Interferometric phase measurement is widely used to precisely determine quantities such as length, speed and material properties^1,2,3. Without quantum correlations, the best phase sensitivity \({\boldsymbol{\Delta }}{\boldsymbol{\phi }}\) achievable using n photons is the shot-noise limit, \({\boldsymbol{\Delta }}{\boldsymbol{\phi }}=1\,/\sqrt{{n}}\). Quantum-enhanced metrology promises better sensitivity, but, despite theoretical proposals stretching back decades^3,4, no measurement using photonic (that is, definite photon number) quantum states has truly surpassed the shot-noise limit. Instead, all such demonstrations, by discounting photon loss, detector inefficiency or other imperfections, have considered only a subset of the photons used. Here, we use an ultrahigh-efficiency photon source and detectors to perform unconditional entanglement-enhanced photonic interferometry. Sampling a birefringent phase shift, we demonstrate precision beyond the shot-noise limit without artificially correcting our results for loss and imperfections. Our results enable quantum-enhanced phase measurements at low photon flux and open the door to the next generation of optical quantum metrology advances.

干涉式相位测量被广泛用于精确确定数量，例如长度，速度和材料特性^1,2,3。如果没有量子相关，则使用n个光子可获得的最佳相位灵敏度\（{\ boldsymbol {\ Delta}} \\\ boldsymbol {\ phi}} \\是散粒噪声极限\（{\ boldsymbol {\ Delta}} { \ boldsymbol {\ phi}} = 1 \，/ \ sqrt {{n}} \）。量子增强的计量技术有望带来更高的灵敏度，但是，尽管理论建议可以追溯到数十年前^3,4。，没有任何使用光子（即确定的光子数）量子态的测量能够真正超过散粒噪声极限。取而代之的是，通过消除光子损失，探测器效率低下或其他缺陷，所有这些演示都只考虑了所用光子的一个子集。在这里，我们使用超高效光子源和检测器来进行无条件纠缠增强光子干涉测量。通过对双折射相移进行采样，我们证明了超出散粒噪声极限的精度，而没有人为地校正损失和瑕疵的结果。我们的结果使得能够在低光子通量下进行量子增强的相位测量，并为下一代光学量子计量技术的发展打开了大门。