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  • Print publication year: 2016
  • Online publication date: August 2018

7 - Elementary Concepts of Quantum Physics



It is correctly told that mathematics is the queen of all sciences; in the same spirit, quantum physics or quantum mechanics may be called the king of all sciences. Our knowledge in any field of science is incomplete as long as we remain unacquainted with quantum physics. The concepts of quantum physics form the basis for our present understanding of physical phenomena on an atomic and microscopic scale. The concepts of quantum physics can be applied to most fields of science and engineering starting from biology to quantum computers to cosmology. Within engineering, important subjects of practical significance include semiconductor transistors, lasers, quantum optics, and molecular devices where quantum physics plays the most vital role. As technology advances, quantum concepts give birth to an increasing number of new electronic and opto-electronic devices. Their fabrications and functions can only be understood by using quantum physics. Within the next few years, fundamentally quantum devices such as single-electron memory cells and photonic signal processing systems may be available commercially. As nano-and atomicscale devices become easier to manufacture, these sophisticated manufacturing units will require an increasing number of individuals with sound knowledge of quantum physics. Therefore, all universities in the world have included quantum physics as a subject in their technical course curricula. Quantum physics is no longer a theoretical subject with mathematical complexities but an engineering subject!

Need for Quantum Physics

Two time-tested proverbs are, ‘Failure is the pillar of success’ and ‘Necessity is the mother of invention’. Classical physics based on Newtonian laws, thermodynamical laws and classical laws of electromagnetism explained successfully the macroscopic world. The macroscopic world is directly observable or can be made observable by relatively simple devices. However, classical physics failed seriously in explaining the phenomena in the realm of atoms, nucleons and elementary particles. These failures gave birth to a new branch in physics called quantum physics. In the following, we mention a few examples of the failures of classical concepts, though the list is endless.

An accelerated charge emits energy and the electron revolving around a nucleus should emit energy [its energy then should go to zero] resulting in the collapse of the atom; but atom is a stable entity! According to classical theory, the excited hydrogen atom should emit electromagnetic radiations of all the wavelengths continuously.