Quantum Vacuum in Matter

TL;DR

This paper reviews how quantum vacuum fluctuations influence matter within photonic cavities, leading to altered material properties and new possibilities for engineering materials through vacuum-matter interactions.

Contribution

It provides a comprehensive overview of recent experimental and theoretical advances in vacuum-modified condensed matter systems and discusses promising cavity designs for enhancing vacuum effects.

Findings

Vacuum fluctuations can modify electronic and vibrational states in materials.

Engineering the quantum vacuum enables control over material properties.

Recent developments have demonstrated the potential for new material functionalities.

Abstract

An intriguing consequence of quantum field theory is that vacuum is not empty space; it is full of quantum fluctuating electromagnetic fields, or virtual photons, corresponding to their zero-point energy, even though the average number of photons is zero. These short-lived vacuum fluctuations are behind some of the most fascinating physical processes in the universe, including spontaneous emission, the Lamb shift, and the Casimir force. Recent theory and experiments indicate that the properties of materials placed in photonic cavities may be altered, even in the complete absence of any external fields, through interaction with the fluctuating vacuum electromagnetic fields. Judicious engineering of the quantum vacuum surrounding the matter inside a cavity can lead to significant and nonintuitive modifications of electronic and vibrational states, producing a ``vacuum dressed'' material. These exciting new ideas have stimulated discussions regarding the fundamental physics of vacuum-matter interactions and also broadened the scope of potential applications using zero-point fluctuations to engineer materials. This Perspective will first discuss recent experimental and theoretical developments on vacuum-modified condensed matter systems, which usually require the realization of the so-called ultrastrong light-matter coupling regime. Then, we will overview some of the most promising cavity designs for enhancing vacuum electromagnetic fields in materials with various energy scales. Finally, we will discuss urgent open questions and technical challenges to be solved in this emerging field.