What is superposition

By Clint Brown

Quantum computers are on the verge of revolutionising many industries, opening opportunities that have been ruled out by enterprise in the past. Once mainstream and leveraged in daily life, the use cases will begin appearing throughout the world. It has been said, building a quantum computer is more complicated than sending a man to mars.

The super powers of quantum physics are what differentiate quantum computer from classical computers and a primary function of this is called superposition. This short example definition will answer a very common question when new to this emerging field: “what is superposition”.

Breaking Down Superposition

In this article we will break down what superposition is through three different explanations. Each will resonate with a different audience to depending on their knowledge and understanding of quantum computing.  The post is designed to be short, targeting the very specific function of superposition, with little fluff but yet simplicity.

Generally, understanding the quantum physics can be challenging to start with, primarily due to our close tie with the classical world we live in.

Explanation Level 1 – Basics

In this explanation, we will use the most simplest terms to describe superposition, providing examples of different states atom’s can exist within the world of quantum physics.

In a superposition state, the following conditions are possible:

  • An atom can exist in two positions or locations at the same time. This is a strange concept to comprehend, but imagine being in the bedroom and bathroom at the same time. While we are talking at the microscopic level, these crazy little things called atoms can exist in two locations simultaneously. Its these incomprehensible properties that enables the performance of quantum computers. In the below diagram, consider the lady in two places at the same time.
lady in purple dress standing with hands on hip. Image demonstrating she is in two places at the same time
  • An atom can be excited (happy) and unexcited (sad) at the same time. In effect, having a smile on your face while also frowning and looking sad. Take the below photo an example, imagine both faces overlaid into one being happy and sad concurrently.
Face with a man happy and sad at the same time demonstrating a superposition state

A superposition state can apply to any quantum particle such as ion, photon, molecule and spin.

See the following article for more details around the different types of particles or qubits.

Explanation Level 2 – Video

This reference video provided by toutestquantique.fr delivers a short to the point with great examples at to what superposition means. 

video ref: toutestquantique.fr

Explanation Level 3 – Basic Physics

Let’s look at superposition with a simple analogy. If your regular computer wants to solve a problem, it looks at every possible corridor, including dead ends, until it is able to arrive at the solution. But quantum technology tries all the best possible pathways simultaneously until it figures out the shortest route.

Hence, they are extremely fast and efficient. This ability to exist in multiple states at the same time while trying to figure out how to solve a problem (in the example above) is known as superposition. Each qubit could undertake 2^n, where n represents the number of qubits used.

It may comprise 500 qubits; this implies 2^500 calculations in just a single step – something today’s devices cannot do. By and large, experts achieve superposition using precision lasers or microwave beams.

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