Introduction to Quantum Computing

Quantum computing & beyond

Quantum Computing 101

What is a Quantum Computer?
A Quantum Computer (QC) is a machine that uses the principles of Quantum Mechanics to do things which are practically impossible for a traditional (Classical) computer.

Classical computing power has historically been doubling every two years (Moore’s law). Progress appears to be slowing and certain problems require computational power that, mathematically, cannot be achieved efficiently using Classical computers.

Quantum Mechanics is a fundamental theory in physics describing the properties of nature on an atomic (i.e. really small) scale. Quantum Mechanics has certain features which do not occur in standard or “classical” physics such as “Superposition” and “Entanglement”.

Whilst development is required, Quantum Computers are expected to be faster than Classical Computers for certain use cases by harnessing such features. We cover this in more detail here.

Why are Quantum Mechanical behaviours important?
Quantum Mechanical behaviours are important to understanding the potential power of Quantum Computers. However, the relevant concepts are not intuitively easy to understand because we don’t observe them in our daily lives. We can easily understand and interact with the physics of throwing a ball, but not with small particles like atoms, electrons and photons.

The two most important Quantum Mechanical behaviours to understand are Superposition and Entanglement

Superposition is the ability of a quantum object such as an electron to simultaneously exist in multiple “states” until it is measured (when the superposition collapses). A lot of theoretical and experimental work has gone into explaining exactly how this actually happens but for these purposes it is best not to think too literally about the concept and instead observe that existing in multiple states allows one quantum object to store more information than a binary classical bit.

Entanglement describes a strong correlation between quantum particles so that two or more quantum particles can be linked in unison, even if separated by great distances. Again this is so hard to intuitively understand (Einstein described it as “spooky action at a distance”) it should suffice to say for our purposes that it allows for greater connectivity of information.

The basic idea behind quantum computing is to utilise Quantum Mechanical behaviours to our advantage. Most articles incorrectly write that quantum computers obtain their power by trying every possible answer to a problem in parallel. Whilst a helpful heuristic, this is not strictly true. Quantum Computers use entanglement between qubits and the probabilities (which can be negative or positive and are technically known as amplitudes) associated with superpositions to carry out a series of operations such that certain probabilities are enhanced and others reduced, even to zero. By pushing the probabilities of a wrong answer to zero, you can find helpful answers.

What is a Qubit?
We purposely avoided using the term qubit in the previous section. If you read anything about quantum computers, you are bound to have come across the term. Every big development within creating quantum computers seems to revolve around adding more qubits, making them more stable and less ‘noisy’. But what does this mean?

First we must remind ourselves of ‘bits’. A bit is the smallest unit of classical information and can be in one of two states (we call these states 0 and 1). We can make a bit from anything that has two states; computer scientists used to store bits by punching holes in card, a hole represented a 1 and the absence of a hole represented a 0. Newer technology such as compact disks (CDs) stored bits using tiny dents in the metal surface of the disk, where a variation in the surface represented a 1 and a constant surface represented a 0.

Quantum mechanics is a more accurate model of the world that emerged in the early 20th century. One of the many results of this new model was that the most basic unit of information was not the bit but instead the quantum bit, or “qubit”. More interestingly, it turned out that this new unit of information could be useful for computations and communications, and since then there has been an effort to create a physical qubit.

As with bits, the qubit is an abstract idea that isn’t tied to a specific object and we must find a suitable system to store them. Unfortunately, qubits are much harder to implement than the classical bit; while we can carry round billions of bits on a hard drive in a rucksack, it’s difficult to sustain a handful of qubits under laboratory conditions. As a result of this, many qubits in the computer must be used for error correcting.

You can read more at our Introduction to Qubits, part 1.

What types of Quantum Computers are being made?
As outlined above, a qubit is an abstract idea that isn’t tied to a specific object. We are able to use electrons, atoms, ions and even superconducting circuits to represent qubits. Each approach has its advantages and disadvantages, and there is no clear winner yet emerging. We provide a deep dive into this in the following article.

For those of you already familiar with the basics, we maintain a table of qubit implementations here.

What do Quantum Computers look like?

The core of a Quantum Computer is its processor which contains qubits, the quantum equivalent of a classical computer’s bits (the most basic unit of information). As outlined above, qubits can be represented in a number of different ways and thus the kit that is required to make them useful varies too.

Common to most Quantum Computers today is that they are large, complex engineering feats. As covered in more detail here, much of this engineering goes into isolating the qubits from the outside world so that they maintain their quantum mechanical properties.

This is easiest to visualise with the Superconducting Quantum Computers as used by the likes of IBM and Google. These are essentially large refrigerators with wires to carry signals back and forth. The actual quantum processor (and indeed the qubits) represent a small chip that you could hold in your hand that sits right at the bottom of the machine.

Quantum Computers may not always need to be this large and cumbersome. One only needs to look at computers from the 1950s to get a sense for how technology can develop.

Large companies like IBM are aware that captivating design can bring new technologies to life. Indeed, IBM worked with the Italian design company Goppion on the concept and construction of the case for their IBM Q System One, which was unveiled at the Consumer Electronics Show (CES) in Armonk, New York in 2019.

How long have we been working on Quantum Computing?
If you really want to go back in time you need to go back to the concept of an abacus. However, the computer in the form we broadly recognise today stems from the work of Charles Babbage (1791-1871) and Ada Lovelace (1815-1852). Programmable electromechanical computers were developed in the 1940s and work since then (from a hardware standpoint) has focussed on the development of greater computing power through expanding the amount of information that can be mechanically / electrically represented and processed. This has been supported through innovations from vacuum tubes in the 1940s to microprocessors in the 1970s. Whilst processing power has continued to advance at a rapid pace since then, much of the development of the core processors are iterations on top of the core technology developed. Today’s computers are a story of further abstraction including the development of software and middleware and miniaturization (with the development of smaller and smaller microprocessors).

