Physicists 'entangle' individual molecules for the first time, hastening possibilities for quantum computing

Princeton researchers have connected individual molecules into unique states that are "entangled" in quantum mechanics for the first time. Even if the molecules are located far apart or even on opposite sides of the universe, they can still interact concurrently in these strange states because they maintain their correlation with one another. The journal Science just published this research.

The basic significance of quantum entanglement, according to Lawrence Cheuk, senior author of the research and assistant professor of physics at Princeton University, "makes this a breakthrough in the world of molecules." "But it is also a breakthrough for practical applications because entangled molecules can be the building blocks for many future applications."

These include, for instance, quantum simulators that can simulate complicated materials with hard-to-model characteristics, quantum computers that can solve certain tasks far quicker than standard computers, and quantum sensors that have faster measurement speeds than their conventional equivalents.

A graduate student in the physics department and co-author of the paper, Connor Holland stated, "One of the motivations in doing quantum science is that in the practical world, it turns out that if you harness the laws of quantum mechanics, you can do a lot better in many areas."

"Quantum advantage" refers to the capacity of quantum devices to outperform classical ones. Furthermore, the ideas of quantum entanglement and superposition are at the heart of quantum advantage. Quantum bits, or qubits, are computer bits that may concurrently be in a superposition of 0 and 1, unlike traditional computer bits, which can only have a value of either 0 or 1.

The latter idea, entanglement, is a fundamental tenet of quantum physics and arises when two particles entangle themselves in a way that makes them persistently linked, even when one particle is light years far from the other. Albert Einstein initially questioned the legitimacy of this occurrence, referring to it as "spooky action at a distance."

Since then, physicists have shown that entanglement does, in fact, accurately describe the structure of reality and the physical universe.

"Quantum entanglement is a fundamental concept," stated Cheuk, "but it is also the key ingredient that bestows quantum advantage."

However, developing a controlled quantum entanglement and constructing a quantum advantage are still difficult tasks, in part because scientists and engineers are still unsure of the ideal physical platform for producing qubits.

Many various technologies have been investigated as potential candidates for quantum computers and devices over the last few decades, including photons, trapped ions, and superconducting circuits, to mention a few. The ideal qubit platform or quantum system may vary depending on the particular use case.

However, molecules had long resisted controlled quantum entanglement until this discovery. However, Cheuk and his associates managed to manipulate individual molecules into these interconnecting quantum states through meticulous laboratory work.

Additionally, they thought that molecules were particularly well-suited for several applications in quantum information processing and quantum modeling of complex materials because of specific advantages they had over atoms, for example. For instance, molecules have more quantum degrees of freedom and can interact in novel ways than atoms.

Yukai Lu, a doctoral student in electrical and computer engineering and co-author of the article, explained that "what this means, in practical terms, is that there are new ways of storing and processing quantum information," A molecule, for instance, has many modes of rotation and vibration. Therefore, encoding a qubit can be done using two of these modes. Two molecules can interact even when they are separated by space if the chemical species is polar."

However, due to their complexity, molecules have proven to be infamously hard to regulate in the laboratory. In lab settings, their very degrees of freedom that draw them in also make them challenging to manage or restrain.

Cheuk and his colleagues used a well-planned experiment to address a number of these issues. They began by selecting a type of molecular organism that is both polar and laser-coolable. The molecules were subsequently subjected to ultracold laser cooling, where quantum mechanics is brought to life.

Following that, individual molecules were captured by an intricate network of closely concentrated laser beams, sometimes known as "optical tweezers." They were able to produce vast arrays of single molecules and individually arrange them into any desired one-dimensional arrangement by manipulating the placements of the tweezers. For instance, they produced strings of molecules devoid of flaws and separated pairs of molecules.

They then encoded a qubit into the molecule's revolving and non-rotating states. It was demonstrated that this molecular qubit retained its coherent state, meaning it was able to recall its superposition. In summary, the scientists showed that it is possible to construct coherent, well-controlled qubits from discretely controlled molecules.

They needed to get the molecules to interact in order to entangle them. They were able to induce coherent interactions between individual molecules by applying a sequence of microwave pulses.

A two-qubit gate that entangled two molecules was implemented by letting the contact continue for a predetermined period of time. This is important because a universal digital quantum computing system and the modeling of complicated materials both depend on such an entangling two-qubit gate.

With the novel qualities this new molecular tweezer array platform offers, there is much possibility for applying this discovery to other fields of quantum physics. The Princeton group is particularly interested in studying the physics of many interacting molecules since these systems may be used to replicate quantum many-body systems and exhibit intriguing emergent phenomena, such new types of magnetism.

"Using molecules for quantum science is a new frontier, and our demonstration of on-demand entanglement is a key step in demonstrating that molecules can be used as a viable platform for quantum science," Cheuk stated.

Similar findings were obtained by an independent study team headed by Wolfgang Ketterle at the Massachusetts Institute of Technology and John Doyle and Kang-Kuen Ni at Harvard University in a different publication that was published in the same issue of Science.

"The fact that they got the same results verifies the reliability of our results," Cheuk stated. "They also show that molecular tweezer arrays are becoming an exciting new platform for quantum science."

Provided by Princeton University