Experimental Observation of Screening and Amplification of Quantum Fluctuation in Aqueous Electrolyte Solution

In a classical liquid, the static dielectric constant is always larger than 1, meaning that external static electric fields are always screened by the solvent. Under quantum mechanics, instantaneous electric fields exist due to the zero-point motion of electrons, and it is so far unexplored whether those instantaneous fields will always be screened by the solvent. Here, we show that a small-angle liquid electron scattering experiment is able to quantitatively measure the quantum fluctuation of the instantaneous dipole moment of hydrated ions. Counterintuitively, we found that the quantum fluctuation of different ions can be either reduced (K⁺ and Cl^-), unaffected (Na⁺), or amplified (Li⁺) by the aqueous environment, defying classical electrostatic intuition. This ion specificity of quantum fluctuation supports the postulation that specific ion effects originated from quantum many-body interactions. Our measurement proves that screening, a fundamental concept of classical liquid, can behave completely differently in the quantum regime.