论文标题
单个电荷波动器扰动的Si孔零量零量矩形中的自旋破坏性的建模
Modelling of spin decoherence in a Si hole qubit perturbed by a single charge fluctuator
论文作者
论文摘要
半导体量子点中的自旋矩形是实现量子处理器的承诺设备之一。因此，更好地了解影响这种量子线相干性的噪声源至关重要。在这项工作中，我们研究了单个电荷波动引起的电报噪声的效果。我们尽可能地在量子点中通过沿硅纳米线通道的一组门来定义的量子点中的孔旋转值。将泊松和时间依赖性的schrödinger方程相结合的计算允许模拟孔旋转的放松和脱落，作为经典随机电报信号的时间的函数。我们表明，DePhasing Time $ T_2 $由两级模型以广泛的频率赋予。值得注意的是，在低频波动器的最现实配置中，系统具有非高斯行为，在该行为中，一旦波动器改变状态，相位相干性就会丢失。当两级系统对波动器状态的统计分布做出反应时，高斯描述仅超过阈值频率$ω__{th} $才能有效。我们表明，通过播放磁场和栅极电位的方向，可以通过沿“甜蜜”线运行量子线，可以通过播放磁场和栅极电位的方向来大大提高dephasing时间$ t_ {2}（ω__{th}）$。但是，$ t_ {2}（ω__{th}）$由于由随机扰动Hamiltonian的非二角性术语引起的逐渐限制。我们的模拟表明，在两级模型中无法清晰地描述自旋弛豫，因为与较高能量孔的耦合非常强烈地影响自旋的熔融。该结果表明，对于描述这种类型的量子中的弛豫现象，需要进行多层次模拟，包括与声子耦合。
Spin qubits in semiconductor quantum dots are one of the promizing devices to realize a quantum processor. A better knowledge of the noise sources affecting the coherence of such a qubit is therefore of prime importance. In this work, we study the effect of telegraphic noise induced by the fluctuation of a single electric charge. We simulate as realistically as possible a hole spin qubit in a quantum dot defined electrostatically by a set of gates along a silicon nanowire channel. Calculations combining Poisson and time-dependent Schrödinger equations allow to simulate the relaxation and the dephasing of the hole spin as a function of time for a classical random telegraph signal. We show that dephasing time $T_2$ is well given by a two-level model in a wide range of frequency. Remarkably, in the most realistic configuration of a low frequency fluctuator, the system has a non-Gaussian behavior in which the phase coherence is lost as soon as the fluctuator has changed state. The Gaussian description becomes valid only beyond a threshold frequency $ω_{th}$, when the two-level system reacts to the statistical distribution of the fluctuator states. We show that the dephasing time $T_{2}(ω_{th})$ at this threshold frequency can be considerably increased by playing on the orientation of the magnetic field and the gate potentials, by running the qubit along "sweet" lines. However, $T_{2}(ω_{th})$ remains bounded due to dephasing induced by the non-diagonal terms of the stochastic perturbation Hamiltonian. Our simulations reveal that the spin relaxation cannot be described cleanly in the two-level model because the coupling to higher energy hole levels impacts very strongly the spin decoherence. This result suggests that multi-level simulations including the coupling to phonons should be necessary to describe the relaxation phenomenon in this type of qubit.
