**What is pico-electrodynamics?**

PED deals with the exploration of electrodynamic fields inside matter at the atomistic level. Some of the phenomena unique to the PED regime include new topological electrodynamic phases of matter, anomalous atomistic waves, and angular momentum of gauge fields coupled to charges.

**What is classical electrodynamics (CED)?**

Classical Electrodynamics encompasses the interactions between electric charges and currents based on the classical Newtonian model. Length scales and interaction strength are large enough that the quantum mechanical effects are minuscule. Electromagnetic phenomena studied within classical electrodynamics include electrostatics, charged bodies in motion, time varying electric and magnetic fields, electromagnetic induction, and radiation. Classical electrodynamics was pioneered by Maxwell, Ampère, Ørsted, Hertz, Heaviside, Faraday, and others in the early 19th century.

**What is quantum electrodynamics (QED)?**

The relativistic quantum field theory of electromagnetic fields is classified within the quantum electrodynamics. When the velocities of the charged particles are comparable with the speed of light, the relativistic effects are dominated. QED explains that the electric charges interact by means of photon exchange. Dirac, Heisenberg, Pauli, Wigner, and others pioneered the formulation of quantum electrodynamics in the 1930s.

**What is cavity QED?**

Cavity quantum electrodynamics deals with the interaction between light and atoms, or other particles confined within a reflective cavity. Within these conditions, a single photon can coherently couple to atoms and significantly modify their emission properties. Cavity QED was pioneered by the theoretical methods developed in the 1960s by Edwin Jaynes & Fred Cummings.

**What is quantum optics?**

Quantum optics is the study of how particle-like properties of photons interact with atoms and molecules. One of the main themes of quantum optics is to formulate, manipulate, and process the physical systems that operate on quantum mechanical principles. Works by R. Klauder, G. Sudarshan, R. J. Glauber, and L. Mandel established the field of quantum optics in the 1950s and 1960s.

**What is circuit QED? **

In circuit quantum electrodynamics, the photon is confined to a one-dimensional on-chip resonator and the quantum object is an artificial atom such as mesoscopic devices which exhibit an atom-like energy spectrum. The field of circuit QED has gained significant attention in the 21st century with its relevance in quantum computation and quantum information processing of superconducting circuits.