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What is a quantum computer and how does it work? J …



Last Wednesday, an article in the magazine Nature, one of the most prestigious scientific publications, realized what could be a milestone in the field of quantum computing. The information said that Google Quantum Processorcalled Sycamore, He completed a calculating operation in 200 seconds, which would take the fastest conventional computer in the world in about 10,000 years. The result of the experiment allowed computer giant researchers to claim that they achieved quantum supremacy, a concept coined by the American physicist. John Preskill in 2012. This notion argues that this state will be reached when a quantum system performs a computational task that exceeds those that can be performed with a classical computer.

After the publicity of the feat, IBM, a Google competitor in this field, dropped the price for the ad, saying it wasn't thousands of years that would take a classic system to solve the task, but two and a half days. However, apart from the trade battle, few argue is that the world is facing a new technological threshold.

For this reason, to try to understand what this milestone means and to try to find out what quantum computing is, Page / 12 He spoke with one of the country's leading references in this area, Juan Pablo Paz, PhD in Physical Sciences at UBA, Senior Professor and Senior Researcher Conicet. Who, besides being declared a Researcher of the Argentine Nation and a multi-member, is also director of the Quantum Information and Foundations Group of the Faculty of Exact Sciences; and co-responsible with Christian Schmiegelow of the first Cold Ion and Atoms Laboratory (LIAF) in Latin America, formally opened last July with the presence of the 2012 Nobel Prize in physics, David Wineland.

From conventional computers to quantum computers

To begin contextualizing where we started and where we are going, Paz explained that "Ordinary computers are devices used to store and process information, which is represented in the state of a material object in binary code (sequences of zeros and ones). For example, on computer hard drives, magnetic material, which, when viewed with a magnifying glass, is like small magnet granites like those in the refrigerator, has a north pole and a south pole by convention. If they point up, it's zero, down, one. Binary states that are used to represent information. They are the bits. But these magnetic granites are large from the point of view of atoms: they have a hundred billion atoms and only two possible states. "

In 1981, Richard Feynman, a brilliant and eccentric physicist who received the Nobel Prize in Physics 1965"He began to fantasize about the idea of ​​processing information at atomic scale and the possibility of processing calculations on a device that evolves following the laws of quantum physics," Paz said. Why? As explained by the expert "at the atomic scale Atoms reveal certain characteristics, a duality between the behavior of waves and particles, where electrons sometimes manifest as particles and sometimes as delocalized waves. They have the property of being in more than one place at a time, of traveling many paths at once.. Feynman's idea was to take advantage of this unfolding feature that can't be obtained on an ordinary computer, because otherwise we would never simulate the laws of nature in which particles obey quantum physics and calculus problems increase exponentially. "

From bits to qubits

But to achieve that leap, the challenge was to design computers that would respond not to the laws of classical physics, but to for quantum, where objects can be in two simultaneous states. And this step was taken from the bits to the qubits to store, process and transmit the information. While classic computers store information in bits, sequences of zeros and ones, which can have only two possible states, in quantum computers, the minimum unit of information is the qubit (quantum bit). An almost esoteric object that, fulfilling the laws of quantum mechanics, You can adopt states 0 or 1, or both at the same time. This state of quantum overlap increases the ability to process information, allowing multiple paths to be traversed simultaneously.. But besides that, it has another strange property: the quantum entanglement, which allows atoms to be affected even though they are separated by great distances.

Natural Atoms vs Artificial Atoms

Conventional computers mainly use silicon semiconductors for their integrated circuits. But what are quantum devices based on? In this regard, Paz said that "there are different technologies competing at the moment. One is the one used by Google, the other we use in the laboratory, which is the trapped atoms. ion trap, and allows to manipulate individual atoms. "And he pointed out that" one virtue is that atoms are all the same, but trapping them is more difficult and control methods are complicated, although many advances have been made. "

"Google and IBM computers do not use natural but artificial atoms. They are systems larger than a natural atom, but have similar properties and behave according to the laws of quantum mechanics. They are small rings of superconducting material, What is a material that, if sufficiently cooled, ceases to have electrical resistance, in which current flows in one direction or the opposite. The clockwise direction is zero and counterclockwise is one. The physics of these devices behave like real atoms. They can exist in these two states and overlap. The difference is that, for natural atoms, it is difficult to stabilize devices to capture them when it comes to many atoms, which also need to make them interact. With the artificial ones, the advantage is that to make them you can use the existing microelectronics industry and the science of highly developed materials, and you can let that technology see the light. "

