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Transport spectroscopy of non-equilibrium many-particle spin states in self-assembled quantum dots.

Marquardt B, Geller M, Baxevanis B, Pfannkuche D, Wieck AD, Reuter D, Lorke A - Nat Commun (2011)

Bottom Line: For these systems, great progress has been made in addressing spin states by optical means.The excitation spectra of the one- (QD hydrogen), two- (QD helium) and three- (QD lithium) electron configuration are shown and compared with calculations using the exact diagonalization method.An exchange splitting of 10 meV between the excited triplet and singlet spin states is observed in the QD helium spectrum.

View Article: PubMed Central - PubMed

Affiliation: Fakultät für Physik and CeNIDE, Universität Duisburg-Essen, Lotharstraße 1, Duisburg 47048, Germany.

ABSTRACT
Self-assembled quantum dots (QDs) are prominent candidates for solid-state quantum information processing. For these systems, great progress has been made in addressing spin states by optical means. In this study, we introduce an all-electrical measurement technique to prepare and detect non-equilibrium many-particle spin states in an ensemble of self-assembled QDs at liquid helium temperature. The excitation spectra of the one- (QD hydrogen), two- (QD helium) and three- (QD lithium) electron configuration are shown and compared with calculations using the exact diagonalization method. An exchange splitting of 10 meV between the excited triplet and singlet spin states is observed in the QD helium spectrum. These experiments are a starting point for an all-electrical control of electron spin states in self-assembled QDs above liquid helium temperature.

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Time evolution of the QD charging spectrum.(a) Coloured surface plot of dΔISD/dVp—corresponding to the QD states—as a function of time and pulse bias Vp. The initial bias is set so that the QDs are empty at t=0. The inset in (a) illustrates the harmonic model potential, together with the common labels for the QD states and their angular momentum m. (b–e) show the charging spectra for different time delays. The electron configurations of the final states, obtained from a comparison between measured and calculated energies, is depicted above the different resonances. For the shortest possible time delay of 0.5 ms (b), the data exhibit roughly equidistant charging peaks, as expected from the single-particle harmonic oscillator model. At around t=3 ms (c), many-particle charging peaks start to appear, and tunnelling into the ground and excited states of the two-electron system ('QD helium') is visible at Vp=−0.53 V and Vp=−0.26 V, respectively. An additional structure at Vp=−0.4 V (d) is caused by a phonon replica of the lowest single-electron charging process. At t=10 ms (e), the system is close to equilibrium and the charging peaks resemble those found in capacitance spectroscopy, with two s-states (s1 and s2 separated by the Coulomb energy) and a broad structure with the four p-states.
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f2: Time evolution of the QD charging spectrum.(a) Coloured surface plot of dΔISD/dVp—corresponding to the QD states—as a function of time and pulse bias Vp. The initial bias is set so that the QDs are empty at t=0. The inset in (a) illustrates the harmonic model potential, together with the common labels for the QD states and their angular momentum m. (b–e) show the charging spectra for different time delays. The electron configurations of the final states, obtained from a comparison between measured and calculated energies, is depicted above the different resonances. For the shortest possible time delay of 0.5 ms (b), the data exhibit roughly equidistant charging peaks, as expected from the single-particle harmonic oscillator model. At around t=3 ms (c), many-particle charging peaks start to appear, and tunnelling into the ground and excited states of the two-electron system ('QD helium') is visible at Vp=−0.53 V and Vp=−0.26 V, respectively. An additional structure at Vp=−0.4 V (d) is caused by a phonon replica of the lowest single-electron charging process. At t=10 ms (e), the system is close to equilibrium and the charging peaks resemble those found in capacitance spectroscopy, with two s-states (s1 and s2 separated by the Coulomb energy) and a broad structure with the four p-states.

Mentions: Figure 2a displays a three-dimensional plot of dΔISD/dVp spectra for a transient time t between 0.5 ms and 10 ms. The initial bias is set to Vini=−0.9 V, so that the dots are completely empty before Vp is applied. The data demonstrates how the QD states in the ensemble evolves, as the dots are filled subsequently with up to six electrons.


