Molecules ‘entangled’ in major physics breakthrough could advance quantum computing

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Scientists have linked molecules into bizarre special states that make them interact simultaneously with each other even if they are miles apart, a breakthrough that could propel quantum computing.

Quantum computers can solve some problems much faster than conventional computers as they can carry out several parallel calculations at the same time at breakneck speeds.

While a classical computer bit assumes the value of either 0 or 1, quantum bits – or qubits – can simultaneously be in a superposition of 0 and 1, allowing for a wide range of calculations to happen at the same time.

These computers harness the quantum physics phenomenon of “entanglement” – a special state dubbed “spooky action at a distance” by physicist Albert Einstein – in which particles interact simultaneously even if they occupy opposite ends of the universe.

It happens when two particles become inextricably linked with each other so that this link persists, even if one particle is light years away from the other particle.

Further advances in quantum entanglement can help develop computer models of complex materials whose behaviors are difficult to simulate, and make quantum sensors that measure faster than their traditional counterparts.

However, achieving controllable quantum entanglement remains a challenge.

This is because researchers are still unclear about which platform – ions, photons, or atoms to name a few – is best for creating qubits.

Now, the new study, published in the journal Science, has shown for the first time that individual molecules can be carefully manipulated into these interlocking quantum states.

“What this means, in practical terms, is that there are new ways of storing and processing quantum information,” study co-author Yukai Lu from Princeton University in the US said.

Since molecules can interact in more ways than atoms, researchers say their entanglement can be well-suited for some applications like the simulation of complex materials.

For instance, a molecule can vibrate and rotate in multiple modes and two of these modes can be used to encode a qubit.

However, the very degrees of freedom that make molecules attractive to quantum computing also make them hard to control in laboratory settings.

In the latest study, scientists overcame these challenges using several careful approaches, including the use of a laser to cool the molecules to ultracold temperatures, where quantum mechanics takes center stage.

Then using microwave pulses and “optical tweezers” – used to manipulate ultrasmall molecules – they could make individual molecules coherently interact with each other and be entangled.

Researchers say such an entangling is a building block for both quantum computing and for simulation of complex materials.

“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,” Lawrence Cheuk, another author of the study, said.