Quantum measurement remains a puzzle through its stormy history from the birth of quantum mechanics to state-of-the-art quantum technologies. Two complementary measurement schemes have been widely investigated in a variety of quantum systems: von Neumann’s projective ‘strong’ measurement and Aharonov’s weak measurement. Here, we report the observation of a weak-to-strong measurement transition in a single trapped ⁴⁰Ca⁺ ion system. The transition is realized by tuning the interaction strength between the ion’s internal electronic state and its vibrational motion, which play the roles of the measured system and the measuring pointer, respectively. By pre- and post-selecting the internal state, a pointer state composed of two of the ion’s motional wavepackets is obtained, and its central-position shift, which corresponds to the measurement outcome, demonstrates the transition from the weak-value asymptotes to the expectation-value asymptotes. Quantitatively, the weak-to-strong measurement transition is characterized by a universal transition factor \({e}^{-{\varGamma }^{2}/2}\), where Γ is a dimensionless parameter related to the system–apparatus coupling. This transition, which continuously connects weak measurements and strong measurements, may open new experimental possibilities to test quantum foundations and prompt us to re-examine and improve the measurement schemes of related quantum technologies.

从量子力学的诞生到最先进的量子技术，从其漫长的历史中看，量子测量仍然是一个难题。已经在各种量子系统中广泛研究了两种互补的测量方案：冯·诺伊曼的投射“强”测量和阿哈罗诺夫的弱测量。在这里，我们报告了在一个单独的⁴⁰ Ca ^+中捕获到的从弱到强的测量转变的观察结果离子系统。通过调节离子内部电子状态与其振动运动之间的相互作用强度来实现过渡，离子的内部电子状态与其振动运动分别作用于被测系统和测量指针。通过预先和内部选择内部状态，获得了由两个离子运动波包组成的指针状态，并且其中心位置偏移与测量结果相对应，表明了从弱值渐近线向负值渐近线的过渡。期望值渐近线。从数量上看，弱到强的测量转换的特征在于通用转换因子\（{e} ^ {-{\ varGamma} ^ {2} / 2} \），其中Γ是与系统-设备耦合相关的无量纲参数。这种持续连接弱测量和强测量的过渡，可能会开辟新的实验可能性来测试量子基础，并促使我们重新审查和改进相关量子技术的测量方案。