Cross-Polarization-Extinction Enhancement and Spin-Orbit Coupling of Light for Quantum-Dot Cavity Quantum Electrodynamics Spectroscopy

P. Steindl, J.A. Frey, J. Norman, J.E. Bowers, D. Bouwmeester, and W. Löffler

Phys. Rev. Applied 19, 064082 – Published 29 June 2023

Abstract

Resonant laser spectroscopy is essential for the characterization, operation, and manipulation of single-quantum systems such as semiconductor quantum dots. The separation of the weak resonance fluorescence from the excitation laser is key for high-quality single- and entangled-photon sources. This is often achieved by cross-polarization laser extinction, which is limited by the quality of the optical elements. Recently, it was discovered that Fresnel-reflection birefringence in combination with single-mode filtering counteracting spin-orbit-coupling effects enables a three-order-of-magnitude improvement of polarization extinction [Benelajla et al., Phys. Rev. X 11, 021007 (2021)]. Here, we demonstrate this method for cross-polarization-extinction enhancement in cryogenic confocal microscopy of a resonantly excited semiconductor quantum dot in a birefringent optical microcavity, and observe a $10 \times$ improvement of the single-photon contrast.

Received 10 February 2023
Revised 7 June 2023
Accepted 12 June 2023

DOI:https://doi.org/10.1103/PhysRevApplied.19.064082

Physics Subject Headings (PhySH)

Angular momentum of light Cavity quantum electrodynamics Nanophotonics Polarization of light Semiconductor quantum optics Single photon sources

Optical microcavities Quantum dots

Atomic, Molecular & OpticalQuantum Information, Science & TechnologyCondensed Matter, Materials & Applied Physics

Authors & Affiliations

P. Steindl ^1,*, J.A. Frey², J. Norman³, J.E. Bowers³, D. Bouwmeester^1,2, and W. Löffler ^1,†

¹Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, Leiden 2300 RA, Netherlands
²Department of Physics, University of California, Santa Barbara, California 93106, USA
³Department of Electrical & Computer Engineering, University of California, Santa Barbara, California 93106, USA

^*steindl@physics.leidenuniv.nl
^†loeffler@physics.leidenuniv.nl

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Vol. 19, Iss. 6 — June 2023

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Images

Figure 1
The effect of scattered light on the cross-polarization-extinction ratio. (a) Black symbols: free-space detected PER for increasing detector distance $d$ from the analyzing polarizer [inset (b) shows a sketch of the experimental configuration]. Blue symbols: extinction measured using single-mode fiber filtering [inset (c) shows the setup]. The black curve is a model fit as described in the main text.
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Figure 2
Polarization extinction and spin-orbit coupling upon multiple reflections. (a)–(c) A series of setups with a different number of optical reflections between the polarizers, (d) the maximum achievable polarization extinction, and (e)–(g) the residual unwanted light pattern measured in cross polarization before coupling into the single-mode fiber, wherein the dashed circle shows the fiber mode before the collimation lens. In (d), the PER as a function of the analyzing polarizer angle $α$ relative to the conventional cross-polarization angle $α_{0} = β \pm π / 2$ is shown. The maximal PER for each configuration with $n$ reflections is indicated.
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Figure 3
Polarization-extinction improvement (blue symbols) by reflection in a nonpolarizing beam splitter in a cryogenic microscope. Shown is the PER as a function of the angle of the analyzing polarizer $α$ relative to the conventional cross-polarization angle $α_{0}$ . (a) First, the case is shown where the cryostat is replaced by a flat mirror, where beyond- $10^{8}$ improvement is obtained. (b) Then the beam is focused into the cryostat and reflected there, and we obtain beyond $10^{7}$ contrast. (c) Finally, the case is shown where a half-wave plate is added before the objective in order to align the linearly polarized cavity modes of the device in the cryostat to the polarization frame of the optical setup.
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Figure 4
Resonant cross-polarized single-quantum-dot spectroscopy for (a) the conventional cross-polarization configuration and (b) the optimized case. Shown is the cross-polarized resonance fluorescence of a negatively charged trion tuned through the cavity resonances by the quantum-confined Stark effect, as a function of laser detuning $Δ f_{l}$ and gate voltage $V_{G}$ . The incident laser light is polarized along the $V$ cavity axis. Dashed lines indicate both cavity resonance frequencies determined by fits of a semiclassical model [41].
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Figure 5
Maximum conventional (without mirror reflection) polarization-extinction ratio for various analyzer types and conditions. The dashed horizontal lines show the PER using a single-mode fiber; the symbols show the PER using a free-space photodetector at various distances $d$ behind P2. As analyzing polarizer, we used a nanoparticle polarizer (red), and a Glan-Thompson polarizer without (black) and with (gray) AR coating. Solid lines show the model fit.
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Figure 6
Polarization-extinction ratio for a different number of reflections for (a) $s$ -polarized and (b) $p$ -polarized incident light, for a Glan-Thompson analyzer (triangles) and a nanoparticle analyzer (squares).
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