How Do Quantum Computers Work?

WHAT IS QUANTUM COMPUTING?

This branch of computer science is based on the principles of the superposition of matter and quantum entanglement and uses a different computation method from the traditional one. In theory, it would be able to store many more states per unit of information and operate with much more efficient algorithms at the numerical level, such as Shor's or quantum annealing.

This new generation of supercomputers uses knowledge of quantum mechanics — the area of physics that studies atomic and subatomic particles — to overcome the limitations of classic computing. Although in practice, quantum computing faces evident problems regarding scalability and incoherence, it makes it possible to perform multiple simultaneous operations and eliminates the tunnel effect that limits current nanometric scale programming.

Quantum computers perform calculations based on the probability of an object's state before it is measured - instead of just 1s or 0s - which means they have the potential to process exponentially more data compared to classical computers.

Classical computers carry out logical operations using the definite position of a physical state. These are usually binary, meaning its operations are based on one of two positions. A single state - such as on or off, up or down, 1 or 0 - is called a bit.

In quantum computing, operations instead use the quantum state of an object to produce what's known as a qubit. These states are the undefined properties of an object before they've been detected, such as the spin of an electron or the polarization of a photon.

Rather than having a clear position, unmeasured quantum states occur in a mixed 'superposition', not unlike a coin spinning through the air before it lands in your hand.

These superpositions can be entangled with those of other objects, meaning their final outcomes will be mathematically related even if we don't know yet what they are.

The complex mathematics behind these unsettled states of entangled 'spinning coins' can be plugged into special algorithms to make short work of problems that would take a classical computer a long time to work out... if they could ever calculate them at all.

Such algorithms would be useful in solving complex mathematical problems, producing hard-to-break security codes, or predicting multiple particle interactions in chemical reactions.

Types of quantum computers

Building a functional quantum computer requires holding an object in a superposition state long enough to carry out various processes on them.

Unfortunately, once a superposition meets with materials that are part of a measuring system, it loses its in-between state in what's known as decoherence and becomes a boring old classical bit.

Devices need to be able to shield quantum states from decoherence, while still making them easy to read.

Different processes are tackling this challenge from different angles, whether it's to use more robust quantum processes or to find better ways to check for errors.

DIFFERENCES BETWEEN QUANTUM AND TRADITIONAL COMPUTING

Quantum and traditional computing are two parallel worlds with some similarities and many differences, such as the use of qubits rather than bits. Let's take a look at three of the most significant:

Programming language:

Quantum computing does not have its own programming code and requires the development and implementation of very specific algorithms. However, traditional computing has standardized languages like Java, SQL, and Python, to name but a few.

Functionality:

Quantum computers are not intended for widespread, everyday use, unlike personal computers (PC). These supercomputers are so complex that they can only be used in the corporate, scientific, and technological fields.

Architecture:

Quantum computers have a simpler architecture than conventional computers and they have no memory or processor. The equipment consists solely of a set of qubits that makes it run.

Quantum computing supremacy

For the time being, classical technology can manage any task thrown at a quantum computer. Quantum supremacy describes the ability of a quantum computer to outperform their classical counterparts.

Some companies, such as IBM and Google, claim we might be close, as they continue to cram more qubits together and build more accurate devices.

Not everybody is convinced that quantum computers are worth the effort. Some mathematicians believe some obstacles are practically impossible to overcome, putting quantum computing forever out of reach.