Quantum Computing with Cs Atoms in a 3D Optical Lattice

量子计算机是围绕量子位构建的。与可以是0或1的经典比特不同，量子位可以是这两种状态的量子叠加。此外，两个量子位可以量子纠缠。两个量子比特纠缠状态的一个例子是00+11，其中系统处于状态0的两个量子比特和状态1的两个量子比特的叠加。有了N个量子比特，一个系统可以同时处于2^N个唯一状态。这种纠缠赋予了量子计算机强大的能力，使得一些在经典超级计算机上难以解决的问题可以用60个量子比特来解决。在这个项目中，该团队将研究一种新的方法来纠缠中性原子量子位，这是一个在过去几年里取得最显著进展的平台。这些量子位是相同的，它们可以很好地与环境隔离，它们的内部状态可以被精确地控制和测量，所有这些都是关键的量子位特征。该实验系统的独特之处在于，它可以密集地捕获原子的3D阵列，从而实现量子位之间的最高级连接和高密度的量子信息。纠缠过程也可以应用于更常见的一维和二维中性原子阵列。该小组将实现一种双量子位里德伯门的变体，用于纠缠中性原子。通过紫外光子和微波光子的双光子跃迁，将一个基量子比特态激发到一个高立德伯态。该方法具有使用里德伯S态的优点，即对光离和电场的敏感性降低，各向同性偶极子-偶极子耦合，结构简单精细。它避免了使用高可见光功率，可以引起光电离，自发发射，和大的，不必要的交流斯塔克位移。微波部分的大偶极矩阵元件允许快速栅极。虽然UV +微波里德伯激发技术可以用于任何中性原子阵列，但它将在这里开发用于被困在三维光学晶格中的原子。为此，该小组将实施一种“反寻址”技术，该技术能够选择哪些原子纠缠，同时将对双量子比特门保真度或周围量子信息的影响降到最低。目标是让每个原子选择性地与周围24个原子中的任何一个纠缠在一起，这是一种非常高的连通性。与以前的里德堡门相比，该门将在更冷、更好的局部原子上实现，这将有助于达到0.999的双量子比特门保真度目标。其他实验修改，包括为初始加载实施灰色糖蜜，增加可以使用一个和两个量子比特寻址技术访问的原子体积，将使3D阵列中的可寻址量子比特数量增加到250个。该奖项反映了美国国家科学基金会的法定使命，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 computers are built around quantum bits, or qubits. Unlike classical bits, which can be either 0 or 1, qubits can be in quantum superpositions of these two states. Furthermore, two qubits can be quantum entangled. An example of an entangled two qubit state is 00+11, where the system is in a superposition of both qubits in state 0 and both qubits in state 1. With N qubits, a system can simultaneously be in 2^N unique states at once. Such entanglement gives a quantum computer its power, allowing some properly framed problems that are intractable on classical supercomputers to be solved with as few as 60 qubits. For this project, the troup will be working on a new method to entangle neutral atom qubits, a platform that has seen the most dramatic advances in the last few years. These qubits are identical, they can be well isolated from their environment, and their internal states can be precisely controlled and measured, all critical qubit features. The experimental system is unique, in that it is possible to densely trap 3D arrays of atoms, which allows for superlative connectivity among qubits and a high density of quantum information. The entangling procedure could also be applied in more common 1D and 2D neutral atom arrays.The group will implement a variant of a two-qubit Rydberg gate for entangling neutral atoms. One ground qubit state will be excited to a high lying Rydberg state by a two-photon transition using an ultraviolet (UV) photon and a microwave photon. This approach has most of the advantages of using a Rydberg S state, which are reduced sensitivity to photoionization and electric fields, isotropic dipole-dipole coupling, and a simple fine structure. It avoids the use of high visible light powers that can cause photoionization, spontaneous emission, and large, unwanted ac Stark shifts. The large dipole matrix element for the microwave part of the transition allows for fast gates. Although the UV plus microwave Rydberg excitation technique could be used for any neutral atom array, it will be developed here for atoms trapped in a 3D optical lattice. Toward this end, the group will implement an “anti-addressing” technique that is able to select which atoms to entangle while minimally affecting the two-qubit gate fidelity or the surrounding quantum information. The goal is for each atom to be selectively entanglable with any of 24 surrounding atoms, a very high connectivity. The gate will be implemented on significantly colder and better localized atoms than previous Rydberg gates, which should help to reach the two-qubit gate fidelity goal of 0.999. Other experimental modifications, including implementing gray molasses for the initial loading and increasing the volume of atoms that can be accessed using one and two qubit addressing techniques, will raise the number of addressable qubits in the 3D array to 250.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.