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Frontiers of Physics

ISSN 2095-0462

ISSN 2095-0470(Online)

CN 11-5994/O4

Postal Subscription Code 80-965

2018 Impact Factor: 2.483

Front. Phys.    2023, Vol. 18 Issue (1) : 13310    https://doi.org/10.1007/s11467-022-1225-7
RESEARCH ARTICLE
Demonstration and operation of quantum harmonic oscillators in an AlGaAs−GaAs heterostructure
Guangqiang Mei, Pengfei Suo, Li Mao, Min Feng, Limin Cao()
School of Physics and Technology, Center for Nanoscience and Nanotechnology, and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Wuhan University, Wuhan 430072, China
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Abstract

The quantum harmonic oscillator (QHO), one of the most important and ubiquitous model systems in quantum mechanics, features equally spaced energy levels or eigenstates. Here we present a new class of nearly ideal QHOs formed by hydrogenic substitutional dopants in an AlGaAs/GaAs heterostructure. On the basis of model calculations, we demonstrate that, when a δ-doping Si donor substitutes the Ga/Al lattice site close to AlGaAs/GaAs heterointerface, a hydrogenic Si QHO, characterized by a restoring Coulomb force producing square law harmonic potential, is formed. This gives rise to QHO states with energy spacing of ~8−9 meV. We experimentally confirm this proposal by utilizing gate tuning and measuring QHO states using an aluminum single-electron transistor (SET). A sharp and fast oscillation with period of ~7−8 mV appears in addition to the regular Coulomb blockade (CB) oscillation with much larger period, for positive gate biases above 0.5 V. The observation of fast oscillation and its behavior is quantitatively consistent with our theoretical result, manifesting the harmonic motion of electrons from the QHO. Our results might establish a general principle to design, construct and manipulate QHOs in semiconductor heterostructures, opening future possibilities for their quantum applications.

Keywords quantum harmonic oscillator      AlGaAs/GaAs semiconductor heterostructure      single-electron transistor      gate tuning     
Corresponding Author(s): Limin Cao   
Issue Date: 23 November 2022
 Cite this article:   
Guangqiang Mei,Pengfei Suo,Li Mao, et al. Demonstration and operation of quantum harmonic oscillators in an AlGaAs−GaAs heterostructure[J]. Front. Phys. , 2023, 18(1): 13310.
 URL:  
https://academic.hep.com.cn/fop/EN/10.1007/s11467-022-1225-7
https://academic.hep.com.cn/fop/EN/Y2023/V18/I1/13310
Fig.1  Schematics of model calculations for the formation of a hydrogenic Si QHO in AlGaAs/GaAs heterostructure. (a) A hydrogen-like Si+ center is formed resulting from the released valence electron being trapped in the heterointerface quantum well. (b) Under external stimulus, such as an electric field, an electron may re-fill the lowest hydrogen-like orbit, forming the neutral hydrogen-like Si atom. Under its ground state, the electron forms the diffuse electron cloud within the spatial extent of radial radius R=1.5R1, here R1 is the effective Bohr radius. (c) A small displacement between the electron cloud center (denoted by O) and Si+ nucleus introduces a restoring Coulomb force that is proportional to displacement resembling the Hooke harmonic oscillator. The harmonic restoring force gives rise to an inherent square law potential, which is the signature of a QHO for a microscopic quantum system.
Fig.2  Schematic of the SET-QHO device architecture. The SET is fabricated on the surface of AlGaAs/GaAs 2DEG heterostructure substrate. The hydrogenic QHOs take place in the Si δ-doping layer. The SET is capacitively coupled to the hydrogen-like Si QHOs beneath the surface. The gate electrodes are used to tune the potentials of both SET and QHOs, and manipulate and operate them simultaneously. S, D, and Gate denote the source, drain, and gate electrodes, respectively.
Fig.3  SEM image of the typical device design for the detection and operation of QHOs. D1(2) and S1(2) denote the drain and source terminals of SET1(2), and G1T(B) and G2T(B) denote the top and bottom gates of SET1(2), respectively.
Fig.4  Conductance oscillations versus gate bias applied to top gate. (a) Current passing through SET1 as a function of the gate bias, VG1T, applied to top gate G1T. The drain-source bias, VDS1, is fixed at 0.2 mV for the measurements. (b) Zoomed-in view of the fast oscillation region showing rather uniform and equally spaced resonance peaks with average period of ~7.4 mV. However, the spacing between the 1st and 2nd peaks is ~11.4 mV, about ~1.54 times that of average value. (c) The spacing between neighboring peaks versus peak position.
Fig.5  Conductance oscillations versus gate bias applied to bottom gate. (a) Current through SET1 as a function of the bottom gate bias, VG1B, at fixed drain-source bias of 0.2 mV. (b) Zoomed-in view of the fast oscillation region showing evenly spaced resonance peaks with average period of ~7.5 mV. The spacing between the 1st and 2nd peaks is ~11.7 mV, about ~1.56 times that of average value. (c) The spacing between neighboring peaks versus peak position.
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