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。与可以是0或1的经典比特不同，量子比特可以是这两种状态的量子叠加。此外，两个量子比特可以实现量子纠缠。一个纠缠的两个量子比特态的例子是0011，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，系统可以同时处于2^N个唯一态。这种纠缠为量子计算机提供了强大的力量，使得一些在经典超级计算机上难以解决的、框架合理的问题只需60个量子比特就能解决。对于这个项目，该小组将致力于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了最戏剧性进展的平台。这些量子比特是相同的，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，这些都是关键的量子比特特征。这个实验系统是独一无二的，因为它可以密集捕获3D原子阵列，这允许量子比特之间的最高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。该小组将实现两量子比特里德伯格门的变体，用于纠缠中性原子。一个基态量子比特态将通过一个紫外光和一个微波光子的双光子跃迁激发到高位里德堡态。这种方法具有里德堡S态的大部分优点，即对光致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。它避免了高可见光功率的使用，因为高可见光功率会导致光致电离、自发辐射和巨大的、不必要的交流斯塔克位移。转换过程中微波部分的大偶极矩阵元允许快速门。虽然紫外加微波里德堡激发技术可以用于任何中性原子阵列，但它将在这里发展为捕获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，该技术能够选择要纠缠的原子，同时将对两个量子比特门的保真度或周围量子信息的影响降至最低。我们的目标是让每个原子能够选择性地与周围24个原子中的任何一个原子纠缠，这是一个非常高的连接性。与之前的里德堡门相比，这种门将在温度更低、局域化程度更高的原子上实现，这将有助于实现两量子位门0.999的保真度目标。其他实验性的修改，包括为初始加载实施灰色糖蜜，以及增加可以使用一个和两个量子比特寻址技术访问的原子的体积，将把3D阵列中可寻址的量子比特的数量增加到250个。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 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.