Quantum computers mean engineering ahead of its time and, most of all, physics. With capital PH. In order to really comprehend the way they work, one needs to be really familiar with quantum mechanics... So, we will not even try. Which does not mean we cannot, in great simplification, talk about the rules governing this area, enabling us to play with quants. So how, in the most general way, does a quantum computer work?
Two kinds of physics and one cat
Let us start with the fact that there are two kinds of physics: classical, Newtonian physics that we know from school, and that weird, non-intuitive kind – quantum physics.
Classical physics explains the world and the laws governing it as we see them. Action-reaction, mechanics-dynamics, etc. And quantum physics focuses on the world not accessible to us, invisible, on the scale smaller than nano, composed not of things that exist but of events and probability. This world runs according to different laws – it is possible to catch up to light, there is true randomness, and events can exist and not exist at the same time. This subsequent being and non-being is the biggest unknown that destroys the foundations of our thinking, makes us uneasy (although it can also be pleasant) and throws us way out of our comfort zone. Even worse – when we finally establish that something does exist, it stops existing at the very same moment.
When we open the box, Schroedinger’s Cat – meaning that beautiful possibility that the cat is either alive or dead – is no longer inside. As soon as we say “check” and lift the lid, we are left with only an alive or dead cat, unequivocal, defined. It is no longer the Schroedinger’s Cat, defined only by the rules of probability. It is no longer there. And that is the beauty of it.
Quants and qubits
Quantum computers use that uniqueness of subsequent being and non-being for… calculations. This is how qubits work – the mad cousins of traditional, digital bits. Those cousins arrive from the faraway land of quantum physics and start brawls.
And what are quants? They are the smallest, non-divisible “portions” of various phenomena (e.g., such as diverse types of energy). And so, light is composed from “portions” of quants known as photons. This is electromagnetic energy. Photons are also heat energy, while magnetism is “packages” of magnons, etc.
Too many difficult names?
Let us not even look at the elementary particles that make up matter. These are various fermions, leptons, bosons, and – the best – quarks. Among those we can fins such beauties as, e.g., charm quarks, truth (top) quarks, and my favourite – strange quarks… And in this quantum world beautiful and strange things happen. But this story is not about that. Let us go back to quants.
Entanglement
Among many qualities of quants there is one that is key to the creation of quantum technologies: they can… ENTANGLE. Entanglement happens in pairs and is a type of unusual connection. No matter where one quant is located, the other, entangled one goes though the same changes of state. If something happens to it, it is mirrored in the other simultaneously. This phenomenon is so distressing and incomprehensible that Einstein called it spooky action at the distance.
A quantum computer is based on entanglement and Schroedinger’s characterisation of quants.
Between 0 and 1
For the above-mentioned qubit to work, it must be in a superposition. This term is easiest understood with an example of a coin. If we throw it, we will see heads or tails – 0 or 1. But there is also a third possibility – the coin may spin on its edge and become neither heads nor tails but all the possibilities between those two. This is how qubits work and this ailment of theirs is the key to understanding the difference between a quantum computer and a classic digital one.
Classic vs. quantum
A classic digital computer is based on a system of zeros and ones. The current is either flowing or it is not. There is a signal or there is not. Simple. This is how bites work. The result of calculation is a series of variously ordered zeros and ones making up a solution. The faster the computer, the quicker the series is created. This is a strictly linear action.
In a quantum computer, on the other hand, everything happens at once, zeros and ones both are and are not there. Only probabilities exist. Instead of bits we get qubits. Calculations happen in multiple channels simultaneously; all possibilities are checked out. In the end we read the “result” – 0 or 1. But along the way, everything probable happened. Multiple options.
This multiplicity is exactly the enormous difference between what is happening in a classical, one-line computer, and a quantum one. On top of that, the qubits are entangled, so they are constantly influencing each other; in effect, EVERYTHING is happening EVERYWHERE and AT ONCE!
Madness. And this is where the unimaginable potential computing power of quantum computers comes!
Instead of Apocalypse
What can a quantum computer do? It will help us create and test new medication in a few seconds – checking never-ending combinations of molecules, currently impossible to analyse with traditional methods. It will allow a vaccine for covid or another dangerous virus to be created immediately, it will help tailor medication to our individual DNA, it will help solve other problems of utmost complexity – such as the stock exchange and financial prognoses, or optimising road traffic. We will also be able to really predict weather – in an exceptionally long term. All that is too difficult even for the best supercomputer connected to the most developed AI.
