Understanding “Quantum” and “Quantum Computer”

Before we talk about Quantum computers or even normal computers, let’s do a refresher course in Physics. If you really want to understand the fantastic science behind quantum computers, then it is important to understand certain behavior of mother nature. If you feel that you are a version of Schrodinger’s cat where you either possess and not possess (at the same time) the knowledge of basic quantum behavior of nature, then you can directly jump to the section “What is a Qubit”.

Intro to Quantum Mechanics

In our school, it was told to us that, everything in this world is made up of atoms. Whatever you see around, the air you feel, the water you drink, the mobile phone in your hand, the watch on your wrist, your own body, this earth, the moon, the sun — all are made up of atoms. Just like a house is constructed brick by brick, the brick becomes the smallest unit of that house. Similarly, whatever is present in this world, if you try to break it into the smallest unit, that will be ATOMS.

We were able to find out all those distinct smallest units or atoms, like Hydrogen, Oxygen, Iron, Gold, Uranium, etc. They are all tabulated in “Periodic Table”. There are around 98 such distinct atoms that exist naturally.

Newton and other scientists have already formulated the laws of physics known as classical mechanics or Newtonian mechanics. Those laws were able to explain the movements of planets, the motion of objects, trajectories. Basically, those laws were followed by bigger objects. Objects like apples, stones or even as big as planets, stars or even galaxies. But when those laws were applied to predict the behavior of smallest units of the universe or better call atoms, then those laws failed miserably.

Later, in the first 3–4 decades of the 20th century, scientists like Einstein, Max Planck, Neil Bohr, Erwin Schrödinger, Richard Feynman, Lorentz, Heisenberg, Pauli, de Brogli, Dirac, Langmuir, etc started to derive laws for those smallest units. They were astonished by the calculations and results based on this new theory that they were not believing even themselves.

They gave birth to the most interesting field of physics — Quantum Mechanics. Quantum mechanics deals with the laws and theories which are followed by those smallest indivisible units of the universe, atoms.

But there is a twist in the story, as believed the smallest units are not the atoms. The atom itself is made up of smaller particles like protons (made up of quarks), electrons, and neutrons. Those are called as sub-atomic particles. It was necessary to maintain this particle flood. It was observed that many sub-atomic particles can be categorized in some kind of logical groups, just like there are atoms classified in the periodic table.

The sub-atomic particles were categorized into something called — The Standard Model. In layman’s term, the Standard Model is kind of like the periodic table for subatomic particles, where subatomic particles are categorized, like electrons, quarks, photons, neutrinos, etc. Now it is fairer to say that each and everything in this world is made up of sub-atomic particles. Even the natural forces which govern the universe like electromagnetism, strong and weak nuclear force can also be explained by the standard model.

Mother Nature is weird, not the Quantum Mechanics

1. Quantum Tunneling

Imagine a scenario, you are playing snooker. A red ball suddenly disappears from its place, and suddenly appears somewhere else on the table instantly. The ball didn’t roll, you didn’t touch the ball. The ball just automatically disappeared in one place and appeared at another place instantly. That’s hard to imagine, but that’s what really happens at Quantum level, at the level of subatomic particles. Electrons do not revolve around atoms, as taught in
schoolbooks, in reality, an electron appears and disappears in its probabilistic clouds or orbitals. Sometimes, the electron also crosses the energy barrier, and appears at such place where it reaches without the sufficient energy. But that’s an experimentally confirmed phenomenon. It’s called Quantum Tunneling. Read more about quantum tunneling here https://www.quora.com/What-is-quantum-tunneling-How-is-it-used/answer/Vivek-Keshore

2. Quantum Superposition: (most important for quantum computers)

Imagine a scenario, that you are wearing a high-tech shirt that changes its color as either red or blue randomly. If I see you in the red color shirt, it might be possible that another person would see you in the blue shirt, because by the time color must have changed. But, let’s say there is a catch, the shirt changes colors only when someone is looking at it. So, when I looked at you, your shirt changed the color to red, and when another person looked at you,
your shirt changed the color to blue. So, when no one is looking at you, what is the color of your shirt? It’s neither red nor blue. We can say that your shirt is in a Superposition state where it is like both red and blue when no one is looking, but when someone looks then it’s either red or blue.

Your shirt has two superposition states. Let’s say I have observed you in the red shirt 7 out of 10 times. So, I would say the probability of someone else observing you in the red shirt is 0.7 or 70%. So, your shirt wave function can be written as 0.7 red and 0.3 blue. But when anyone observes you, your wave function collapses, and your shirt is either red or blue i.e. no more 0.7 (red) and 0.3 (blue), but full 1.0 (red) or 1.0 (blue).

In terms of subatomic particles, we can say that the electron is a wave as well as a particle, both, unless you observe it. Young’s double-slit experiment confirms the dual nature. This is a basic idea. Superposition can be of any type, for example, the one particle is at two places at the same time. Impossible to imagine, but it happens.

If you want to understand Superposition better with more details then read here -
https://www.quora.com/Why-new-results-are-not-observed-in-quantum-mechanics-when-the-wave-function-collapses-after-the-first-measurement/answer/Vivek-Keshore

3. Quantum Entanglement:

Now imagine, you have a twin brother, and you both are wearing the same high-tech shirt which changes colors when someone looks at you.

