Laterally coupled few-electron quantum dots

Wensauer, Andreas; Steffens, Oliver; Suhrke, Michael; Rößler, U.

doi:10.1103/physrevb.62.2605

Cited by 77 publications

(76 citation statements)

References 23 publications

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“…It can further be concluded that the spontaneous polarization and ferromagnetic ordering predicted for weakly-coupled double QD's in Refs. [13,14] is an artifact of the molecular-orbital structure implicit [32] in the framework of LSD calculations.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, we show that the onset at a moderate interdot barrier or interdot distance d 0 , as well as the permanency for all separations d > d 0 , of spontaneous magnetization and ferromagnetic ordering predicted for Double QD's by local-spin-density (LSD) calculations [13,14] is an artifact of the MO structure implicit in the framework of these density-functional calculations.…”

Section: Introductionmentioning

confidence: 99%

“…A natural extension of this theoretical effort has also developed in the direction of lateral 2D QD Molecules (QDM's, often referred to as artificial molecules), aiming at elucidating [7,10,13,14,15,16] the analogies and differa email: constantine.yannouleas@physics.gatech.edu ences between such artificially fabricated nanostrustures and the natural molecules.…”

Section: Introductionmentioning

confidence: 99%

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Coupling and dissociation in artificial molecules

Yannouleas

Landman

2001

The European Physical Journal D

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Abstract. We show that the spin-and-space unrestricted Hartree-Fock method, in conjunction with the companion step of the restoration of spin and space symmetries via Projection Techniques (when such symmetries are broken), is able to describe the full range of couplings in two-dimensional double quantum dots, from the strong-coupling regime exhibiting delocalized molecular orbitals to the weak-coupling and dissociation regimes associated with a Generalized Valence Bond combination of atomic-type orbitals localized on the individual dots. The weak-coupling regime is always accompanied by an antiferromagnetic ordering of the spins of the individual dots. The cases of dihydrogen (H2, 2e) and dilithium (Li2, 6e) quantum dot molecules are discussed in detail. PACS

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Coupling and dissociation in artificial molecules

Yannouleas

Landman

2001

The European Physical Journal D

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“…As our theory is based on a sophisticated quantum chemistry approach [26], our results should have general qualitative and semi-quantitative validity. There have been several recent theoretical calculations of the ground state spin polarization properties of multielectron quantum dot systems using the density functional theory [27][28][29]. For the purpose of quantum computation of interest to us in this paper, however, the knowledge of the excited states is crucial in determining whether a particular number of electrons can serve as an effective qubit-in particular, we need an accurate evaluation of the singlet-triplet energy splitting in the system.…”

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confidence: 99%

Spin-based quantum computation in multielectron quantum dots

Sarma

2001

Phys. Rev. A

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In a quantum computer the hardware and software are intrinsically connected because the quantum Hamiltonian (or more precisely its time development) is the code that runs the computer. We demonstrate this subtle and crucial relationship by considering the example of electron-spin-based solid state quantum computer in semiconductor quantum dots. We show that multielectron quantum dots with one valence electron in the outermost shell do not behave simply as an effective single spin system unless special conditions are satisfied. Our work compellingly demonstrates that a delicate synergy between theory and experiment (between software and hardware) is essential for constructing a quantum computer.PACS numbers: 03.67. Lx, 85.30.Vw Ever since the pioneering work on quantum computation and quantum error correction [1][2][3][4] To help overcome these difficulties, more theoretical work is needed to explore the optimal operating regimes, figure out the operational constraints and tolerances, and discover potential sources of errors, just to name a few directions [15][16][17][18]. While the optical and atomic physics based architectures have been crucial in demonstrating the proof of principle for quantum computation, it is generally believed that solid state QC architectures, with their obvious advantage of controllable scale-up possibilities, offer the most promising potential for realistic large scale QC hardwares. The fundamental problem plaguing the solid state QC architectures has been the fact that the basic quantum bit (qubit), the QC building block, has not been compellingly demonstrated in any solid state QC architectures, although there is no reason to doubt that they exist in nature. Thus, the construction of successful QC hardwares has faced the somewhat embarrassing dichotomy: the architectures (ion traps, etc.) demonstrating existence of quantum bits cannot be easily scaled up, while the architectures (solid state QCs) which may be easily scaled up have not yet experimentally demonstrated quantum bits! Quantum computation with fermionic spins is considered to be a potentially promising prospect for solid state quantum computers [9][10][11][12]19]. Among the many proposed solid state QC architectures the spin quantum computer has several intrinsic advantages: (1) A fermionic spin, being a quantum two-level system, is a natural qubit with its spin up and down states; (2) it is fairly straightforward to carry out single-qubit operations on spin up and down levels by applying suitable magnetic fields (or through a purely exchange-based scheme [15]); (3) two-qubit operations can, in principle, be carried out rather easily (in theory, at least) by using the exchange interaction between two neighboring spins; (4) quantum spin is fairly robust and does not decohere easily (typical electron spin relaxation times in solids are many orders of magnitude longer [20] than the momentum relaxation time)-in particular, electron spin relaxation times could be microseconds in semiconductors [21].Our work presented in this...

