Charge Frustration in a Triangular Triple Quantum Dot

Seo, Myung Won; Choi, Hyung Kook; Lee, S.-Y.; Kim, N.; Chung, Yunchul; Sim, Hyun Sub; Umansky, V.; Mahalu, D.

doi:10.1103/physrevlett.110.046803

Cited by 78 publications

(59 citation statements)

References 24 publications

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“…Advances in device size, connectivity and homogeneity are underway as well in the pursuit of scalable quantum computing, the results of which can be directly leveraged. Examples include scalable gate layouts for 1D arrays [37,38] as well as square [39] and triangular [40] geometries, industrial-grade fabrication processes [41] and magnetically quiet 28 Si substrates [42], that open up further possibilities for quantum simulation experiments with quantum dots.…”

Section: Resultsmentioning

confidence: 99%

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

Hensgens

Fujita

Janssen

et al. 2017

Nature

324

329

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Interacting fermions on a lattice can develop strong quantum correlations, which lie at the heart of the classical intractability of many exotic phases of matter [1, 2, 3, 4]. Seminal efforts are underway in the control of artificial quantum systems, that can be made to emulate the underlying Fermi-Hubbard models [5, 6, 7, 8,9,10,11]. Electrostatically confined conduction band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical pure-state initialisation and readily adhere to an engineerable Fermi-Hubbard Hamiltonian [12,13,14,15,16,17,18,19,20,21,22,23]. Until now, however, the substantial electrostatic disorder inherent to solid state has made attempts at emulating Fermi-Hubbard physics on solid-state platforms few and far between [24,25]. Here, we show that for gate-defined quantum dots, this disorder can be suppressed in a controlled manner. Novel insights and a newly developed semi-automated and scalable toolbox allow us to homogeneously and independently dial in the electron filling and nearest-neighbour tunnel coupling. Bringing these ideas and tools to fruition, we realize the first detailed characterization of the collective Coulomb blockade transition [26], which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition [1]. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here show how quantum dots can be used to investigate the physics of ever more complex many-body states.

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Section: Resultsmentioning

confidence: 99%

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

Hensgens

Fujita

Janssen

et al. 2017

Nature

324

329

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“…11-15 Recent nanofabrication techniques have facilitated various geometric configurations of multiple QDs. [16][17][18][19] Multicoupled QDs are considered as variants of a molecule in which spin and charge degrees of freedom play a crucial role through strong electron correlation.Such innovation of the Kondo physics motivates us to study a triangular triple quantum dot (TTQD) as the simplest multiple QD system with a closed loop. 16,18 When the three equivalent QDs form an equilateral triangle, doubly degenerate molecular orbitals of TTQD play the same role as a spin.…”

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confidence: 99%

“…16,18 When the three equivalent QDs form an equilateral triangle, doubly degenerate molecular orbitals of TTQD play the same role as a spin. At half-filling, the TTQD ground state is fourfold-degenerate with respect to both spin and orbital degrees of freedom, namely, SU(4)-symmetric.…”

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confidence: 99%

SU(2)–SU(4) Kondo Crossover and Emergent Electric Polarization in a Triangular Triple Quantum Dot

