基于半导体门型量子点的高保真度单量子比特逻辑门

In the past few years, we realized logical gates for single and double qubits based on GaAs gate defined quantum dots. To realize quantum computation with error-correction, it’s necessary to improve the fidelity of quantum gates. Theories predict that a qubit will be tremendously less sensitive to noise after a parallel energy spacing is introduced into the two-energy level structure of the qubit. Based on this idea, there have been reports on high fidelity quantum gates for a single qubit utilizing an accidentally formed excited energy state. However, these experiments have limited applications because these accidentally formed excited states are not controllable. We propose to extend the traditional double-dot structure to specially designed triple-dot structure and therefore introduce a controllable parallel energy spacing into the traditional two-energy level. In this way, we anticipate an improvement of the fidelity of single-qubit logical gates.

我们在过去几年中，已经实现了基于砷化镓门型量子点的单量子比特和双量子比特的量子逻辑门。为了实现可纠错的量子计算，我们亟需进一步提高量子比特的逻辑操作的保真度。根据理论预期，如果能对量子比特的二能级结构在平衡点附近做平行化处理，将大幅降低噪声对量子比特的影响，从而提高量子比特的消相干时间以及量子逻辑门的保真度。国际上已经有实验通过偶然形成的激发态对二能级结构产生平行化，从而实现了高保真度的单量子逻辑门。但是，这种偶然形成的激发态缺乏可控性，因此不具有可扩展性。我们提出在三量子点器件中，利用可调控的参数形成平行化的二能级结构，并进行单量子比特的逻辑操作，从而实现高保真度的单量子比特逻辑门。

我们在三量子点器中，实现了可调的平行二能级结构。对电荷-自旋混合量子比特的能级结构的主动控制，表明我们能实现工作频率2GHz 到15GHz范围内的调控。我们实现了对混合量子比特的相干操作。实验结果表明，混合量子比特对电荷噪声的敏感度下降，因而相干时间实现1ns到20ns的增长，单量子比特逻辑门的保真度提高。利用这种多量子点结构，我们还实现了三个电荷量子比特的强耦合与可控逻辑门。 这些进展提高了半导体量子比特的质量，我们期望能在此基础上进一步实现高保真度的多混合量子比特体系。