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Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field.

Ghali M, Ohtani K, Ohno Y, Ohno H - Nat Commun (2012)

Bottom Line: Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices.Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field.A forward voltage was applied to a Schottky diode to control the fine-structure splitting.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.

ABSTRACT
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.

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Electric field-dependence of fine-structure splitting energy and QD exciton polarization.(a) Variation of ΔFSS (closed-down triangles) with the electric field. The inset shows a sketch of the biexciton–exciton cascaded emission for E~29 kV cm−1 (ΔFSS~0). (b) Linear polarization dependence of the exciton X at various electric fields (from top): E=−45, 22, 27 and 29.2 kV cm−1, relative to , the sample's crystallographic axis. All polar plots have an axis scale increment of 10 μeV. The solid lines represent a fit to the data with a sinusoidal function. (c) Variation of the exciton polarization angle ϕ with the electric field. The inset describes the angle ϕ relative to the crystal axis . The exciton PL emission cannot be seen when −30<E<−0.2 kV cm−1. (d) Evolution of the degree of exciton PL circular polarization Pc (closed-up triangles) with the electric field. (e) Circular polarization resolved detection σ+ (open-circles) and σ− (closed-squares) of the exciton PL spectra at two different electric fields: 23 kV cm−1 (top) and 29.2 kV cm−1 (bottom).
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f2: Electric field-dependence of fine-structure splitting energy and QD exciton polarization.(a) Variation of ΔFSS (closed-down triangles) with the electric field. The inset shows a sketch of the biexciton–exciton cascaded emission for E~29 kV cm−1 (ΔFSS~0). (b) Linear polarization dependence of the exciton X at various electric fields (from top): E=−45, 22, 27 and 29.2 kV cm−1, relative to , the sample's crystallographic axis. All polar plots have an axis scale increment of 10 μeV. The solid lines represent a fit to the data with a sinusoidal function. (c) Variation of the exciton polarization angle ϕ with the electric field. The inset describes the angle ϕ relative to the crystal axis . The exciton PL emission cannot be seen when −30<E<−0.2 kV cm−1. (d) Evolution of the degree of exciton PL circular polarization Pc (closed-up triangles) with the electric field. (e) Circular polarization resolved detection σ+ (open-circles) and σ− (closed-squares) of the exciton PL spectra at two different electric fields: 23 kV cm−1 (top) and 29.2 kV cm−1 (bottom).

Mentions: The in-plane asymmetry of GaAs QDs is reflected in the polarization anisotropy exhibited by the integrated PL spectra of the exciton and the biexciton. By carefully following the evolution of the exciton and the biexciton PL energies with the polarization angle, we obtained a clear behaviour that could be fitted with a sinusoidal function, from which we extracted ΔFSS. The polarization axis of the PL was determined by the angle that represents the maximum splitting energy, and ΔFSS was measured with an accuracy of 2–3 μeV. Figure 2a shows a clear nonlinear change of ΔFSS with the electric field, where ΔFSS decreased from 38 μeV at E=0 to below our detection limit when the field approached 30 kV cm−1. We studied five quantum dots; three of them showed a similar FSS suppression behaviour with the increase in the electric field. Moreover, on tuning ΔFSS over the measured range of the electric field, we observed a clear rotation of the exciton polarization axis. Figure 2b summarizes the relationship between the electric field and ϕ, which describes the orientation of the exciton polarization axis relative to the crystal axis . We found that as the field increased, the exciton polarization axis continuously rotated from ϕ=90°, where it aligned with the crystal axis [110] at E=−45 kV cm−1, until it approached 45°, and it became independent of the polarization axis at E=29.2 kV cm−1, where ΔFSS was minimized within our detection limit (Fig. 2c). Similar results have recently been reported for InAs/GaAs QDs using a large electric field of up to a few hundred kV cm−1 (ref. 12).


Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field.

Ghali M, Ohtani K, Ohno Y, Ohno H - Nat Commun (2012)

Electric field-dependence of fine-structure splitting energy and QD exciton polarization.(a) Variation of ΔFSS (closed-down triangles) with the electric field. The inset shows a sketch of the biexciton–exciton cascaded emission for E~29 kV cm−1 (ΔFSS~0). (b) Linear polarization dependence of the exciton X at various electric fields (from top): E=−45, 22, 27 and 29.2 kV cm−1, relative to , the sample's crystallographic axis. All polar plots have an axis scale increment of 10 μeV. The solid lines represent a fit to the data with a sinusoidal function. (c) Variation of the exciton polarization angle ϕ with the electric field. The inset describes the angle ϕ relative to the crystal axis . The exciton PL emission cannot be seen when −30<E<−0.2 kV cm−1. (d) Evolution of the degree of exciton PL circular polarization Pc (closed-up triangles) with the electric field. (e) Circular polarization resolved detection σ+ (open-circles) and σ− (closed-squares) of the exciton PL spectra at two different electric fields: 23 kV cm−1 (top) and 29.2 kV cm−1 (bottom).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3293408&req=5

f2: Electric field-dependence of fine-structure splitting energy and QD exciton polarization.(a) Variation of ΔFSS (closed-down triangles) with the electric field. The inset shows a sketch of the biexciton–exciton cascaded emission for E~29 kV cm−1 (ΔFSS~0). (b) Linear polarization dependence of the exciton X at various electric fields (from top): E=−45, 22, 27 and 29.2 kV cm−1, relative to , the sample's crystallographic axis. All polar plots have an axis scale increment of 10 μeV. The solid lines represent a fit to the data with a sinusoidal function. (c) Variation of the exciton polarization angle ϕ with the electric field. The inset describes the angle ϕ relative to the crystal axis . The exciton PL emission cannot be seen when −30<E<−0.2 kV cm−1. (d) Evolution of the degree of exciton PL circular polarization Pc (closed-up triangles) with the electric field. (e) Circular polarization resolved detection σ+ (open-circles) and σ− (closed-squares) of the exciton PL spectra at two different electric fields: 23 kV cm−1 (top) and 29.2 kV cm−1 (bottom).
Mentions: The in-plane asymmetry of GaAs QDs is reflected in the polarization anisotropy exhibited by the integrated PL spectra of the exciton and the biexciton. By carefully following the evolution of the exciton and the biexciton PL energies with the polarization angle, we obtained a clear behaviour that could be fitted with a sinusoidal function, from which we extracted ΔFSS. The polarization axis of the PL was determined by the angle that represents the maximum splitting energy, and ΔFSS was measured with an accuracy of 2–3 μeV. Figure 2a shows a clear nonlinear change of ΔFSS with the electric field, where ΔFSS decreased from 38 μeV at E=0 to below our detection limit when the field approached 30 kV cm−1. We studied five quantum dots; three of them showed a similar FSS suppression behaviour with the increase in the electric field. Moreover, on tuning ΔFSS over the measured range of the electric field, we observed a clear rotation of the exciton polarization axis. Figure 2b summarizes the relationship between the electric field and ϕ, which describes the orientation of the exciton polarization axis relative to the crystal axis . We found that as the field increased, the exciton polarization axis continuously rotated from ϕ=90°, where it aligned with the crystal axis [110] at E=−45 kV cm−1, until it approached 45°, and it became independent of the polarization axis at E=29.2 kV cm−1, where ΔFSS was minimized within our detection limit (Fig. 2c). Similar results have recently been reported for InAs/GaAs QDs using a large electric field of up to a few hundred kV cm−1 (ref. 12).

Bottom Line: Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices.Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field.A forward voltage was applied to a Schottky diode to control the fine-structure splitting.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.

ABSTRACT
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.

Show MeSH
Related in: MedlinePlus