Quantum Computing with Cs Atoms in a 3D Optical Lattice

量子计算机是围绕量子比特或量子比特构建的。与经典比特不同，它可以是0或1，量子比特可以是这两种状态的量子叠加。此外，两个量子比特可以量子纠缠。纠缠的两个量子比特状态的一个例子是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中。有了N个量子比特，一个系统可以同时处于2^N个唯一的状态。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，该团队将致力于研究一种新的方法来纠缠中性原子量子比特，这是一个在过去几年中取得最大进展的平台。这些量子位是相同的，它们可以与环境很好地隔离，并且它们的内部状态可以精确控制和测量，所有这些都是关键的量子位特征。 该实验系统是独一无二的，因为它可以密集地捕获3D原子阵列，这使得量子位之间的最高连接性和高密度的量子信息成为可能。纠缠过程也可以应用于更常见的1D和2D中性原子阵列。该小组将实现一种用于纠缠中性原子的双量子位里德堡门的变体。一个基态量子比特态将通过使用紫外（UV）光子和微波光子的双光子跃迁被激发到高位里德堡态。这种方法具有使用Rydberg S态的大部分优点，这些优点是对光电离和电场的敏感性降低，各向同性偶极-偶极耦合，以及简单的精细结构。它避免了使用高可见光功率，可导致光电离，自发辐射，和大的，不必要的交流斯塔克位移。大偶极子矩阵元素的微波部分的过渡允许快速门。虽然紫外加微波里德伯激发技术可以用于任何中性原子阵列，它将在这里被开发的三维光学晶格中捕获的原子。为此，该小组将实施一种“反寻址”技术，该技术能够选择纠缠哪些原子，同时最小限度地影响两个量子比特门的保真度或周围的量子信息。目标是每个原子都能选择性地与周围24个原子中的任何一个纠缠，这是一个非常高的连接性。该门将在比以前的里德堡门更冷和更好的局域化原子上实现，这应该有助于达到0.999的双量子位门保真度目标。其他实验修改，包括实施灰色糖蜜的初始加载和增加原子的体积，可以使用一个和两个量子位寻址技术访问，将提高可寻址的量子位在3D阵列的数量到250.这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持.

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.