Transport spectroscopy of non-equilibrium many-particle spin states in self-assembled quantum dots.

Marquardt B, Geller M, Baxevanis B, Pfannkuche D, Wieck AD, Reuter D, Lorke A - Nat Commun (2011)

Time evolution of the QD charging spectrum.(a) Coloured surface plot of dΔISD/dVp—corresponding to the QD states—as a function of time and pulse bias Vp. The initial bias is set so that the QDs are empty at t=0. The inset in (a) illustrates the harmonic model potential, together with the common labels for the QD states and their angular momentum m. (b–e) show the charging spectra for different time delays. The electron configurations of the final states, obtained from a comparison between measured and calculated energies, is depicted above the different resonances. For the shortest possible time delay of 0.5 ms (b), the data exhibit roughly equidistant charging peaks, as expected from the single-particle harmonic oscillator model. At around t=3 ms (c), many-particle charging peaks start to appear, and tunnelling into the ground and excited states of the two-electron system ('QD helium') is visible at Vp=−0.53 V and Vp=−0.26 V, respectively. An additional structure at Vp=−0.4 V (d) is caused by a phonon replica of the lowest single-electron charging process. At t=10 ms (e), the system is close to equilibrium and the charging peaks resemble those found in capacitance spectroscopy, with two s-states (s1 and s2 separated by the Coulomb energy) and a broad structure with the four p-states.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105341&req=5

f2: Time evolution of the QD charging spectrum.(a) Coloured surface plot of dΔISD/dVp—corresponding to the QD states—as a function of time and pulse bias Vp. The initial bias is set so that the QDs are empty at t=0. The inset in (a) illustrates the harmonic model potential, together with the common labels for the QD states and their angular momentum m. (b–e) show the charging spectra for different time delays. The electron configurations of the final states, obtained from a comparison between measured and calculated energies, is depicted above the different resonances. For the shortest possible time delay of 0.5 ms (b), the data exhibit roughly equidistant charging peaks, as expected from the single-particle harmonic oscillator model. At around t=3 ms (c), many-particle charging peaks start to appear, and tunnelling into the ground and excited states of the two-electron system ('QD helium') is visible at Vp=−0.53 V and Vp=−0.26 V, respectively. An additional structure at Vp=−0.4 V (d) is caused by a phonon replica of the lowest single-electron charging process. At t=10 ms (e), the system is close to equilibrium and the charging peaks resemble those found in capacitance spectroscopy, with two s-states (s1 and s2 separated by the Coulomb energy) and a broad structure with the four p-states.
Mentions: Figure 2a displays a three-dimensional plot of dΔISD/dVp spectra for a transient time t between 0.5 ms and 10 ms. The initial bias is set to Vini=−0.9 V, so that the dots are completely empty before Vp is applied. The data demonstrates how the QD states in the ensemble evolves, as the dots are filled subsequently with up to six electrons.

Bottom Line: For these systems, great progress has been made in addressing spin states by optical means.The excitation spectra of the one- (QD hydrogen), two- (QD helium) and three- (QD lithium) electron configuration are shown and compared with calculations using the exact diagonalization method.An exchange splitting of 10 meV between the excited triplet and singlet spin states is observed in the QD helium spectrum.

View Article: PubMed Central - PubMed

Affiliation: Fakultät für Physik and CeNIDE, Universität Duisburg-Essen, Lotharstraße 1, Duisburg 47048, Germany.

ABSTRACT
Self-assembled quantum dots (QDs) are prominent candidates for solid-state quantum information processing. For these systems, great progress has been made in addressing spin states by optical means. In this study, we introduce an all-electrical measurement technique to prepare and detect non-equilibrium many-particle spin states in an ensemble of self-assembled QDs at liquid helium temperature. The excitation spectra of the one- (QD hydrogen), two- (QD helium) and three- (QD lithium) electron configuration are shown and compared with calculations using the exact diagonalization method. An exchange splitting of 10 meV between the excited triplet and singlet spin states is observed in the QD helium spectrum. These experiments are a starting point for an all-electrical control of electron spin states in self-assembled QDs above liquid helium temperature.

Show MeSH