Quantum Computing
Form bits to qubits: how computers leverage quantum quirks run things even faster.
By now, I think you’ve got a pretty basic idea of what quantum mechanics is, and how things behave in the quantum world. But in this last part, I would like to shine some light on the topic “quantum computing”, which (as you might have guessed) uses quantum physics in the field of computers.
So let’s start with the basics of computing. Not of quantum computing, but of traditional computing. In classical computers, everything is represented by 0’s and 1’s, and these are known as “bits”. Each bit of information is just that. Either “yes” (or “on”, or “1”) or “no” (or “yes”, or “0”) answer to a question.
You might wonder: how does a computer, that does millions of different things, use only two numbers for all of that? To get that, let’s clear up some basics.
Computer chips are up made of potatoes. Okay, that was bad. Computer chips are made up of modules, which contain logic gates, where transistors are stored.
A transistor is the basic unit of a computer. You can think of transistors as a switch that, when turned off, simply stops the flow of electrons in the circuit — and therefore, the flow of bits as well. Those bits can combine in different ways to represent complex information.
As mentioned earlier, these transistors combine to form Logic Gates, which do very simple stuff like “open if both signals are on”. The formations of several logic gates make up modules, that are finally able to perform some of the functions we’re familiar with. Like adding two numbers.
That may not sound much but, think of this as a bunch of 10-year-olds. They only know how to add and subtract, but thousands of them can collectively solve literally any math problem.
There is one problem, however. You see, over time our computers have transformed from being entire rooms to just wrist watches.
The transistors that interrupted the flow of electrons are so tiny, they now measure about seven nanometres in diameter — a thousand times smaller than a typical cell in our body. If they continue to shrink, they’ll soon hit atom-size territory.
And we all know what happens when things become that small.
Everything changes.
The transistors that previously blocked the flow of electrons are so small, electrons simply quantum-tunnel through them. So essentially, they stop working. And when they stop, everything stops. That’s the main reason why we haven’t seen a breakthrough in the classical computer for years.
I think we’ve reached the dead end.
But scientists were smart. Instead of finding a solution to this problem, they turned these weird quantum phenomena to their advantage
They knew that the old “bits ”won’t work in the Quantum Realm, so they invented some new bits for the new Quantum computers. And they named them “quantum bits”, or “qubits” for short.
There are a number of physical objects that can be used as a Qubit. A single photon, a nucleus or an electron. Quantum Bits are pretty complicated, so I’ll explain them in the simplest manner.
Let’s assume an electron to be a Qubit. All electrons have magnetic fields, so they are basically like tiny bar magnets. And this property is called spin. If you place them in a magnetic field they will align with that field, just like how, a compass needle lines up with the magnetic field of the earth.
Now, this is the lowest energy state, when the electrons align themselves with some other magnetic field. We call it the zero states or we call it the electron, spin down(0). W can put it in one state, or spin up, which means putting the electron, in just the opposite direction of spin down. But that takes some energy. And that is the highest energy state(1).
Now so far this is basically just like a classical bit. It has got two states, spin up and spin down, which are like the classical one and zero. But the funny thing about quantum objects is that they can be in both states at once. Now when you measure the spin, it will be either up or down. But before you measure it, the electron can exist in a Superposition.
Remember Schrodinger’s cat? It was both dead and alive at the same time, exactly like that, a Qubit is a superposition of both the 0 and 1, and you can’t predict which of the two it is, as long as you don’t force it to collapse into one by measuring it.
But what’s the point of having qubits if you can only read them as 1s and 0s? How are they different from a normal bit?
If you tried to “read” or measure a qubit each time, you’d keep collapsing it into a 1 or a 0. The trick is to not measure it all at once: computers leave it alone in whatever state it’s in — 1, 0, or a combination of the two. They run their calculations with the qubit, assuming it’ll do its job right. Calculations become faster because of stuff like interference (constructive for the right answer, destructive for the wrong one). And then, when the algorithm’s over, it finally measures it — collapses the wavefunction, unbags the cat — to get an ordinary, binary, result.
Qubits are way more efficient than bits — but only when you’re not looking at them.
The real trick to Qubits, however, is Quantum Entanglement. Entangling two bits can be very beneficial because as we add more and more bits together, we turn them into a combined system. This means that measuring just one Qubit, or one combination, will directly give us the properties of the others.
Which, when programmed with complex algorithms, can provide a huge increase in processing power.
So in a nutshell, what happens is this: A quantum computer sets up Qubits, entangle them with each other, and uses fancy maths to manipulate probabilities. Then, it finally measures the outcome, collapsing superposition into an actual sequence of 0s and 1s.
