Electrical control of quantum-dot fine-structure splitting for high-fidelity hole spin initialization

Abstract

We demonstrate electrical control of the neutral exciton fine-structure splitting in a single InAs/GaAs selfassembled quantum dot by significantly reducing the splitting to near zero through the application of a vertical electric field in the fast electron tunneling regime. This is verified by performing high-resolution photocurrent spectroscopy of the two fine-structure split exciton eigenstates as a function of reverse bias voltage. Using the qubit initialization scheme for a quantum-dot hole spin based on rapid electric-field ionization of a spin-polarized exciton, our results suggest a practical approach towards achieving qubit initialization with near-unity fidelity in the absence of magnetic fields.

Two-Photon Rabi Splitting in a Coupled System of a Nanocavity and Exciton Complexes

“…The solid red line shows the fitted results with sine function. The energy difference oscillates with a period of π with an amplitude of 37 µeV, which is typical for the fine structure splitting energy of InAs QDs [42][43][44][45]. Therefore, we can conclude that peak2 and peak3 originate from XX and X transitions of a single QD respectively.…”

Comparison of different concurrences characterizing photon pairs generated in the biexciton cascade in quantum dots coupled to microcavities

“…The question now arises how to interpret the quantity C R (∆t, ∆τ ) defined in Eq. (15), which is obtained by first taking a coherent superposition of signal contributions associated with different emission times and then constructing the concurrence by taking twice the absolute value of the off-diagonal element of the normalized superposition. At this point it is helpful to discuss in more detail the emission process from the cavity.…”

“…However, the situation in real quantum dots often deviates from the ideal picture described above. First of all, the exchange interaction typically introduces an energetic splitting between the two excitonic states on the order of several tens to hundreds of µeV 7,15,16 . Thus, the two paths become asymmetric, leading to a deviation from the usually desired state |ψ + .…”

“…These detrimental effects can be suppressed by engineering the quantum dot devices accordingly. For example, the fine structure splitting between the excitonic states can be reduced by applying electrical 15,16 or strain fields 17 or by growing quantum dots within highly symmetric structures such as nanowires 18 . Here, we consider another approach to obtain more symmetric paths, which is achieved by embedding the quantum dot in a microcavity.…”

Fundamental Intrinsic Lifetimes in Semiconductor Self-Assembled Quantum Dots

“…1a), in which their energy difference, called fine structure splitting (FSS), is much larger than the homogeneous broadening of the emission lines (Γ ∼ 1 µeV [8][9][10]), thus the "which-way" information is erased and only classically corrected photons instead of maximally entangled photon pairs can be created from this cascade process. In the past decade, strenuous efforts have been devoted to eliminate this splitting by applying various experimental techniques, including thermal annealing [11][12][13][14][15], electric field [16][17][18][19][20][21][22][23], magnetic field [24][25][26][27] and external stress [28][29][30][31][32][33][34][35][36][37][38] etc.. However, none of them is efficient.…”