QUANTUM-MECHANICS AND PRECISION-MEASUREMENTS

The accuracies of measurements of almost all fundamental physical cons tants have increased by factors of about 10000 during the past 60 year s. Although some of the improvements are due to greater care, most are due to new techniques based on quantum mechanics. Although the Heisen berg Uncertainty Principle often limits measurement accuracies, in man y cases the validity of quantum mechanics makes possible the vastly im proved measurement accuracies. Seven quantum features that have a prof ound influence on the science of measurements are: (1) Existence of di screte quantum states of energy. (2) Energy conservation in transition s between two states. (3) Electromagnetic radiation of frequency nu is quantized with energy hu per quantum. (4) The identity principle. (5) The Heisenberg Uncertainty Principle. (6) Addition of probability amp litudes (not probabilities). (7) Wave and coherent phase phenomena. Of these seven quantum features, only the Heisenberg Uncertainty Princip le limits the accuracy of measurements, and its affect is often neglig ibly small. The other six features make possible much more accurate me asurements of quantum systems than with almost all classical systems. These effects are discussed and illustrated.