Coherent control of quantum dynamics is key to a multitude of fundamental studies and applications¹. In the visible or longer-wavelength domains, near-resonant light fields have become the primary tool with which to control electron dynamics². Recently, coherent control in the extreme-ultraviolet range was demonstrated³, with a few-attosecond temporal resolution of the phase control. At hard-X-ray energies (above 5–10 kiloelectronvolts), Mössbauer nuclei feature narrow nuclear resonances due to their recoilless absorption and emission of light, and spectroscopy of these resonances is widely used to study the magnetic, structural and dynamical properties of matter^4,5. It has been shown that the power and scope of Mössbauer spectroscopy can be greatly improved using various control techniques^{6,7,8,9,10,11,12,13,14,15,16}. However, coherent control of atomic nuclei using suitably shaped near-resonant X-ray fields remains an open challenge. Here we demonstrate such control, and use the tunable phase between two X-ray pulses to switch the nuclear exciton dynamics between coherent enhanced excitation and coherent enhanced emission. We present a method of shaping single pulses delivered by state-of-the-art X-ray facilities into tunable double pulses, and demonstrate a temporal stability of the phase control on the few-zeptosecond timescale. Our results unlock coherent optical control for nuclei, and pave the way for nuclear Ramsey spectroscopy¹⁷ and spin-echo-like techniques, which should not only advance nuclear quantum optics¹⁸, but also help to realize X-ray clocks and frequency standards¹⁹. In the long term, we envision time-resolved studies of nuclear out-of-equilibrium dynamics, which is a long-standing challenge in Mössbauer science²⁰.

量子动力学的相干控制是众多基础研究和应用的关键¹ 。在可见光或更长波长领域，近共振光场已成为控制电子动力学的主要工具² 。最近，演示了极紫外范围内的相干控制³ ，其相位控制的时间分辨率为几阿秒。在硬 X 射线能量（高于 5-10 千电子伏）下，穆斯堡尔核由于其无反冲吸收和发射光而具有窄核共振，这些共振的光谱被广泛用于研究物质的磁性、结构和动力学特性^4,5 .事实证明，使用各种控制技术可以大大提高穆斯堡尔光谱的功率和范围^{6,7,8,9,10,11,12,13,14,15,16} 。然而，使用适当形状的近共振 X 射线场对原子核进行相干控制仍然是一个悬而未决的挑战。在这里，我们演示了这种控制，并使用两个 X 射线脉冲之间的可调相位来在相干增强激发和相干增强发射之间切换核激子动力学。我们提出了一种将最先进的 X 射线设备发出的单脉冲整形为可调谐双脉冲的方法，并证明了相位控制在几泽秒时间尺度上的时间稳定性。我们的结果解锁了原子核的相干光学控制，并为核拉姆齐光谱¹⁷和类自旋回波技术铺平了道路，这不仅应该推进核量子光学¹⁸ ，而且还有助于实现 X 射线时钟和频率标准¹⁹ 。 从长远来看，我们设想对核不平衡动力学进行时间分辨研究，这是穆斯堡尔科学中长期存在的挑战²⁰ 。