Johan and Claudia are both physicists, working in the field of research in quantum computing.  They met as students at university and got married later.  Both attend the School in Pretoria.  Read on to hear about this exciting area of physics, where this year the motto is “100 years of quantum is just the beginning” in celebration of the United Nations having declared 2025 the International Year of Quantum Science and Technology.

Quantum Computing: Where Physics Meets Philosophy

Claudia and Johan van Rensburg, Pretoria, South Africa

What drew you both to physics research?

Claudia: From a young age both Johan and I have been curious about how the physical world works. To his mother’s astonishment Johan was able to (mostly) reassemble things he took apart in order to figure out how they worked and sometimes even improve them. Becoming an experimental physicist was no surprise. In my case I tried to get hold of as much information on how the universe works as was possible. I also really enjoyed mathematics, so becoming a theoretical physicist followed naturally.

From 2000 we studied together at the University of Pretoria after which we were both fortunate in getting lecturing positions there. I had completed my PhD but Johan was still busy with his. I joined the Philosophy School in 2008 and after we were married Johan joined too.

Do you have a common research interest?

Johan: Our common interest is quantum physics, in particular quantum computers. 

Just as the space race in the 1960’s was driven by the desire to prove technological superiority (with the ultimate goal of landing on the Moon), the quantum race is driven by the desire to achieve cutting-edge technological breakthroughs. The nation that achieves a “quantum advantage” — where quantum computers can outperform classical systems in real-world applications — will be seen as leading the way in one of the most transformative fields of the 21st century.

Today, nations want to be seen as global leaders in science and technology. This enhances their national prestige and influence on the world stage.

Just as the space race had military applications (e.g. missile guidance systems, satellite technology), the quantum race also has significant implications for national security. Quantum technologies could lead to new ways to break encryption, harness quantum communication networks, or even create unbreakable encryption systems. The ability to safeguard sensitive data and outpace adversaries in cybersecurity is a key reason why quantum research is seen as a matter of national security. Countries that control quantum technology could dominate cybersecurity, supply chains, and international trade.

The first nation to achieve meaningful breakthroughs in quantum computing, communication, and related fields will gain a strategic advantage on many fronts — from scientific leadership to economic and military power. Just like the space race, the quantum race is not just about technological superiority but also about shaping the future in profound ways, with the potential to change industries and redefine global power structures.

Can you explain something about quantum theory?

Quantum theory applies to the microscopic realm and is different to our normal macroscopic world where we live and perceive things.

All quantum technologies exploit specific quantum mechanical properties, a fundamental one being superposition of different states. The famous Schrödinger’s cat* thought experiment tries to illustrate how counterintuitive this is to our usual experience and understanding of the world. Superposition leads to a phenomenon called entanglement. Entangled states are a crucial resource for many quantum applications. Einstein himself struggled with the implications of entanglement, thinking that the theory of quantum mechanics was not complete.

Superposition (in the simplest terms):

Imagine you’re flipping a coin. When you flip it, it can be either heads or tails when it lands. This is like how regular (classical) objects work — they are in one state or the other.

Now, imagine that instead of just flipping the coin, you could have the coin both heads and tails at the same time while it’s in the air. You can’t actually see both at once, but the coin exists in a kind of “both-heads-and-tails” state while it’s still spinning in the air. It’s only when it lands that it “chooses” one of the two possibilities (heads or tails).

Quantum Superposition:

In quantum mechanics, particles like electrons or photons can do something like this, but on a much smaller scale. These particles can exist in multiple states at the same time—sort of like the coin spinning in the air, being in both heads and tails, until it’s measured or observed.

For example, a quantum bit, or “qubit” (the basic unit of information in quantum computing), doesn’t just represent a 0 or a 1 like a regular bit in a computer. Instead, it can represent both 0 and 1 at the same time with variable probability, thanks to superposition. Only when you measure it do you “force” it to pick one of those values, just like the coin when it lands.

Why is this important?

Superposition allows quantum computers to process many possibilities simultaneously, which can make them extremely powerful for certain kinds of problems. Instead of just trying one path at a time, quantum computers can explore many paths at once — just like how the spinning coin can be both heads and tails before it lands.

Entanglement (in the simplest terms):

Imagine you have two magic dice. These aren’t ordinary dice — they have a special property. When you roll them, no matter how far apart they are, they always land on the same number. If one die shows a 4, the other will show a 4 too. If one shows a 1, the other shows a 1. This happens instantly, even if the dice are on opposite sides of the world.

At first, this might seem impossible. After all, how could they “communicate” with each other that quickly? But that’s what makes these dice “entangled”.

Now, imagine that you roll one die, and it lands on 4. Even though you haven’t rolled the second die yet, you already know it will also land on 4 — even if the second die is thousands of miles away.

Quantum Entanglement:

In the quantum world, particles can become entangled in a similar way. When two particles are entangled, their properties (like their spin or polarization) are linked, no matter how far apart they are, provided they do not get disturbed in any way. So, if you measure one particle’s property, you instantly know the property of the other particle, even if it’s light-years away. 

For example, if you have two entangled particles, one might be spinning “up” and the other “down”. Once you measure one particle and find that it’s spinning “up”, you immediately know the other particle must be spinning “down”, even if you measure it on the other side of the universe.

Why is this special?

