利用液氦上电子自旋实施量子信息处理的理论研究

Electrons on the liquid helium is an important physical system utilized to implement quantum computation [Science,284,1967(1999)]。The most advantange in this system is that the electronic spins (serve as the qubits) may possess very long coherent times [up to 100s theoretically, PRA 74, 052338; PRL 107,266803(2011)]. In the previous approaches, the weakly magnetic dipole-dipole coupling is utilized usually to implement the quantum information processing. In this project, we research the quantum information processing with electronic spins on the liquid helium based on the strongly spin-orbit coupling. The strong Coulomb interaction between the electrons is used as the data bus to transfer the quantum information from a spin to another. The typical models, e.g., Cirac-Zoller, M?lmer-S?rensen, and Coupled oscillators, worked well for trapped ions, are applied in the present system of electronic spins on the liquid helium for implementing the desirable quantum computation. Compared with the trapped ions, the mass of electron is much less than that of the trapped ions, and thus the electron-electron coupling strength is far stronger than that between the ions, and the present system may be more effective for building a scalable quantum computer.

液氦上电子[Science 284,1967(1999)]是几种重要的物理系统之一用于实施量计算。该系统的一个最大优点是用于编码量子比特的电子自旋态具有极长的相干时间[理论预言达100s；PRA 74, 052338(2006); PRL 107,266803(2011)]. 在先前的研究中，主要利用自旋之间直接的磁偶极-偶极弱相互作用来实施量子信息处理。本项目将研究液氦上电子自旋-轨道耦合的量子相干调控，研究如何利用电子之间的强库仑相互作用来构建数据总线，进而实现自旋之间的快速量子信息交换。本项目将把囚禁离子系统中的相关方法创新性地应用到液氦上电子系统中去，如获得著名的Cirac-Zoller，M?lmer-S?rense以及Coupled oscillators等量子计算模型。因电子的质量远小于囚禁离子，所以电子之间的有效耦合远强于囚禁离子之间的耦合，进而或更有助于实施大规模量子计算。

文献[Science 284, 1967 (1999)]，[PRA 74, 052338 (2006)]，[PRL 105, 040503 (2010]，[PRL 107, 266803 (2011)] 等提出了液氦表面上束缚电子可被用于实施单量子态操纵以及量子计算。基于这些文献，本项目研究了液氦上电子的自旋相干操作。利用液氦上囚禁电子的自旋-轨道耦合和电子-电子之间的强库仑相互作用，在理论上获得了电子自旋-自旋之间的强耦合，这达到了项目申请书的预计。提出的这种耦合的最大优点是可以实现电子自旋的快速两比特操作，进而可以在有限的相干时间内实现多个电子自旋的纠缠。相关的研究成果发表在期刊Physical Review B和Communications in Theoretical Physics上。另一方面，我们还研究了液氦上电子的光谱性质，利用液氦表面电子的对称性破缺在理论上获得了光的倍频散射。这一效应是天然原子所不具有的，因而具有一定的意义。该成果发表在期刊Physica B上。