernike formula for the intensity interferometry of extended sources, demonstrate how our proposal supports enhanced resolution of sources with different spectral character, and suggest potential applications.

中文翻译：

---

不同波长光的纠缠使能强度干涉测量

我们提出了对具有两种不同波长的光子进行强度干涉测量的方法。可区分的粒子通常不会相互干扰，但我们通过纠缠和投影处理粒子来克服这个障碍，以便它们在检测设备上产生相同的最终状态。具体而言，我们讨论了如何使用准相位匹配非线性晶体将不同波长的光的量子叠加转换为公共波长，同时保留对其有意义的干涉必不可少的相位信息。因此，我们可以获得大量新的可观测数据，这些数据可以探测微妙的频率相关性和纠缠。此外，我们推广了扩展源强度干涉测量的 van Cittert-Zernike 公式，