Quantum computing: Facts about the ultra-powerful computers that use quantum mechanics

Classical computers process data using binary bits, which can be in one of two states — 0 or 1. The bits are encoded on transistors, which can be made from silicon, germanium or other semiconductors.

Quantum computers use particles such as electrons or photons that behave as quantum bits, or qubits, which represent a superposition of both 0 and 1 — meaning they can exist in multiple states at once. The strange laws of quantum physics also mean that qubits can become entangled, in which the state of multiple qubits are linked despite the distance between them.

Quantum computers have an iconic chandelier structure. This structure hosts a series of interconnected tubes and wires that contain different layers of the computer. Most quantum computers are linked with massive, powerful refrigerators that cool the processors to near absolute zero to minimize thermal noise and vibrations. Quantum computers all have slightly different architecture, but they tend to have the following elements.

Quantum data plane: The quantum data plane houses the qubits and is where data is processed via quantum gates. Some qubits are made of solid superconductors cooled to just above absolute zero. Others use electromagnetic fields to trap ions, or charged atoms that act as the qubits in high-vacuum chambers. The vacuum pressure minimizes interference from vibrations and stabilizes the qubits.

Control and measurement plane: The control and measure plane converts a digital signal from the processor, which uses classical computing, into the analog signals used in the quantum data plane.

Control processor plane and host processor: The control processor plane and host processor implement quantum algorithms, which are a sequence of operations designed to run on a quantum computer. After performing a quantum calculation, the host processor relays a classical digital signal to the control and measurement plane.

Quantum software: Getting the processor output into the control and measurement plane requires another element: quantum software. Quantum software is made up of quantum algorithms.

In theory, quantum computers could be far faster than classical computers and simultaneously solve multiple complex problems. They are particularly promising for optimization tasks, which involve finding the best possible solution to a problem. Classical computers struggle when a problem has an extremely large number of possible solutions. A quantum computer, however, could consider all potential solutions and quickly find the optimal one. Drug discovery or material science — where the fastest classical computers are currently deployed — are two examples of how quantum computers could be used.

Quantum computers could also transform artificial intelligence (AI). AI systems are trained using large data sets, so quantum computers could enable bigger and more complex data sets to be used for training AI, thereby leading to increasingly sophisticated systems.

Quantum computers are delicate and susceptible to interference from external sources, such as temperature changes or stray particles. When there is interference, qubits are susceptible to decoherence, or the collapse of their quantum state. Decoherence makes quantum computers far more error-prone than conventional computers. While roughly 1 in 1 billion billion bits fail, the failure rate for qubits is roughly 1 in 1,000 — that's 1,000,000 times more errors.

Although there are ways to protect a quantum system from external influences, errors can still creep in. Scientists have made quantum algorithms to compensate for errors in quantum computers, but these require qubits to run, reducing how many are available to process the data. Another quirk of quantum mechanics is that directly observing or measuring the state of a particle or atom in superposition destroys it. That means researchers must use tricky workarounds to read the quantum state of the output, as direct observation risks corrupting the data.

Quantum computers will be a disruptive technology once we achieve quantum supremacy — the point at which quantum computers can outperform the best classical computers. But it's uncertain when scientists will build a quantum computer powerful enough, with millions of error-corrected qubits.

Even then, classical computers will remain the easiest way to solve most problems. Quantum computers will likely only be used to tackle problems that are beyond the capabilities of classical computers.

One area that will likely be affected, however, is encryption, which protects sensitive data such as financial records and personal information. Modern encryption methods rely on mathematical problems that are too complex for classical computers to solve. However, a quantum computer would easily be able to solve them. Quantum cryptography is now a burgeoning field as researchers attempt to develop quantum-resistant encryption to protect sensitive data from being cracked by quantum computers.