Hi, this post will talk about what is a quantum computer. At first, we will simply find out the mechanism of classical computer’s computation Second, we will study differences between a classical computer and quantum computer In this section, we are going to learn about Qubit in detail At last, we will talk about the usage of quantum computers Before we study about quantum computer let’s check computational mechanism of classical computer use binary numbers for their calculation. And each of those numbers is called Bit Bits are created by transistors.

## What is a Quantum computer

When an electric current flows through transistors, Bit becomes 1. If there is no current flow then bit becomes 0 Calculation of computer is made from CPU which is set of transistors So, the quality of CPU which is related to the fast calculation is the main point of classical

computer’s speed CPU’s ability improves steadily until these days. But, there exists a physical limit on CPU’s speed For these days, transistor’s size is almost nanoscale When are the transistors getting smaller than this level, tunneling effect occurs Than transistors can’t play the role of on/off switch To overcome this computation speed limit, scientists make parallel connection computers which is called supercomputer

## Quantum computers

But even if we connect more and more computers, there exists limit also Solution for this problem is quantum computer Then how can quantum computer overcome the limit of the classical computer? To answer this question, we need to find out about Qubit While classical computers use bits for their calculation, Quantum computers use Qubits for calculation Qubit is the word which is combined with quantum and bit.

Qubit is similar to Bit which is measured to 0 and 1 But, Qubits have quantum mechanical properties like superposition and entanglement In the case of a qubit, 0 and 1 coexist at the same time before measurement This is called superposition.

So, we can’t predict the exact value of an unmeasured qubit But, when we measure a qubit, it collapses to a definite state which is 0 or 1 To generate a qubit, we use an electron or proton in the nucleus We define that low energy state, spin down is 0 and high energy state, spin up is 1 In case of the electron, we can change spin down to spin up by producing an electromagnetic wave which is a resonance with an electron.

## electron Producing specific frequency

For computation, we should make superposition state of electron Producing specific frequency of electromagnetic wave which can make super position state between spin up and spin down can make it possible, However, just with room temperature case energy, the electron can repeat spin up and spin down So we have to keep the very low temperature near 0 kelvin for exact calculation Let’s learn about superposition’s power by comparing 4 bits and 4 qubits 4 bits can produce 16 combinations, but it can use just one of them, However, in case of a qubit, 16 combinations are in a superposition state.

So we can calculate all of them at once If the qubits’ number getting larger and larger, the calculation speed of the quantum computer become exponentially faster Qubit’s another special characteristic is entanglement Entanglement is a phenomenon when more than two qubits exist Two qubits interact with each other by their own magnetic field So if one of them becomes spin up, then other one becomes spin down Let’s imagine that there are two entangled quantum particles which names are A and B If A become superposition state B also become superposition state.

### computer code by quantum

Even if they are at the superposition state, A and B interact with each other, because they are entangled And if we measure A or B and check that it is spin up or spin down, than the other one which is not measured also become spin down or spin up simultaneously In classical computer, there is no way to write a code where two bits have no value but have the opposite value Quantum computing represents strikingly non-classical computer code by quantum entanglement Increasing.

the number of qubits make entangled quantum computing code’s number grow exponentially This is the main point of quantum computer’s computing ability But entangled states are very fragile, so it can be easily destroyed by outside interference In that case, making quantum computer needs a lot of efforts According to previous slides making superposition state and entangled state qubits is really hard work.

### quantum computers make many companies and countries

Then, which point of quantum computers make many companies and countries try to make a quantum computer? As we learned. Quantum computer is much stronger than a classical.

computer at the exponential amount of computation That kind of computation’s example is a searching data from a huge database To find something in a database, normal computer have to test every single one of its entries But in case of quantum computers, they need only the square root of that time.

When the scale of the database becomes larger and larger, the quantum computer becomes more and more powerful And another example is ruining IT security These days IT security is based on huge numbers factorization Even if the high-quality computer, it needs few years to ruin IT security But in the case of quantum computer it can be done at just a few seconds This is the end of my presentation, and I hope that this video helps you guys for understanding quantum computer.