Chinese team sets record for preserving quantum states of Schrödinger’s cat | Technology

Although it may seem counterintuitive to the human mind accustomed to the macroscopic world and its laws, atomic particles can exist in two states at the same time. This is exactly what the Austrian physicist Erwin Schrödinger tried to explain with his famous mental paradox: a cat in a box can be both alive and dead at the same time. This property is known as superposition of states and is a fundamental principle of quantum computing. However, it is very fragile and lasts only milliseconds under extreme conditions of isolation and cold. Zheng-Tian Lu’s team from the University of Science and Technology of China claims in a study published in Arxviv (an open research repository) that it has broken all records to date by maintaining a stable quantum superposition for 23 minutes.

According to Alberto Casas, CSIC Research Professor at the Institute for Theoretical Physics (CSIC-UAM) and author Quantum revolution (Ediciones B, 2022), “in our ordinary life we ​​are accustomed to objects occupying one and only one position.” “However,” he adds, “quantum physics allows the electron to exist in a superposition of states, and as long as we do not measure this position, the two realities will coexist. This has been proven experimentally ad nauseum. We don’t see this in the macroscopic world, but in the microscopic world it is more than proven.”

This property is fundamental in quantum computing. A classical computer works by manipulating bits, which are sequences of ones and zeros. In contrast, the building block of most advanced computing is the qubit, an arbitrary superposition of the states of zero and one. Thus, while a modern supercomputer can perform millions of byte operations (IBM’s Summit is capable of processing over 200,000 million calculations per second), a quantum supercomputer can perform trillions due to its exponential increase in power.

But these pads are very sensitive. The same atoms that make up a computer cannot be completely motionless, which causes disturbances (noise), which they try to reduce by cooling the systems to a temperature close to absolute zero (-273 ºC). Moreover, any interaction with the environment degrades the superposition until it becomes useless, an effect known as decoherence.

The fragility of quantum virtue means that the superposition of states only lasts for milliseconds. Until now. Chinese researchers claim they were able to keep the states of Schrödinger’s cat, as they themselves called the published study, stable for 1,400 seconds, about 23 minutes, an all-time record for consistency.

The experiment used ytterbium atoms in an optical trap – a combination of lasers that form a network of electromagnetic forces in which the particles are trapped, reducing their speed and temperature to almost absolute zero.

Barry Sanders, a physicist at the University of Calgary in Canada who was not involved in the study, considers the experiment a significant achievement because of the time it took to keep the system stable, he said. NewScientist in the research information. “It can be used to detect and study subtle forces, or to explore new and exotic effects in fundamental physics, providing instantaneous data, capturing effects that occur both very quickly and more slowly,” explains Sanders.

The study’s seven authors echo the same sentiments, calling the experiment “a promising path toward improving the precision of physical measurements” and a doorway to “measurement errors below the standard quantum limit.”

The theorem or uncertainty principle, as Casas explains, states that “there are physical quantities that we cannot know simultaneously, such as the position and velocity of a particle. When measuring position, the speed is disrupted, and it is impossible to know both at the same time.” “But it goes deeper than that,” he adds, “the principle states that the position and velocity of a particle cannot be determined simultaneously. If one is clearly defined, the other cannot be.”

“Physics places limitations on experimentation and especially on precise measurements,” explains John Robinson, a physicist at quantum computing company QuEra, on the QuEra website. MIT Technology Review.

The study authors argue that, in addition to pushing measurements to the limit, the system could be applied to quantum memory and thus provide the redundancy needed for error correction, one of the biggest challenges of computing based on this physics. calculations.

This is the fundamental race of this technology: achieving reliable operation without reaching absolute zero temperatures, increasing runtime and reducing error rates.

Errors are inevitable at this point due to the nature of quantum physics. However, mitigating or correcting them by using violation control systems or applying formulas to the results that correct the failures is starting to bear fruit. A team of Google researchers claims to have made significant progress in correcting quantum errors in a paper also published on ArXiv.

Scientists say they have achieved failure rates below the critical threshold required for efficient quantum error correction, which they see as a fundamental step towards scalable and fault-tolerant quantum computing.