Scientists have used ultra-cold molecules to perform a quantum logic operation, marking a key step towards building quantum computers that could one day surpass classical machines.

The researchers at Harvard University have harnessed sodium-caesium molecules as qubits — basic units of quantum computing that can exist in multiple states simultaneously — and demonstrated their controlled interactions, a crucial requirement for quantum processing.

Their feat, described in a paper published recently in the journal Nature, opens new possibilities for exploiting the complexity of molecular structures for future applications in quantum computing, according to a report in The Harvard Gazette.

“As a field, we’ve been trying to do this for 20 years,” Kang-Kuen Ni, professor of chemistry and physics who led the research, was quoted by the Gazette as saying.
“And we’ve finally been able to do it.”

Quantum computers, based on rules that govern the subatomic world, are expected to enable computational tasks that would take too long or would be impossible to be done by classical computers.

They could be used in secure communications, drug discovery and scientific simulations, among other fields. But error-free and large-scale quantum systems capable of outperforming classical computers in practical tasks are still under development.

Most efforts to design prototype quantum computers have involved ions, single atoms, or superconducting circuits. The internal structure of molecules make them attractive candidates for quantum computing applications, but they have been viewed as difficult to manipulate as qubits. Unpredictable movements of molecules have challenged efforts at maintaining a condition called “coherence,” crucial for quantum computing operations.

Now, Ni and colleagues have used so-called “optical tweezers” — laser beams that help trap and manipulate tiny particles — to control the sodium-caesium molecules to “entangle” them, creating the quantum state called qubit.