But, let’s say, someone has connected your shirts in such a way that, when anyone looks at you and if your shirt becomes red, then your twin brother shirt instantly becomes blue (even if no one is observing your brother). So, you and your brother appear both red and blue, but when you appear red, your brother appears blue instantly and vice versa. This is Entanglement. How your brother would appear, can be derived by just by observing you. The
best part of this is that the wave function collapse of entangled particle or object happens instantly even if you are at the different ends of the universe. Entangled particles somehow communicate instantly even if there is lightyears of distance.

To understand Entanglement better — https://www.quora.com/Why-was-the-Schrodingers-cat-experiment-originally-devised/answer/Vivek-Keshore

There are other quantum mechanic principles which can boggle anyone’s mind, but for the purpose of understanding quantum computer, the above three principles are enough.

QuBit

To understand why a Qubit was created and what is the need of the quantum computer, first, understand what is a normal bit in today’s computer, or directly scroll down towards a maze image below.

1. Bit before Qubit:

A bit is a basic unit of information in the digital world. The bit is a word derived from Binary Digit — Bit. So, a bit is the basic unit of information that can store a binary value. We know that binary values are only 1 and 0.

In computers, you might have heard about 32 bit or 64-bit processors. What does that mean? A 32-bit processor means the processor is capable of working with 32-bit binary numbers at once. That is why though modern computers appear to perform basic tasks very fast (browsing the internet, watching movies, playing games). it miserably fails to compute highly complex problems. Imagine if you need to simulate how a protein molecule would
behave in water for 1 second. It seems a fairly small problem, but with a modern computer and efficient algorithms, it would take months to compute the results. That much slow are our computers. Even supercomputers that have numbers of parallel processors are slow when it comes to solving a bigger complex problem.

2. Why computers are slow and take so much time to compute complex problems?

Because each bit takes part in one process. Once the process will get completed, that same bit will hold information for another process. You see, even if you do parallel programming, you will utilize multiple processors but technically a physical bit in the processor is not shared. All bits in those processors are separate.

3. Why and what is Qubit?

A Qubit by definition is a quantum bit (of course everyone knows that).
A quantum bit can hold both 1 and 0 at the same time. It is called a superposition state, a basic feature of quantum world — Superposition.

A bit can hold only either 0 or 1 at one time, Qubit can hold both 1 and 0 at the same time, so theoretically a single qubit can take part in millions of process at a single time. Thus making quantum computer super fast. One qubit can also be in entangled state with another qubit. Suppose, if we entangle the qubit A with opposite state of qubit B, and if we measure qubit A holding binary 1 after superposition collapse, then we immediately know
without measuring the qubit B that qubit B is holding binary 0. We can also entangle same state of qubits, where both qubit will show either 1 or 0 after superposition collapse.

Why super-fast… okay, here is an example:

Let’s say, there is a maze that has only one or two correct way out, and millions of other ways which will result in a dead-end. Now, imagine yourself at the entry corner of this maze. You don’t know the way out, so you will start exploring each and every way one by one, and after millions of tries and years of time, you will be able to find the correct way out. (Modern computer works this way).

Second case

Now again imagine you have your millions of clones also along with you.
You and your clones will start exploring all the ways together at once. And because all clones are exploring all the possible ways together, one of the clones will find the correct way out in the first go itself. Thus, you have your solution or way out in the first try. You will get your solution very fast on the first go, isn’t it?

Those clones of yours which are present and finding all the ways at once are actually your superposition states. You were present in many places at once.

Now you see why Qubits are needed and why quantum computers are required. Theoretically, the more complex the problems are, the faster the solution will be achieved by a quantum computer.

The Problem

The problem is only: How to get a physical realization of the above-mentioned model? Trying all the possibilities to solve a problem is good for this theoretical Quantum Computer. The first way to a solution finishes the search. So, it`s a sort of “selector” by trying all possibilities. It’s remarkable that all actual forms of Quantum Computers are so as it’s described. But a Computer must be able to compute in a mathematical way. Otherwise, it’s a single specialty for one special problem.

What’s missing is a mathematical, repeatable and predictable way for a solution. Parallel Computing is possible in the classical Computer System too.

We need a Quantum Logic like BOOL’sche Algebra. Now Quantum Computing is a mixture of Quantum Mechanics and a little bit of Mathematics.

The above questions are common, and in reality, they are research areas to develop better quantum computers.

The Solution

Here, consider the computer has only 8 bits, represented above as filled and empty circles. These are the same bits in three different processes holding different boolean value, 0 or 1. Physical bits are the same for all three processes, but the boolean value held by the bit is only different. A qubit can hold both 0 and 1 at the same time. So, computer will perform on boolean value only, just like it does today. It will compute in mathematical way. Processes could be any independent processes or child threads, it depends on the problem.

But theoretically, if this is the case, then it should be able to solve all the problems at once, no matter what is the nature of the problem. Because all that is required by the computer to compute are boolean values, and those boolean values are stored in a qubit, instead of normal flip flop bit.

The quantum computer work in a mathematical way, the only thing it is doing differently is to hold different values for different processes, so that all processes can be processed at the same time (because of entanglement and superposition). Thus making it able to process countless processes parallel without using any parallel processor.

In classical computer, if you want to run 8 parallel processes, then you should have 8 parallel processors because each processor will hold different bit values for its problem processing. That is why Quantum Computers are a threat to our modern days encryption technologies. A quantum computer can find the key of encryption instantly, whereas a normal computer would take millions of years to break the encryption.

I am visualizing more from a hardware perspective, where I visualize the limited number of qubits holding the boolean values in all possible combinations, because of superposition.