2016

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We study an orbitally degenerate Kondo effect in a triangular triple quantum dot (TTQD), where the three dots are connected vertically with a single metallic lead through electron tunneling. Both spin and orbital degrees of freedom play an important role in the SU(4) Kondo effect. This is demonstrated by an equilateral TTQD Kondo system at half-filling, by Wilson's numerical renormalization group method. We show how an emergent electric polarization of the TTQD is associated with a crossover from SU(4) to SU(2) symmetry in the low-temperature state. A marked sign reversal of the electric polarization is generated by the fine-tuning of Kondo coupling with degenerate orbitals, which can be utilized to reveal orbital dynamics in the SU(4) Kondo effect.Since Kondo's pioneering work, 1 quantum impurities coupled to conduction electrons have been one of the major issues of strongly correlated electron systems for over half a century. 2-4 Nowadays, the accumulation of knowledge about the Kondo effect in bulk systems is applied to nanoscale or mesoscopic devices such as quantum dots (QDs) and molecular junctions, which extends the frontiers of quantum phenomena. 5-10 Indeed, typical Kondo behavior is observed in the conductance between metallic leads through a single QD, whose quantized energy levels are highly tuned by the gate voltage. 11-15 Recent nanofabrication techniques have facilitated various geometric configurations of multiple QDs. [16][17][18][19] Multicoupled QDs are considered as variants of a molecule in which spin and charge degrees of freedom play a crucial role through strong electron correlation.Such innovation of the Kondo physics motivates us to study a triangular triple quantum dot (TTQD) as the simplest multiple QD system with a closed loop. 16,18 When the three equivalent QDs form an equilateral triangle, doubly degenerate molecular orbitals of TTQD play the same role as a spin. At half-filling, the TTQD ground state is fourfold-degenerate with respect to both spin and orbital degrees of freedom, namely, SU(4)-symmetric. It is expected that the orbital dynamics leads to a highly symmetric SU(4) Kondo effect as a theoretical extension of a conventional spin SU(2) Kondo effect. 2, 3 Previous theoretical studies of TTQD systems have so far paid much attention to a lateral metallic contact that brings about rich Kondo physics related to three-site spin configurations of TTQD. [20][21][22][23][24][25][26][27][28] In such a lateral geometry, it is not practical to search for the SU(4) Kondo effect since the molecular orbital is not classified as a good quantum number. On the other hand, it is more appropriate to investigate a different TTQD system in which each QD is point-contacted vertically with a single lead. In this case, the SU(4) Kondo effect is realized by the C 3 symmetry of TTQD.In a related context, the SU(4) Kondo physics has been frequently studied using carbon nanotube devices whose dynamical properties come from valley degrees of freedom as well as spins, which correspond to the clockwis...

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“…The two-dimensional (2D) arrangement of tunnelcoupled QDs is intriguing for studies on complicated spin correlations including geometrical frustration of energetically degenerate states [1][2][3][4][5] , underlying physics of high critical temperature cuprate superconductors 6 and applications to fault tolerant scalable quantum computing [7][8][9][10] . Triangles and squares with QDs at each apex are the basis for the 2D arrangement.…”

Section: Introductionmentioning

confidence: 99%

“…Triangles and squares with QDs at each apex are the basis for the 2D arrangement. Especially, a triangularshaped triple quantum dot (TTQD) provides the simplest platform for studying the geometrical frustration since the frustration manifests itself even in a single unit cell [1][2][3][4][5] . In all these studies, interdot tunnel coupling is a key parameter.…”

Section: Introductionmentioning

confidence: 99%

A triangular triple quantum dot with tunable tunnel couplings

Noiri

Kawasaki

Otsuka

et al. 2017

Semicond. Sci. Technol.

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Abstract:A two-dimensional arrangement of quantum dots with finite inter-dot tunnel coupling provides a promising platform for studying complicated spin correlations as well as for constructing large-scale quantum computers. Here, we fabricate a tunnel-coupled triangular triple quantum dot with a novel gate geometry in which three dots are defined by positively biasing the surface gates. At the same time, the small area in the center of the triangle is depleted by negatively biasing the top gate placed above the surface gates. The size of the small center depleted area is estimated from the Aharonov-Bohm oscillation measured for the triangular channel but incorporating no gate-defined dots, with a value consistent with the design. With this approach, we can bring the neighboring gate-defined dots close enough to one another to maintain a finite inter-dot tunnel coupling. We finally confirm the presence of the inter-dot tunnel couplings in the triple quantum dot from the measurement of tunneling current through the dots in the stability diagram. We also show that the charge occupancy of each dot and that the inter-dot tunnel couplings are tunable with gate voltages. Keywords:Semiconductor quantum dot, two-dimensional array, tunnel coupling, Aharonov-Bohm oscillation 2 Introduction:

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Charge Frustration in a Triangular Triple Quantum Dot

Cited by 78 publications

References 24 publications

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

SU(2)–SU(4) Kondo Crossover and Emergent Electric Polarization in a Triangular Triple Quantum Dot

A triangular triple quantum dot with tunable tunnel couplings

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