Quantum Computing with CS Atom Qubits

量子计算正在使用量子比特（qubit）的几种实现进行探索，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。每个候选量子位都有其优点和缺点。该项目将朝着使用原子进行可扩展量子计算的方向迈出几个重要步骤。 被困在光学晶格中的中性原子可以与它们的环境很好地隔离，因此它们具有相对较长的相干时间，这是量子比特的基本特征。 用光捕获原子为在同一系统中放置许多量子位提供了一条直接的途径。 该团队最近展示了涉及单个原子的高保真量子门，并在50个晶格位置中的每个位置捕获了一个原子。该团队将致力于在没有粒子损失的情况下测量量子比特状态。 该团队还将研究使被困原子更冷的方法，这可能会使新的方法使用碰撞来纠缠这些原子。使用改进的方法来控制和冷却原子，该团队的目标是显着提高纠缠中性原子的最新技术水平。 纠缠是量子力学的基本特征。例如，如果两个相同的粒子可以分别处于状态A或B，它们可以处于纠缠态AA+BB，这意味着粒子处于两个都处于A或两个都处于B的叠加状态，而从来没有一个处于A而另一个处于B。这些高度非经典的状态是量子计算机工作的核心。 这一点很重要，因为拥有50个量子比特的量子计算机可以解决某些无法解决的问题。该团队将开发中性原子量子计算机所需的实验技术，该技术使用3D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，以及在任何位置执行单量子位门的能力，具有0.997门保真度和很少的串扰。在此期间，他们将开发一种新技术，通过基于内部状态相干分裂原子来测量量子比特状态，然后用较短长度尺度的光学晶格将它们锁定在适当的位置。通过这种方式，它们的位置编码了它们的初始内部状态，这将使它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，超过目前的情况，90%的人口处于3D振动基态。如果它们能够达到99%以上，这将为通过几次碰撞产生大规模纠缠提供可能性，这可能实现单向量子计算。在追求上述目标的同时，该团队将致力于展示一种新形式的双量子位里德堡门，使用紫外线和微波光子的组合。他们将从单量子位门的3D寻址中调整原则，探索实现与单量子位门相当的选址的方法。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扩展性潜力奠定基础。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.