Quantum computers are often considered the next generation of computing. They trust the laws of quantum mechanics — the strange behavior of particles on a subatomic scale — to process information. Currently, quantum computers are too small, too difficult to maintain, and too error-prone to compete with today’s best classical computers. However, many experts hope quantum computing will one day surpass classical computing for specific tasks.

Technologies enabling quantum computing have advanced rapidly in recent years. One day, they may be able to solve problems too complex for even today’s most powerful conventional computers. This huge performance gain could open the door to many interesting uses, including in pharmaceutical products , climate modeling It is manufacturing all of which rely on extremely complex simulations.

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

Quantum computers use particles like electrons or photons that behave like quantum bits, or qubits, which represent a superposition of 0 and 1 – meaning they can exist in multiple states at the same time. Qubits can also be encoded in semiconductor materials, such as silicon, or even in superconductor materials, such as spinel (MgAl2O4) and lanthanum aluminate (LaAlO3).

To fully achieve quantum supremacy, quantum computers need different algorithms that take advantage of the unique way qubits encode and process data. Scientists are developing quantum algorithms, which have lower computational complexity, which means they require less execution time or number of operations compared to conventional algorithms. However, quantum algorithms would need to run on large, fault-tolerant quantum computers, which are not yet available.

Entangled quantum particles are linked in space and time and share information, even if they are thousands of kilometers apart. (Image credit: Getty Images)
Qubits: Qubits are quantum particles equivalent to binary bits in classical computers. Given that qubits can be in more than one state, they offer exponentially greater processing capabilities than binary bits if they can be joined together and used to perform calculations.

Qubits process data using quantum gates, which are analogous to binary gates in classical computers. However, unlike binary gates, quantum gates are reversible. Some binary gates lose data as information is processed through them, but quantum gates preserve it. Combined, quantum gates form quantum circuits.

Overlay: The main difference between qubits and binary bits is that qubits operate in superposition, which means that the qubit can represent 1 and 0 simultaneously. This superposition allows quantum computers to perform calculations in parallel, processing all states of a qubit at the same time.

Entanglement: Quantum entanglement is a phenomenon associated with superposition, in which two subatomic particles – or qubits in a quantum computer – are linked in space and time. They are physically separated, but share information and interact simultaneously. Regardless of the distance between the particles, if one is observed, the state of the other will be known.

How powerful are quantum computers?
Quantum superposition and entanglement make the processing potential of a quantum computer much greater than that of a classical computer.

While adding more classical bits linearly increases the number of calculations a computer can do, adding more qubits to a quantum computer exponentially increases its computing power – far surpassing a classical binary computer once there are enough qubits. Scientists estimate that a quantum computer with about 20 million qubits will achieve quantum supremacy – the point at which a quantum computer solves a problem that a classical computer cannot.

Related: Scientists just built a massive 1,000-qubit quantum chip, but why are they more excited about a chip 10 times smaller?

However, quantum computers are still very experimental. For one, the superposition that creates qubits and the entanglement that joins them are easily destroyed – because the qubits interact with the external environment and become entangled with it . When this occurs, the information they carry is lost or corrupted. This makes quantum computers extremely prone to errors. To overcome this situation, companies are implementing multiple approaches, such as supercooling to just above absolute zero and using electromagnets to isolate the qubits.

How do quantum computers work?
Quantum computers have an icon chandelier-like architecture , comprising a series of interconnected tubes and wires that host different layers of the computer. Most quantum computers are hooked up to huge, powerful coolers so that processors can be cooled to near absolute zero to mitigate thermal noise and vibrations. Many of the chandelier’s layers work to make the quantum processor, housed near the bottom layer, very cold.

All quantum computers have slightly different architecture, but they tend to have the following elements.

Quantum computers have an iconic chandelier-like architecture, but different models are configured slightly differently. (Image credit: John D/Getty)
Quantum Data Plane: The quantum data plane houses the qubits and is where data is processed through quantum gates. The structure that holds the qubits in place differs between different types of quantum computers. Some qubits are made of solid superconductors cooled to just above absolute zero . Others use electromagnetic fields to capture ions or charged atoms that act as qubits, in high vacuum chambers. Vacuum pressure minimizes interference from vibrations and stabilizes the qubits.

Control and measurement plan: The control and measurement plane converts a digital signal from a classical computer into analog signals used to change the states of qubits in the quantum data plane.

As with the quantum data plane, quantum computers send signals in various ways, such as microwaves or lasers.

Control the processor plane and host processor: The control processor plane and the host processor implement the quantum algorithm, which is a sequence of operations designed to be performed on a quantum computer to process data. After performing a quantum calculation, the host processor provides 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 computers require specially designed devices algorithms , which are most commonly described by a quantum circuit or a routine that defines a series of quantum operations on qubits. Quantum software is made up of quantum algorithms. Other quantum software is used to correct errors generated when performing calculations on qubits.

Why do we need quantum computers?
In theory, quantum computers can potentially be much faster than classical computers and can solve multiple complex problems simultaneously. They are particularly promising for optimization tasks. Classical computers struggle or fail 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 solution. Drug discovery or materials 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 allow larger, more complex datasets to be used to train AI, thus leading to increasingly sophisticated systems.

Why are quantum computers so difficult to build?
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 – which is the collapse of the quantum state. This decoherence makes quantum computers much more prone to errors than conventional computers. Although about 1 in 1 billion billion bits fail, the failure rate is approximately 1 in 1,000 for qubits .

Although there are ways to protect a quantum system from external influences, errors can still arise. Even a single error can cause the validity of an entire calculation to collapse. And because qubits are fundamentally different from bits, conventional error correction methods don’t work.

Scientists have created quantum algorithms to compensate for errors in quantum computers, but these require qubits to function, reducing how many are available to process data. Another peculiarity of quantum mechanics is that directly observing or measuring the state of a particle or atom in superposition destroys it. This means researchers must use complicated workarounds to read the quantum state of the output, as direct observation risks corrupting the data.

What are the implications of quantum computing?
Quantum computers will be a disruptive technology when we achieve quantum supremacy. But it’s uncertain when scientists will build a powerful enough quantum computer — with millions of error-corrected qubits — and so far the most powerful quantum computers have only approximately 1,000 qubits .

Even so, classical computers will continue to be the easiest way to solve most problems because they do not need to maintain quantum states. Quantum computers will likely only be used to solve problems that are beyond the capabilities of classical computers.

However, one area that will likely be affected 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, the processing power of a quantum computer would easily be able to solve them. Quantum cryptography is now a booming field, as researchers try to develop quantum-resistant cryptography to protect sensitive data from being cracked by quantum computers in the future.