Quantum information is often carried in the frequency and polarization degrees of freedom (DoFs) in single photons and entangled photons. We demonstrate an approach to couple and decouple the frequency and polarization DoFs of broadband biphotons. Our approach is based on a nonlinear interferometer consisting of a linear dispersive medium and a polarization controller in between the two biphoton sources (nonlinear media). When the two DoFs are decoupled, maximally polarization-entangled biphotons are observed in the polarization DoF, while interference fringes are observed in the spectrum of the biphotons. When the two DoFs are coupled, by adjusting the polarization controller, interference fringes disappear from the spectrum and instead appear in the degree of polarization entanglement, varying between 0 and 1, depending on the signal and idler frequencies. Our approach offers a convenient means of tuning the polarization entanglement and can be employed for arbitrary biphoton polarization state generation.

量子信息通常以单光子和纠缠光子的频率和偏振自由度 (DoF) 形式携带。我们演示了一种耦合和解耦宽带双光子的频率和偏振自由度的方法。我们的方法基于非线性干涉仪，该干涉仪由线性色散介质和两个双光子源（非线性介质）之间的偏振控制器组成。当两个自由度解耦时，在偏振自由度中观察到最大偏振纠缠双光子，而在双光子的光谱中观察到干涉条纹。当两个自由度耦合时，通过调整偏振控制器，干涉条纹从频谱中消失，取而代之的是偏振纠缠程度，在 0 和 1 之间变化，具体取决于信号频率和闲频频率。我们的方法提供了一种调节偏振纠缠的便捷方法，并且可用于任意双光子偏振态生成。