What is quantum computing?
A quantum computer uses the properties of quantum mechanics to execute calculations. Quantum computers are much faster than classical computers at certain types of calculations (i.e., all of today’s widely used computing devices such as smartphones, servers, and desktop computers). Most importantly, however, quantum computers might be able to decode certain extraordinarily difficult mathematical problems that classical computers cannot solve efficiently at all, which would compromise current encryption methods and expose sensitive data.
Imagine you want to find a chapter in a book. You turn the pages one by one until you reach the desired section. Now imagine that instead, you first look at the table of contents and almost instantly flip to the right chapter. Quantum computing is like using a table of contents: it quickly and simultaneously checks all possible solutions to a calculation, instead of trying different solutions until the right one is found.
What are bits and qubits?
A traditional computer stores information in a series of bits. A bit is the smallest possible unit of information; its value is either 0 or 1.
A quantum computer stores information in qubits, not bits. A qubit can have the value 0, 1, or a mixture of both states (the technical term for such a mixture is “superposition”). In fact, the value of a qubit is uncertain —unlike a classical bit, which is always known to be either 0 or 1. The value of a qubit remains undetermined until it is measured.
In this way, a quantum computer can store multiple states or versions of information at once. This allows it to process solutions to calculations at an exponentially faster pace than a normal computer – just as a team of people performing multiple tasks simultaneously can complete a project faster than a person doing everything alone.
Imagine an information segment as a globe. A bit can be located at either the north or the south pole of the globe. A qubit can be located anywhere on the surface of the globe – which greatly increases the information it can contain.
On a mechanical level, bits and qubits are not actually globes. A bit is a tiny part of a computer that contains either an electric charge (1) or no electric charge (0). A qubit is the uncertain, unstable position of an electron within an atom.
What are the challenges in building quantum computers?
To date, very few quantum computers have been built. These quantum computers are small, unstable, and unusable outside of a laboratory.
This is because quantum computing has to overcome a number of major challenges:
Disturbances caused by the external environment
Qubits are fragile. Noise, vibrations, temperature fluctuations, and electromagnetic waves can disrupt or destroy a qubit’s internal state. For quantum computers to function properly, they must be located in highly controlled environments where these and other types of disturbances are absent. Such environments are difficult to establish and maintain outside of a laboratory.
Environmental factors also affect conventional computers – for example, high temperatures or strong magnetic forces can slow down or destroy a computer. But with quantum computers, the problem is much more serious, making it uncertain whether they can function under real-world conditions.
(Eventually, we might be able to counteract the disturbances, just as a desktop computer’s fan helps to balance high temperatures).
Error Correction
Quantum computers are generally less stable than their classical predecessors. This makes them more prone to errors. All computers make mistakes. That’s why classical computers have built-in memory and a processor responsible for error correction. But quantum computers have to devote far more resources to error correction relative to their processing capacity than classical computers
Temperature
To keep the qubits stable, quantum computers must be kept extremely cold – just a few degrees above absolute zero. This makes it difficult to operate them outside of tightly controlled laboratory environments
The result of these and other challenges is that very few quantum computers with more than a handful of qubits have been built. (A 256-qubit quantum computer was announced in 2021, and one company hopes to build a 1,000-qubit quantum computer by 2025. )
How would quantum computing affect the world?
The impact of quantum computers is difficult to assess, as it is not yet clear whether quantum computers are feasible on a large scale, let alone whether mass production of such computers is possible. This contrasts sharply with classical computing – in most societies, miniature computers are used in almost all areas of life, and many people carry the equivalent of a supercomputer in their pocket (as a smartphone).
Powerful, stable quantum computers could have a very positive impact on society. But it is also clear that such computers would pose new risks to data privacy and security.
Potential Positive Effects
There are many potential applications for quantum computers. With more powerful computers, the financial industry could analyse and predict the stock market more accurately. Climatologists could analyse and predict weather patterns more accurately. Transportation systems could become more efficient if quantum computers could better predict traffic
These developments are still theoretical. And even if it were possible to build large, highly stable quantum computers, their processing results would only ever be as accurate as the data they are fed. Nevertheless, quantum computing could have a major positive impact on these or similar fields.
It would be possible to crack the current encryption methods.
These days, sensitive information is often protected by encryption. Encryption involves encrypting a message with a key so that only someone who possesses the key can read it. Encryption protects personal data that users enter on websites; business data stored on hard drives and servers; confidential government data; and other sensitive information.
Many types of encryption rely on difficult mathematical problems (e.g., prime factorisation). The difficulty of these problems ensures that the encryption cannot be cracked within a reasonable timeframe. Although known algorithms exist for decrypting the encryption, it is always possible to use larger encryption keys. This task requires exponentially more time (for classical computers) to find the key and decrypt the encryption.
Theoretically, quantum computers can solve the difficult tasks used in current encryption methods. In this scenario, a larger key does not make the task exponentially more difficult. Therefore, it could take significantly less time to crack the encryption. Thus, quantum computers could break most current encryption methods, and all encrypted data could be exposed.
What is the difference between a quantum computing and a supercomputer?
Quantum computers have the potential to perform complex calculations that push a supercomputer to its limits. Supercomputers cannot solve mathematical problems with a very large number of possible solutions, or can only do so very slowly. Consider, for example, the challenge faced by a sales representative: How do you calculate the shortest route that passes through a series of cities before heading home? At first glance, the solution seems simple. However, the major challenge lies in the fact that the number of possible routes increases exponentially with each stop the sales representative makes. With three cities, there are only two possible routes; with ten cities, there are already 362,880. With 50 or more cities, the calculation becomes so complex that it can no longer be solved by a supercomputer.
Thus, quantum computing opens up the possibility of applying simulations, cryptography, artificial intelligence and machine learning in industry.