Quantum Gates, Algorithms, and Error Correction with a Neutral Atom Qubit Array

量子计算因其解决经典计算机难以解决的实际问题的潜力而引起了人们的极大兴趣。应用领域包括密码学，数据库搜索，模式分类，求解大型耦合方程组，以及设计新的功能材料或化合物。量子计算机是由量子比特构成的，量子比特存储量子信息，并通过量子逻辑门进行处理。该项目将继续使用在单个原子内部状态中编码的量子比特来发展量子计算。虽然目前的技术水平涉及10-20个量子位的实验，但人们相信，要实现量子计算的前景，需要拥有数千个量子位的计算机。在这方面，在这个项目中开发的基于原子的方法特别有吸引力，因为大量的中性原子可以被保持和控制在很近的距离，而不会相互干扰。该项目旨在提高几个关键性能指标的技术水平：量子位长时间保持其量子状态的能力，逻辑门操作和量子位测量的保真度，以及可以在单个系统中准备的量子位的数量。这些进展将用于演示数据库搜索的量子算法。该项目将通过培养学生和博士后研究人员来促进科学劳动力的发展。培训将是跨学科的，借鉴原子和激光物理、电子和计算机控制系统以及量子信息理论的方法和思想。研究成果将纳入大学的教学课程。实验方法将使用铯和铷原子的二维阵列，这些原子被困在由光定义的势阱中。势阱将通过组合几种不同频率的激光来制备，以保护存储的量子信息不退相干。一个可移动的光学镊子系统将用于排列捕获原子，使其100%占据一个多达50个量子位的阵列。产生纠缠的量子逻辑门将通过用激光脉冲将原子激发到里德伯态来实现。将使用具有成形时间剖面的绝热脉冲来提高纠缠操作的保真度。原子状态的测量将不会与其他量子位串扰，也不会使用两种方法损失原子，其中一种（铯）将用于记忆和量子逻辑，另一种（铷）将用于测量。要测量的量子态将通过种间里德伯门从铯原子转移到铷原子。然后将利用这些功能来演示多量子位量子算法，该算法为数据库搜索提供二次加速。该团队还将实施量子纠错，以保护量子比特免受位翻转或相位翻转错误的影响。

Quantum computing is attracting great interest due to its potential for solving practical problems that are intractable on classical computers. Areas of application include cryptography, database searching, pattern classification, solving large systems of coupled equations, and design of new functional materials or chemical compounds. A quantum computer is built from quantum bits, or qubits, that store quantum information which is processed using quantum logic gates. This project will continue the development of quantum computing using qubits encoded in the internal states of individual atoms. While the current state of the art involves experiments with 10-20 qubits, it is believed that computers with many thousands of qubits will be needed to realize the promise of quantum computation. In this respect the atom based approach being developed in this project is particularly attractive since a large number of neutral atoms can be held and controlled in close proximity without undesired interference with each other. The project seeks to advance the state of the art of several key performance metrics: the ability of qubits to preserve their quantum states for a long time, the fidelity of logic gate operations and qubit measurements, and the number of qubits that can be prepared in a single system. These advances will then be used to demonstrate a quantum algorithm for database searching. The project will contribute to scientific workforce development through training of students and postdoctoral researchers. The training will be interdisciplinary, drawing on methods and ideas from atomic and laser physics, electronic and computer based control systems, and quantum information theory. Research results will be incorporated into the University teaching curriculum. The experimental approach will use a two-dimensional array of cesium and rubidium atoms trapped in potential wells defined by light. The potential wells will be prepared by combining laser light of several different frequencies in a way that protects stored quantum information from decoherence. A movable optical tweezer system will be implemented to arrange trapped atoms for 100% occupancy of an array with up to 50 qubit sites. Quantum logic gates to create entanglement will be performed by exciting atoms to Rydberg states with laser pulses. Adiabatic pulses with shaped temporal profiles will be used to improve the fidelity of the entangling operations. Atomic states will be measured without crosstalk to other qubits or loss of atoms using a two-species approach whereby one species (cesium) will be used for memory and quantum logic, and a second species (rubidium) will be used for measurements. The quantum states to be measured will be transferred from cesium to rubidium atoms using an interspecies Rydberg gate. These capabilities will then be leveraged to demonstrate a multi-qubit quantum algorithm that provides quadratic speedup for database searching. The team will also implement quantum error correction to protect qubits against bit flip or phase flip errors.