Recently, Wu Kaifeng's team, a researcher in the Optoelectronic Materials Dynamics Research Group of Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made important progress in quantum dot spin photophysics research, taking the lead in achieving spin coheren

Recently, Wu Kaifeng's team, a researcher in the Optoelectronic Materials Dynamics Research Group of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made important progress in the study of quantum dot spin optical physics, taking the lead in realizing spin coherent control of colloidal quantum dots prepared by low-cost solution methods at room temperature. This achievement is of great significance in the fields of quantum information science and ultrafast optical coherent control.

Quantum information technology refers to the technology that uses the quantum state of microscopic particles (or quasiparticles) to represent information, and uses the principles of quantum mechanics to store, transmit and process information. Coherent manipulation of spin qubits in solid-state materials is one of the important ways to realize quantum information technology. At present, the related solid-state systems that have been reported mainly include epitaxially grown quantum dots and "point defect" materials (such as diamond color center, etc.). However, the preparation process of epitaxial growth of quantum dots is complex and expensive, and its spin control generally needs to be performed at the temperature of liquid helium . Although room-temperature coherent control of "point defect" spins has been achieved, how to prepare such materials in a large-scale and controllable manner is quite challenging. Therefore, if spin coherent control of low-cost materials can be achieved at room temperature, it will have a profound impact on the development of quantum information technology.

Wu Kaifeng's research team is committed to ultrafast photophysics and photochemistry research on colloidal quantum dots. This type of quantum dots can be prepared in large quantities in solution using relatively mild chemical methods, with strong confinement effects and precisely adjustable photoelectric and spin properties. The spin-orbit coupling effect of lead halide perovskite quantum dots that has emerged in recent years is conducive to the efficient injection of spin polarization through optical methods. At the same time, its strong light-matter interaction can promote optical coherent manipulation of spins. The research team observed the ensemble quantum beat frequency of exciton spins in CsPbI₃ perovskite quantum dots and analyzed its physical mechanism (Nat. Mater.).

In this work, taking into account the complex exciton splitting and optical orientation behavior caused by the electron-hole exchange in quantum dots, the single-hole spin polarization state of perovskite quantum dots was innovatively prepared, and room temperature coherent control was achieved based on self-developed multi-pulse femtosecond magneto-optical technology. The study chemically modified anthraquinone molecules on the surface of CsPbBr₃ quantum dots to capture the photogenerated electrons of the quantum dots at the sub-picosecond scale, quench the electron-hole exchange interaction, and obtain hole spins of hundreds of picoseconds at room temperature. The hole spin undergoes Larmor precession under a magnetic field; with the help of a femtosecond pulse with sub-bandgap photon energy, the optical Stark effect is used to generate a pseudomagnetic field, achieving coherent control of the quantum state of the hole spin. Considering that the spin coherence lifetime is on the order of hundreds of picoseconds, with the help of laser pulse of hundreds of femtoseconds (approximately 0.1 picoseconds), researchers can in principle carry out effective manipulations thousands of times before spin decoherence.

related research results were published in "Nature Nanotechnology" under the title Room-temperature coherent optical manipulation of hole spins in solution-grown perovskite quantum dots. Research work The Chinese Academy of Sciences stably supports the support of the Youth Team Program in the Basic Research Field, National Key R&D Program , the National Natural Science Foundation, and the Dalian Institute of Chemical Physics Innovation Fund.

Dalian Institute of Chemical Physics realizes room-temperature ultrafast coherent control of colloidal quantum dot spins

Source: Dalian Institute of Chemical Physics, Chinese Academy of Sciences

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