Path-dependent initialization of a single quantum dot exciton spin in a nanophotonic waveguide

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Path-dependent initialization of a single quantum dot exciton spin in a nanophotonic waveguide

R. J. Coles, D. M. Price, B. Royall, E. Clarke, M. S. Skolnick, A. M. Fox, and M. N. Makhonin

Phys. Rev. B 95, 121401(R) – Published 6 March 2017

Abstract

We demonstrate a scheme for in-plane initialization of a single exciton spin in an InGaAs quantum dot (QD) coupled to a GaAs nanobeam waveguide. The chiral coupling of the QD and the optical mode of the nanobeam enables spin initialization fidelity approaching unity in magnetic field $B = 1$ T and $> 0.9$ without the field. We further show that this in-plane excitation scheme is independent of the incident excitation laser polarization and depends solely on the excitation direction. This scheme provides a robust in-plane spin excitation basis for a photon-mediated spin network for quantum information applications.

Received 6 September 2016

DOI:https://doi.org/10.1103/PhysRevB.95.121401

Physics Subject Headings (PhySH)

Angular momentum of light Integrated optics Photonics Quantum information with atoms & light Semiconductor quantum optics

Fluorescence Optical spectroscopy Photon counting

Quantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

R. J. Coles¹, D. M. Price¹, B. Royall¹, E. Clarke², M. S. Skolnick¹, A. M. Fox^1,*, and M. N. Makhonin^1,†

¹Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom
²Department of Electronic and Electrical Engineering, EPSRC National Centre for III-V Technologies, University of Sheffield, Sheffield S1 3JD, United Kingdom

^*[email protected]
^†[email protected]

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Issue

Vol. 95, Iss. 12 — 15 March 2017

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Images

Figure 1
(a) Schematic illustrating the relationship between photon polarization $(σ^{+}, σ^{-})$ , propagation direction $(- k_{x}, + k_{x})$ , and trion pseudospin $(↑, ↓)$ for optical readout and initialization of a quantum dot spin at a chiral point. (b) Scanning electron microscope image of the device. (inset) Schematic cross section of the waveguide. (c) and (d) Schematic of the experimental arrangement for QD exciton spin initialization from the (c) right and (d) left coupler. The QD is located at a chiral point in the waveguide. (e) and (f) Schematics showing the excitonic species involved in quasiresonant (QR) excitation of the $X^{+}$ transition for (e) $σ^{+}$ (f) $σ^{-}$ -polarized excitation and emission. The longitudinal optic phonon is denoted as LO.
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Figure 2
(a), (b) PL spectra obtained at $B_{z} = 1$ T when quasiresonantly exciting the QD from each grating coupler with detection fixed at the (a) left and (b) right coupler. (c), (d) PL spectra as in (a), (b) but with $B_{z} = 0$ T. The legends in (a) and (b) refer to the couplers on which the QR excitation laser and PL detection were located, respectively (L=left coupler, R=right coupler). Spectral data are shown as solid and hollow symbols, with Gaussian fits as solid lines. Spectra with only the weak NR laser applied are shown as hollow circles. (e), (f) Excitation maps obtained by performing a raster scan of the $σ^{-}$ polarized QR laser over the device while keeping detection fixed at the (e) left and (f) right coupler. (g), (h) Excitation maps as in (e), (f) but with $σ^{+}$ laser polarization. All maps recorded PL emission filtered at the QD wavelength at $B_{z} = 0$ T, and a schematic outline of the waveguide and couplers are overlaid. The apparent rotation of the device from horizontal is due to a small rotation induced by the detection optics.
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Figure 3
(a), (b) Excitation maps obtained by a raster scan of QR excitation over a device containing a nonchirally coupled QD while keeping detection fixed at the (a) left and (b) right grating couplers at $B_{z} = 0$ T. All maps recorded PL emission filtered at the QD wavelength and a schematic outline of the waveguide and couplers is overlaid. As in Fig. 2, the apparent rotation of the device from horizontal is due to a small rotation induced by the detection optics. (c), (d) Corresponding PL spectra obtained when exciting the QD from each coupler with detection fixed at the (c) left and (d) right coupler when an external magnetic field of $B_{z} = 1$ T is applied. Spectral data are shown as solid symbols, with an experimental Gaussian fit to the data shown as a solid line.
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