So if quantum computers are so powerful and effective, why haven’t they taken over the world? Cause we need to have at least a hundred qubits entangled in them. And till now, we successfully managed to cramp only fifteen.
That’s one of the main problems in quantum computing, at least for now.
Why can’t we just slap in some more qubits into the system? The reason is: decoherence.
Decoherence is a situation where the results from our calculations don’t match the input we gave to the computer. Like if we entered 2 + 3 =? and the result we got was Hello world. What! But why? Well, this happens mainly due to a change in the qubits, by something random that’s not being monitored.
What sort of things can change these qubits? Almost everything, I guess. In the quantum world, anything can bump into our qubits and cause these changes. Qubits are extremely delicate. A single photon, for example, can affect the qubits in ways that cannot be tracked. And this can seriously change the results.
That’s a real concern, because quantum computers will probably be used for heavy calculations and simulations — like calculating the trajectory of the spaceship carrying millions of dollars’ worth of cargo to Mars — where there’s literally no space for error.
So the more qubits you add, the more chances you have of encountering decoherence, because now more qubits are exposed to external changes. So you’re just multiplying your problems with each qubit you add.
The problems don’t end there. To accurately measure qubits and collapse them into usual bits, we need to have these sub-atomic particles as stationary as possible. That means keeping them cool. Because of this, you can only find quantum computers in high-end labs, installed with freezers maintaining the temperatures at around -273 C.
That’s just 0.15 Kelvin above Absolute Zero, the lowest temperature possible in the universe.
Also, till now, scientists haven’t managed to keep superposition for very long.
All this suggests that a quantum computer is probably is not a replacement for our classical computers. In fact, because of all this, an ordinary calculation might take more on a quantum computer than on a classical one, at least for now. So we’ll still be having traditional computers in our hand, for quite some time.
If our desktops and our phones aren’t going quantum anytime soon, is the “quantum revolution” even significant to us? Actually, it is.
While quantum computers might not replace ordinary machines, they’d be vastly superior in other areas — once the above-mentioned problems are solved, that is.
One useful area is database-searching. See, what your classical computer does is, if asked the question Are apples there in the grocery list?, it checks each entry for apples, and gets the answer back in 0 or 1. If it gets back 0, then it moves on to the next entry. This process keeps on looping until one of the entry matches “Apples”.
A Quantum Computer, on the other hand, needs only the square-root of that time, because it can look through all the entries at once. For larger databases, with millions of entries, that is one huge difference.
But the most famous use of quantum computers, by far, is ruining IT security.
Right now, what happens is, all your passwords and bank information and even nuclear codes are kept secure by highly advanced encryption systems. These encryption systems run some random math functions on your password, and store it in that form.
For example, suppose your password was 123. Suppose, the encryption software your bank uses performs the following function: it adds 24 to each digit, multiplies the result with 92, and finally subtracts it by 42024588. The actual password is known as the private key, whereas the random number generated would be called a public key.
After running this, your password would now be encoded and stored in that form. Now, if someone by chance, a hacks into the bank database, he would find all the passwords in some random sequence of numbers. In our scenario, he would see 37667823 instead of 123. Well, actually he can, in theory, use the public key to find the private key, using all combinations. Luckily, doing the necessary math on any normal computer would take years of trial and error.
But a quantum computer, with its exponential speed-up, could crack it in minutes.
At the same time, quantum computing opens up new possibilities of improving encryption by creating the whole new field of “quantum cryptography”. This could potentially allow for new approaches, and enable brilliant minds to fundamentally change how we think about security in the modern age.
Another possibility is that of cloud computing. Suppose you have a tremendously difficult calculation to make, which is almost impossible for your traditional computer to make.
What you will be able to do is, you can send this calculation to a supercomputer installed in a lab, via the cloud. The computer will solve the problem in minutes and send you back the results.
In this way, supercomputers instead of replacing our computers, work as an aid to them. And this is game-changing.
Think of all the problems, in fields like medicine or environment, that we’ve not been able to solve because of the complex calculations that come with them. With the help of quantum computers, we’ll be able to improve the inefficient processes — in ways we haven’t been able to for the last 100 tears.
Today, however, all of these ideas are in their infancy.
Right now, instead of focusing on building quantum computers, companies are trying to build the algorithms that’ll make these things possible. Because in order to use quantum mechanics, collapse superpositions, and entangle qubits, we have to work and think in Quantum Mechanics.
Which, by far, has been the most difficult thing to do.
Quantum computing exhorts us to see the world from a different angle. And will we be able to achieve what even brilliant minds like Richard Feynman couldn’t?
Will quantum computing revolutionise the world? Maybe.
That totally depends on us.
Quanta in a Nutshell: This article is last of a four-part series on quantum mechanics. Parts One, Two and Three are available here.
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