The super chip

Google's Sycamore Chip, detailed the Argentine physicist ",is a grid of six rows by nine columns consisting of 54 rings, of which one did not work for them. This superconducting grid is connected to each other by small waveguides, small cavities that transmit light, not in the visible range. They are microwaves that travel from one qubit to another sending information and changing status as needed to execute a program. Human ingenuity was able to construct objects larger than atoms, made up of many atoms, that behave as a single atom. But these artificial atoms, whose fabrication is complex, are not all exactly alike, as are natural ones. That is, these qubits will have certain differences, although the problem has been solved for 54. It is a mystery as to whether it can scale to reach a computer with thousands of qubits. There is a huge step forward and it is not clear whether this technology will do it. "

A little universe in a big box

But despite the progress, think about have a quantum computer on the table look like a distant horizon. Not just for the cost, but also for the size. At this point, Quantum technology seems to be in a similar situation to that of early electronic computing when computers occupied a room.

Because while the super speed chip is a few inches, about 3 by 3, with many connectors coming out of the sides, which are the control devices, everything is within a cryostat, "a large three-by-three-meter thermos because it should be cooled to temperatures near absolute zero (-273.15 ° C)". However, your achievement is nothing less. "This Google computer is experimental, but it is the first fully programmable that can perform any calculation. Although at 54 qubits it is still small," Paz said.

A strange world and no affection to look at

"The main problem that affects quantum computers is their extreme fragility when interacting with any external object. A qubit can be zero, it can be one, and if you don't measure it, it can be zero and one at a time.. But if something is interacting with the quantum computer, it's like measuring and defining a state. For quantum overlays to be durable, what is needed to do quantum computation, it has to be extremely isolated outside. And that is the basis of why 54 qubits were made and not 54,000, because it is very difficult to get an object of a few centimeters to behave as quantum mechanics predicts. On the scale we live in, when you throw a ball and it hits someone else, what we see is a trajectory, one way. In the quantum world, an electron, which would be our ball, would have traveled many paths at once to reach. It's something that seems impossible and it's anti-intuitive, but that's how it works. "

Noise and errors

Minimal interactions with the outside generate an evolution in the quantum process, which can be considered a mistake. And while traditional computers also have data transmission noise and redundancy protocols to correct and protect information, the phenomenon is most critical in the quantum world. In this field, quantum error correction theory worked Paz, who noted that "the quantum is much more difficult and, in fact, it was thought for a long time that it was not possible. In the quantum case, when you are sending something that is neither a zero nor a qubit, you can't look at it. because it's destroying and turning it into something different. The development of correction theories is very advanced and it seems that Google's next experiment will be to implement an algorithm that uses these quantum error protection protocols. "

This addresses another area in which Paz and his team investigate, the transition between quantum and classical behavior, to "understand how these overlaps are lost when the object interacts with its surroundings, a process called decoherence, which determines how things that are zero and one at a time become zero or one. "

A small step for the machine, but a big leap for technology

"So far, existing quantum computers were smaller than this 54-qubit computer and were not fully programmable. There is an IBM with five qubits that can connect and operate remotely. Any of these actions can be simulated on an ordinary computer to achieve the same result. Therefore, in the scientific community, the result of the Google experiment is viewed with great respect and considered very significant, "said the Quantum Group director.

For the expert, what comes next is the challenge of developing larger computers with hundreds of quantum bits, to be useful from the point of view of scientific disciplines and materials engineering. So much for study the properties of natural systems of interest to physics, chemistry and engineering or cryptography, which involves large number factorization, more computing power is required. In this last field, what is played is computer security. A quantum computer can easily violate public key encryption algorithms, whose operation is based on the product of two very large prime numbers randomly chosen to form the decryption key, which is why there are many researchers working on what is known as post-quantum cryptography. For Peace, "there is really a paradigm shift." In a "race where five big corporate investors came in to play five years ago."

A quantum pavilion

Although development is embryonic, in the The UBA Faculty of Exact Sciences, on the first floor of University City Pavilion 1, operates the LIAF, founded by Paz and Schmiegelow. "We were able to build a laboratory we are proud of, although the experience of working over the last four years with zero support has not been easy," said the researcher. There they were able to trap individual ions in a vacuum chamber, an achievement in Latin America.


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