Measurement-based entanglement of single-dopant As spin qubits

这个研究项目的目的是通过使用基于测量的方法来产生量子比特之间的纠缠，来展示一种全电子的、可扩展的基于测量的或单向的量子处理器。处理器中将使用硅中的单砷掺杂自旋量子比特。电子的自旋是二能级系统量子比特的自然基础。通过塞曼效应，单独的能级很容易被磁场控制，通过电子的电荷可以隔离和操纵单独的量子比特。电子自旋量子位通常被实现在基于硅的器件中，因为它们可以更容易地与传统的CMOS技术集成，并且通常被实现为由栅电极定义的量子点，或者作为掺入硅中的掺杂剂。据报道，硅中的磷掺杂相干时间超过0.5秒，是一个很有希望的量子计算机平台。与磷不同，使用的掺杂剂将是砷。砷掺杂具有i=3/2核自旋流形，允许磁场下的四态塞曼分裂和d=4qudit编码的核自旋。随着长得多的核自旋相干时间超过30秒，通过电子和核自旋之间的超精细耦合，可以将量子态存储在掺杂的核自旋中作为一种量子存储形式。状态的存储是实现基于测量的量子计算机的关键，基于测量的量子计算机依赖于初始资源状态，例如簇态，这是一个高度纠缠的量子比特簇，需要足够的时间来增长。量子比特之间的纠缠测量将使用反射测量量子比特读出技术来实现。基于测量的纠缠也为量子比特之间的全对全连接打开了大门，克服了更传统的基于门的量子计算方法中基于交换相互作用的两个量子比特门的最近邻限制。这将在形成通用量子计算机的资源状态方面提供完全的灵活性。

The aim of this research project is to demonstrate an all-electrical and scalable measurement-based or one-way quantum processor, through using a measurement-based approach to generating entanglement between qubits. Single arsenic dopant spin qubits in silicon will be used in the processor. The spin of an electron is a natural basis for a two-level system qubit. The individual energy levels are easily controllable by magnetic fields through the Zeeman effect, and isolation and manipulation of individual qubits is possible through the electron's charge. Electron spin qubits are often implemented in silicon-based devices as they can be more easily integrated with conventional CMOS technology, and are usually implemented as quantum dots defined by gate electrodes, or as dopants incorporated into the silicon. Phosphorus dopants in silicon have reported long coherence times in excess of 0.5 seconds, and are a promising platform for a quantum computer.Rather than phosphorus, the dopants used will be arsenic. Arsenic dopants have a I = 3/2 nuclear spin manifold, allowing 4-state Zeeman splitting under a magnetic field and d = 4 qudit encoding in nuclear spins. With the much longer nuclear spin coherence times in excess of 30 seconds, the storage of quantum states in the nuclear spins of dopants as a form of quantum memory is made possible through the hyperfine coupling between electron and nuclear spins. The storage of states is key to the realisation of the measurement-based quantum computer which relies on an initial resource state such as a cluster state, a highly entangled cluster of qubits that will require sufficient time to grow. Entangling measurements between qubits will be realised using reflectometry qubit readout techniques. Measurement-based entanglements also open the door to all-to-all connectivity between qubits, overcoming the nearest neighbour limitation for two-qubit gates based on exchange interactions in the more conventional method of gate-based quantum computation. This will give full flexibility in forming the resource state for a universal quantum computer.