Scientists in Japan claim quantum coherence breakthrough

12 Jan 2024

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While coherence – crucial for functioning quantum computers – was only observed for nanoseconds, the team is optimistic about the potential of the findings.

A team of researchers in Japan claim to have achieved one of the most elusive feats in modern scientific experimental research: quantum coherence at room temperature.

Led by Prof Nobuhiro Yanai of Kyushu University in Fukuoka, the team has detailed in a paper published in Science Advances recently how they were able to observe the quantum coherence of a “quintet state with four electron spins” in molecular systems at room temperature.

Quantum coherence is the ability of a quantum system to maintain a well-defined state over time without getting affected by surrounding disturbances. This process is dependent on the ability to reliably control a quantum bit or qubit.

While classic computers (the ones we use today) use bits to store and manipulate information, quantum computers rely on quantum bits or qubits.

The team said that chromophores, dye molecules that absorb light and emit colour, can be used to excite electrons with desirable electron ‘spins’ – a quantum property related to a particle’s magnetic moment – at room temperatures through a process called ‘singlet fission’.

Electrons have two spin states: spin up and spin down. Qubits based on spin can exist in a combination of these states and can be ‘entangled’, allowing the state of one qubit to be inferred from another.

However, quantum information stored in qubits loses its quantum superposition and entanglement at room temperature, meaning it is only possible to achieve quantum coherence at liquid nitrogen-level temperatures.

By introducing a chromophore based on pentacene, or polycyclic aromatic hydrocarbon consisting of five linearly fused benzene rings, in a metal-organic framework (MOF), the team was able to suppress the molecular motion and achieve room-temperature quantum coherence.

“The MOF in this work is a unique system that can densely accumulate chromophores. Additionally, the nanopores inside the crystal enable the chromophore to rotate, but at a very restrained angle,” said Yanai, an associate professor at the university’s Faculty of Engineering.

“This is the first room-temperature quantum coherence of entangled quintets,” added Prof Yasuhiro Kobori of Kobe University, who was also involved in the research along with Prof Kiyoshi Miyata of Kyushu University.

While the quantum coherence was only observed for nanoseconds, the team hopes its findings will pave the way in designing materials for the generation of multiple qubits at room temperatures.

“It will be possible to generate quintet multiexciton-state qubits more efficiently in the future by searching for guest molecules that can induce more such suppressed motions and by developing suitable MOF structures,” explained Yanai.

“This can open doors to room-temperature molecular quantum computing based on multiple quantum gate control and quantum sensing of various target compounds.”

Last September, scientists based in Canada made significant progress in quantum computing by developing a new method that claimed to reliably process quantum information.

Before that, researchers at the University of Chicago claimed to have observed the phenomenon known as “quantum superchemistry”, whereby particles in the same quantum state exhibit accelerated chemical reactions.

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Vish Gain is a journalist with Silicon Republic