T he journey from quantum mechanics to quantum computing spans over a century, starting in 1900 with Planck’s proposal of quantized energy to explain black-body radiation. This pivotal development laid the foundation for quantum mechanics, a branch of physics that describes the behavior of energy and matter at the atomic level using probabilistic and non-intuitive aspects.
T he journey from quantum mechanics to quantum computing spans over a century, starting in 1900 with Planck’s proposal of quantized energy to explain black-body radiation. This pivotal development laid the foundation for quantum mechanics, a branch of physics that describes the behavior of energy and matter at the atomic level using probabilistic and non-intuitive aspects.
One of the first inklings of a problem in physics at the end of the 19th century was the nature of the radiation emission spectrum from a black body. This could not be explained in terms of established and irrefutable methods of statistical mechanics. It was Planck’s idea to divide up the energy spectrum of a series of harmonic oscillators each with a different state of energy but whose energy steps depended upon the frequency of the oscillation that marked the beginning of quantum physics. As a result, Planck introduced a fundamental constant of nature, Planck’s constant.
You have probably heard of quantum computing or quantum in general; otherwise, you would not have bought this book. Quantum is a concept from the world of physics, where it goes by the name quantum mechanics. Its development started in the beginning of the 20th century by well-known physicists like Max Planck, Niels Bohr, Werner Heisenberg, Albert Einstein, Erwin Schrödinger, Richard Feynman, and many others. Quantum mechanics studies the behavior and properties of nature on an atomic scale. Thanks to the discoveries in the field of quantum mechanics, we can leverage these discoveries and create a new tenor in computer science.
The Interest in the interaction of electromagnetic radiation with matter was the first impulse to structure a series of formulas, postulates and theories that would become the foundation for quantum physics.Under the shadow of statistical determinism, in the XIX and XX centuries, started the studies on the blackbody radiation, a consequent reformulation of various theories of classical physics and the introduction of the concepts of energy quantization, radiation and particles.This article will deal, briefly and chronologically, with the evolution of the old quantum theory.
This chapter provides a foundational overview of the physics essential to understanding quantum computing. It begins with atomic structure and the stability challenges posed by classical models, leading to Planck's quantization and the resolution of blackbody radiation. Einstein's photoelectric effect and Bohr's quantized orbits introduced discrete energy levels, later refined through quantum probability, half-life, and spectral transitions. The chapter details the shift from deterministic to probabilistic physics, introducing quantum numbers, the Pauli Exclusion Principle, and electron spin. It distinguishes fermions and bosons by spin statistics and explores Heisenberg's uncertainty principle and Schrödinger's wave function. Dirac's theory of antimatter is introduced through energy equations. The role of the strong nuclear force, quantum tunneling, and the implications for modern chip design are discussed. The double slit experiment illustrates superposition, interference, and the collapse of the wave function—concepts central to quantum computing. The chapter bridges quantum mechanics to computing by connecting atomic behavior to qubit operations.
Science has developed through a variety of investigations more or less over the time scale of human existence. On this scale, quantum mechanics is an extremely young field, existing essentially for only just over a century. Even our understanding of classical mechanics has existed for a comparatively long period—roughly having been formalized with Newton's equations published in his Principia Mathematica , in April 1686 (1687). Up until the very end of the nineteenth century, mechanics in the form of Newton's laws were comfortable, being understood and accepted by all who dealt with the motion of reasonable bodies. With the turn of the new century, however, mechanics would be shaken to its roots. The change began already on December 14, 1900, when Planck (1900) presented his new theory of black-body radiation to the German Physical Society, and this change would affect mechanics in physically small structures (and lead to quantum mechanics). Mechanics of large bodies would similarly be changed in 1905 with the arrival of Albert Einstein's (1905a) relativity theory. In this book, we will deal with only the first of these two great breakthroughs.
Toward the end of the nineteenth century, it became clear that some experiments cannot be explained on the basis of known physics, now referred to as classical physics. In 1900, Max Planck was able to correctly describe the distribution of blackbody radiation energy as a function of wavelength λ or frequency ν = c/λ. He had to accept the existence of energy packets (quanta) with energy E = hν. A few years later, Albert Einstein found that this unexpected relation between energy and frequency is also necessary in order to understand photoemission from metallic surfaces. A decade later, Niels Bohr arrived at the correct equation for the electronic spectrum of the hydrogen atom by applying “quantum conditions” on the motion of the electron around the nucleus and the Planck’s relation E = hν on the energy difference between the energy levels (1916). A decade later, Heisenberg, Born, and Jordan introduced “quantum mechanics” and de Broglie and Schrödinger (1925-1926) introduced “wave mechanics.”