This article, Francesco Sisini, presents the basics of quantum computing; therefore, if you have never heard of it or heard about it but still don’t understand it, this article is the best place to start!
As you can imagine, quantum computation is based on the principles of quantum mechanics, a science that Richard Feynman himself, one of the leading quantum physicists of the recent past, said he did not fully understand, and that still presents problems interpretative challenges that are absolutely unsolved.
So if you think you will have a hard time understanding it, know that you are in great company!
In the 60s, the maxim was in vogue among quantum physicists: “shut up and calculate!” which implied the uselessness of asking philosophical questions about quantum theory since experimental results constantly confirmed it.
Obviously, it was a provocation. In fact, physicists have continued to study the theory thoroughly and have not been satisfied with just doing the calculations. The theoretical study of quantum mechanics has given several important results; first, the concept of entanglement is one of the fundamental concepts of quantum computation.
Is it worth the effort to understand the quantum basis of quantum computing?
It is common to wonder if it is necessary to understand the basics of quantum mechanics. The question is legitimate given that in the last 70 years, most of humanity has enjoyed the automation brought by information technology even without knowing the fundamentals of microelectronics that have allowed its realization in terms of computers and telecommunications systems.
The answer to the question is, therefore, “no”. It is not necessary to understand quantum mechanics if we want to limit ourselves to witnessing the advent of the quantum computing era.
The situation is similar to that which faced companies and electronics experts in the early 1950s at the dawn of the information technology age. In 1945 Von Neumann presented the first concrete project for the realization of a digital computer. In 1948, Shannon presented the first formal theory for the transmission and processing of information by computers.
Companies such as IBM understood the extent of these events and invested in the study of microelectronics, gaining a leading position in the market that they still retain. The same was true for leading scientists and professionals who first grappled with the new emerging challenges. The work of the early pioneers brought them economic and strategic benefits and allowed the company to rise to a new technological level.
Scientific discoveries and related technologies are rapidly absorbed by society, losing their competitive value and entering into common use. To give an example, think of a simple mirror for everyday use. The physics that explains the reflection of all wavelengths are quantum mechanics, and it is by no means trivial, even for an insider.
Furthermore, the industrial procedure for obtaining a mirror results from hundreds of years of perfecting the glass processing technique and that for coating a metal layer through the phenomenon of electrolysis.
So, for those who want to find themselves among the indistinct mass that in the next twenty years will enjoy the benefits of quantum cryptography, of machine learning, based on quantum neural networks, of drugs designed using intrinsic parallelism algorithms, of optimized logistics on the solution of problems that today take years to solve for classical computers, etc., there is no need to understand quantum mechanics and quantum computation.
On the other hand, those who want to be able to understand today the potential of the second quantum revolution in which we are living in order to be able to exploit them when their knowledge is a real plus must pay the price because, like everything of value,
Why is it so difficult?
Nature protects beautiful and valuable things to prevent them from being grasped by listless hands and therefore wasted and forgotten. Humanity has been studying the secrets of nature at least since history has existed, but perhaps it has never been so close to understanding its most intimate essence.
Quantum computing is not just a technology that speeds up accounts; the structure of matter hides the project capable of transforming an atom into a fundamental component of a computer, and therefore, perhaps a primordial design is hidden that has in the existence of intelligence not a random result but its original goal.
This is why quantum mechanics is so difficult: in quantum mechanics, there is the primitive concept of information medium that we do not find in classical mechanics.
 Nature, however, does not judge morality; thus, both sublime and morally righteous minds have dedicated themselves to the study of its mysteries, as well as minds that are equally finished but with destructive and nefarious objectives for humanity, and both these categories have often obtained the desired results.
First step in the quantum world
The first experience with classical computation
Try to think of a number between 1220 and 1347. Done? Now choose which of the following three categories your number falls into:
- Between 1220 and 1280
- Between 1281 and 1310
- Between 1311 and 1347
Which of the three categories did you fall into? A, B or C?