Further miniaturization of components has forced engineers to consider quantum mechanical effects. As chipmakers have added more transistors onto a chip, transistors have become smaller, and the distances between different transistors have decreased. Today, electronic barriers that were once thick enough to block current are now so thin enough that electrons can tunnel through them (known as quantum tunnelling). Though there are further ways we can increase computing power avoiding further miniaturization, scientists have looked to see if they can harness quantum mechanical effects to create different kinds of computers. Most people will point to the 1980s as the start of physicists actively looking at computing with quantum systems.

You can learn more in our history of quantum computing.

Are Quantum Computers better than Classical Computers?
The short answer is no for two reasons:

Firstly Quantum Computers are not just a natural improvement of today’s computers; rather they are a different approach to computing utilising Quantum Mechanics (as outlined above).

Secondly, we are still in a relatively early development stage for Quantum Computers. Humanity have been refining the “ingredients” of fast Classical Computing for nearly 100 years (vs. about 20 years for Quantum Computing).

With that being said, a team at Google were able to demonstrate what has been unfortunately termed Quantum Supremacy using their 53 Qubit Sycamore Chip. John Preskill defined Quantum Supremacy as the point where quantum computers “can do things that classical computers can’t, regardless of whether those tasks are useful”. As outlined here, Google’s achievement, whilst remarkable, was purposely contrived to be easy for a Quantum Computer and hard for a Classical Computer. It was able to do a calculation in three minutes which would have taken the world’s fastest supercomputer anywhere from 2.5 days to 10,000 years (depending on who you ask). The calculation itself has no known useful applications.

The commercial market for QC

Are Quantum Computers being used commercially?
We are yet to use a Quantum Computer for a useful commercial application. So why is there so much interest in the market? Indeed, why does The Quantum Daily exist?

Few, if any QC companies, are making any money (leaving aside Xanadu’s T-shirts). This is primarily because we have not made a Quantum Computer which is able to solve a practical problem faster / better than our existing supercomputers.

As John Preskill outlines in his – now relatively well known – paper, we are currently in what has been termed the Noisy Intermediate State Quantum era of QC. One of the fundamental challenges with using qubits (basic unit of quantum information) is that they are required to represent states other than zero and one, and therefore any external factors which affect their state are hard to normalise out (we don’t need to represent precise probabilities or amplitudes in Classical Computers – we just need zero and one). Errors build on errors, unless qubits can be subject to some more nuanced error correction, which results in challenges in creating meaningful outputs. The likes of Google, Rigetti and IBM are taking different approaches, but part of what they are working on is solving this problem.

In the last 20 years we have worked out that, at least theoretically, QCs should be able to deal with noise through more advanced error correction using more “correcting” qubits. Whilst this technically means that we should be able to build fault-tolerant QCs, it imposes an “overhead” in that manufacturers will need potentially thousands of qubits to support one qubit that is not subject to noise, or one “fault tolerant” qubit.

This is a long way of saying that the fundamental technology that underpins creating commercially useful Quantum Computers, is still in its infancy. As Scott Aaronson wrote in the New York Times, Quantum Computing is “now, finally, in the early vacuum tube era of quantum computing”. Some have argued that even this is an optimistic assessment.

Which companies are investing in Quantum Computing?
There are hundreds of companies involved in some way with Quantum Computing. We classify them as follows:

Company Types

wdt_ID Type Description

We track and update these regularly on our company profiles page.
Why do all these companies exist if there’s no proven commercial application?
Coming soon.
Which companies are investing in Quantum Computing?
Investment in Quantum Computing is from a mix of large listed corporations (e.g. IBM, Google, Microsoft).

These companies both have their own research institutions (e.g. Google AI Quantum) but also invest in other companies.

Venture capital (VC) does invest in quantum computing . That said, compared to other nascent “deep tech” VC has invested relatively little capital, which we provide more background on in this article.

We provide a full report on the investment landscape here.

How big is the Quantum Computing market?
It may be surprising to some, but market sizing is more of an art than a science. Market Size / Total Addressable Market (TAM) is a commonly used, but poorly understood term. The Quantum Computing TAM is currently negligible. Assessing the future size of the market is not something we can accurately do in any nascent industry, particularly because we don’t know what new markets will be created, in addition to disrupting old markets.

However, the impact of Quantum Computing could be very large, and it is not unreasonable to expect the value of the market hits multi-billion dollars in the coming years. The timing is highly dependent on further scientific breakthroughs which, by their very nature, are hard to forecast.We cover the complexity of this in more detail in this article.

Still, many large consulting houses like McKinsey are excited about the potential opportunity.

What applications are envisaged for Quantum Computers?
Coming soon
How do you invest in Quantum Computing?
We should state up front that writers for The Quantum Daily may hold securities discussed in content published on the website. Our articles are not a recommendation to buy or sell securities and you should be careful and do your research.

Most quantum computing companies are small, relatively young, and private. The short answer is that it’s not easy to invest purely in Quantum Computing. We provide more detail on this (including our view on ETFs) here:

Nonetheless there are a few companies that are linked to Quantum Computing and publicly traded. Approach with care!

Quantum Computing Incorporated has an interesting story which we cover here.
D-Wave is not directly publicly traded, but you can invest in it through a listed investor in private companies. You can find out more here.
Archer Materials doesn’t just focus on quantum computing but is small enough to be considered. We cover it here.

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wdt_ID Term Definition