Entanglement seems strange because it challenges our everyday understanding of how things should work. Normally, objects need to be close together to “communicate” or influence each other. But with entanglement, particles can affect each other instantly, even across huge distances, without anything traveling between them. This phenomenon has been called “spooky action at a distance” by Albert Einstein, but it has been shown that it does not violate special relativity, which says that information cannot travel faster than the speed of light.

Is there a philosophical aspect to quantum physics?

Claudia: My interest has always been the foundations of quantum physics, trying to understand what it really is, especially entanglement. The interpretation of the theory remains an open question for more than a hundred years. Quantum mechanics also challenges our understanding on ideas such as what is the role of an observer, what is the nature of time and even what is the nature of consciousness, so it is an area where Philosophy and Physics meet.

What has personally intrigued me are the descriptions of space, time, matter and even essentially the early universe in scriptures such as the Shrimad Bhagavatam, Mahabharata and the Upanishads.

Johan: Despite the open questions, we know that the theory of quantum mechanics works superbly well, so my interest is in the practical applications of quantum physics including the software side of quantum computers and experimentally for instance creating quantum dots with a molecular beam epitaxy (MBE) machine with which one can grow single atomic layers at a time on a substrate. With this technique very interesting devices can be created that exhibit a range of quantum phenomena that otherwise do not exist in nature.

What is quantum computing and what are the possible applications for this in future?

Johan: Quantum computers operate on fundamentally different principles. They rely on quantum bits (qubits), which can exist in multiple states simultaneously (superposition), and they use quantum entanglement for processing. These properties enable quantum computers to solve certain types of mathematical problems faster, but they also require entirely new ways of thinking about computation. Although a lot of progress has been made, current quantum computers are still large, very complex systems, requiring very special laboratories and facilities for them to function.

Quantum computers could for instance simulate complex biological systems at the molecular level, thus greatly facilitating the development of new therapeutic drugs. A lot of research is going on worldwide both on the hardware and software side. In theory, quantum computers would be able to solve complex mathematical models exponentially faster than the best possible classical supercomputers.

Unfortunately, in practice these entangled states are very susceptible to any environmental influences, which makes the hardware development extremely difficult and expensive. Access to quantum computers would remain via traditional computer networks and they would only be used to solve problems where classical computers would take up to billions of years. Current quantum computers are not yet able to be applied to any real-life problems such as climate or in the medical sciences, but the race is on.

Claudia: There are, however, a number of other quantum technologies which are already being successfully applied in medicine and secure communication. Quantum cryptography is a flourishing field, whether it’s via fibre or satellite communication. Here the fact that entangled states are so fragile is actually being used to ensure that sender and receiver of a quantum key will necessarily know if there has been eavesdropping, thus allowing them to decide whether the key is safe to use for encoding normal classical information. If eavesdropping did occur, the key is discarded and a new key is sent. One very promising medical application is quantum-based brain scanning, both for early detection of neurological problems and for offering insights into those conditions which have previously been difficult to study using conventional scanning.

Any weird ideas to dispel?

Johan: Some misconceptions that exist is that quantum computers will replace classical computers completely and that it will also be able to solve all the problems that classical computers cannot do. There is also no foreseeable future where you will have a quantum computer in your home as was the case with the advent of personal computers in the late 70’s!

Claudia: Quantum mechanics is just a theory, although one of the most successful and well-tested theories in science. It has been experimentally validated for over a century, and its predictions are accurate to an extraordinary degree. Technologies like semiconductors, lasers, and MRI machines rely on principles from quantum mechanics. The double-slit experiment, quantum tunnelling, and quantum entanglement have all been experimentally observed and verified. The theory is highly reliable in explaining and predicting the behaviour of particles at the atomic and subatomic levels.

There is also the myth that quantum mechanics provides a complete explanation for everything in the universe. While in reality, quantum mechanics provides a fundamental description of the behaviour of matter and energy at the microscopic scale, it does not explain everything. For instance, quantum mechanics does not provide answers to larger-scale phenomena like gravity (which is described by general relativity). The search for a unified theory that combines quantum mechanics and general relativity is still ongoing (known as the theory of everything).

How has philosophy influenced your work?  

Johan: Patience and creativity for research experiments, paying attention to fine detail and having an open mind to new ideas. In terms of lecturing and supervision of students, communicating effectively with undergraduate and postgraduate students from a variety of backgrounds, making students feel at ease and heard, and giving general guidance.

Claudia: In terms of teaching, trying to apply the Socratic method, guiding students to answer their own questions and trying to teach them to ask themselves those questions. For quite a few years, I have been interested in physics and the mind, however, the Philosophy School has given me insight that consciousness cannot be explained by physics as we know it. 

Anything else readers would like to hear about?

The official website of the International Year of Quantum Science and Technology is: https://quantum2025.org/

There is a very nice book called “How to Teach Quantum Mechanics to your Dog” by Chad Orzel, our Scottish Terrier has enjoyed us reading it to him as it doesn’t involve equations!

The Stanford Encyclopedia of Philosophy (online) is a comprehensive resource with all their articles listed under Quantum Mechanics and then under Quantum Theory. These have long bibliographies, mainly of philosophy journal articles.

* Schrödinger’s Cat is a famous thought experiment in quantum mechanics that illustrates the concept of superposition. In the experiment, a cat is placed in a sealed box with a device that has a 50% chance of killing the cat. Until the box is opened and the cat is observed, it is said to be in a superposition of states, meaning it is both alive and dead at the same time. 

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