What do Quantum Computers have that Classical Computers don’t?
Quantum Computing is not entirely an Engineering field. Just like AI, a huge amount of research is being done in this area, where researchers and academics are trying to narrow down the the best possible approaches to deal with a specific problem. Let me put it this way; back in the very late 19th century, and earlier 20th century, Electronics was a hot subject. The concept of electricity was rare, and precious. Researchers were investing time and effort in order to come up with solutions, where the power of electricity could be harnessed in an optimal way. Several gas molecules were being bombarded with high-speed particles, several metals were being tested for good conductivity results, relationship between electricity and magnetism was being studied, semi-conductors were being synthesized, advantages of copper coils were studied in the design of transformers; all these studies taking place at different Universities and research laboratories were finally merged together by roughly the mid-20th century, and that was the time when “Electronics” was not mere a theoretical problem, but it became an engineering problem, and ways of designing hardware which could support Electricity were industrialized.
Read more: https://www.smithsonianmag.com/innovation/extraordinary-life-nikola-tesla-180967758/#RhwUOixKsCl2DvOi.99
If we compare Electronics with Quantum Mechanics (QM), I personally believe that QM is still in the phase where Electronics was in the earlier 20th century. Considerable research has been done, some materials are being studied which can maintain quantum states of particles for longer periods of time, research projects across the World are being funded, and almost every tech-giant of today (as of October 28, 2018) is racing towards building a fully-working Quantum Computer. But as I said, it’s still a research problem, no one actually knows how to build one correctly. There will be a long series of “Study-Research-Build-Trial” cycles, before people finally figure out what to do, and what NOT to do in order to design a hardware which supports Quantum Mechanical phenomena.
Question! Who do we even NEED Quantum Computers?
Well, a very simple answer is: They’re very (like veryyy) fast. Exponentially fast, to be specific. A more complex answer can be that the building blocks of computers are getting smaller and smaller in size, which their performance is getting better and better. By now, the transistors have become so small, that going further small in size has become a challenge, but we also know that transistors are not the ideal building blocks, as we have figured out through intensive research that computations can be performed even on single atoms, or even single electrons, instead of a stream of billions and trillions of electrons. So, in order to achieve that precision, we need Quantum Computers (QCs).
Question! What do Quantum Computers have that Classical Computers don’t?
The answer to that question is based on literally more than a century old research in Physics, at the most prestigious Universities and research labs in the World. When we dive into the Quantum Mechanical World, we get these two “power-up” kind of things. One of them is called “Quantum Superposition”, and the other one is called “Quantum Entanglement”.
A Q-bit is supposed to have these two Quantum Mechanical properties. Q-bit = Quantum Bit = Quantum Binary Digit. Bits are used to store, manipulate, show, and manage information on Classical computers, but in order to represent a Classical bit, a stream of many many electrons needs to pass through a circuit so that an appropriate amount of voltage can be observed and mark a transistor as 1 or 0. With Q-bits, we can save all that metal needed for the flow of electrons, and can precisely perform computation(s) on a single Q-bit itself.
Quantum Superposition refers to the ability of a Quantum Particle to exist in more than one position. Let’s build an analogy in here. A ordinary coin has two different sides, right? We call one side “One”, and the other side “Zero”. Now, when you see your coin placed in front of you, you’ll know what is the “state” or “position” of that coin. You know it because you’re looking at it. But what happens when you flip it up in the air? The coin will have 50% chance of ending up in a 1, and 50% chance of ending in a 0, but you can’t tell it for sure, because you’re not observing the coin. Your coin will be in a state of superposition as long as you don’t observe the results. If it lands on the ground on a side, at some distance from you, and you’re not observing it, even then the coin will be in a state of superposition for you, because you still don’t know if it’s a 1, or a 0. If some other person looks at the coin, the coin will lose its superposition for that specific person, but not for you; and that’s a reason why reality differs for different observers in the Quantum Mechanical world. When you finally look at the coin, or someone informs you truly about the state of the coin, only then the coin would have broken its superposition for you. That’s always the case with the Quantum Particles (QPs). When I use the term QP, that can be any particle which holds Quantum Mechanical properties of superposition, and entanglement, for example electrons, photons, nuclei, etc. In case of electrons, we can define superposition in terms of the “spin” of an electron. We can say an electron is in a state of 1 if it has an “Up-Spin”, and 0 if it has a “Down-Spin”. In case of photons, we can encode information in the polarization of light.
Question! QPs got superposition. So what?
Apart from sounding really cool, superposition is the ability which lets the electrons exist in all possible states at a single instance of time. If we say that electron is a Q-bit (since information of 1 and 0 can be specified based on its spin), we can claim that a Q-bit can exist in a spate of 0 and 1 at the same time. A 1-bit classical system can either be in a 0 state, or a 1 state, but a 1-bit quantum system will be in 0 and 1 states at the same time, with different probabilities. A 2-bit classical system has 4 possible states; 00, 01, 10, and 11, but it can only be in one state at a time for each bit. That means, 2 bits can have two independent states. But a 2-bit quantum system can be in all 4 possible states at a time with varying probabilities. Similarly, for 3 bits, a classical system can have a configuration of 3 bits at a time, while a quantum system will exist in 8 states, and this goes on and on with increasing number of bits. That’s why quantum computers are said to be exponentially faster than classical computers, since they can look for an exponential number of possible scenarios at once. That’s the power superposition gives us.
Quantum Entanglement can be thought of as two or more particles in a relationship of some kind, which still hasn’t been explained clearly. Think of it like you have two coins, and they are “entangled” in such a way, that a 1 on one coin always results as a 0 on the other coin. This happens with quantum particles, with no strings attached, no means of communication, nothing in between them, but it’s said that even if we place the whole Universe between two entangled particles, the change in state of one particles results in a corresponding change of state in the other particle. That’s what we informally call “Spooky Action at a distance” (I’m glad that I’m writing this near Halloween).
Question! We got entanglement as well. So what now?
If we could observe the state of one of our coins, we could simply infer the state of the other coin without observing it directly. So, entanglement helps us to infer the state of one Q-bit, without directly observing it, and observing one entangled Q-bit instead. Why would we do it? Because if we observe the actual Q-bit we’re concerned about, its superposition will break down, and it won’t remain any better than a classical bit, and we certainly don’t want that. If we somehow change the state of one Q-bit from 0 to 1, the state of the other Qbit will automatically be converted from 1 to 0. In this way, entanglement gives us the power to infer results from a quantum system without observing it and letting it maintain its superposition, and manipulate the system accurately without directly interacting with it (because direct interaction would again require us to observe the system).
Coming to the end, let’s just summarize everything we covered in here.
- Quantum Computing remains a research problem as long as they aren’t industrialized, just like Electricity.
- Quantum Computers got these properties of Superposition and Entanglement which make them super fast.
- Superposition lets QCs work on all possible outputs of a problem at once.
- Different kinds of QPs hold information in different manners, and require different architectures to operate on.
- QCs without a superposition are as good as a simple classical computer.
- Entanglement helps in maintaining the superposition state of a QC system.
- Your applause/clap might mean a click to you, but means a lot more than that to me.
Good luck, and Cheers!
P.S: The link the the caption of that bulb image leads to a really nice blog which explains quantum computing in a more technical, and mathematical way, and also guide on how to program quantum computers.