Well, follow me in this simple exercise that we will call selection rules: if the category is A, touch your head with a finger; if it’s B, touch your nose; if it’s C, touch your ear.
So far, I think you have found the exercise quite easy, let’s say so easy that it can be performed without using intelligence. Because you have simulated a Turing Machine, the automaton designed by Alan Turing, the famous mathematician, represents the unsurpassed calculation model of any classic computer or supercomputer that has ever appeared on earth.
The first quantum experience
Now think of a number again, in the same range as above (between 1220 and 1347) and again check which of the three categories below your number fell into:
- Between 1220 and 1280
- Between 1250 and 1400
- Between 1220 and 1347
and apply the selection rules again.
This time completing the exercise will be more difficult for you as regardless of the number you have chosen, you will have found yourself in at least two categories.
This is the ambiguity that is intrinsically defined in the quantum Turing Machine. The classification of the category did not lead you to a single class but to two or three classes to which the number belongs simultaneously. This is called the superposition principle of states and is the cornerstone on which quantum mechanics is built.
The deception … which is not there!
It could reasonably be objected that the problem arises because the three classes are non-disjoint intervals, so it is natural that any number chosen belongs to one and the other. This is true, but it was just an example, perhaps a bit forced, to bring attention to a phenomenon that truly occurs in nature. Let us consider for a moment that the three intervals are disjoint:
- Between 1220 and 1250
- Between 1251 and 1300
- Between 1301 and 1347
but that your mind did not produce a single number when asked but made you imagine two numbers simultaneously, say 1250 and 1300.
In this situation, to continue with the exercise, you have two possibilities: the first is to choose randomly between the first and the second number, the second is to accept that you have chosen both numbers and look for the class to which they belong.
This kind of ambiguity is exactly what happens in quantum mechanics: physical states that are mutually exclusive in classical physics can be simultaneously present in quantum mechanics; this brings the Quantum Turing Machine into the same difficult situation you have found yourself in. In the difficulty of choosing which selection rule to apply when the number is actually the simultaneous presence of two different numbers.
From problem to resource
What may seem like a limitation of technologies built at the quantum level can become a resource. The superposition of states can be exploited in two different ways. The first way consists in accepting that only one of the two imagined numbers can be used and then proceeding in the random choice of one of the two. This leads to the concrete realization of a probabilistic Turing Machine, useful in implementing search strategies in complex systems.
The second way is to apply both selection rules simultaneously, allowing more calculations in parallel, and therefore hypothetically drastically reducing the search times for solutions.
The quantum computer
It is natural to ask the complexity of this technology allows exploiting the intrinsic characteristics of the superposition principle of quantum mechanics. One would probably expect a quantum computer to be considerably more complex than a classical computer.
The reality is that a quantum computer is absolutely simpler than a classical computer. To realize this, think, for example, of the complex microelectronic technology necessary to keep a single bit in state 0 or state 1 and compare it with that necessary to do the same with a qubit that can be made from an atom and switched from 0 to 1 and 1 to 0 with a laser pulse.
The problem is that while the quantum computer is really that simple, to function properly, it must be kept isolated from the surrounding world or, as they say in technical jargon, kept in a coherent state.
So the quantum computer is a straightforward system but surrounded by a highly complex system whose goal is to make it simple. Therefore, we can compare the quantum computer system to a nursery where children play in total safety inside because outside a group of adults has worked on a system made up of rules, specific materials, assistance protocols, etc. This allows children to manifest their simple and spontaneous nature.
Quantum computing is not a technological optimization of classical computation but a new computer science based on a new concept of information.
Learning the fundamentals now makes the difference between being among the protagonists who will apply it first and the spectators who will enjoy the results in a few decades!
If you want to learn the business applications and technical basics of the new frontier of information technology and apply them to enhance your professional future, check out the School of Disruption.
Francesco Sisini, physicist,Master degree in nuclear physics, PhD in radioisotopic techniques