Depolarization of Electronic Spin Qubits Confined in Semiconductor Quantum Dots

Abstract

Quantum dots are arguably the best interface between matter spin qubits and flying photonic qubits. Using quantum dot devices to produce joint spin-photonic states requires the electronic spin qubits to be stored for extended times. Therefore, the study of the coherence of spins of various quantum dot confined charge carriers is important both scientifically and technologically. In this study we report on spin relaxation measurements performed on five different forms of electronic spin qubits confined in the very same quantum dot. In particular, we use all optical techniques to measure the spin relaxation of the confined heavy hole and that of the dark exciton -a long lived electron-heavy hole pair with parallel spins. Our measured results for the spin relaxation of the electron, the heavy-hole, the dark exciton, the negative and the positive trions, in the absence of externally applied magnetic field, are in agreement with a central spin theory which attributes the dephasing of the carriers' spin to their hyperfine interactions with the nuclear spins of the atoms forming the quantum dots. We demonstrate that the heavy hole dephases much slower than the electron. We also show, both experimentally and theoretically, that the dark exciton dephases slower than the heavy hole, due to the electron-hole exchange interaction, which partially protects its spin state from dephasing. arXiv:1808.00284v1 [cond-mat.mes-hall] 1 Aug 2018

Complete state tomography of a quantum dot spin qubit

“…In addition to the natural coherent precession, the excited-qubit state undergoes decoherence [13,38], which results in decay of the initial precession amplitude:…”

“…The first two are Kramers' degenerate, but the third one is not. All three qubits form a natural Π−system with circularly polarized optical selection rules to their excited qubits [13]. Thus, tomography as in the BE case [26] is impossible.…”

Multiplexed Single Photons from Deterministically Positioned Nanowire Quantum Dots

“…Our candidate of choice to demonstrate spatially multiplexed streams of single photons from solid-state emitters is a sample of (In,As)P QDs embedded in deterministically positioned InP nanowires [40]. Nanowire QDs offer an excellent coherent light-matter interface [41] and can emit high-quality entangled photons [42,43], while providing near-unity coupling into optical fiber due to their wave-guiding properties [44,45] and Gaussian-modeprofile emission [46]. This gives a nominal extraction efficiency of 18%, as reported previously [42,43].…”

Emission properties and temporal coherence of the dark exciton confined in a GaAs/AlxGa1−xAs quantum dot

“…However, its weak coupling to light as reported in strained InAs QDs has enabled the demonstration of a very long spin coherence time of ∼100 ns [2] compared to ∼300 ps for the bright exciton (BE) [3]. Moreover, similar to a hole spin [4,5], a DE is rather insensitive to nuclear spin noise [6]. Recently, a DE was proposed as an intermediate state in the generation of photon cluster states [7] showing that the DE can be considered as a coherent electronic excitation and a promising solid-state qubit.…”