用於平面型離子阱晶體之容受微動的快速量子糾纏閘

Abstract

離子阱被視為最有前景的量子計算平台之一，不僅是因為它的量子比特具有長時間的同調性，同時也是因為離子間的強相互作用致使多量子比特閘得以實現。雖然傳統的離子阱量子計算是透過讓離子們排列成一條直鏈來進行操作的，但其較差的可擴展性已然成為一個棘手的問題。在這篇論文中，我展示出一種更具擴展性的配置，即令離子排列於一張平面上，形成一個二維晶體的結構。對此離子阱作理論分析後，可得知離子在平面內必定產生某種微小運動；而若不適度把該運動列入考量，更將會不可避免地防礙量子閘的實際表現。因鑑於此，本文提出一種基於段氏方案的脈衝型雙量子比特快速閘，用以產生兩量子比特間之糾纏態，展示出即使在微運動的影響之下仍然可以獲得高保真度和較短的閘時間。實驗模擬選用的是鈣離子以及波長393奈米之雷射脈衝光，而此波長對應到的即是4S態和4P態之間的共振躍遷。

Ion traps are one of the most promising platforms for quantum computing, not only because of their long qubit coherence time, but also because of the strong ion-ion interaction that enables the multi-qubit gates. While traditional trapped-ion quantum computing is implemented by ions arranged in a linear chain, its poor scalability has become an intractable problem. In this thesis I present a more scalable configuration, ions arranged in a plane forming a two-dimensional crystal structure. A theoretical analysis of this ion trap shows that there must be some in-plane micromotion, which inevitably hinders the actual performance of quantum gates if the motion is not properly taken into account. In light of this, a pulsed two-qubit entangling fast gate based on Duan's scheme is proposed in the thesis, demonstrating that high fidelity and short gate time can still be available even in the presence of micromotion. The simulation is carried out with calcium ions, using laser pulses resonant to the 393-nm transition between the 4S and 4P states.