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Coupling of quantum dots with superconductors- towards long-range coupling of qubits

量子点与超导体的耦合——实现量子位的长程耦合

基本信息

批准号：
387743155
负责人：
Professor Dr. Joachim Knoch
金额：
--
依托单位：
Institut für Halbleitertechnik (IHT)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2021-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/387743155?language=en
关键词：
Coupling quantum dots superconductors towards

项目摘要

Coupling spin qubits in quantum dots over a long distance is one of the big remaining challenges, when it comes to realizing large scale quantum computer systems. So far only neighbouring quantum dot systems were coupled directly by electrostatic means using control gate electrodes. The goal of this project is to explore the possibility of a long-range coupling of quantum dot spin qubits using superconducting electrodes. Since this approach is rather unexplored up to now, mainly fundamental questions concerning the feasibility of this concept will be addressed within the project. Two different mechanisms are employed for the coupling: The first is based on the virtual exchange of an electron between two quantum dots via a superconducting bridge by means of excited quasiparticles above the superconducting band gap. As has been recently shown, for a proper coupling over distances larger than the coherence length of the superconductor a hard superconducting gap and a moderate coupling between quantum dot and superconductor is necessary. As a second method we will also study the coupling based on crossed Andreev reflection. Here, one electron from each quantum dot tunnels into the superconductor and combines to a Cooper pair before it tunnels back. In this case the expected coupling length would be in the order of the superconducting coherence length, thus much smaller than in the previous case. The present proposal is devoted to an experimental investigation of the coupling of quantum dots realized in III-V semiconductors as well as in silicon. The approach based on III-V semiconductors enables to cover the full range of coupling strengths due to an in-situ fabrication process and thus allows assessing and evaluating both regimes, i.e. coupling via excited quasiparticles as well as crossed Andreev reflection. The Si-approach, on the other hand, allows assessing the suitability of the long-range coupling with superconductors within the most mature material system that has recently regained a strong and increasing interest for qubit circuits. A successful demonstration of a coupling of quantum dots over longer distances would be of great benefit for the long-range coupling of qubits and thus of a major step forward towards a realization of a scalable quantum information processor.

在实现大规模量子计算机系统时，远距离耦合量子点中的自旋量子比特是剩余的一大挑战之一。到目前为止，只有相邻的量子点系统通过使用控制栅电极的静电手段直接耦合。这个项目的目标是探索利用超导电极实现量子点自旋量子比特远程耦合的可能性。由于到目前为止，这一方法还未得到探索，有关这一概念的可行性的基本问题将在该项目中得到解决。耦合采用了两种不同的机制：第一种是通过超导带隙上方的激发准粒子，通过超导桥在两个量子点之间进行电子的虚拟交换。正如最近所表明的那样，对于大于超导体相干长度的距离的适当耦合，硬超导间隙和量子点与超导体之间的适度耦合是必要的。作为第二种方法，我们还将研究基于交叉安德列夫反射的耦合。在这里，每个量子点中的一个电子通过隧道进入超导体，并在库珀对通过隧道返回之前结合到库珀对中。在这种情况下，期望的耦合长度将是超导相干长度的数量级，因此比前一种情况要小得多。本方案致力于对在III-V半导体和硅中实现的量子点耦合的实验研究。这种基于III-V半导体的方法能够覆盖由于原位制造工艺而产生的全部耦合强度，因此可以评估和评估两种状态，即通过激发准粒子的耦合以及交叉安德列夫反射。另一方面，Si方法允许评估与最成熟的材料系统中的超导体进行远程耦合的适宜性，该材料系统最近重新引起了人们对量子比特电路的强烈和日益增长的兴趣。量子点远距离耦合的成功演示将大大有利于量子比特的远程耦合，从而朝着实现可扩展的量子信息处理器迈出重要的一步。