标题： 纠缠增强的光学离子钟 显示英文标题

标题： Entanglement-enhanced optical ion clock

摘要： 纠缠态有望提高量子传感器的精度和准确性。我们通过实验表明，使用纠缠态的光学钟跃迁光谱可以优于其经典对应方法。两个 ^{40}\text{卡德安} ^{+}离子被制备在一个量子态中，其一阶磁场敏感度为零，这延长了原子的相干时间，并实现了长达550毫秒的接近寿命限制的探测时间。在我们的方案中，纠缠离子达到与非相关离子相同的不稳定度，但所需的探测时间仅为后者的一半，从而使钟的循环时间更快。 我们运行两个纠缠的 ^{40}\text{卡} ^{+}离子作为光学原子钟，并将其频率不稳定度与一个 ^{87}\text{Sr} 光晶格钟的不稳定度进行比较。 对于所有探测时间，纠缠离子钟的不稳定度都低于用经典关联态操作的时钟。 当探测时间小于 100 毫秒时，我们观察到纠缠离子钟的不稳定度低于理论上预期的两个非相关离子的量子投影噪声极限。 最低的分数频率不稳定度为 7e-16 / sqrt(τ / 1 s)，出现在 250 毫秒的探测时间下，受限于探测激光的剩余相位噪声。 这代表迄今为止 reported 的 ^{40}\text{卡德安} ^{+}离子钟的最低不稳定性。 显示英文摘要

摘要： Entangled states hold the promise of improving the precision and accuracy of quantum sensors. We experimentally demonstrate that spectroscopy of an optical clock transition using entangled states can outperform its classical counterpart. Two ^{40}\text{Ca}^{+} ions are entangled in a quantum state with vanishing first-order magnetic field sensitivity, extending the coherence time of the atoms and enabling near lifetime-limited probe times of up to 550 ms. In our protocol, entangled ions reach the same instability as uncorrelated ions, but at half the probe time, enabling faster cycle times of the clock. We run two entangled ^{40}\text{Ca}^{+} ions as an optical clock and compare its frequency instability with a ^{87}\text{Sr} lattice clock. The instability of the entangled ion clock is below a clock operated with classically correlated states for all probe times. We observe instabilities below the theoretically expected quantum projection noise limit of two uncorrelated ions for interrogation times below 100 ms. The lowest fractional frequency instability of 7e-16 / sqrt(tau / 1 s) is reached for 250 ms probe time, limited by residual phase noise of the probe laser. This represents the lowest instability reported to date for a ^{40}\text{Ca}^{+} ion clock.