Because they are so large and difficult to manipulate, molecules have long defied physicists’ attempts to lure them into a state of controlled quantum entanglement, where molecules are closely linked even at a distance.
Now, for the first time, two separate teams have succeeded in entangling pairs of ultra-cold molecules using the same method: microscopically precise optical “tweezer traps.”
Quantum entanglement is a strange but fundamental phenomenon in the quantum world that physicists are trying to take advantage of to create the first commercial quantum computers.
All objects – from electrons to atoms to molecules and even entire galaxies – can be theoretically described as a spectrum of possibilities before they are observed. Only by measuring the property does the wheel of chance settle on a clear description.
If two objects are entangled, knowing something about the properties of one object—its spin, position, or momentum—immediately serves as an analogy on the other, bringing both of their potential wheels of rotation to a complete halt.
So far, researchers have been able to connect ions, photons, atoms and superconducting circuits in laboratory experiments. For example, three years ago, a team bound trillions of atoms into a “hot and chaotic” gas. Impressive, but not very practical.
Physicists have been entangled, too Atom and molecule Before, even Biological complexes Found in plant cells. But controlling and manipulating pairs of individual molecules — with sufficient precision for quantum computing purposes — was a more difficult task.
Molecules are difficult to cool and interact easily with their surroundings, which means they easily fall out of fragile quantum entanglement states Decoherence).
One example of such interactions is Dipole-dipole interactions: The way in which the positive end of a polar molecule can be pulled toward the negative end of another molecule.
But these same properties make molecules promising candidates for qubits in quantum computing because they offer new possibilities for computation.
“Their long-range molecular spin states form strong qubits while providing long-range dipole interaction between the molecules Quantum entanglement“,” He explains Harvard physicist Yicheng Bao and his colleagues, in their paper.
Qubits are the quantum version of classical computing bits, which can assume a value of 0 or 1. Qubits, on the other hand, can represent Many combinations possible 1 and 0 at the same time
By entangling qubits, the combined quantum fuzziness of 1’s and 0’s can act as fast calculators in specially designed algorithms.
Molecules, being more complex entities than atoms or particles, have more inherent properties or states, which can be coupled together to form a qubit.
“What this means, in practical terms, is that there are new ways to store and process quantum information.” He says Yucai Lu, a graduate student in electrical and computer engineering at Princeton, who co-authored the second study.
“For example, a molecule can vibrate and rotate in multiple modes. So, you can use two of these modes to encode a qubit. If a molecular species is polar, two molecules can interact even when they are spatially separated.”
Both teams produced ultra-cold calcium monofluoride (CaF) molecules and then trapped them, one by one, in optical tweezers.
Using these tightly focused beams of laser light, the molecules were placed in pairs, close enough that the CaF molecule could sense the long-range electrical dipole interaction of its partner. This bound each pair of molecules into an entangled quantum state, shortly before they became strange.
This method, through its precise manipulation of individual molecules, “paves the way for the development of new, versatile platforms for quantum technologies.” He writes Augusto Summerzi, a physicist at the National Research Council in Italy, in an accompanying perspective.
Summerzy was not involved in the research, but he sees its potential. By taking advantage of the dipole interactions of molecules, he says the system may one day be used to develop ultra-sensitive quantum sensors capable of detecting ultra-weak electric fields.
“Applications extend from electroencephalography to measure electrical activity in the brain to monitoring changes in electrical fields in the Earth’s crust to predicting earthquakes.” He speculates.
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