Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
Nature. 2010 Sep 16;467(7313):297-300. doi: 10.1038/nature09359.
Reliable preparation, manipulation and measurement protocols are necessary to exploit a physical system as a quantum bit. Spins in optically active quantum dots offer one potential realization and recent demonstrations have shown high-fidelity preparation and ultrafast coherent manipulation. The final challenge-that is, single-shot measurement of the electron spin-has proved to be the most difficult of the three and so far only time-averaged optical measurements have been reported. The main obstacle to optical spin readout in single quantum dots is that the same laser that probes the spin state also flips the spin being measured. Here, by using a gate-controlled quantum dot molecule, we present the ability to measure the spin state of a single electron in real time via the intermittency of quantum dot resonance fluorescence. The quantum dot molecule, unlike its single quantum dot counterpart, allows separate and independent optical transitions for state preparation, manipulation and measurement, avoiding the dilemma of relying on the same transition to address the spin state of an electron.
可靠的制备、操控和测量方案对于将物理系统作为量子比特加以利用是必要的。在光学活性量子点中，电子自旋提供了一种潜在的实现方案，最近的演示表明其具有高保真度的制备和超快相干操控能力。最后一个挑战，也就是对电子自旋的单量子比特测量，已被证明是这三个挑战中最困难的一个，到目前为止，仅报道了时间平均的光学测量。在单量子点中用光读取自旋的主要障碍是探测自旋态的激光同样也会翻转被测量的自旋。在这里，我们通过使用栅控量子点分子，展示了通过量子点共振荧光的间歇性实时测量单个电子的自旋态的能力。与单个量子点不同，量子点分子允许为状态制备、操控和测量分别且独立地进行光学跃迁，从而避免了依赖于相同跃迁来确定电子自旋态的困境。
