Incorrect light: Russian scientists have made a significant breakthrough in quantum computing.

Russian researchers have made a significant breakthrough in the field of quantum computing. Their article has not only been published in the high-ranking journal Advanced Quantum Technologies but has even made it to the cover. This is quite remarkable in today's world, where Russians are treated like vampires fleeing from sunlight in the West.

The article is titled "Solid-State Qubit as an Embedded Controller for Non-Classical States of the Field." It’s not something we can easily grasp at first glance. Let’s break it down from the basics, with help from the co-authors, Igor Solovyev, PhD, leading researcher at the Nuclear Physics Institute of Moscow State University, and Nikolai Klenov, PhD, professor at the physics department of Moscow State University.

ESSENTIALLY, THE SAME ABACUS

We are accustomed to laptops and smartphones, but let's take a fresh look—it's a marvel.

What if I told you that an electric computer is only slightly more advanced than a regular abacus? Indeed. An abacus counts beads that you move with the energy of your hands. Do you understand the principle? There is external energy, and there is some object that changes its state (the bead moves), and that’s how it counts.

In an electric (ordinary) computer, electric current (external energy) changes the state of semiconductor elements (transistors and the like). Transistors are essentially no different from beads. They can be closed or open. They are controlled by electric currents.

Of course, technologically, an electric computer is light-years ahead of an abacus. The first computers, before transistors were invented, used vacuum tubes. You can't make a vacuum tube very small. It needs to be heated. That’s why the monstrous computers of the past were like cabinets and rooms, consuming a lot of energy. A transistor can be made very small. In smartphones, it consists essentially of a handful of atoms. This is where compactness comes from. But the wonders of technology and engineering do not negate the fact that the underlying principle is quite primitive.

The cover of the journal "Advanced Quantum Technologies," where the article by Russian scientists was published.

LET THE PHOTON WORK

What if we could make not "rough-material objects" (beads, transistors) count, but the electrons themselves? Or photons?

Thus, we are approaching an understanding of the concept of a quantum computer.

A photon—a quantum of light—can exist in different states. Do you catch the analogy? Yes, like a transistor. A photon can be blue or red (wavelength). A photon can be polarized or unpolarized (meaning the fields in "its" wave oscillate, roughly speaking, in one plane or another).

From the example of the abacus, we already understood: to compute something, we need something that changes (at our command) its state. There was a bead on the left of the abacus—we moved it to the right. There was a transistor open—we closed it. Imagine controlling photons; they would do the counting.

However! Humans make light perform calculations! Isn’t that cool?

Igor Solovyev, PhD, leading researcher at the Nuclear Physics Institute of Moscow State University.

OPTICAL FRANKENSTEIN

You can change the state of a photon right at home.

Take the 3D glasses you might have lying around after a trip to the cinema. Most often, they are made from polarization filters. You see those semi-transparent dark "lenses"? They are not made of glass but rather from polymer film, with fibers stretched in one direction.

When a photon hits such a film, it "cheats," and only those photons pass through whose oscillation planes match with the fibers. Such photons are called polarized. So, ordinary light hits the glasses, and polarized light comes out. You just interfered with the photon world at the quantum level!

But if it’s all so simple, where are the quantum computers? For now, they exist only as prototypes and projects. What’s the problem?

There are actually two problems:

First, we seemed to want to move as far away as possible from all "rough-material" things. From beads and transistors. But here’s the polarization filter… It’s a physical object. It needs to be somehow moved, probably by electricity. It seems we are creating a quantum-mechanical Frankenstein, which is like powering a computer with a steam engine.

Second, the world of photons, quantum objects, is not as linear and straightforward as our world. For example, passing through a wall can only happen in the movie "The Sorcerers," "I see the goal—I see no obstacles." A photon has a certain (non-zero) probability of overcoming an opaque barrier because in the world of Schrödinger's cats, this is possible. A photon can, "knowing" that it is about to travel through a polarization filter, seemingly change its properties in advance. What does it mean to "know," and how can it do so "in advance"? This is complex to explain quickly and would distract us from the topic, but that’s how it is.

We end up with a cumbersome toy that also behaves strangely within itself. Not good.

Nikolai Klenov, PhD, professor at the physics department of Moscow State University.

WHAT IS A QUBIT

Currently, quantum computers look like this. The heart of the computer is a "chip" with qubits; it is tiny. Surrounding it is the "packaging," which gives the "chip" the ability to function. It is enormous. We have, like in the 1950s, ended up with a "cabinet" again.

But what is a qubit?

A qubit is an element that can take on the state of "1" or "0," like a byte in ordinary computers. However, due to quantum uncertainty, it can also be both "1" and "0" at the same time. Moreover, qubits can become "entangled" with each other, just like living beings. Have you heard of quantum entanglement? I change the state of one particle, and immediately the state of another changes, even though it is far away, and I have not manipulated it.

All of this makes quantum computers potentially much more powerful than ordinary ones. The analogy: in an ordinary box, you can fit, say, two sweaters. In a magician's quantum box, you can fit two sweaters, a rabbit, and it can even talk to another box.

Physically, a qubit looks like a tiny wire, functioning as a single artificial atom (even though it consists of many atoms). For it to work this way, it must be cooled to nearly absolute zero. Superconductivity occurs within it, leading to unusual properties. The wire-atom can be set to the desired state using electromagnetic fields (light). You set the task, and then it does the rest itself.

A refrigerator cools several dozen qubits (more cannot be achieved yet), making the system cumbersome.

Currently, achieving quantum supremacy—creating a quantum computer that computes better than an ordinary one (even for specially selected tasks)—is extremely challenging.

"The solution we proposed should allow for the creation of a practically useful quantum computer," says Nikolai Klenov.

Well, it’s time to discuss our scientists' discoveries.

CONTROLLING A QUANTUM "ZOOPARK"

In brief: in the article, our scientists proposed a method for easily controlling the states of photons associated with the qubit. The key component of the recipe is non-classical, or