各向异性限制势和椭圆驱动在Ge空穴量子比特动力学中的作用
Role of anisotropic confining potential and elliptical driving in dynamics of a Ge hole qubit
AI总结：
研究Ge平面量子点中椭圆限制与驱动场极化对重空穴量子比特Rabi频率的影响，推导了解析表达式并确定了实现干净Rabi翻转的工作区域，同时提出了一种测量有效重空穴质量的方法。
摘要：
由于在这种几何结构中存在强的Direct Rashba自旋轨道相互作用，Ge平面量子点的压缩使电偶极自旋共振的Rabi频率提高了几个数量级（Bosco等人 2021 Phys. Rev. B 104 115425）。我们研究了椭圆（压缩）限制的几何效应及其与驱动场极化的相互作用，以确定平面Ge量子点中重空穴量子比特的Rabi频率。为了计算Rabi频率，我们仅考虑p线性SOI，即电子型Rashba、空穴型Rashba和空穴型Dresselhaus，近期关于平面Ge异质结构的研究声称它们是主导项。我们使用Schrieffer-Wolff变换推导了在小SOI和驱动强度下Rabi频率的近似解析表达式。首先，对于大小为B的面外磁场，我们得到了一个关于B、压缩和极化参数的工作区域，在此区域内操作量子比特可获得“干净”的Rabi翻转。在该区域边界及边界附近，较高轨道能级与两能级量子比特子空间发生强烈干涉并破坏Rabi振荡，从而对限制的压缩造成了限制。对于电子型和空穴型Rashba SOI，Rabi频率表现出不同的行为。在圆形限制下，存在纯电子型（空穴型）Rashba SOI时，对于右（左）圆极化，Rabi频率消失。对于面内和面外磁场，当极化椭圆和限制等势椭圆的长轴对齐但具有不同偏心率时，在压缩构型下可获得更高的Rabi频率。我们还推导出一个简单的公式，利用该装置通过测量Rabi频率来计算有效重空穴质量。
英文摘要：
The squeezing of a Ge planar quantum dot enhances the Rabi frequency of electric dipole spin resonance by several orders of magnitude due to a strong Direct Rashba spin-orbit interaction in such geometries (Bosco et al 2021 Phys. Rev. B 104 115425). We investigate the geometric effect of an elliptical (squeezed) confinement and its interplay with the polarization of driving field in determining the Rabi frequency of a heavy-hole qubit in a planar Ge quantum dot. To calculate the Rabi frequency, we consider only the p-linear SOIs viz. electron-like Rashba, hole-like Rashba and hole-like Dresselhaus which are claimed to be the dominant ones by recent studies on planar Ge heterostructures. We derive approximate analytical expressions of the Rabi frequency using a Schrieffer-Wolff transformation for small SOI and driving strengths. Firstly, for an out-of-plane magnetic field with magnitude B, we get an operating region with respect to B, squeezing and polarization parameters where the qubit can be operated to obtain 'clean' Rabi flips. On and close to the boundaries of the region, the higher orbital levels strongly interfere with the two-level qubit subspace and destroy the Rabi oscillations, thereby putting a limitation on squeezing of the confinement. The Rabi frequency shows different behaviour for electron-like and hole-like Rashba SOIs. It vanishes for right (left) circular polarization in presence of purely electron-like (hole-like) Rashba SOI in a circular confinement. For both in- and out-of-plane magnetic fields, higher Rabi frequencies are achieved for squeezed configurations when the ellipses of polarization and the confinement equipotential have their major axes aligned but with different eccentricities. We also deduce a simple formula to calculate the effective heavy hole mass by measuring the Rabi frequencies using this setup.
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