Quantum effects have opened a new era in metrology for realizing (providing standards for) the physical units. The conventional standards of our macroscopic world (collectively termed “artifacts”) alter with time, temperature, and weather; suffer from mechanical shock during transportation; and depend on unwanted side effects and on geometric dimensions that often cannot be measured with sufficient precision. In contrast, quantum effects in the atomic world are unchangeable and can be described with extraordinary precision using only a few fundamental constants.