Quantum Computing with Cs Atom Qubits

纠缠是量子力学的一个基本特征。例如，如果两个相同的粒子都可以处于A或B状态，它们可能处于纠缠态AA+BB，这意味着两个粒子都处于A或B状态的叠加，但绝不是A中的一个和B中的另一个。这些高度非经典的状态对量子计算机的工作至关重要。到目前为止，已经用多达14个量子比特(量子比特)制造了原始量子计算机，但它们的输出可以很容易地在经典计算机上复制。随着纠缠态变得越来越复杂，它们不能再以经典计算机为模型。一台拥有50多个量子比特的量子计算机可以解决某些原本无法解决的问题。人们正在使用几种不同类型的量子比特进行量子计算，包括离子、超导约瑟夫森结、量子点、光子、钻石中的氮空位中心和中性原子。每个候选量子比特都有自己的长处和短处。被困在光学晶格中的中性原子可以很好地与环境隔离，因此它们具有相对较长的相干时间，这是量子比特的一个基本特征。用光捕捉它们提供了一条相对简单的途径，可以实现远远超过50个量子比特的可扩展性。尽管如此，与大多数其他量子比特候选者相比，关于囚禁中性原子的工作要少得多。这里提出的工作是为了开发用于量子计算的中性原子。将开发中性原子量子计算机所需的实验技术。以前，在5微米间距的3D光学晶格中的原子被捕获并冷却，其中一半的位置上有一个原子。使用准确的站点占用图和在5×5×5站点卷内寻址单个站点的能力，将执行对该卷内的原子进行任意排序的程序。例如，将创建完美占用的3×3×3立方体和5×5个平面。由于原子在分类后可以冷却到接近它们的振动基态，所以分类过程可以被检查，如果需要的话，可以修正小的误差，这为量子计算提供了一个理想的起点。我们将展示一种新的技术，通过基于原子的内态相干分裂原子，然后用较短的尺度光学晶格将它们锁定在适当的位置来测量中性原子量子比特的内态而不会造成原子损失。然后，它们可以在这个新的晶格中被可靠地检测到，它们的位置编码了它们的初始内部状态。将展示一种新型的单量子比特微波门，其中原子不需要离开其存储基础，它承诺极高的保真度。此外，还将继续利用原子的低温和相关的出色局域化来展示两量子比特里德伯格门。在所有这些技术被开发出来之后，该系统将允许在预期的原子损失之前对25个原子实施~3000个门。这将构成中性原子系统中可伸缩性原则的充分证据，以刺激在这些系统中纠错和缩放方面的进一步工作。

Entanglement is an essential feature of quantum mechanics. For instance, if two identical particles can each be in either state A or B, they can be in an entangled state AA+BB, which means that the particles are in a superposition of both being in A or both being in B, but never one in A and the other in B. These highly non-classical states are central to the working of quantum computers. To date, proto-quantum computers have been made with up to 14 quantum bits (qubits), but their outputs can be readily reproduced with classical computers. As entangled states become increasingly complex they can no longer be modeled on classical computers. A quantum computer with more than 50 qubits could solve certain kinds of problems that are otherwise unsolvable.Quantum computing is being pursued using several different types of qubits, including ions, superconducting Josephson junctions, quantum dots, photons, nitrogen vacancy centers in diamonds, and neutral atoms. Each candidate qubit has its strengths and weakness. Neutral atoms trapped in optical lattices can be well-isolated from their environment, so they have relatively long coherence times, an essential qubit feature. Trapping them with light presents a relatively straightforward path to scalability well beyond 50 qubits. Still, there has been less work on trapped neutral atoms than on most other qubit candidates. The work proposed here is directed toward developing neutral atoms for quantum computation.Experimental techniques needed for a neutral atom quantum computer will be developed. Previously atoms in a 5 micron spaced 3D optical lattice have been trapped and cooled, with an atom at half the sites. Using accurate site occupancy maps and the ability to address individual sites within a 5×5×5 site volume, a procedure to arbitrarily sort the atoms within that volume will be executed. For instance, perfectly occupied 3×3×3 cubes and 5×5 planes will be created. Since the atoms can be cooled to near their vibrational ground state after sorting, the sorting procedure can be checked and small errors corrected if need be, giving an ideal starting point for a quantum computation.A new technique for measuring the internal states of a neutral atom qubit without atom loss by coherently splitting atoms based on their internal states, and then locking them in place with a shorter length scale optical lattice will be demonstrated. They can then be reliably detected in this new lattice, where their location encodes their initial internal state. A new type of single qubit microwave gate where atoms do not need to leave their storage basis will be demonstrated, which promises exceptionally high fidelity. Also work will continue to demonstrate two-qubit Rydberg gates, taking advantage of the low temperature of the atoms and the associated excellent localization. After all these techniques are developed, the system will allow for the implementation of ~3000 gates on 25 atoms before any atom loss is expected. This would constitute a sufficient proof of principle of scalability in neutral atom systems to stimulate further work in error correction and scaling in these systems.