Quantum entanglement

What are qubits and what computer is best today?

A research paper by Japanese scientists was recently published in the scientific journal, npj Quantum Materials. The group of researchers stated that their findings could create the prerequisites for the development of more efficient and accessible quantum computers, capable of functioning in near-room temperature conditions. While studying an alloy of cerium, rhodium and tin, and applying a specific influence to it, heavy fermions began to exhibit superconductivity and even turned out to be quantum entangled, which opened up prospects for a scientific breakthrough. Let’s break it all down.

Great ‘calculator’

Our classic computers are binary — they work on transistors that recognise only two states (conduct current — 1; do not conduct current — 0). As a result, they operate on bits: zeros and ones. Quantum hardware, conversely, operates on qubits, which are simultaneously in all states between 0 and 1, but when measured, they collapse into the values we are used to, and we can get some kind of answer. 
This is a bit like looking at an aeroplane propeller with the naked eye; we only see a blurry circle, but if we take a photo of it with a fantastically short exposure, we can see in what position the blades were at the moment of shooting. However, until we press the button, the blades are in all positions at the same time for us. 
You can compare a quantum ‘machine’ with a classical one using a simple example. If you give them both the task of finding a way out of a maze, then our familiar smart technology will calculate all the paths and look for the correct one, while the quantum know-it-all will simply pour water into the maze and see where it starts to pour out. After all, it already has all possible values. Strictly speaking, calling this system a computer in our classical understanding is not entirely correct; it is more of a ‘calculator’.
What would happen if, theoretically, we tasked it with finding the keys to the most advanced encryption protocols? Well, it would find them in a very short time. Furthermore, we could probably unlock the secrets of the Universe, find a cure for cancer and fulfil a vast multitude of other useful things. 

Touching on science fiction

Some might wonder where to get such a thing. Some may have heard about the astronomical cost of such systems, liquid nitrogen cooling, underground laboratories… I will surprise you: you can actually buy such a tricky gadget. Depending on the configuration, it costs a little more than the average classic computer. Obviously, you will not be able to hack all the banks in the world or learn all the secrets of the internet; otherwise you would not be able to pay for this ‘calculator’ with a credit card. So what can you do with it right now? Let me clarify right away: if you really bought such a ‘trifle’, then you are an extremely extraordinary person and clearly live a very exciting life. And after such a purchase, you will be able to brag to all your friends that you have a real quantum ‘wizard’ at home, and even show it off to your guests. You can also download algorithms for it from the internet and run them on it without any practical meaning. Perhaps that is all you can do with it. Disappointing, isn’t it?

Harsh reality

We are used to thinking that the more transistors a processor has, the more powerful it is. The same rule applies to quantum ‘toys’, but unlike classic computers, they are analogue devices, not digital. We, quite literally, try to use quanta for calculations, and as a result, there is a certain degree of error in every qubit, known as noise. The more qubits we use, the greater the error will be.
That is not the only problem. For qubits to work properly they need to be connected; that is, any two of them need to be able to perform operations with each other. This is called a fully connected system. Yet, so far, no one has managed to implement this type of interaction adequately. Of course, they can be connected using other qubits, which again increases the accumulated error.
And now, the cherry on the cake. Every existing quantum computer has coherence time — a period of time in which calculations can be performed. Thus, for superconducting qubits, this is at best up to 100 milliseconds (ms). This is not a case where we can solve the problem in parts; we need to get the answer straight away. So, the more complex the problem, the more qubits we need. At that point, we remember that the more qubits there are, the greater the error will be, making the whole endeavour pointless. 

Practical application

Here we come to the question: where are quantum ‘calculators’ used in practice? Almost nowhere; they are used to solve highly specialised, abstract mathematical problems. It was assumed that with the development of technology, these ‘machines’ would be able to predict the properties of molecules, but then neural networks arrived and said that it was all rather complicated and unclear; just tell us what properties of the molecule you need and we will do it. And they did.
Last year, Google offered $5m to anyone who could figure out how these quantum ‘toys’ could be applied in real life. Such is the crisis of the genre.
What about those personal ‘calculators’ that you can buy for home use? Well, the power of what you can buy for relatively reasonable money is only two qubits. Then why are quantum computers sold in a domestic format? Only because people buy them. It is an interesting high-tech souvenir for enthusiasts.
At the same time, if you do not research anything, you will not learn anything new; that is the essence of progress. Someday the future for quantum computers may come, although personally, I do not believe in the prospects of analogue systems, but the situation today is like this. Going back to the beginning of the material, it is resolutely impossible to use quantum ‘calculators’ in the national economy today in any way. As for the discovery of Japanese scientists, perhaps it will one day lead to a breakthrough — and this cannot be ruled out — but only time will tell.

TEMPERATURE DROP

What is striking in the discovery by Japanese scientists is that the unusual properties of the cerium, rhodium and tin alloy are maintained at temperatures close to room temperature. Usually, quantum effects are observed only at extremely low temperatures, which creates serious technical obstacles for practical application.

The new discovery could fundamentally change approaches to processing quantum information and create the prerequisites for the development of more efficient and accessible quantum computers capable of operating in near-room temperature conditions.

TO THE POINT

Currently, the situation with quantum ‘calculators’ is approximately as follows: 
 
  Google — 77 qubits, 
  Rigetti — 80 qubits, 
  IonQ — 29 qubits. 

Calculations can theoretically be performed on capacities up to 100 qubits, whereas beyond that, the accumulated error makes the result completely useless. For reference: a system of several million fully connected qubits is needed to solve real-world problems.

By Yuri Terekh