Proposed Scheme to Generate Bright Entangled Photon Pairs by Application of a Quadrupole Field to a Single Quantum Dot

M. Zeeshan, N. Sherlekar, A. Ahmadi, R. L. Williams, and M. E. Reimer

Phys. Rev. Lett. 122, 227401 – Published 7 June 2019

Abstract

Entangled photon sources are crucial for quantum optics, quantum sensing, and quantum communication. Semiconductor quantum dots generate on-demand entangled photon pairs via the biexciton-exciton cascade. However, the pair of photons are emitted isotropically in all directions, thus limiting the collection efficiency to a fraction of a percent. Moreover, strain and structural asymmetry in quantum dots lift the degeneracy of the intermediate exciton states in the cascade, thus degrading the measured entanglement fidelity. Here, we propose an approach for generating a pair of entangled photons from a semiconductor quantum dot by application of a quadrupole electrostatic potential. We show that the quadrupole electric field corrects for the spatial asymmetry of the excitonic wave function for any quantum dot dipole orientation and fully erases the fine-structure splitting without compromising the spatial overlap between electrons and holes. Our approach is compatible with nanophotonic structures such as microcavities and nanowires, thus paving the way towards a deterministic source of entangled photons with high fidelity and collection efficiency.

Received 6 September 2018

DOI:https://doi.org/10.1103/PhysRevLett.122.227401

Physics Subject Headings (PhySH)

Biexcitons Excitons Nanoantennas Quantum entanglement Semiconductor microcavities Stark effect

Nanorods Quantum dots

Quantum Information, Science & TechnologyCondensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Zeeshan^1,*, N. Sherlekar¹, A. Ahmadi², R. L. Williams³, and M. E. Reimer¹

¹Institute for Quantum Computing and Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, N2L 3G1, Canada
²Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, N2L 3G1, Canada
³National Research Council of Canada, Ottawa, Ontario, Canada, K1A 0R6

^*m5zeeshan@uwaterloo.ca

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Vol. 122, Iss. 22 — 7 June 2019

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Images

Figure 1
Device design. (a) Schematic view of the proposed device architecture consisting of a single quantum dot in a standing nanowire, dielectric coating and four electrical contacts in-plane of the quantum dot. (b) Calculated far-field emission profile from the device using a finite-difference time-domain method in Lumerical, assuming an in-plane dipole on the nanowire waveguide axis.
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Figure 2
Single particle wave functions with an applied quadrupole field. (a) Schematic view of applied quadrupole potential. We use the convention that the top and bottom gates are positive at $+ 0.5 V$ and the left and right gates are negative at -0.5 V. The electron wave function is shown schematically in solid blue and hole wave function in dashed red. (b) Calculated 2D electric potential for configuration (a). The black circles represent the edges of the dielectric (largest), nanowire (medium), and quantum dot (smallest). (c),(d) Calculated 2D probability density of electron (c) and hole (d) wave functions with configuration from (a). (e) Schematic view of applied quadrupole potential with polarities reversed with respect to (a) and magnitude increased to 0.7 V. (f) Calculated electric potential for configuration from (e). (g),(h) Calculated 2D probability density of electron (g) and hole (h) wave function with configuration from (e). $L x$ and $L y$ are the dimensions in the $x$ and $y$ direction of the simulated structure, whereas $ε$ is the degree of single particle wave function elongation of the electron and hole.
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Figure 3
(a) Calculated FSS (circles, left axis) and $e − h$ overlap (stars, right axis) as a function of quadrupole potential. (b) Calculated FSS (circles, left axis) and $e − h$ overlap (stars, right axis) as a function of the lateral potential. Insets: Schematic view of applied quadrupole [in (a)] and lateral potential [in (b)]. The probability density of the electron (solid blue) and hole (dashed red) wave functions are schematically shown by the ellipses.
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Figure 4
Universal FSS tuning. (a) Schematic view of an applied asymmetric quadrupole potential. Inset: electron (solid gray) and hole (dashed gray) wave functions of a quantum dot with asymmetric axis aligned at an angle $θ$ with respect to the gates along the $x$ axis. (b) Calculated FSS as a function of quadrupole potential with the quantum dot major axis oriented at three different angles with respect to the gates along the $x$ axis ( $θ = 0 °, 10 °$ , and 20°). (c) Gray scale plot of FSS as a function of $Δ V_{RL}$ and $Δ V_{TB}$ for $θ = 2 0^{0}$ . (d) High resolution gray scale plot of the zoomed-in region [white dotted line box from (c)] showing near-zero FSS. (e) Gray scale plot of $e − h$ overlap as a function of $Δ V_{RL}$ and $Δ V_{TB}$ for $θ = 2 0^{0}$ .
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