Kyushu and Kobe Universities have teamed up to hold four electron spins in quantum coherence at room temperature.

KyushuU quantum chromophores energy
“Their findings mark a crucial advancement for quantum computing and sensing technologies,” according to Kyushu University.

The researchers chose a particular chromophore (a pentacene-based dye molecule) to host electrons whose spins could be entangled, as electrons spins within it can be excited at room temperatures through ‘singlet fission’ (right).

However, quantum coherence among these spins can usually only be achieved at liquid nitrogen level temperatures.

KyushuU quantum chromophores structure

To increase temperature tolerance, the researchers embedded their chromophore within a ‘UiO’ type of metal-organic framework (MOF, left).

“The MOF in this work is a unique system that can densely accumulate chromophores,” said Kyushu engineer Nobuhiro Yanai. “Additionally, the nanopores inside the crystal enable the chromophore to rotate, but at a very restrained angle.”

KyushuU quantum chromophores energy“The framework allowed enough motion in the pentacene for electrons to transition from the triplet state to a quintet state, while also sufficiently suppressing motion at room temperature to maintain quantum coherence of the quintet multi-exciton state,” according to Kyushu.

When excited by microwave pulses, the quantum coherence initiated lasted for more than 100ns at room temperature.

“This is the first room-temperature quantum coherence of entangled quintets,” said fellow researcher Professor Yasuhiro Kobori, of Kobe University.

Now the hunt is on for longer-lasting qubits.

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