Challenging to manage and unwieldy, molecules have historically resisted physicists’ efforts to induce them into a state of controlled quantum entanglement, where these molecular entities are intricately linked even over long distances.
Breaking new ground, two independent teams have achieved a groundbreaking feat by successfully entangling pairs of ultra-cold molecules, marking the first instance of this achievement. The key to this success lies in the application of microscopically precise optical ‘tweezer traps.’
Quantum entanglement, a peculiar yet fundamental phenomenon in the quantum realm, holds immense potential for physicists aiming to harness it for the creation of the inaugural commercial quantum computers.
In the quantum domain, all entities, ranging from electrons and atoms to molecules and entire galaxies, exist as a spectrum of possibilities before observation. Measurement of a property determines the specific description, bringing the inherent uncertainty to a conclusion.
Entangled objects exhibit a unique connection; knowledge of one object’s properties instantaneously influences the measurement of the other, putting an end to both of their probabilistic states.
While previous experiments successfully entangled trapped ions, photons, atoms, and superconducting circuits in laboratory settings, controlling and manipulating pairs of individual molecules with the precision required for quantum computing purposes proved to be a formidable challenge.
Molecules, being challenging to cool and prone to interactions with their environment, often succumb to decoherence, disrupting fragile quantum entangled states.
One type of interaction affecting molecules is dipole-dipole interactions, wherein the positive end of a polar molecule is attracted to the negative end of another molecule.
Despite these challenges, molecules present promising potential as qubits in quantum computing due to their complex nature, offering new avenues for computation.
“Their long-lived molecular rotational states form robust qubits while the long-range dipolar interaction between molecules provides quantum entanglement,” Harvard University physicist Yicheng Bao and colleagues explain in their paper.
Qubits, the quantum counterparts of classical computing bits, can represent numerous possible combinations of 1 and 0 simultaneously, offering significant advantages in specially designed algorithms when entangled.
Both research teams successfully generated ultra-cold calcium monofluoride (CaF) molecules and individually trapped them using optical tweezers. The precise positioning of these molecules in pairs, facilitated by tightly focused laser beams, allowed them to sense each other’s long-range electric dipolar interaction, leading to the establishment of entangled quantum states.
This groundbreaking method, with its meticulous manipulation of individual molecules, “paves the way for developing new versatile platforms for quantum technologies,” notes Augusto Smerzi, a physicist at the National Research Council of Italy, in an accompanying perspective.
While Smerzi was not directly involved in the research, he sees potential applications, suggesting that leveraging dipole interactions of molecules could lead to the development of super-sensitive quantum sensors capable of detecting ultraweak electric fields for various applications, ranging from electroencephalography to earthquake predictions.
Both studies detailing these advancements have been published in the journal Science, accessible here and here.
