Quantum Computing: Stabilizing qubits at room temperature

A team of researchers in Japan reported that they have successfully achieved quantum coherence at room temperature. Quantum coherence refers to a quantum system’s ability to maintain a well-defined state over time, unaffected by surrounding disturbances.

The team led by Associate Professor Nobuhiro Yanai from Kyushu University’s Faculty of Engineering, in collaboration with Associate Professor Kiyoshi Miyata from Kyushu University and Professor Yasuhiro Kobori of Kobe University, published the study in Science Advances.

The team incorporated a chromophore, a light-absorbing and color-emitting dye molecule, into a metal-organic framework (MOF), a nanoporous crystalline material composed of metal ions and organic ligands.

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The implications of this discovery extend to advancements in quantum computing and sensing technologies. Quantum computing, considered the next frontier in computing, and quantum sensing, a technology utilizing the quantum mechanical properties of qubits (quantum analogs of classical bits), stand to benefit significantly.

Employing microwave pulses

One approach to implementing qubits involves leveraging the intrinsic spin, a quantum property related to a particle’s magnetic moment, of an electron. Qubits based on electron spin can exist in a superposition of spin-up and spin-down states, allowing for entanglement where the state of one qubit can be inferred from another.

However, achieving quantum coherence in systems involving four entangled electrons and their response to external molecules, particularly in a nanoporous MOF, has been a challenging task.

The researchers addressed this challenge by introducing a chromophore based on pentacene — a polycyclic aromatic hydrocarbon with five linearly fused benzene rings — into a UiO-type MOF. This MOF structure allowed controlled motion in the pentacene units, facilitating the transition of electrons from a triplet state to a quintet state. The molecular motion was sufficiently suppressed at room temperature to maintain the quantum coherence of the quintet multiexciton state.

By employing microwave pulses to photoexcite electrons, the researchers observed the quantum coherence of the state persisting for over 100 nanoseconds at room temperature, an unprecedented achievement. While the coherence was observed on a nanosecond scale, these findings lay the foundation for designing materials capable of generating multiple qubits at room temperature.

Associate Professor Yanai anticipates future developments in this field, suggesting that the search for guest molecules inducing suppressed motions and the development of suitable MOF structures could enhance the efficiency of generating quintet multiexciton state qubits. This breakthrough opens avenues for room-temperature molecular quantum computing, centered on multiple quantum gate control and quantum sensing of various target compounds.