With the advent of new innovations in quantum information science, the field of quantum physics has received a great deal of attention and excitement over the past decade. Everything from elementary particles to black holes can be explained by this theory. It is crucial to have a foundational knowledge of quantum physics, even though we currently cannot anticipate how far we will go in this pursuit. Many of the fundamentals of physics that we learned in school and that we were taught in the context of classical physics are fundamentally different in quantum physics. Most importantly, quantum physics describes and interacts with infinitesimally small particles, which are only observed and studied at the microscopic scale. Since this phenomenon isn’t immediately apparent to the naked eye, it can come across as strange or even “absurd.” Even though ideas like entanglement, superposition, and the uncertainty principle may seem far removed from reality, they are essential to grasping quantum’s many practical applications. So let’s go back in time and explore the origins of quantum mechanics as we study the fundamentals.

# Light And The Wave-Particle Duality Dilemma

The main protagonist of the quantum world is light. Light is an energy form that can be created by changing other energy sources, such as chemical or electrical. Light reflects off of surfaces and enters our eyes, allowing us to view the world as it truly is. Pioneering scientists like Galileo, Young, Maxwell, and Faraday have been experimenting with light since the 16th century. For decades, scientists and philosophers assumed that light traveled in waves, but in the twentieth century, Max Planck proposed a theory that energy is absorbed and emitted in tiny, unbreakable packets called quanta. This discovery paved the way for quantum physics. Energy, which had been thought to be continuous for centuries, was shown to actually exist in discrete packets for the first time. This led Einstein to demonstrate the spectacular photoelectric effect in 1905, which earned him the Nobel Prize in Physics. By using a beam of light to eject electrons from a metal surface, he was able to disprove the wave theory of light and show that photons are the fundamental units of light. The particle theory of light was further validated by Compton in an altogether different experiment using scattering electrons from an X-ray tube, which could only be explained by the particle nature of light. However, the particle nature of light cannot explain all the experiments proving the wave nature of light. After years of deliberation, scientists settled on the idea of wave-particle duality to explain how light can exhibit properties of both waves and particles, depending on the conditions.

# De Broglie’s Wave-Particle Duality Generalization And Schrӧdinger’s Quantum Theory

Based on the discovery that light can act as both a wave and a particle, de-Broglie postulated that all matter in the cosmos shares this dual nature. To demonstrate this, he conducted the double-slit experiment, but instead of light, he used a beam of electrons. After passing through the slit, the electrons produced a diffraction pattern on the screen, demonstrating that matter can behave like a wave. Everything from a planet in the universe to a ball in the air has wavelength as long as it has mass and velocity, which is specified by de-Broglie’s equation.

However, due to the small value of h or Planck’s constant, the wavelength of objects visible to the human eye is not perceived by us. Next came Schrӧdinger, who changed the principles of quantum physics by offering his new quantum theory and his now-famous wave equation, generally known as Schrӧdinger’s equation.

This equation is often considered as analogous to Newton’s second law of motion (F = ma). One of the key elements of quantum mechanics that sets it apart from classical physics is that one cannot know the exact location of a particle at a particular instant in time, one can only predict with some probability. The chance of locating a particle at a specific location can be calculated using this wave equation. It also inspired Schrӧdinger to modify the atomic model that was earlier offered by Bohr.

# Quantum Superposition And Heisenberg’s Uncertainty Principle

According to quantum physics, a particle can exist in several states at once, and its true state is only revealed by measurement or observation. In quantum physics, this is known as the principle of quantum superposition. The quantum state can be calculated as the superposition (vector sum) of these multiple states. This is a fundamental idea in quantum computing, where bits can exist as a superposition of classical binary bits 0 and 1. The measurement of this specific state of a quantum particle has some uncertainty involved, as given by Heisenberg in 1927, popularly known as Heisenberg’s Uncertainty principle. He formalized the fact that it is impossible to precisely determine both the position and velocity of an item at the same time. This uncertainty occurs because of wave-particle duality. If we calculate the quantum object’s momentum using de-Broglie’s equation, we directly assume the object to be a wave, and since a wave cannot have a precise position, we can only be able to know its momentum with certainty. On the other hand, if we calculate the object’s position by assuming it to be a particle, then we lose the ability to measure its exact momentum. This uncertainty is brilliantly captured by the following equation, which states that uncertainty in position and momentum will always be greater than or equal to a certain value. In fact, this is also true for all the matter in the universe, but since the uncertainty is negligible at that level, we cannot perceive it.

# Dirac’s Quantum Field Theory And Quantum Entanglement

In 1905, Albert Einstein presented his special theory of relativity, which states that the speed of light is the same for all observers in a vacuum regardless of the motion of the light source or observer and that the laws of physics are invariant in all inertial frames of reference, i.e., frames of reference with no acceleration. Special relativity, in contrast to general relativity, can be applied to events that take place when gravity is absent. In 1928, Dirac merged the theory of special relativity and quantum mechanics to give the Quantum Field Theory. This hypothesis is mostly utilized to explain the behavior of subatomic particles and their interactions. While the aforementioned quantum theories were adequate for describing and analyzing isolated particles with no external forces acting upon them, more recent quantum concepts taking into account subatomic forces between particles are required to describe the interactions of multiple particles in the real world. Despite its incompleteness, quantum field theory guides the development of particle physics and string theory and facilitates the finding of new particles. Entanglement is another significant quantum phenomenon that occurs when two or more particles interact in such a way that it becomes hard to evaluate the properties of each particle individually, regardless of their proximity. Popularly known as the EPR paradox, the concept was first introduced by Einstein, Podolsky, and Rosen in a thought experiment in which they prepared a pair of particles in an entangled condition. Popularly known as the EPR paradox, the concept was first introduced by Einstein, Podolsky, and Rosen in a thought experiment in which they prepared a pair of particles in an entangled condition. In fact, this year’s Nobel Prize in Physics was awarded to recognize and honor the contributions of physicists to quantum mechanics, specifically the entanglement phenomenon. Read more about it here. New technologies based on quantum mechanics make extensive use of this concept.

From advances in semiconductor systems to advances in medical treatment and diagnostics, most of the technical advances of the past decade can be traced back to quantum mechanics. As more is learned about quantum physics, the number of potential applications will grow exponentially. One arena where quantum mechanics has made contributions and can potentially spark a revolution is the computing industry. Learn more about it here.