Physicists ‘touch’ individual molecules for the first time, paving the way for quantum computing.

For the first time, a team of Princeton physicists has been able to link together individual molecules in specific states that operate quantum mechanically. In these unique states, molecules remain connected to each other—and can interact simultaneously—even if they are miles apart, or indeed, even if they live on opposite ends of the spectrum. the universe. This research was recently published in the journal Science.

“This is a problem in the world of molecules because of the importance of quantum entanglement,” said Lawrence Cheuk, assistant professor of physics at Princeton University and senior author of the paper. “But it’s also a challenge for practical applications because complex molecules can become building blocks for many future applications.”

These include, for example, quantum computers that can solve certain problems faster than conventional computers, quantum simulators that can simulate complex objects whose behavior is difficult to model, and quantum sensors that can then measure up faster than they normally do.

“One of the motivations in doing quantum research is that in the practical world, it seems that if you use the rules of quantum mechanics, you can be better in many areas,” he said. said Connor Holland, a graduate student in physics. department and a co-author on the project.

The ability of quantum devices to outperform conventional devices is called the “quantum advantage.” And at the core of the quantum advantage are the principles of superposition and quantum entanglement. While a normal computer can store the value of 0 or 1, quantum bits, called qubits, can exist at the same time in a superposition of 0 and 1.

The last concept, entanglement, is a major cornerstone of quantum mechanics and occurs when objects become connected to each other so that this connection continues, even at a distance. one group from another group. This phenomenon was described by Albert Einstein, who first questioned its validity, describing it as a “spectacular movement at a distance.”

Since then, physicists have shown that chaos is, in fact, an accurate description of the physical world and how reality is structured.

Cheuk says, “The technical problem is an important concept,” Cheuk said, “but it’s also the key to achieving great success.”

But building the quantum advantage and achieving quantum entanglement remains a challenge, not least because engineers and scientists are not clear what physical conditions are best for creating qubits. .

Over the past several years, many different technologies—such as trapping ions, photons, and superconducting circuits, to name just a few—have been explored as candidates for computers and devices. The use of a quantum system or a qubit platform may well depend on the specific application.

However, until this experiment, the molecules had long resisted genetic interference. But Cheuk and his colleagues found a way, through careful manipulation in the laboratory, to control individual molecules and force them into these unified states.

They also believed that molecules have special advantages – over atoms, for example – that made them suitable for certain applications in the production of quantum information and quantum simulation of complex objects. Compared to atoms, for example, they have more degrees of freedom and can interact in new ways.

“This means that, in practical terms, there are new ways to store and process quantum information,” said Yukai Lu, a graduate student in electrical and computer engineering and a author of the paper. “For example, a molecule can vibrate and rotate in many ways. So, you can use these two ways to install a qubit. If the type of molecule is polar, there are two molecules can interact even if space is divided.”

However, the molecules have proven difficult to control in the laboratory due to their complexity. The very degrees of freedom that make them so exciting make them difficult to control or house in a laboratory.

Cheuk and his team tackled many of these challenges through a well-thought-out approach. They first chose a type of molecule that is both polar and can be heated with lasers. They then laser-cooled the molecules to much cooler temperatures, where quantum mechanics is central.

Individual molecules are then picked up by a complex system of focused laser beams, called “optical tweezers.” By engineering the position of tweezers, they were able to create large arrays of individual molecules and place them individually in any desired single configuration. . For example, they created lone pairs of molecules and unbroken strings of molecules.

Next, they labeled a qubit in a non-rotating and rotating state of the molecule. They were able to show that this molecular qubit remains coherent; that is, he remembered his superiority. In short, the researchers demonstrated the possibility of creating efficient and accurate qubits from individual molecules.

In order for the molecules to bind, they must make the molecule interact. Using a series of microwave pulses, they were able to get individual molecules to interact with each other in a unique way.

By allowing the interaction to continue for a precise amount of time, they were able to implement a two-qubit gate where two molecules were attached. This is important because a large two-qubit gate is a building block for general digital computing and for modeling complex objects.

The potential of this research for the study of different areas of quantum science is great, because of the new features offered by this new state of molecular tweezer arrays. In particular, the Princeton team is interested in the study of the physics of many interconnected molecules, which can be used to model many bodies-bodies in which behavior can appear, such as shape new magnetism.

“Using molecules for quantum science is a new frontier, and our on-demand experiments are an important step to show that molecules can be used as a useful platform for quantum science,” Cheuk said.

In what different stories published in the same issue of Sciencea group of independent studies led by John Doyle and Kang-Kuen Ni at Harvard University and Wolfgang Ketterle at the Massachusetts Institute of Technology reached similar results.

“The fact that they’re getting the same results proves the validity of our results,” Cheuk said. “They also show that molecular tweezer arrays are an exciting new platform for quantum research.”