Theory of quantum phased arrays: A proposal for wireless quantum technologies

The seminal work on antenna theory led to the first steerable and directional transmission of electromagnetic waves over free space with phased arrays. Antenna arrays laid the foundation for classical wireless sensing and communication technologies, which have had a transformative impact on the modern world. Here, we extend the operating principles of phased arrays to quantum fields in a concept we name quantum phased arrays. A quantum phased array (QPA) is an array of quantum coherent elements that can transmit or receive quantum fields over free space. By controlling the field at each element, wavefunctions can be engineered through quantum interference of these fields. We present an analysis of phased arrays in the second quantization formalism and connect the key concepts of classical antenna theory to their nonclassical counterparts. We introduce protocols for quantum state synthesis and entanglement distribution with QPAs. Lastly, we discuss the prospect of wireless quantum technologies and mobile quantum devices based on the experimental realizations of QPAs with chip-scale systems.