Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Nat Nanotechnol. 2013 Sep;8(9):654-9. doi: 10.1038/nnano.2013.168. Epub 2013 Sep 1.
Quantum-dot spin qubits characteristically use oscillating magnetic or electric fields, or quasi-static Zeeman field gradients, to realize full qubit control. For the case of three confined electrons, exchange interaction between two pairs allows qubit rotation around two axes, hence full control, using only electrostatic gates. Here, we report initialization, full control, and single-shot readout of a three-electron exchange-driven spin qubit. Control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in less than 2 ns. Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified. The methods developed here are generally applicable to systems with state leakage, noisy measurements and non-orthogonal control axes.
量子点自旋量子位通常使用振荡磁场或电场，或准静态塞曼场梯度来实现全量子位控制。对于三个受限电子的情况，两对之间的交换相互作用允许使用仅静电门围绕两个轴进行量子位旋转，从而实现完全控制。在这里，我们报告了三电子交换驱动自旋量子位的初始化、全控制和单拍读出。通过交换相互作用进行控制非常快，在不到 2ns 的时间内展示了 75 个量子位旋转。使用最大似然估计器方法进行测量和态层析成像，允许量化退相干、量子位态空间泄漏和测量保真度。这里开发的方法通常适用于具有状态泄漏、噪声测量和非正交控制轴的系统。
