ETH Zurich, Institute of Quantum Electronics, Zurich, Switzerland.
Nature. 2019 Apr;568(7751):202-206. doi: 10.1038/s41586-019-1083-9. Epub 2019 Apr 10.
Quantum mechanics ascribes to the ground state of the electromagnetic radiation zero-point electric field fluctuations that permeate empty space at all frequencies. No energy can be extracted from the ground state of a system, and therefore these fluctuations cannot be measured directly with an intensity detector. The experimental proof of their existence therefore came from more indirect evidence, such as the Lamb shift, the Casimir force between close conductors or spontaneous emission. A direct method of determining the spectral characteristics of vacuum field fluctuations has so far been missing. Here we perform a direct measurement of the field correlation on these fluctuations in the terahertz frequency range by using electro-optic detection in a nonlinear crystal placed in a cryogenic environment. We investigate their temporal and spatial coherence, which, at zero time delay and spatial distance, has a peak value of 6.2 × 10 volts squared per square metre, corresponding to a fluctuating vacuum field of 0.25 volts per metre. With this measurement, we determine the spectral components of the ground state of electromagnetic radiation within the bandwidth of our electro-optic detection.
量子力学认为，电磁辐射的基态存在零点电场波动，这些波动以所有频率充斥着真空中的所有空间。一个系统的基态无法提取能量，因此这些波动无法用强度探测器直接测量。因此，它们存在的实验证据来自更间接的证据，如兰姆位移、紧密导体之间的卡西米尔力或自发辐射。到目前为止，还没有一种直接的方法来确定真空场波动的光谱特性。在这里，我们通过在低温环境中放置的非线性晶体中的电光探测，在太赫兹频率范围内对这些波动进行了场相关的直接测量。我们研究了它们的时间和空间相干性，在零时延和零空间距离处，相干性的峰值达到 6.2×10 伏特平方/平方米，对应于波动的真空场为 0.25 伏特/米。通过这项测量，我们确定了电光探测带宽内电磁辐射基态的光谱分量。
