To build tomorrow’s quantum computers, some researchers are turning to dark excitons, which are bound pairs of an electron and the absence of an electron called a hole. As a promising quantum bit, or qubit, it can store information in its spin state, analogous to how a regular, classical bit stores information in its off or on state. But one problem is that dark excitons do not emit light, making it hard to determine their spins and use them for quantum information processing.
然而，在新实验中，研究人员不仅可以阅读黑暗激子的旋转状态，但它们也可以比以前更有效地进行。他们的演示，本周描述了APL Photonics., from AIP Publishing, can help researchers scale up dark exciton systems to build larger devices for quantum computing.
“柏林技术大学的Tobias Heindel说：”需要大量的光子提取和收集效率来推动原则上的实验。“
When an electron in a semiconductor is excited to a higher energy level, it leaves behind a hole. But the electron can still be bound to the positively charged hole, together forming an exciton. Researchers can trap these excitons in quantum dots, nanoscale semiconductor particles whose quantum properties are like those of individual atoms.
如果电子和孔具有相反的旋转，则两个颗粒可以容易地重新组合并发出光子。这些电子孔对称为亮激子。但如果它们具有相同的旋转，则电子和孔不能轻易重新组合。激子不能发光，因此称为黑暗的激子。
This darkness is part of why dark excitons are promising qubits. Because dark excitons cannot emit light, they can’t relax to a lower energy level. Therefore, dark excitons persist with a relatively long life, lasting for over a microsecond — a thousand times longer than a bright exciton and long enough to function as a qubit.
不过,黑暗构成challenge. Because the dark exciton is closed off to light, you can’t use photons to read the spin states — or any information a dark exciton qubit may contain.
但2010年，Technion-以色列理工学院的物理学家团队讨论了如何渗透黑暗。事实证明，两个激子在一起可以形成亚稳态。当这种所谓的旋转阻断的Biexciton状态放松到较低的能量水平时，它在发射光子时留下深色激子。通过检测这个光子，研究人员会知道创造了一个黑暗的激子。
To then read the spin of the dark exciton, the researchers introduce an additional electron or hole. If the new charge carrier is a spin-up electron, for example, it combines with the spin-down hole of the dark exciton, forming a bright exciton that quickly decays and produces a photon. The dark exciton is destroyed. But by measuring the polarization of the emitted photon, the researchers can determine what the dark exciton’s spin was.
Like in the 2010 experiments, the new ones measure dark excitons inside quantum dots. But unlike the earlier study, the new experiments use a microlens that fits over an individual quantum dot that was selected in advance. The lens allows researchers to capture and measure more photons, crucial for larger-scale quantum information devices. Their approach also lets them choose the brightest quantum dots to measure.
“This means we can detect more photons of the related exciton states per time, which allows us to access the dark exciton spins more often,” Heindel said.
测量黑暗的激子旋转还揭示了它的进程频率，在旋转的状态上的状态之间的振荡。知道这个号码，在使用黑色激子生成对量子信息应用的光的光线的量子态时，需要进行Heindel解释。对于这些状态，称为缠结光子的集群状态，即使状态的部分被破坏 - 耐堵塞量子信息系统也被破坏了量子机械性能。
Filed Under:M2M (machine to machine)
