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Applied Physics Letters

Three-level structure design and optically controlled current in coupled quantum dots

Weidong Chu, Suqing Duan, Jia‐Lin Zhu

Published May 28, 2007• 19 citations
Publisher

Abstract

Two-mode photon-assisted transport through coupled nonidentical quantum dots is studied by designing the level structure of the system. It is found that a Λ-type three-level structure can be formed by modulating the shape and size of dots or by applying electric field. Based on the three-level system, current antiresonance phenomenon occurs due to the effect of coherent population trapping. Using the asymmetry of quantum dots, oscillating current can be produced by rotating the polarization direction of linearly polarized microwave.

DOI
10.1063/1.2743906

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Two-mode photon-assisted transport through coupled nonidentical quantum dots is studied by designing the level structure of the system. It is found that a Λ-type three-level structure can be formed by modulating the shape and size of dots or by applying electric field. Based on the three-level system, current antiresonance phenomenon occurs due to the effect of coherent population trapping. Using the asymmetry of quantum dots, oscillating current can be produced by rotating the polarization direction of linearly polarized microwave.
Spectral and squeezing properties of the resonance fluorescence of two coupled quantum dots forming an effective Λ-type three-level structure and connected with two normal metal leads are studied. We assume that one of the dots is driven by a strong light field and find that by modulating the bias voltage and the dot-lead coupling strengths, the electron can be selectively trapped in one of the two dressed states produced by the light field. The trapped electron possesses large coherence, and the resulting unbalanced dressed-state populations can lead to a significant enhancement or suppression of the sidebands in the resonance fluorescence spectrum. Moreover, a wideband squeezing can be generated that may be significantly enhanced by modulating the gate voltage.
We theoretically study the photon-assisted transport (PAT) in a double quantum dot (QD) which is conditionally controlled by the optical excitation in an adjacent QD. Based on a real three-QD model, a double-electron level configuration needed for the conditional PAT is designed. Interesting conditional dynamics are demonstrated for the double QD and its adjacent QD. Depending on various conditional frequencies, the conditional behaviors can be manifested as the current peaks or collapses of the PAT. They correspond to coherent excitations or trapping of double-electron states. Our results present a possible way to optically manipulate electron states and monitor them via the signals of current spectrum.
We theoretically investigate the coherent transfer of one electron between the ground states of a double coupled quantum dot structure. The coherent transfer of the electron is externally controlled by applied electromagnetic fields with on- or close-resonance driving frequencies and various shapes and duration. We derive the analytical expressions for the parameters of the external fields by approximating the quantum dot system as a three-level Λ-type system. The analytical solutions are compared with numerical results and good agreement is found. The control methods developed here are applicable in symmetric and asymmetric quantum dot nanostructures.
We investigate how to control single-photon transport along the photonic crystal waveguide with the recent experimentally demonstrated artificial atoms [i.e., $\ensuremath{\Lambda}$-type quantum dots (QDs)] [S. G. Carter et al., Nat. Photon. 7, 329 (2013)] in an all-optical way. Adopting full quantum theory in real space, we analytically calculate the transport coefficients of single photons scattered by a $\ensuremath{\Lambda}$-type QD embedded in single- and two-mode photonic crystal cavities (PCCs), respectively. Our numerical results clearly show that the photonic transmission properties can be exactly manipulated by adjusting the coupling strengths of waveguide-cavity and QD-cavity interactions. Specifically, for the PCC with two degenerate orthogonal polarization modes coupled to a $\ensuremath{\Lambda}$-type QD with two degenerate ground states, we find that the photonic transmission spectra show three Rabi-splitting dips and the present system could serve as single-photon polarization beam splitters. The feasibility of our proposal with the current photonic crystal technique is also discussed.
Three-level systems exhibit quantum interference effects absent in two-level systems, making them important for quantum optics. Here, we study the coherent interaction of a Lambda-type three-level system with free electrons shaped by optical near fields. By treating the electron train as a quantum drive, we show that the interplay between electron modulation and the three-level system's transition pathways induces tunable interference patterns. This interaction effectively realizes electron-mediated coherent population trapping (CPT). We identify a regime that enables complete population transfer between the two lower states and the preparation of a high-coherence superposition, manifested as dark states. In particular, these driven-dissipative steady states are independent of the initial state. Our work proposes shaped free electrons as a platform for steady-state coherent control of three-level systems, enabling atomic-scale state engineering.
Three-level systems exhibit quantum interference effects absent in two-level systems, making them important for quantum optics. Here, we study the coherent interaction of a Λ-type three-level system with free electrons shaped by optical near fields. By treating the electron train as a quantum drive, we show that the interplay between electron modulation and the three-level system's transition pathways induces tunable interference patterns. This interaction effectively realizes electron-mediated coherent population trapping. We identify a regime that enables complete population transfer between the two lower states and the preparation of a high-coherence superposition, manifested as dark states. In particular, these driven-dissipative steady states are independent of the initial state. Our Letter proposes shaped free electrons as a platform for steady-state coherent control of three-level systems, enabling atomic-scale state engineering.