Today’s computing systems, although having significantly improved decade after decade, can only solve problems up to a certain size and complexity. More complex issues require advanced computational power, and quantum computing promises to deliver such power.
Classical computers rely on individual bits to store and process information as binary 0 and 1 states. Quantum computers rely on quantum bits – qubits – to process information; in doing so, they use two key quantum mechanical properties: superposition and entanglement.
Superposition is the ability of a quantum system to be in multiple states at the same time. Qubits still use the binary 0 and 1 system, but the superposition property allows them to represent a 0, a 1, or both at the same time. Instead of analysing 0s and 1s sequence by sequence, two qubits in superposition can represent four scenarios at the same time, thus reducing the time needed to process a data set.
Entanglement is a strong correlation between quantum particles, allowing them to be inextricably linked in perfect unison, even if separated by great distances. When two qubits are entangled, there is a special connection between them: If the individual qubits are measured, the outcome of the measurements could be 0 or 1; but the outcome of the measurement on one qubit will always be correlated to the measurement on the other qubit. And this is always the case, even if the particles are separated from each other by a large distance.
In essence, superposition allows quantum computers to solve some problems exponentially faster than classical computers, while entanglement makes quantum computers significantly more powerful.
Qubits can be created through different methods, such as using superconductivity to create and maintain a quantum state. Superconductivity requires low temperatures, which is why quantum computers need to be kept cold to maintain their stability.
One main problem with qubits is that they are very tricky to manipulate: Any disturbance makes them fall out of their quantum state or ‘decohere’. Significant research is being carried out on identifying ways to overcome this decoherence problem and make qubits co-operate.
While quantum computers can work with classical algorithms, quantum algorithms are obviously more appropriate as they can solve some problems faster. One example of a quantum algorithm is Grover’s algorithm, which can search through an unstructured database or unordered list significantly faster than any classical algorithm.
It is important to note that problems fundamentally unsolvable by classical algorithms (called undecidable class problems) cannot be solved by quantum algorithms either.
Applications of quantum computing
The unprecedented power of quantum computers makes them useful in many scenarios where classical computers would require an impractical amount of time to solve a problem. For example, they could simulate quantum systems, allowing scientists to study in detail the interactions between atoms and molecules. This, in turn, could help in the design of new materials (e.g. electronics, chemical materials) or new medicines. As they are significantly faster than classical computers, quantum computers will also be far more efficient at searching through a space of potential solutions for the best solution to a given problem.
Quantum computers can thus pave the way for unparalleled innovations in medicine and healthcare, allowing for the discovery of new medications to save lives or of new AI methods to diagnose diseases. They can also support the discovery of new materials, the development of enhanced cybersecurity methods, the elaboration of much more efficient traffic control and weather forecasting systems, and more.
Researchers around the world are working on and with quantum technology in various fields. Airbus has launched a quantum computing challenge to encourage the development of quantum solutions in aircraft climb and loading optimisation, as well as wingbox design optimisation. Daimler is working with Google on using quantum computing in the fields of materials science and quantum chemical simulation. The US Department of Energy is funding research projects that could lead to the development of very sensitive sensors (with applications in medicine, national security, and science) and provide insights into cosmic phenomena such as dark matter and black holes.
Google, IBM, Intel, Microsoft, and other major tech companies are allocating significant resources to quantum computing research, in their efforts to pioneer breakthroughs in areas such as AI and machine learning, medicine, materials, chemistry, supply chains and logistics, financial services, astrophysics, and others.
Quantum communication and cryptography
Beyond powerful quantum computers, quantum technology has applications in other areas too, such as quantum cryptography and quantum communication, both of which are closely interlinked.
Quantum cryptography is a method used for the secured, encrypted transfer of information. Unlike other forms of cryptography, it ensures security by the laws of physics; it is not dependent on mathematical algorithms and unsecure exchanges of keys. Quantum communication based on quantum cryptography currently qualifies as highly secure, making it impossible to wiretap or intercept. Here, the most well known application is quantum key distribution (QKD), which relies on the use of quantum mechanical effects to perform cryptographic tasks.
