Quantum computing, as the name suggests, is an intersection field of quantum physics and computer science. In this article, I tried to explain the basics of quantum computing for non-majors to get a grasp of the foundation of how computational technology might look like in an almost foreseen future. Before going further into the topic, it is essential to know what is a qubit.

Qubit: A qubit is a quantum bit that is used in quantum computation. Similar to a bit in classic computation, which is a unit of information used to describe computational problems to a machine, qubits are another way of interpreting information used in quantum computers. A bit is a binary unit digit number that can either have a one or zero state. However, qubits are more interesting in the sense that they can be at two states at the same time, which is referred to as a quantum superposition. Unlike classic physics, qubits can be realized by using subatomic particles and their behavior, which has duality nature, and so are the best candidates for qubits. Given its nature, qubits have a different representation convention.

Qubits are mathematically denoted by ψ, which is defined in the form of a vector consisting of two states, with weights α and β that represents the amplitude of each state. The square of these amplitudes gives us the probability of each state. Therefore, to make our life easy, the sum of the square of α and β is always equal made to be one, also called normalization. This nature of the qubit can be exploited for the computational advantages, which what makes quantum computing the future of technology.

As quantum computers are based on fundamentally different concepts, they must be built from entirely different technology; because it cannot be realized using the classical current flow model, which either flows or doesn't flow and thereby defines the state for that bit. However, the flow of current cannot be in a state where it both flows and not flows. It sounds silly? Yes, that's why quantum computers cannot be explained, and even more so, it cannot be realized using classic physics. Quantum computers are still in their infancy, and so there are many different candidates for the technology to build them. These technologies can be based on optics, superconductors, or possibly molecules. It is still unclear if any of these are more preferred over the others, and it is even more unclear if all future quantum computers will be built from the same technology or if there will be many different types of quantum computers available.

To understand quantum computing, it is essential to know the three fundamental concepts of it, namely, superposition, quantum measurement, and entanglement.

Superposition:

You must have heard of the superposition in classic physics, in which two physical quantities are added together to make another third physical quantity that is entirely different from the original two. In Quantum physics, it is similar to the waves in classical physics, which refers to a physical system that can be in one of many configurations, thereby the most general state is a combination of all of these possibilities, where the amplitude in each configuration is specified by a complex number as was described in the definition of qubits.

Quantum systems can exist in a superposition state, and measuring the system will collapse the superposition state into one definite classical state. This might be hard to understand from a classical point of view, as we usually do not see quantum superposition in macroscopic objects.

Quantum Measurement:

Measurement in quantum physics is referred to as the testing or, in other words, manipulation of a physical system for the purpose of obtaining a numerical result. So, measuring a quantum system causes it to change (manipulate)—one of the strange but fundamental aspects of quantum mechanics. Mathematically speaking, a measurement operator should essentially be carefully chosen matrix that manipulates the initial state of the system.

Quantum measurement collapse is used in many applications such as cryptography, where one could detect if a message has been intercepted. Moreover, this property of quantum states implies a qubit is in an unknown state and so cannot be copied. This property is known as the no-cloning theorem. Classical computers can make a copy of a text, and the original stays the same. If you try to copy an unknown qubit, you first have to measure it, which collapses its superposition state. Therefore, quantum computers are unlikely to replace your laptop. However, for certain applications, the hidden information in superposition states allows information processing beyond what is possible in a classical computer.

Entanglement:

Entanglement in quantum mechanics is a physical phenomenon that occurs when multiple qubits are correlated with each other. Entanglement can have strange and useful consequences that could make quantum computers faster than classical computers. Qubits can be "entangled," providing hidden quantum information that does not exist in the classical world. It is this entanglement that is one of the main advantages of the quantum world!

A well-known application of the entanglement phenomenon is quantum teleportation, which is a technique for transferring an unknown quantum state from one location to another. Unlike some theories that relate the entanglement to classic physics, it has now been widely accepted that entanglement is, in fact, a purely quantum concept and, by far, has no reasonable explanation in classic physics.

In summary, quantum computing is an exciting advancement in computational capabilities. Even while it is in its infancy, it has great potential to address some of the major bottlenecks of computational limitations for many applications. However, it doesn't seem like quantum computers will replace classic computers entirely. They are more like enhancements to classic computers similar to GPUs that enhances computational capabilities when certain CPU tasks are outsourced to them, but cannot entirely replace them.