One of the biggest challenges in quantum computing is to preserve the quantum state of a system from the noise and interference of the environment. Usually, this requires extremely low temperatures and sophisticated isolation techniques. However, a team of scientists has claimed that they have achieved quantum coherence at room temperature, meaning that their quantum system can retain its state for a long time without losing information. This breakthrough could have significant implications for the development of scalable and practical quantum devices.
Breakthrough Mechanism: Chromophores in Metal-Organic Frameworks (MOFs)
The researchers achieved this breakthrough by inserting a chromophore, a dye molecule that can absorb light and produce color, into a metal-organic framework (MOF). A MOF is a nanoscale crystalline material made of metal ions and organic molecules. The journal Science Advances published their research.
Quantum Leap at Room Temperature: Nanoporous MOFs and Electron Entanglement
A group of researchers from Kyushu University, Kobe University, and other institutions made this breakthrough in quantum computing and sensing by using a nanoporous metal-organic framework (MOF) to entangle four electrons and detect external molecules at room temperature. This is a significant improvement over previous methods that required much lower temperatures to achieve quantum coherence.
Decoding Quantum Technologies: Qubits and Electron Spin
Their findings mark a crucial advancement for quantum computing and sensing technologies. While quantum computing is positioned as the next major advancement of computing technology, quantum sensing is a sensing technology that utilizes the quantum mechanical properties of qubits (quantum analogs of bits in classical computing that can exist in a superposition of 0 and 1).
Various systems can be employed to implement qubits, with one approach being the utilization of intrinsic spin—a quantum property related to a particle’s magnetic moment—of an electron. 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.
By leveraging the extremely sensitive nature of a quantum entangled state to environmental noise, quantum sensing technology is expected to enable sensing with higher resolution and sensitivity compared to traditional techniques. However, so far, it has been challenging to entangle four electrons and make them respond to external molecules, that is, achieve quantum sensing using a nanoporous MOF.
Notably, chromophores can be used to excite electrons with desirable electron spins at room temperatures through a process called singlet fission. However, at room temperature causes the quantum information stored in qubits to lose quantum superposition and entanglement. As a result, it is usually only possible to achieve quantum coherence at liquid nitrogen level temperatures.
To suppress the molecular motion and achieve room-temperature quantum coherence, the researchers introduced a chromophore based on pentacene (polycyclic aromatic hydrocarbon consisting of five linearly fused benzene rings) in a UiO-type MOF. “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,” says Yanai.
The MOF structure facilitated enough motion in the pentacene units to allow the 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 multiexciton state. Upon photoexciting electrons with microwave pulses, the researchers could observe the quantum coherence of the state for over 100 nanoseconds at room temperature. “This is the first room-temperature quantum coherence of entangled quintets,” says Kobori.
Novel Horizons: Quantum Computing with Nanoporous Materials
While the coherence was observed only for nanoseconds, the findings will pave the way for 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,” says Yanai. “This can open doors to room-temperature molecular quantum computing based on multiple quantum gate control and quantum sensing of various target compounds.”
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