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

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.

Asymmetry of charge relaxation times in quantum dots: The influence of degeneracy

“…. shell filling sequence has been verified repeatedly [1,4,12,15,28], it was not quite clear whether Hund's rule applies to the filling of the p-shell [18,29] or whether it is lifted by an anisotropy of the confinement potential in the dot [7,9,28]. Our time-resolved transconductance spectroscopy provides an excellent tool to clarify which scenario is realized.…”

“…To monitor the tunneling dynamics between the dot ensemble and the 2DEG, we use a recently developed transconductance spectroscopy technique [14][15][16]. At a time t = 0, a voltage pulse is applied to the gate, and the time-resolved response of the 2DEG conductivity σ(t) is recorded.…”

Time‐resolved detection of many‐particle hole states in InAs/GaAs quantum dots using a two‐dimensional hole gas up to 77 K

“…Due to their discrete density of states and their small sizes self-organized quantum dots (QDs) [3] are ideal systems to study the coupling of confined carriers to an adjacent two-dimensional system (2DEG or 2DHG). QDs facilitate carrier confinement also at temperatures higher than some mK and are also advantageous to study many-particle effects, such as Coulomb charging or spin states in non-equilibrium [4,5] at higher temperatures. Furthermore, QDs are very promising for memory units with nano-scale feature sizes.…”

3 ns single-shot read-out in a quantum dot-based memory structure

“…In this letter, we use the time-resolved transconductance spectroscopy method [11][12][13] to determine the s and p electron charging states of self-organized InAs/GaAs QDs embedded in a modulation-doped field-effect transistor (MODFET). The conductance change of the 2DEG for QDs filled with two or six electrons enables us to detect the charge state in a very fast single-shot experiment, with read times down to $ 3 ns for both charge states.…”

“…The number of electrons stored in the QDs and the corresponding gate voltages were determined before by transconductance spectroscopy (for details, see Refs. [11][12][13]. The charging spectrum for the electrons is shown in Fig.…”