Abstract
A fault-tolerant quantum repeater or quantum computer using solid-state spin-based quantum bits will likely require a physical implementation with many spins arranged in a grid. Self-assembled quantum dots (QDs) have been established as attractive candidates for building spin-based quantum information processing devices, but such QDs are randomly positioned, which makes them unsuitable for constructing large-scale processors. Recent efforts have shown that QDs embedded in nanowires can be deterministically positioned in regular arrays, can store single charges, and have excellent optical properties, but so far there have been no demonstrations of spin qubit operations using nanowire QDs. Here we demonstrate optical pumping of individual spins trapped in site-controlled nanowire QDs, resulting in high-fidelity spin-qubit initialization. This represents the next step towards establishing spins in nanowire QDs as quantum memories suitable for use in a large-scale, fault-tolerant quantum computer or repeater based on all-optical control of the spin qubits.
Highlights
The development of site-controlled quantum dots (QDs), and demonstration of their suitability for hosting spin-based qubits, is a key objective in the roadmap towards a scalable quantum information processing system implemented with QDs [1,2,3]
Magneto-photoluminescence spectroscopy studies [10, 11] of InAsP QDs in InP nanowires have shown that QDs in nanowires may be a promising platform for hosting spin qubits, but to our knowledge, far there have been no demonstrations of the fundamental spin manipulation operations [12,13,14,15,16,17,18,19,20] on spins trapped in nanowire-hosted QDs, nor in any other site-controlled QD devices
Spin qubits in nanowire QDs are perhaps better suited to quantum computing or repeater architectures in which the stationary qubits are entangled indirectly, by interfering and detecting photons that are entangled with the spins [2], which is the one of the leading approaches for scaling free-space trapped-ion qubits [21]
Summary
The development of site-controlled quantum dots (QDs), and demonstration of their suitability for hosting spin-based qubits, is a key objective in the roadmap towards a scalable quantum information processing system implemented with QDs [1,2,3]. Nanowire QDs are a substantially different platform—with respect to both material and structural characteristics—than selfassembled QDs in a bulk host (the system with which the majority of spin qubit studies using optically active QDs have been performed to date). Nanowire QDs have high brightness due to the waveguiding effect of the needle-like structure in which each QD is embedded. Brightness is an advantage that nanowire QDs share with QDs embedded in micropillars, but they currently offer the additional advantage of being deterministically positionable without compromising optical quality. We demonstrate all-optical initialization of spin qubits embedded in several deterministically positioned InP nanowire QDs, which is a first step towards realizing more complex spin experiments with nanowire QDs, including coherent spin control [3] and spin-photon entanglement generation [2]
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