Quantum Computing

Quantum Mechanics in Everyday Language

In our everyday world, objects behave in predictable ways. A ball sits in one place at a time and if you throw it at a wall, it bounces back from the same side every time. This is the world described by classical mechanics.

Quantum mechanics describes a very different world; the world of atoms and subatomic particles. Here, objects don’t have a single definite position. Instead, they exist in terms of probabilities. A particle might have a chance of being in one place, another chance of being somewhere else, and so on.

If we tried to imagine this using the tennis‑ball example, the “quantum ball” wouldn’t always bounce back from the same side of the wall. Instead, it would have a probability of appearing on the front, the back, or even the side of the wall. It’s not that the ball chooses a path. It’s that quantum objects behave according to probability rather than certainty.

How Quantum Computing Emerged

Quantum computing grew out of the early 20th‑century revolution in physics. Max Planck first proposed that energy comes in tiny packets called quanta, and scientists like Einstein, Bohr, Heisenberg, and Schrödinger built the foundations of quantum theory.

The idea of using quantum physics for computation came much later. In 1981, Richard Feynman pointed out that quantum systems are incredibly hard for classical computers to simulate. However, a quantum computer could do it naturally. This insight sparked the field of quantum computation.

A few key milestones followed:

• 1984 — David Deutsch introduced the idea of a universal quantum computer.
• 1994 — Peter Shor created an algorithm showing that a quantum computer could factor large numbers efficiently, challenging the security of RSA encryption
• 1996 — Lov Grover developed an algorithm that speeds up searching through unstructured data.
• 1998 — First two‑qubit demonstration using nuclear magnetic resonance (NMR).
• 2001 — IBM and Stanford built a 7‑qubit system that successfully ran Shor’s algorithm to factor the number 15.

These breakthroughs showed that quantum computers could solve certain problems far more efficiently than classical machines.

What Quantum Physics Actually Describes

Quantum physics studies how energy and matter behave at the smallest scales. Atoms, electrons, photons, and other tiny particles. One of its most important discoveries is that energy is quantised. Instead of changing smoothly, energy comes in fixed amounts called quanta.

This idea explains many phenomena:

• Light behaves not just as a wave but also as particles called photons.
• Electrons in atoms don’t move freely; they occupy specific energy levels.
• When an electron jumps between levels, it must absorb or release a precise amount of energy, no more, no less.
• These jumps produce the distinct colours seen in atomic spectra. This quantised behaviour is the foundation of modern technologies such as lasers, semiconductors, and, ultimately, quantum computing.

Electrons and Energy Levels

Inside an atom, electrons don’t orbit the nucleus like planets around the sun. Instead, they occupy defined orbitals, each with a specific energy. An electron can only exist in these allowed levels; never in between.

• When an electron absorbs energy, it moves to a higher level (excitation).
• When it releases energy, it drops to a lower level (relaxation), emitting a photon with a very specific colour or wavelength.

This precise, quantised behaviour is one of the clearest examples of how the quantum world differs from the everyday world we’re used to.