# Introduction to Quantum Computer ?

A quantum computer is a special type of computer that uses quantum mechanics to perform computation more faster than a regular computer can.

When we look at a classical computers, the data is in the form of 0’s an 1’s. So an information here exists in two states 1 or 0.

But when it comes to quantum computer, then don’t behave like classical computers. Quantum Computers stores and processes data and information in form of something called as Qubits or Quantum bits.
However, unlike a usual bit, they can store a lot more information than 1 or 0. This is because such quantum bits can exist in any superposition of these values. So these qubits are not only in state 1 or 0, but it can also be set to 1 and 0.

Let us understand what does that mean exactly?

In a quantum computer, we can have a number of elemental particles like electrons or photons. Such particles are called qubits. The nature and behaviour of these particles form the fundamental basis of quantum computing.

A qubit can be imagined as an sphere. So state of a qubit can be at any point on the sphere. So that means we can store a huge amount more information using less energy than a classical computer.
Now let us see the two cardinal facet of quantum physics, that are the principles of superposition and entanglement.

### Superposition

In quantum mechanics, superposition is the state when an electron can be at two different position at the same time. We can also apply this to spin of an electron, according to uncertainty principle. Electron can spin in any direction. But when we measure the spin, it will be either aligned to the field known as spin-up state or in opposite direction known as spin-down state. We can think of the qubit like these electrons in a magnetic field.

Let look at this in one more way. What if we try to change the spin of the electron? This can be achieved by using a pulse of energy, such as from a laser. Let’s say that we need 1 unit of laser energy to change the spin of the electron. But what if we use only half a unit of laser energy and the electron is isolated from all external influences? In that case, according to quantum law; the particle then enters a superposition of states, in which it behaves as if it were in both states simultaneously. Each qubit can take a superposition of both 0 and 1.

Lets assume we have n qubits that have two states. Then they can perform s 2^n calculation, since they can be in all the 2^n states at the same time. If a quantum computer contains 100 qubits, then it would have the potential to do 2^100 calculations in a single step.

### Entanglement

Quantum entanglement is the phenomenon when more than one particle that are generated together or closely interacted, can start a relationship. The quantum state of such particle cannot be independently described.

Quantum particles generated together or interacted retain a type of connection. They can be entangled together in pairs by a process known as correlation. For Example, let us take two electrons that are entangled. Assume net spin of electrons is zero when it is generated. Now when we measure their spin independently we find that, if one of the electron measures a spin up, then the other one will be always spin down and vise versa.

An amazing thing here is that, before the electron is measured they can be in any state due to the phenomenon of superposition. It is simultaneously in both a spin-up and spin-down state. But the electron losses its superposition as soon as it is measured and this if affect the other entangled particle instantaneously.

The spin state of a particle is decided at the time of measurement. This state is then communicated to the correlated particle. Correlated particle simultaneously assumes the opposite spin direction to that of the measured particle. This is a real phenomenon (Einstein called it “spooky action at a distance”).

Quantum entanglement allows qubits that separated by an incredible distances to interact with each other instantaneously (not limited to the speed of light). No matter the distance between the correlated particles, they will remain entangled as long as they are isolated.

Taken together, quantum superposition and entanglement creates an very sophisticated, enhanced computing power. A 2-bit register in our computers can store only one of four configurations (00, 01, 10, or 11) at a time. But a 2-qubit register in a quantum computer can store all four numbers/states at the same time. The capcity can be increased exponentially if more qubits are added.

### Simplistic Overview

​In simple term, the power of a quantum computer comes from the fact that a qubit or quantum bit can be in multiple states simultaneously and they can interact with each other to pass information. Though Quantum Computers sound impressive, it could take quite a few years for quantum computers to achieve their full potential.

Thanks for reading. You can also check out our posts on Machine Learning.