Quantum computing’s roots can be traced back to work done in the late 1800s and early 1900s. Ludwig Boltzmann beginning in 1877 had suggested that energy states in a physical system could be discrete. By 1900 the atomic hypothesis was becoming widely accepted and Max Planck had discovered what is to be known as Plank’s Law, which describes the electromagnetic radiation on an object near thermodynamic equilibrium. In 1905 Einstein hypothesized that the energy in light could consist of indivisible “energy quanta”, successfully explaining the photoelectric effect. Over the next twenty years, more and more support of these quanta was put forward which accumulated in Max Born, Werner Heisenberg, and Pascual Jordan’s matrix formulation of quantum mechanics in 1925. Around the same time, DeBroglie was formulating his theory on equating waves to matter which in turn helped Schrödinger derive his famous wave equation for quantum states. By 1926 it was proved that both Schrödinger and Heisenberg’s formulations were correct.   

Figure 1: Werner Heisenberg

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The next huge breakthrough in quantum mechanics came in 1941, when a graduate student named Richard Feynman stumbled upon some papers relating quantum mechanics to the Lagrangian which he then used to formulate the amplitude method of quantum mechanics (also known as the path integral formulation). With these foundations laid, physicists now had the tools to go about applying quantum theory to all sorts of aspects of physics, resolving questions ranging from the atoms to the stars. Forty years later, in 1982, Richard Feynman showed that a classical Turning machine couldn’t simulate a quantum universe but proposed that a hypothetical quantum computer could, in theory, simulate more particles than the required particles needed without exponentially slowing down in computations. With this idea now on the table, numerous people in the last three decades have refined this concept and now have a theoretical model for how such a quantum computer would behave, as well as working quantum computers that run on a small number of qubits before succumbing to decoherence. Working algorithms have also been created that make use of such quantum properties, namely in the field of cryptography.

Figure 2: Richard Feynman

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