基于里德堡原子偶极阻塞效应的量子比特操控

Rydberg atom has much larger dipole momentum and dipole-dipole interaction. It is proposed as one of the most promising candidates to perform the quantum information storage and quantum computing. The laser-cooling neutral atoms in the ground state have a long decoherence time(up to several seconds). The ground hyperfine-states of neutral atom can be defined as quantum states |0> and |1>. The strong long-range interaction between two Rydberg atoms with the principal quantum number n>>1 separated by a few micrometers becomes prominent interaction. The atom excitation will be blocked to be in Rydberg states when the nearby atom are firstly excited.The blockade effect is the base of the controlled qubits computing and quantum entanglement. The applying project will be proposed to perform the demonstration of controlled quantum bits operation using the effect of dipole blockade between two Rydberg atoms trapped in the closely spaced optical trap. The electric field will be applied to controll the quantum inference of Rydberg atoms.This research will be the important step to accomplish the universal quantum gates and multi-dimensional qubit array. The main content of this project include: (1) The dipole-dipole interaction induced by electric field between two Rydberg atoms in different excitation states will be calculated theoretically. The dynamics of Rydberg excitation will be explored.The detailed analysis of mechanisms inducing to decoherence and loss of Rydberg atoms, which would affect the fidelity and error of universal gate operation, will be performed. (2) The single atom will be loaded in the two far-off-resonance optical trap respectively. Two closely spaced site with a distance of few micrometers will be created and addressed separately. The initialization of single quantum bite defined as the hyperfine ground states and rotation operation between different quantum states |0> and |1> will be performed . (3) The Rydberg atoms in different sites will be prepared using the multi-photon excitation.The qubit measurement will be accomplished using detecting resonance fluorescence photons.The quantum coherence effect of Rydberg atoms will be investigated under different electric field and site separation.The entanglement of two Rydberg atoms induced by the dipole-dipole interaction will be reseached. The controlled quantum operation based on the two Rydberg atoms in the closed spaced sites will be demonstrated by a sequence of optical operation.The multi-bits universal quantum gate will be explored.

里德堡原子由于具有很大的偶极矩以及很强的偶极-偶极相互作用，因此被认为是实现量子信息存储和量子计算最有前景的候选介质之一。 本项目将在间距可调的双光学偶极阱中分别俘获单个铯原子并实现铯原子基态超精细能级的量子态制备和量子态翻转。通过改变原子间距和外电场幅度，调节里德堡原子偶极-偶极相互作用，进行两比特操控的实验研究。研究内容包括：1)利用微扰理论计算外电场作用下的里德堡原子偶极相互作用，研究分析导致量子态退相干及里德堡原子耗散的机制；2)在空间可分辨的双光学偶极阱中分别进行单原子俘获，实现原子基态塞曼精细能级的制备和单量子比特的反转操作；3)通过双光子激发将基态原子制备到里德堡态，调节双光学阱间距和外电场的大小，操控里德堡原子间的偶极阻塞效应，实现两比特的纠缠和可控非门操作。

本项目的研究对于理解超冷原子体系下的里德堡原子基础物理性质和相互作用机理，以及探索外场操控下的里德堡原子，并在实现单原子纠缠和量子逻辑门计方面以及并且利用里德堡原子量具有重要意义。项目执行期内实验系统搭建的基础研究目标基本完成，新建并优化了用于单原子俘获的超高真空系统，利用小光束实现了小系综的原子样品，并通过二级冷却技术获得了2.7μK的超冷原子，搭建了荧光收集系统，并观测了里德堡激发的原子荧光损耗光谱。实现了强聚焦的偶极阱搭建和阱深精确控制。初步完成了单原子的装载和测量。研究了超冷原子中量子相干效应下的AT分裂光谱，研究里德堡原子的长程相互作用导致的失相率对量子相干效应的影响。研究了磁场作用下，里德堡原子激发光偏振组合对里德堡超精细态制备的影响。在热原子中利用微波操控实现了铯原子基态超精细能级的布居数转移，为进一步在单原子中实现量子“非”计算奠定了基础。