Basic Research on Silicon Quantum Computation Based on Isotope Control and Neutron Irradiation

在硅基量子计算机中，在无自旋硅(自旋为零的硅或自旋为30的硅)中，作为一个量子比特，^&lt；31&gt；P应该以大约20 nm的距离成阵列分布。在本工作中，为了制作其基本的器件结构，我们进行了同位素控制硅层的外延生长和中子辐照下^&lt；30&gt；Si转变为^&lt；31&gt；P的实验。这种在硅中分布~(31)P的方法优于离子注入技术，离子注入技术在深度上具有内在的随机性。为此，首先，采用气源分子束外延技术，利用俄罗斯库尔恰诺夫实验室生产的浓缩硅化硅，研制了几乎100%的硅单晶外延技术。因此，这种无自旋硅外延层可以用来作为硅基量子计算机的基础。利用这一技术，我们通过交替提供正常的SiH_4和富集态的SiH_4，成功地制备了天然的Si/t；30&gt；Si/天然的Si(^&lt；28&gt；Si：^&lt；29&gt；Si：^&lt；30&gt；Si=92.2:4.7:3.1)同位素双异质结构。P的热中子注量为1×10^&lt；14&gt；-2&gt；S^-1&gt；16h，通过精确的二次离子质谱仪(Cameca-SIMS)测量，证实了^&lt；31&gt；P的形成。其浓度约为5×10~(-3)cm~(-3)w，与理论预测值基本一致。如果对硅基量子计算机的基本结构--无自旋硅(^&lt；31&gt；Si)进行中子辐照，则核自旋将分布在无自旋的硅中。

In Si-based quantum computer, ^<31>P should be distributed in an array at a distance of about 20 nm in spin-free silicon (spin zero ^<28>Si or ^<30>Si) as a qubit. In the present work, in order to fabricate its basic device structure, we aim to perform the experiments on the epitaxial growth of isotopically controlled silicon layers and the transformation of ^<30>Si to ^<31>P by neutron irradiation. This method for distributing ^<31>P in Si is superior to the ion-implantation technique, which is inherently random to the depth. For this purpose, first, epitaxial growth technique of almost 100% ^<30>Si was developed by the gas source MBE method using enriched ^<30>SiH_4, which was purchased from Kurchatov laboratory, Russia. Thus this spin-free Si epitaxial layer can be available to the base for Si-based quantum computer. Using this technique, we succeeded to fabricate the natural Si/^<30>Si/natural Si (^<28>Si:^<29>Si:^<30>Si=92.2:4.7:3.1) isotope double hetero-structures by supplying alternately normal SiH_4 and enriched ^<30>SiH_4. Then, neutron irradiation was carried out to transform ^<30>Si to ^<31>P at Japan Atomic Energy Research Institute with thermal neutron flux of 1×10^<14> cm^<-2> s^<-1> for 16 h. By the precise secondary ion mass spectroscopy (CAMECA-SIMS) measurement, the formation of ^<31>P from ^<30>Si was confirmed. Its concentration was to be about 5×10^<16> cm^<-3>w, which was almost equal to the theoretically predicted value. If the neutron irradiation is performed to the ^<29>Si/^<30>Si/^<29>Si double hetero-structures, nuclear spin ^<31>P will be distributed in a spin-free silicon (^<31>Si ), which will be used as a basic structure of Si-based quantum computer.