Measurement-based entanglement of single-dopant As spin qubits

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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.