Quantum computing: are we any closer?

Why is quantum computing important?

The production of a viable and efficient quantum computer would revolutionise computing since it would process data much faster than everyday computers.

Quantum computers could especially impact:

• Optimisation of complex real-world problems – they can find the best solution of anenormous set of possible options, such as for industries relating to supply chains or traffic flows.

• Solve ‘hard’ computational problems – current-day cryptography is typically based on factoring huge numbers; Shor’s algorithm can easily break this form of encryption via quantum computing. The latter may, in future, also provide the fabled efficient solution to NP-complete problems.

• Quantum cryptography – on the other hand, schemes such as quantum key distribution couldbe applied that successfully resist any attacks on encryption protocols.

• Artificial intelligence – they can improve machine learning algorithms, based on supervised or unsupervised learning tasks, by efficiently analysing and processing large datasets. This could enable improved decision-making via enhanced pattern recognition and data clustering.

• Simulates quantum systems – they can model complex nanoscale systems, for example, to study the behaviour of complicated biomolecular assemblies and chemical reactions. Advances in the design of biomimetic materials, drugs and catalysts, alongside an improved understanding of fundamental physics, could arise as a result.

• Weather and climate modelling – similarly, the extreme number of variables relating to the environment and its complex interactions influenced by the butterfly effect could be effectively modelled. Therefore, improved weather forecasting and climate patterns could be discovered.

Quantum computing: the fundamentals

Unlike everyday computers based on 0s and 1s(i.e., bits), quantum computers use qubits. Theseare both 0 and 1 simultaneously until an observation (or measurement) is made, following which either a 0 or a 1 occurs – identical to an everyday computer.

Sometimes the qubit is called a quantum coin since only one of two possibilities occurs after an observation. It is analogous to Schrödinger’s cat in that the cat is both alive and dead until an observation is made by opening its box.

Since a quantum computer becomes an everyday computer after an observation, the clever manipulation of qubits before such an event makes a quantum computer a unique and powerful device. For example, certain computations can be performed in parallel before the observation, leading to exponential speedup for specific tasks.

When roughly 500 qubits are available, there is a greater amount of unseen data than the number of particles in the universe. However, following an observation, almost all this data isextinguished. The minute dataset connected to the observation is all that remains.

Quantum phenomena that may arise before the observation (i.e., the final step) in the quantum computing process are as follows:

• Superposition – a qubit is simultaneously both a 0 and a 1 until an observation.

• Entanglement – the interaction between qubits, meaning that they do not act independently. If a qubit is measured, its entangled partners are instantly altered (even if they are a great distance apart).

• Quantum interference – analogous to the constructive and destructive interference of the famous double-slit experiment. Grover’s algorithm is an example in which constructive interference amplifies the correct solution, while destructive interference diminishes all other outcomes.

Requirements for a quantum computer

A programmable quantum information processing machine – in short, a quantum computer –operates by manipulating a set of labelled qubits in a quantum register. It can only exploit quantum phenomena by utilising quantum algorithms, such as Shor’s or Grover’s algorithm.

As proposed by the theoretical physicist DiVincenzo in 2000, there are five basic building blocks for creating a quantum computer. The device must contain:

• Distinguishable and stable quantum states.

• A substantial number of individually addressable qubits.

• Quantum logic gates that can feasibly manipulate a set of qubits.

• Qubits in the quantum registry that are preserved even after many operations.

• Read-out (observation) of the final quantum states of the qubits with high fidelity.

Latest achievements towards a quantum computer

Research on all five criteria has progressed significantly in the last few years.

Practical solutions for creating stable and distinct qubits include those involving superconductors, photonics or trapped ions or particles. The latter, in the form of an optical lattice, may produce a 3D structure that could have individually addressable particles.However, research into all these possible solutions remains at a very early stage.

A major issue to overcome relates to the fourth building block (given above), which arises because of an effect known as quantum decoherence. This occurs because qubits are extremely fragile since their interactions with the surroundings can easily destroy their quantumcharacteristics – i.e., the same effect as an observation.

Quantum decoherence represents a decay of the data encoded into the quantum register so that errors continually arise. Surprisingly, techniques already available for everyday computing canbe adapted for this task. This is a highly active area of research and progress has been continually made over the years.

Unfortunately, quantum decoherence has restricted the ‘scaling up’ to a quantum computer, which requires at least several thousand qubits to be viable. This is because the decay of the quantum characteristics grows as the number of qubits increases.

The current record for the number of qubits in a quantum system is held by IBM’s 433-qubit ‘Osprey’ processor, which was announced in November 2022. They intend to produce a quantum computer with over 4,000 qubits by 2025 and a 100,000-qubit computer by 2033.

Conclusion

Some sceptics have voiced an opinion that quantum computers will never be built and, consequently, the current interest is purely hype from the media and multinational corporations.

While it is true that creating a viable quantum computer is not imminent, this standpoint strongly underplays the many advances over the last few decades.

Clearly, quantum computing is a promising area of research that could transform various aspects of science and technology.

In fact, Google proclaimed quantum supremacy in 2019. This was achieved when their programmable quantum device (based on superconducting qubits) performed calculations that are virtually impossible by a regular machine in a feasible amount of time.

However, it is undoubtedly true that quantum computing remains in a relatively early stage of development – a practical machine for widespread use is well beyond the horizon. Innumerable technical challenges still need to be overcome.

Due to the enormous costs of building suitable quantum devices on a vast scale, only a tinyquantity of quantum computers might ever be produced. Akin to the days when mainframe computers were the size of rooms, although this time we’ll be unable to ‘downsize’ to devices that almost everyone uses.

On the other hand, quantum computation could, before too long, be used for a limited number of select types of applications, such as secure telecommunication.

Giant tech companies (such as IBM, Google, Microsoft and Intel) have already invested extremely heavily in the research and development of quantum computing. In the end, it could be true that a quantum computer is just not viable in practice. Nevertheless, abandoning important endeavours without extensive investigation is not a typical characteristic of humanity.

Bio

Dr.David Bradshaw. Author of Quantum Computing Made Easy. Copywriter | Proofreader | Scientist | quantacopywriting.com