Electronic Structures and Carrier Correlation in Single Pair of Coupled Quantum Dots

Abstract

The electronic structures and carrier correlation in a single pair of InAs/GaAs coupled quantum dots (QDs) are investigated by performing photoluminescence (PL), one-color photoluminescence excitation (PLE) and two-color PLE measurements. Luminescence from the bonding (X+) and anti-bonding (X-) states due to the wave function coupling was observed in the micro-PL (µ-PL) spectra of the coupled QDs. One-color PLE spectra reveal the electronic structures of the coupled QD system in which there is the coexistence of both common excited level series between the X+ and X- states and individual excited level series for each state. In two-color PLE measurement, the suppression of PLE peak intensity at the energy separation of the longitudinal optical (LO) phonon suggests a carrier correlation through the screening effect of the carrier–LO-phonon interaction in the coupled QD system. Additionally, we demonstrate the control of the energy state in the coupled QDs using two-color excitations.

Pulse Area Control of Exciton Rabi Oscillation in InAs/GaAs Single Quantum Dot

“…For X, several peaks appeared at ÁE ¼ 13, 16, 20, 22, and 22.6 meV (e, e 1 , e 2 , e 3 , and e 4 , respectively) in the region of zero absorption, which are attributed to the excited states of the hole. 11) The peaks located at approximately ÁE ¼ 32 and 35 meV are related to the electronic state resonant of InAs and GaAs 1LO phonon states, respectively. 12) The peaks at ÁE ¼ 37:5 and 40 meV (e 5 and e 6 , respectively) originate from the excitons related to the excited states of the electron.…”

Electronic structures in single pair of InAs∕GaAs coupled quantum dots with various interdot spacings

“…In addition, we fabricated an aluminum aperture mask ͑0.2-0.5 m͒ on the sample surface by an electron-beam lithography technique to enable us to observe the single CQDs by selecting the aperture hole that showed the luminescence of only one CQD. 16 In the macrophotoluminescence ͑macro-PL͒ spectra, the luminescence peak from the QD ensemble ranged from 935 to 955 nm. We did not observe any energy splitting caused by the wave-function coupling in the macro-PL spectra because the QD ensemble had a large size distribution due to the thin InAs layer close to the critical thickness of the dot formation.…”

“…In our previous works, 16 we studied the electronic structures and carrier correlation in a single pair of CQDs with narrow and wide interdot spacings, but we have not yet provided detailed discussions of the overall electronic structures in CQDs with various interdot spacings. In this paper, we report the overall electronic structures in a single pair of resonantly coupled InAs/ GaAs QD systems with various interdot spacings.…”

Cascade optical excitation of an artificial exciton molecule in a coupled quantum dot

“…However, it is difficult to increase the number of qubits. Therefore, we proposed a 2-qubit quantum logic gate using artificial exciton molecule states, which consists of two different excitons confined in each quantum dot of a CQD [16][17][18][19] for multi-qubit applications. The application of this device to quantum information processing requires the following three technical steps: (1) the creation of a four-level system using four exciton states (a crystal ground state |00> , oneexciton states of |01> and |10>, an artificial exciton molecule state of |11>) in a CQD, (2) the arbitrary control of the probability density, namely the populations and coherences, of four-exciton states by means of cascade optical excitation, and (3) the demonstration of a 2-qubit controlled rotation (CROT) gate.…”

“…In addition, a Ti:sapphire laser providing 4 ps long pulses at a repetition rate of 76 MHz was used for twocolor PL and PLE measurements. The sample fabrication technique and experimental setup have been detailed elsewhere [19].…”