Physicists unify quantum coherence with nonclassicality of light

Physicists have demonstrated that two independently developed concepts—quantum coherence and the nonclassicality of light—both arise from the same underlying resources. The ability to explain seemingly distinct phenomena within a single framework has long been a fulfilling aspiration in physics, and here it may also have potential applications for quantum information technologies.

The physicists, Kok Chuan Tan, Tyler Volkoff, Hyukjoon Kwon, and Hyunseok Jeong, at Seoul National University, have published a paper on their work in a recent issue of Physical Review Letters.

"The results unify two well-known yet independently developed notions in quantum information theory and quantum optics: the concept of quantum coherence that was recently developed based on the framework of quantum resource theories, and the notion of nonclassicality of light that has been established since the 1960s based on the quantum theory of light," Jeong told Phys.org.

As Jeong explained, an important question in physics is how to draw the line between "quantum" and "classical" and how to quantify the degree of "quantum." In their new work, the physicists developed a procedure that quantifies the amount of coherence in a superposition of coherent states. This information essentially tells how "quantum" vs. how "classical" these states are, which is useful for many quantum information tasks.