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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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Spectroscopy of excited states in QD helium and lithium.(a, b) Charging spectra for tunnelling into the two- and three-electron final states, respectively, taken at the shortest possible time delay t=0.5 ms. The initial states, prepared by appropriately setting Vini, are depicted in the upper left corner of each panel. The electron configurations, drawn above the measured resonances, are taken from a comparison with theoretical calculations. For QD helium, we observe the lowest resonance at Vp=−0.53 V caused by tunnelling into the two-electron ground state (GS) s2. Around −0.25 V, a double-peak structure is seen corresponding to tunnelling into the p-shell. The splitting is caused by the difference in exchange energy between the triplet (Vp=−0.26 V) and the singlet (Vp=−0.2 V) excited state. Three further resonances can be identified around +0.1 V, which are caused by tunnelling into the excited d-shell. For QD lithium, also a clear separation between tunnelling into ground and excited states is possible. Through comparison with the calculated spectrum, the fine structure can be identified as the first four excited states of the three-electron system.
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f3: Spectroscopy of excited states in QD helium and lithium.(a, b) Charging spectra for tunnelling into the two- and three-electron final states, respectively, taken at the shortest possible time delay t=0.5 ms. The initial states, prepared by appropriately setting Vini, are depicted in the upper left corner of each panel. The electron configurations, drawn above the measured resonances, are taken from a comparison with theoretical calculations. For QD helium, we observe the lowest resonance at Vp=−0.53 V caused by tunnelling into the two-electron ground state (GS) s2. Around −0.25 V, a double-peak structure is seen corresponding to tunnelling into the p-shell. The splitting is caused by the difference in exchange energy between the triplet (Vp=−0.26 V) and the singlet (Vp=−0.2 V) excited state. Three further resonances can be identified around +0.1 V, which are caused by tunnelling into the excited d-shell. For QD lithium, also a clear separation between tunnelling into ground and excited states is possible. Through comparison with the calculated spectrum, the fine structure can be identified as the first four excited states of the three-electron system.

Mentions: QD hydrogen has already been discussed above (see Fig. 2b). Here, the spectroscopy of the equidistant excited energy levels with a spacing of ħω=52 meV provides valuable input for the theoretical treatment of the many-particle states. The spectrum of QD helium is shown in Figure 3a. We find a resonance at Vp=−0.53 V, which can be identified as tunnelling into the two-electron ground state (GS; s2), in agreement with equilibrium measurements18 and the results in Figure 2. Further resonances can be identified at Vp=−0.26 V and −0.2 V as well as a broad peak around Vp=+0.1 V. QD lithium is shown in Figure 3b, in which Vini=−0.44 V was chosen so that two electrons occupy the lowest (s) shell and the third electron can be injected either into the p- or the d-shell. One resonance is observed at −0.16 V and four further resonances between +0.06 V and +0.4 V.


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)

Spectroscopy of excited states in QD helium and lithium.(a, b) Charging spectra for tunnelling into the two- and three-electron final states, respectively, taken at the shortest possible time delay t=0.5 ms. The initial states, prepared by appropriately setting Vini, are depicted in the upper left corner of each panel. The electron configurations, drawn above the measured resonances, are taken from a comparison with theoretical calculations. For QD helium, we observe the lowest resonance at Vp=−0.53 V caused by tunnelling into the two-electron ground state (GS) s2. Around −0.25 V, a double-peak structure is seen corresponding to tunnelling into the p-shell. The splitting is caused by the difference in exchange energy between the triplet (Vp=−0.26 V) and the singlet (Vp=−0.2 V) excited state. Three further resonances can be identified around +0.1 V, which are caused by tunnelling into the excited d-shell. For QD lithium, also a clear separation between tunnelling into ground and excited states is possible. Through comparison with the calculated spectrum, the fine structure can be identified as the first four excited states of the three-electron system.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Spectroscopy of excited states in QD helium and lithium.(a, b) Charging spectra for tunnelling into the two- and three-electron final states, respectively, taken at the shortest possible time delay t=0.5 ms. The initial states, prepared by appropriately setting Vini, are depicted in the upper left corner of each panel. The electron configurations, drawn above the measured resonances, are taken from a comparison with theoretical calculations. For QD helium, we observe the lowest resonance at Vp=−0.53 V caused by tunnelling into the two-electron ground state (GS) s2. Around −0.25 V, a double-peak structure is seen corresponding to tunnelling into the p-shell. The splitting is caused by the difference in exchange energy between the triplet (Vp=−0.26 V) and the singlet (Vp=−0.2 V) excited state. Three further resonances can be identified around +0.1 V, which are caused by tunnelling into the excited d-shell. For QD lithium, also a clear separation between tunnelling into ground and excited states is possible. Through comparison with the calculated spectrum, the fine structure can be identified as the first four excited states of the three-electron system.
Mentions: QD hydrogen has already been discussed above (see Fig. 2b). Here, the spectroscopy of the equidistant excited energy levels with a spacing of ħω=52 meV provides valuable input for the theoretical treatment of the many-particle states. The spectrum of QD helium is shown in Figure 3a. We find a resonance at Vp=−0.53 V, which can be identified as tunnelling into the two-electron ground state (GS; s2), in agreement with equilibrium measurements18 and the results in Figure 2. Further resonances can be identified at Vp=−0.26 V and −0.2 V as well as a broad peak around Vp=+0.1 V. QD lithium is shown in Figure 3b, in which Vini=−0.44 V was chosen so that two electrons occupy the lowest (s) shell and the third electron can be injected either into the p- or the d-shell. One resonance is observed at −0.16 V and four further resonances between +0.06 V and +0.4 V.

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
Related in: MedlinePlus