Towards Quantum Repeaters with Solid-State Qubits: Spin-Photon Entanglement Generation Using Self-assembled Quantum Dots

Abstract

In this chapter we review the use of spins in optically-active InAs quantum dots as the key physical building block for constructing a quantum repeater, with a particular focus on recent results demonstrating entanglement between a quantum memory (electron spin qubit) and a flying qubit (polarization-or frequency-encoded photonic qubit). This is a first step towards demonstrating entanglement between distant quantum memories (realized with quantum dots), which in turn is a milestone in the roadmap for building a functional quantum repeater. We also place this experimental work in context by providing an overview of quantum repeaters, their potential uses, and the challenges in implementing them. * pmcmahon@stanford.edu † kdegreve@physics.harvard.edu 1 arXiv:1501.03535v1 [quant-ph]

Initialization of a spin qubit in a site-controlled nanowire quantum dot

“…As is the case with micropillar QDs, the structural characteristics of nanowire QDs render them incompatible with most scalable two-qubit gate proposals for spin qubits, due to the lack of a direct way for the trapped electrons (or holes) to interact. Spin qubits in nanowire QDs (and micropillar QDs) are thus 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 also the one of the leading approaches for scaling free-space trapped-ion qubits [21]. Our experiments make a contribution towards the intermediate-term goal of entangling two spatially separate QD spins on a single chip by showing that one of the steps of the entanglement-generation protocol-spin initialization-can be performed with QDs that are deterministically positioned and have high brightness.…”

“…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]. There has been considerable recent effort in exploring different techniques for fabricating site-controlled QDs, including lithographic patterning of growth substrates [4,5], stress-induced Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.…”

“…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. Here 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].…”

Quantum repeater without Bell measurements in double-quantum-dot systems

“…However, these schemes are based on photons and Bell measurements. Realizing entanglement between two distant QDs is still absent [14,15]. * Corresponding author: xiaofengyi@whu.edu.cn…”

Spin–orbit-induced hole spin relaxation in a quantum dot molecule: the effect of s-p coupling

“…The idea of implementing quantum computing schemes on such a paradigmatic physical qubit [1] has driven physical interest for more than 20 years, leading to the development of sophisticated schemes for spin initialization [2][3][4][5][6], control [7][8][9][10], and readout [11,12]. Coupling and entangling spins to phonons [13][14][15][16] makes it possible to transfer quantum states from stationary to flying qubits [17], entangle distant spins [12], and build quantum repeaters [18], which provides building blocks for quantum networks.…”