Researchers at Harvard University led by Kang-Kuen Ni have successfully achieved a significant step towards creating low-entropy samples of molecules for applications in the quantum field using optical tweezers.
The team employed a technique called magnetoassociation to create a single molecule from a single pair of atoms in a specific, reversible, quantum state. Their study is detailed in Physical Review Letters.
The researchers confined a sodium (Na) atom and a cesium (Cs) atom at the center of an optical trap formed by focusing a laser beam to an intense spot. By ramping up the ambient magnetic field, they then converted the trapped atoms into a molecule. According to Jessie Zhang, the lead author of this study, the molecule’s resulting quantum state is determined entirely by the state of the initial atoms. If the atoms are all prepared in their lowest motional state, then the resulting molecule will be in its lowest motional state and vice versa.
Earlier methods by the team
In their first study, the researchers used a photoassociation process that uses a laser to create a molecule in an excited state. In the second, they used a pair of laser beams to create a weakly-bound molecule. According to Zhang, both methods had drawbacks. In the first method, the molecule decayed into many states that couldn’t be detected. In the second, the laser beam destroyed the molecule. However, the molecule created by the magnetoassociation lived long enough to be dissociated back into atoms in their original states and subsequently detected.
The molecules formed by this new method have a weak atomic bond. Hence, they do not possess a large electric dipole moment, which is necessary for quantum computing applications that require entanglement between the atoms’ quantum states. The researchers will continue their research to bring the molecules to their absolute ground state to overcome this problem. At this stable state, the molecules can interact with each other via dipole-dipole interactions.
The team also hopes to scale up their technique to multiple tweezers, each holding a single molecule that can be controlled individually. Such a system can be used as a quantum computer or quantum simulator.
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