磁性分子的量子相干操控

Quantum coherent manipulation of magnetic molecules

在量子信息科技的发展中,以电子自旋作为信息载体的分子基材料因其突出的可设计性和可扩展性而被寄予厚望.基于系综的量子信息材料研究在分子设计和量子操控策略方面已有较多积累.本文从分子基量子比特的构效关系和分子设计、分子基多能级量子位的研究现状和应用潜力、多功能磁性分子等角度介绍了近年来国内外分子基量子信息材料研究的概况,并总结了该领域已取得的成果和现状,展望了今后实现突破的潜在方向和技术路线要求.我们认为,分子基量子信息材料的发展需要走向单自旋表征和操控的新阶段,并整合自旋化学与量子信息科技,以构建新的研究范式.

In the development of quantum information technologies,molecule-based materials with electron spins as the information carrier is considered highly promising due to their outstanding designability and scalability acquired via the vast variety of chemical synthesis,modification and assembling approaches.Throughout the past decade,researchers have managed to achieve great advances in the molecular design and quantum coherent manipulation methods of molecular quantum information materials,but the effort has been mainly at the ensemble level.This article firstly reviews worldwide studies in the recent years dedicated to the following purposes:(1)To clarify the structure-function relation of molecular qubits and to utilize them to synthesis high-performance qubit units,(2)to fabricate multilevel systems,i.e.,molecular qudits,that outperform two-level systems in handling more information and accommodating more complicated manipulations,and therefore are more promising regarding potential applications,and(3)to integrate multiple functions,such as response to light or pulse electric field,in magnetic molecular or crystalline systems to enrich the toolbox with which quantum manipulations can be applied.Among these,contributions from the authors'group are introduced.Any exploration of this kind may be challenged by a common loophole in the underlying concept:While the behavior of an ensemble can represent that of a quantum system to some extent,it cannot be excluded in principle that the behavior is merely an analogue merging from the statistical effect of the sub-ensemble being observed,with the whole ensemble being classical in nature.For this reason and the unavoidable requirement to address single spin centers coupled together to form applicational devices,the authors stress that further research on the molecule-based quantum information materials needs to be carried out on the single-spin level.After discussions about the stages which this process consists of and technical routes and requirements to implement them,it is suggested that optically detected magnetic resonance(ODMR)is a promising option due to its ability to characterize and coherently manipulate single spins given that the spin carrier have spin-selective opto-physical processes.Since most reported ODMR studies focus solely on a specific kind of defect in solid,the need for a spectrometer that are capable of investigating a variety of single molecules are proposed.This article then discusses functions that the spectrometer needs to integrate and specifies a framework composed of the following subsystems:(1)A liquid helium cryostat with high vacuum sample space,(2)a laser confocal microscope to address and initialize the single spin,(3)antibunching single photon detection to validate the single photon nature of the emitter focused on,(4)3-dimensional nanopositioners to conduct scans and locate the target molecule,(5)a 3-dimensional vector magnet to apply the magnetic field at any direction,(6)a broadband microwave system to cover a large range of resonance frequencies and to apply the coherent manipulation,and(7)a multi-channel arbitrary sequence generator to synchronously control the operation of laser,microwave and detector.In conclusion,with the field of molecule-based quantum information materials being promising in various aspects,the current situation of its development has been indicating a need to enter the regime of single spins and precise characterization and manipulation.The authors expect that the instrumental advancement,along with a new research paradigm constructed by the integration of spin chemistry and quantum information science,may propel the pragmatic development of molecular quantum information technology.