And I almost forgot 😉: quantum calculations will save the world from catastrophe! They will enable us to analyse the climate change conditions and design counteractions. Not bad, huh?
Dominant technology
But before that happens, we need to decide on the technology for creation of quantum computers. There are quite many around at the moment, each one evoking some serious respect with its name 😉 – ion traps, quantum points, topological order, work on photons using interference, nitrogen defects in the diamond crystalline structures. Regular Wild West…
However, the most effective one is probably the superconductor technology. Superconductors are unusual materials, transmitting electricity with no resistance, losing no energy. It is only possible in critically low temperatures. Achieving those temperatures, necessary for the circuit to remain stable, is the hardest challenge faced by the scientists and engineers building quantum computers.
The superconductor technology is currently dominating the worldwide quantum race.
The most beautiful
Quantum computers built using superconductors have one more characteristic, extremely important for me personally. They are THE MOST BEAUTIFUL. The look like golden, glittering and intricately designed baroque chandeliers or lovely jewellery. One can fall in love with them at first sight, get fascinated by the very difference between them and what we are used to consider to be a computer.
These “chandeliers” have on the very bottom a can with chips on which our qubits are happening. And the golden madness around them is just a cooling system – a cryostat. Each segment of the “chandelier” is another cooling stage, from 77 kelvins on the top to almost absolute zero on the bottom.
Cryptography
The quantum entanglement phenomenon is also used in other technologies; it can be a breakthrough in cryptography, i.e. securing information from outside interference. Encryption is the basis of cybersecurity and therefore the safety of our data, of entire countries, and the world’s whole electronic banking system. Quantum cryptography will totally change the approach to security.
Taking over valuable data with quantum protection is practically impossible. Why? Because of ENTANGLEMENT. When someone interferes with one quant, it is immediately visible on the other, no matter what the distance. There is no way to make an imperceptible change. A cypher with quantum protection cannot be broken. Quantum cybersecurity is the best security in the history of the world as it is based simply of the laws of physics. Checkmate!
But there is also a dark, reverse side to using quants in cybersecurity. At the moment encryption is mostly based on the fact that even the fastest supercomputers have problems with large numbers factorisation. Factorisation means reducing large numbers into the product of prime numbers. To attack such a cypher successfully, you need huge computing power that we do not have at present.
Teleportation
In case of quantum communication – also one of the important and currently developed fields of quantum technologies – entanglement gives hope that humanity’s great dream of TELEPORTATION might come true. This is no longer science fiction. If a change of status in one quant may be shared in absolutely the same moment to another at any, infinite distance, we do not only – as some say – break the laws of classical physics and Einstein’s assumption that the speed of light is unsurpassable, but we are also proving that teleportation is possible. For now, we are working on teleporting a single electron…
If we manage to confirm theoretically that it is possible, teleportation of a human will be only a matter of time necessary to develop the suitable hardware.
Dogs in space
Do you know that Russian scientists proved "on paper" that flight into space is possible? Over 50 years before the first successful flight! The scientists knew that it can be done but the available technology took the following years to grow so that the theory might have been put to practice. This happened in 1957 and it was the famous Sputnik 1, while Belka and Strelka were already preparing for their flight… In 1961 in the orbit around Earth, a certain Gagarin made an appearance. And quite recently – a Tesla.
The most beautiful thing about the human species is that while tiny and fragile, with short expiry date, we keep on looking towards the stars and drawing our path towards them. For that, we use our brains and infinite imagination. This is why our theories outrun the present. It will most likely be the same with teleportation.
Everything important
Classical physics and quantum physics exist separately but parallel. For us, they are tools to understand the macro and micro world, depending on the needs. The world in which things are defined and the one where everything is possible. Both possibilities are true – as mush as a theory can be true – so, until some other one is proven correct.
What is the most fascinating is the possibility of destroying the wall dividing those two worlds and joining them into one. Another great proposal of interpreting the world and matter will be built on the discovery of the laws true both for classical physics and the mad quantum physics. And on understanding their common, broader context.
When we understand the common context, we will understand everything.
Almost.
Dr Bianka Siwińska
