Spin-based all-optical quantum computation with quantum dots: Understanding and suppressing decoherence

Calarco, Tommaso; Datta, Animesh; Федичев, П. О.; Pazy, E.; Zoller, P.

doi:10.1103/physreva.68.012310

Cited by 249 publications

(260 citation statements)

References 68 publications

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“…This means that the blocks D and X D are decoupled from the rest of the system over the relevant timescales. Taken together, these approximations mean that the system can be described with just the portion of the Hamiltonian H total consisting of the blocks G, X (3) and Ω (3) . Since these blocks have significant internal structure themselves, the solution of this problem is still by no means trivial.…”

Section: Light-matter Interactionmentioning

confidence: 99%

“…Since the work of Loss and DiVincenzo [1], there have been a number of proposals on how best to achieve the precise manipulations of such spins required for the operation of quantum logic. See, for example, [2,3,4,5].Whilst interest in electrostatic gating remains strong, the use of lasers has several advantages in this role, most notably speed and control. Despite significant theoretical advances in this direction, there has, as yet, been no experimental demonstration of optically-controlled gating between electron spins in QDs.…”

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confidence: 99%

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confidence: 99%

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Optically controlled logic gates for two spin qubits in vertically coupled quantum dots

Emary

Sham

2007

Phys. Rev. B

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We describe an interaction mechanism between electron spins in a vertically-stacked double quantum dot that can be used for controlled two-qubit operations. This interaction is mediated by excitons confined within, and delocalized over, the double dot. We show that gates equivalent to the √ SWAP gate can be obtained in times much less than the exciton relaxation time and that the negative effects of hole-mixing and spontaneous emission do not seriously affect these results.PACS numbers: 78.67.Hc, 03.67.LxThe spin of an electron confined in a quantum dot (QD) is one of the leading candidates for the realization of a practical qubit. Since the work of Loss and DiVincenzo [1], there have been a number of proposals on how best to achieve the precise manipulations of such spins required for the operation of quantum logic. See, for example, [2,3,4,5].Whilst interest in electrostatic gating remains strong, the use of lasers has several advantages in this role, most notably speed and control. Despite significant theoretical advances in this direction, there has, as yet, been no experimental demonstration of optically-controlled gating between electron spins in QDs.In this paper, we describe an interaction mechanism to achieve just this. This qubit-qubit interaction is mediated by interdot tunnelling of photo-excited carriersan area which has been the subject of significant recent experimental advances [6,7]. Our results are of explicit relevance to the current generation of vertically-stacked self-assembled InAs QDs, but are also easily adaptable to the other dots, including horizontally-coupled ones.The interaction we describe has its origin in the so-called optical-RKKY effect, in which two electron spins are coupled via their exchange interactions with optically-generated excitons in the semiconductor bulk [8]. The coupling effect of these bulk excitons between two electron spins in a double QD was examined in Ref.[9]. Here we consider an interaction mediated, not by bulk excitons, but by a single exciton confined in the same double QD structure. We describe a situation in which the excitonic electron is able to tunnel between the dots and form delocalized 'molecular' states. It is the exchange interaction between this electron and the resident qubit electrons that leads to an optically controlled gating. This gate, although not one of the standard quantum computation (QC) gates, can be used to form a controlled-Z operation when used twice in conjunction with single qubit rotations, and is, in this way, similar to the √ SWAP gate. The main factor limiting the speed with which oper- The lowest electron levels in each dot (labeled 1 and 2) are the two qubit levels and an electron permanently resides in each of them. Laser illumination is tuned such that it creates an exciton in the excited levels of dot A only (levels 3). (c) Due to a tunnel coupling τ34 between the dots and a resonance condition met through the tuning of the gate voltage Vg, the excitonic electron can tunnel back-and-forth. The exchange interaction be...

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Section: Light-matter Interactionmentioning

confidence: 99%

mentioning

confidence: 99%

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Optically controlled logic gates for two spin qubits in vertically coupled quantum dots

Emary

Sham

2007

Phys. Rev. B

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“…For QDs with a harmonic confinement potential in which the carriers are coupled to LA phonons via the deformation potential the phonon spectral density is well approximated by [63,64]: with a strength A and a cut-off frequency ω c determined by the size of the QD. For a spherical QD with equal confinement lengths a for electrons and holes this formula is exact and the parameters are given by…”

Section: Quantum Dot Modelmentioning

confidence: 99%

The role of phonons for exciton and biexciton generation in an optically driven quantum dot

Reiter

Kuhn

Glässl

et al. 2014

J. Phys.: Condens. Matter

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Abstract. For many applications of semiconductor quantum dots in quantum technology a well controlled state preparation of the quantum dot states is mandatory. Since quantum dots are embedded in the semiconductor matrix, the interaction with phonons plays often a major role in the preparation process. In this review, we discuss the influence of phonons on three basically different optical excitation schemes which can be used for the preparation of exciton, biexciton, and superposition states: a resonant excitation leading to Rabi rotations in the excitonic system, an excitation with chirped pulses exploiting the effect of adiabatic rapid passage, and an off-resonant excitation giving rise to a phononassisted state preparation. We give an overview over experimental and theoretical results showing the role of the phonons and compare the performance of the schemes for state preparation.

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“…Theoretically, the absorption and emission spectra can be computed using the energy levels of donor and acceptor and the line shape function. The latter is dependent on the spectral density which describes the coupling to phonons [12]. We focus on dielectric effects and the matrix element.…”

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confidence: 99%

Förster Coupling in Nanoparticle Excitonic Circuits

2010

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Exciton transport in semiconductor nanoparticles underlies recent experiments on electrically controlled excitonic circuits and proposals for new artificial light-harvesting systems. In this work, we develop a new method for the numerical evaluation of the Förster matrix element, based on a three-dimensional real space grid and the self-consistent solution of the mesoscopic exciton in a macroscopic dielectric environment. This method enables the study of the role of the nanoparticle shape, spatially varying dielectric environment, and externally applied electric fields. Depending on the orientation of the transition dipole, the Förster coupling is shown to be either increased or decreased as a function of the nanoparticle shape and of the properties of the dielectric environment. In the presence of an electric field, we investigate the relation between excitonic binding and confinement effects. We also study a type II core-shell quantum dot where electron and hole are spatially separated due to a particular configuration of the bandstructure.

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Spin-based all-optical quantum computation with quantum dots: Understanding and suppressing decoherence

Cited by 249 publications

References 68 publications

Optically controlled logic gates for two spin qubits in vertically coupled quantum dots

Optically controlled logic gates for two spin qubits in vertically coupled quantum dots

The role of phonons for exciton and biexciton generation in an optically driven quantum dot

Förster Coupling in Nanoparticle Excitonic Circuits

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