Artificial Atoms Make Microwave Photons Countable

Scanning electron micrograph of an artificial atom (light blue) inside of a transmission line cavity (dark blue). The “atom,” composed of over a billion atoms of aluminum, gives a distinct signal for each possible photon number in the cavity. The theoretical prediction (color plot) was verified by these experiments. (Schuster/Yale). Using artificial atoms on a chip, Yale physicists have taken the next step toward quantum computing by demonstrating that the particle nature of microwave photons can now be detected, according to a report spotlighted in the February 1 issue of the journal Nature. Quantum theories are often considered to apply best to processes that happen on the smallest scale of atoms and molecules. By making artificial atoms larger — to a size that is nearly visible — and using microwaves as the source of energy, the collaborative research from the laboratory of Professor Robert Schoelkopf and the theory group of Professor Steven Girvin in the departments of Applied Physics and Department of Physics at Yale created an electronic circuit that stores and measures individual microwave photons. In the process, they bring quantum mechanics to a larger scale and hope to employ it to build new kinds of quantum machines.