A molecule that responds to light – sciencedaily

Light can be used to operate quantum information processing systems, such as quantum computers, quickly and efficiently. Researchers from the Karlsruhe Institute of Technology (KIT) and Chimie ParisTech / CNRS have now considerably advanced the development of materials based on molecules that can be used as fundamental quantum units addressable by light. As they report in the newspaper Nature communications, they demonstrated for the first time the possibility of treating with light the nuclear spin levels of a molecular complex of rare earth ions europium (III).

Whether for drug development, communication or climate forecasting: fast and efficient processing of information is crucial in many areas. This is currently done using digital computers, which work with so-called bits. The state of a bit is 0 or 1 – there is nothing in between. This severely limits the performance of digital computers and it becomes increasingly difficult and time consuming to deal with complex problems associated with real world tasks. Quantum computers, on the other hand, use quantum bits to process information. A quantum bit (qubit) can be in many different states between 0 and 1 simultaneously due to a special quantum mechanical property called quantum superposition. This allows data to be processed in parallel, which increases the computing power of quantum computers exponentially compared to digital computers.

Qubit superposition states must persist long enough

“In order to develop practically applicable quantum computers, the superposition states of a qubit must persist long enough. Researchers speak of “coherence lifetime”, “explains Professor Mario Ruben, head of the Molecular Materials Research Group at KIT’s Institute for Nanotechnology. (INT). “However, the superposition states of a qubit are fragile and are disturbed by fluctuations in the environment, which leads to decoherence, that is, a shortening of the coherence lifetime. ” To keep the superposition state long enough for the computation operations, it is possible to isolate a qubit from the noisy environment. Nuclear spin levels in molecules can be used to create superposition states with long coherence lifetimes because nuclear spins are weakly coupled to the environment, protecting the superposition states of a qubit from disturbing external influences. .

Molecules are ideal for Qubit systems

A single qubit, however, is not enough to build a quantum computer. Many qubits to organize and address are required. Molecules represent ideal qubit systems because they can be arranged in large enough numbers as identical evolutionary units and can be addressed with light to perform qubit operations. Additionally, the physical properties of molecules, such as emission and / or magnetic properties, can be tailored by modifying their structures using chemical design principles. In their article now published in the journal Nature communications, researchers led by Professor Mario Ruben at KIT’s IQMT and at the European Center for Quantum Sciences in Strasbourg – CESQ and Dr Philippe Goldner from the École nationale supérieure de chimie de Paris (Chimie ParisTech / CNRS) present a europium dimeric containing a nuclear spin (III) molecule in the form of a light-addressable qubit.

The molecule, which belongs to the rare earth metals, is designed to exhibit luminescence, i.e. sensitized emission centered on europium (III), when excited by surrounding ultraviolet light absorbing ligands the center. After absorption of the light, the ligands transfer the light energy to the center of the europium (III), thus exciting it. The relaxation of the excited center to the ground state leads to an emission of light. The whole process is called sensitized luminescence. The burning of spectral holes – special experiments with lasers – detects the polarization of nuclear spin levels, indicating the generation of an efficient light-nuclear nuclear spin interface. The latter enables the generation of light-addressable hyperfine qubits based on nuclear spin levels. “By demonstrating for the first time the light-induced spin polarization in the europium (III) molecule, we have succeeded in taking a promising step towards the development of quantum computing architectures based on molecules containing ions of rare earths ”, explains Dr Philippe Goldner.

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