In the depths of a refrigerator where the temperature almost reaches absolute zero, hides a quantum computer in seclusion from the outside world. Many are determined that such a device is the key to the future, capable of radically changing our lives with the power of its immense calculations.
Before indulging in the fantasy realm on how they might change our world, it’s worth taking a deeper look at the physics behind quantum computing. This is an invitation to a mysterious dimension where the rules of our world do not apply: the world of quantum mechanics.
In the 1980s, the eminent physicist Richard Feynman sought the key to understanding the quantum world. However, quantum systems are extremely difficult to understand, and many of their secrets still remain hidden from us. Feynman faced a problem: he could not observe quantum processes directly and decided to create a model of them.
However, his current computer was not up to the task. As the number of particles in the model increased, the computational load increased significantly. He realized that conventional computers simply could not develop fast enough for quantum computing.
But then he had a real epiphany. What if you create a device based on quantum elements? Such a tool, operating according to the laws of quantum physics, would be ideal for exploring the quantum world. And thus the idea of a quantum computer was born.
In doing so, Feynman created a connection between quantum physics and the world of computer science. To understand the principles of quantum computing, you need to understand its quantum essence. And here we come across the basis of quantum physics: amplitudes.
Imagine that you are tossing a coin 20 times and want to know the odds of landing on heads. Classical probability simply adds up all the possible outcomes for it. Simple and logical, isn’t it?
However, in the quantum world everything is different. If you imagine a subatomic particle, before it is measured, it exists as a wave probability in a black box – with countless possible locations. Quantum mechanics changes our understanding of probability. And in this change lies the power of quantum computing. Amplitudes and probabilities are closely related, but they are not the same thing. A major and Important difference is that probability always ranges from 0 to 1.
Amplitudes are not just numbers, they are complex numbers, and they play by their own rules. When determining the overall amplitude of an event, it is necessary to take into account the amplitudes of all possible ways of its implementation. In this case, there is an interesting point: a particle can move to a point with a positive amplitude by one route and with a negative amplitude by another. And if this happens, the amplitudes can “cancel” each other. The result is absolute zero, and the event is not implemented. These amplitudes determine the probability of something being present at a specific point in space.
At the heart of quantum mechanics is the understanding that the world is described in terms of amplitudes. What about changes over time? This is also about the play of amplitudes, their linear transformation.
How do quantum machines use amplitudes to manipulate information? The basis of their world is the qubit. If you imagine a classical computer bit, which can be either 0 or 1, then a qubit is its quantum “brother.”
Bits are strictly binary, while qubits, being subatomic particles, operate on different rules: they can be 0, 1, or a linear combination of 0 and 1. This ability of qubits to “mix” states is the basis of quantum computing. Until you measure a qubit, it is in a superposition—a state between 0 and 1. Superposition allows quantum computers to store and process data much more efficiently than their classical counterparts.
When several qubits are in a special state called superposition, a surprising phenomenon occurs between them – quantum entanglement. This means that the results of their measurements are interrelated in a complex mathematical way.
By “quantum entanglement” we mean special connections in a quantum system that differ from the ordinary connections of our world. Imagine a book: individual pages have no meaning, the information is hidden in the connections between them. To “read” such a book, you need to look at several pages at the same time.
However, describing highly entangled states using familiar bits is not an easy task. Let’s say you have a basic 10-qubit computer. It is capable of processing 2^10 different values simultaneously. Describing an entangled state on a regular computer is not an easy task. A 500-qubit system would require as much data as there are atoms in the entire known universe. Feynman understood this by pointing out the limitations of classical computers in simulating quantum phenomena.
A quantum computer only becomes useful when it receives data from qubits. But there is a problem: when measured, the quantum system “collapses” into an ordinary state. It’s like asking a qubit: “Are you 0 or 1?” – and make it decide. If this information leaks out of the computer, for example through radiation, it affects the qubit as if it were being measured. When observing a system, our quantum amplitudes turn into simple probabilities. To get a specific response from a quantum system that is not just random, you need to use interference.
Interference is a phenomenon well known in classical physics. Like, for example, waves in a pool, one of which is above the surface and the other below, and they neutralize each other. Interference occurs when the amplitudes are added together.
If an event can occur with an amplitude of half in one case and with an amplitude of minus half in another, then the resulting amplitude will be zero. This point is illustrated in the famous double slit screen experiment. You close one of the paths, and suddenly an event that was previously impossible begins to happen. This is a quantum algorithm in action. Scientists use interference to create a sequence of gates for qubits. These qubit gates cause the amplitudes to add up in such a way that the probability of getting the correct answer increases.
Do you think it is possible to arrive at the correct answer without knowing it in advance? Quantum algorithms are a complex field that has been studied for decades. Since 1994, the world has seen a number of breakthroughs in quantum algorithms. This could change the entire cybersecurity and search optimization industry.
Experts say the true purpose of quantum computers is to help us understand the deep structure of the universe. This new era in physics is exciting! Will quantum technologies bring just profit or revolutionize our world in the coming years? The answer is yet to come. But one thing is clear: the future of quantum computing is full of unexplored possibilities.