One possible means of quantum communication is quantum teleportation. Although the name can be misleading, quantum teleportation is not a form of the transport of physical objects but a form of communication. This teleportation is the process of transporting a qubit from one location to another without having to transport the physical particle to which that qubit is attached. Even quantum teleportation depends on the traditional communication network, making it impossible to exceed the speed of light.
Quantum computers already exist, but their power is still rather limited and several tech companies are continuously working on improving this power. For instance, in January 2019, IBM announced its first commercial quantum computer that can work outside the research lab, but with a power of only 20 qubits. Later on, in October 2019, the company's engineers announced the development of a 53-qubit computer. In another example, the startup Rigetti Computing developed a 32-qubit computer and is now working on a 128-qubit one too.
In October 2019, Google claimed that it achieved ‘quantum supremacy’ with a 53-qubit quantum computing chip that took 200 seconds to carry out a specific calculation which would have taken a classical computer 10 000 years to complete. IBM soon challenged that claim, arguing that the problem solved by Google’s computer could also be solved in just 2.5 days through a different classical technique. We can expect these and other companies to discover further improvements in processing power, allowing quantum computers to solve problems that classical computers cannot.
While this race is ongoing, the hype around this technology should also be looked at with a degree of caution. As the Massachusetts Institute of Technology (MIT) explains, quantum supremacy is an ‘elusive concept’. First of all, we are still far from quantum computers that can do significant work; Wired magazine estimates that at least thousands of qubits would be required for fully functional quantum computers to solve real-life problems (current quantum computers that operate with less than 100 qubits are far from such a reality).
In addition, quantum computers are prone to many more errors than classical computers and, as already explained, the risk of decoherence makes it very difficult to maintain the quantum nature of qubits. The more qubits a quantum computer has, the more difficult it is to overcome such challenges. Moreover, a quantum computer cannot simply speed up the process of solving any task given to it; scientists explain that, for certain calculations, a quantum computer can be even slower than a classical one. Plus, only a limited number of algorithms have been developed so far where a quantum computer would clearly have supremacy over a classical computer.
Governmental initiatives and policy issues
The promises that quantum computing holds also make it the subject of an ongoing ‘race for supremacy’ not only among tech companies, but among nations too. The USA and China are currently at the forefront, while the EU, Japan, and others are following closely.
In the USA, the National Quantum Initiative Act was adopted in December 2018, setting up a ‘federal programme to accelerate quantum research and development for the economic and national security of the United States’. The Act enables the allocation of over US$1 billion to support the research and development (R&D) of quantum technologies, including quantum computing. In March 2019, the White House Office of Science and Technology Policy created a National Quantum Coordination Office to ‘work with federal agencies in developing and maintaining quantum programmes, connecting with stakeholders, [and] enabling access and use of R&D infrastructure’. And in August 2019, President Trump adopted an executive order establishing the National Quantum Initiative Advisory Committee.
China, on the other hand, is allocating substantial financial resources to university-based quantum research centres and is planning to open a National Laboratory for Quantum Information Science in 2020 (with an investment of around US$1 billion). On the R&D side, researchers have built a satellite that can send quantum-encrypted messages between distant locations, and a terrestrial ultra-secure network between Beijing and Shanghai that allows for the transmission of sensitive data with the help of quantum-encrypted keys.
Beyond this ‘race for supremacy’, progress in quantum computing is also paving the way to new policy issues. For example, one immediate concern is that quantum computers could be used to break encryption systems that are utilised nowadays to secure online banking and shopping, for example. While quantum processors do not yet have such power, the potential is real and governments and companies have started to look into this issue.
It is also likely that regulatory and ethical issues will emerge related to the use of the technology: How to ensure that quantum computing will be used for social good? Similar to the ongoing discussions regarding ethics and AI, will there be a need to implement ethical principles in the development of applications based on quantum computing?