Quantum Computing with CS Atom Qubits

人们正在探索量子比特(量子比特)的几种实现方式，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。该项目将朝着可扩展的原子量子计算迈出几个重要的步骤。捕获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。用光捕获原子为在同一系统中放置多个量子比特提供了一条简单的途径。该团队最近展示了涉及单个原子的高保真量子门，并在50个晶格点的每个点阵上恰好捕获了一个原子。这个团队将致力于在没有粒子损失的情况下测量量子比特态。该团队还将研究使被捕获的原子变得更冷的方法，这可能会使使用碰撞来纠缠这些原子的新方法成为可能。使用改进的方法来控制和冷却原子，这个团队的目标是显著提高中性原子纠缠的技术水平。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的叠加状态，而A中永远不会有一个，B中永远不会有一个。这些高度非经典的状态对于量子计算机的工作是至关重要的。这一点很重要，因为一台有50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。这个团队将开发中性原子量子计算机所需的实验技术，该计算机使用三维光学晶格中的冷原子，晶格位置之间的间距为5微米。他们最近展示了4x4x3和5x5x2阵列的完美填充，以及在任何地点执行单个量子位门的能力，门保真度为0.997，串扰很小。在这一授权期的部分时间里，他们将开发一种新的技术来测量量子比特态，方法是根据原子的内部状态将原子相干分裂，然后用较短长度的光学晶格将它们锁定在适当的位置。通过这种方式，他们的位置编码了他们的初始内部状态，这将使他们能够区分原子损失和其他错误。通过动态切换到更深的晶格，他们还将尝试改善原子冷却，使其超过目前90%的粒子处于3D振动基态的情况。如果他们能达到99%以上，这将开启几次碰撞产生大规模纠缠的可能性，这可能会实现单向量子计算。在追求上述目标的同时，该团队将利用紫外线和微波光子的组合，展示一种新型的两量子位里德伯格门。他们将根据一量子比特门的3D寻址原理，探索实现与一量子比特门相当的站点寻址保真度的方法。这将成为一个更好的量子计算机平台，并为更充分地实现冷原子阵列的可伸缩性潜力奠定基础。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Quantum computing is being explored using several implementations for quantum bits (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. This project will pursue several important steps towards scalable quantum computation with atoms. Neutral atoms trapped in optical lattices can be well-isolated from their environment, so they have relatively long coherence times, which is an essential feature for qubits. Trapping atoms with light presents a straightforward path for putting many qubits in the same system. This team has recently demonstrated high fidelity quantum gates involving single atoms, and has trapped exactly one atom at each of 50 lattice sites. This team will work to measure qubit states without particle loss. This team will also investigate ways to make the trapped atoms colder, which might enable new ways to entangle these atoms using collisions. Using improved methods to control and cool atoms, this team aims to dramatically improve the state of the art for entangling neutral atoms. 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 the entangled state AA+BB, which means that the particles are in a superposition of both being in A or both being in B, while there is never one in A and the other in B. These highly non-classical states are central to the working of quantum computers. This is important because a quantum computer with 50 qubits could solve certain kinds of problems that are otherwise unsolvable.This team will develop experimental techniques needed for a neutral atom quantum computer using cold atoms in a 3D optical lattice with 5 micron spacing between the lattice sites. They recently demonstrated perfect filling of 4x4x3 and 5x5x2 arrays, and the ability to perform single qubit gates at any site with 0.997 gate fidelity and little cross talk. For part of this grant period they will develop a new technique for measuring qubit states by coherently splitting atoms based on their internal states, and then locking them in place with a shorter length scale optical lattice. In this way their location encodes their initial internal state, which will allow them to distinguish atom loss from other errors. By dynamically switching to a deeper lattice, they will also attempt to improve atom cooling beyond the current situation with 90% of the population in the 3D vibrational ground state. If they can achieve better than 99%, it will open up the possibility of creating massive entanglement with a few collisions, which might allow for the realization of one-way quantum computing. While pursuing the above goals this team will work on demonstrating a novel form of two-qubit Rydberg gates, using a combination of ultraviolet and microwave photons. Adapting principles from their 3D addressing for one-qubit gates, they will explore ways to achieve site addressed fidelities comparable to the one-qubit gates. This would make a better quantum computer platform, and set the stage for more fully realizing the scalability potential of cold atom arrays.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.