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“…As noted by previous research 4,5,10 , one of the most attractive setup among fewparticle lateral quantum dots is the two-electron case in which the singlet and triplet states can be tuned to be bound into a fourfold degenerate ground state or, depending in the double QD parameters, artificially introducing an energy gap between the singlet and triplet states. This particular characteristic is very similar to that already observed in a two-minima QD subjected to a magnetic field 6 .…”

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confidence: 99%

Electronic correlations in double quantum dots

García

Pietiläinen

Chen

et al. 2008

Physica E: Low-dimensional Systems and Nanostructures

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We present a study of the electronic structure of two laterally coupled Gaussian quantum dots filled with two particles. The exact diagonalization method has been used in order to inspect the spatial correlations and examine the particular spin singlet-triplet configurations for different coupling degrees between quantum dots. The outcome of our research shows this structure to have highly modifiable properties promoting it as an interesting quantum device, showing the possible use of this states as a quantum bit gate.PACS numbers: 73.21. La, The growing significance of mesoscopic quantum dots (QDs) in the development of microelectronic devices attracts great attention, partly due to their promising technological utilization, but also due to their novel quantum properties. These two-dimensional nanostructures offer a high degree of flexibility in their manufacturing process giving as a result a very interesting combination of a highly controllable structure showing quantum effects. Recent advances in the manipulation of electrically defined QDs open a new line of investigation in coupled quantum dots (CQDs) and a very interesting chance for the realization of a solid state implementation of the basic components for quantum computing. The interest on CQDs in the field of quantum computing was brought over since Loss and DiVincenzo proposal 1 on the possibility of an implementation based on the spin states of coupled single-electron quantum dots. Recent studies and experiments 2,3,4,5,6 have proven the feasibility of using the spin degree of freedom in vertically and laterally coupled few-electron QDs as systems in which interactions can be electro-optically tuned and therefore they can potentially taken as candidates for performing quantum operations.It is the purpose of the present paper to present an accurate theoretical study focused on the electronic structure of the two-particle GDQD in the absence of a magnetic field. The exact diagonalization method 7 has been used in order to solve the interacting many-body system as it is a tool of proven reliability for few-particle problems 8 . Electron-electron correlation effects are studied for the different spin superposition states and for a variety of configurations, from a weakly interacting laterally coupled quantum dot molecule to a strongly overlapped situation. The choice of an anisotropic Gaussian confining potential makes it possible to describe a more realistic situation. 4 We will show that not only in vertically coupled QDs interactions can be tuned but also in lateral QDs this effect can be achieved; furthermore, this systems could actually be used as dynamically tunable two-level systems.As shown in our previous research 9 , the special behavior of a GDQD filled with two electrons makes it a very promising arrangement for the creation of a dynamically tunable quantum gate. As noted by previous research 4,5,10 , one of the most attractive setup among fewparticle lateral quantum dots is the two-electron case in which the singlet and triplet states can b...

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Laterally coupled few-electron quantum dots

Cited by 77 publications

References 23 publications

Coupling and dissociation in artificial molecules

Coupling and dissociation in artificial molecules

Spin-based quantum computation in multielectron quantum dots

Electronic correlations in double quantum dots

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