Spin Relaxation Quenching in Semiconductor Quantum Dots

Paillard, M.; Marie, X.; Renucci, Pierre; Amand, T.; Jbeli, A.; Gérard, Jean‐Michel

doi:10.1103/physrevlett.86.1634

Cited by 412 publications

(379 citation statements)

References 25 publications

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“…[3] While some of the idealizations of the original proposal are well fulfilled, for example, for strongly confined self-assembled (In,Ga)As/GaAs quantum dots (such as the long exciton spin relaxation time as com- pared to the radiative lifetime [4], or the almost pure heavy-hole character of the valence band ground state [6]), a fundamental problem arises from the broken D 2d symmetry, which is reduced to at least C 2v or even lower symmetry in realistic dot structures. [7,8,9] As a consequence, angular momentum is no longer a good quantum…”

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confidence: 99%

“…pared to the radiative lifetime [4], or the almost pure heavy-hole character of the valence band ground state [6]), a fundamental problem arises from the broken D 2d symmetry, which is reduced to at least C 2v or even lower symmetry in realistic dot structures. [7,8,9] As a consequence, angular momentum is no longer a good quantum number and the ± 1 excitons become mixed to linearly polarized eigenstates, resulting in an energy splitting δ 1 of the bright exciton doublet (see Fig.…”

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Tailored quantum dots for entangled photon pair creation

et al. 2006

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We compare the asymmetry-induced exchange splitting δ1 of the bright-exciton ground-state doublet in self-assembled (In,Ga)As/GaAs quantum dots, determined by Faraday rotation, with its homogeneous linewidth γ, obtained from the radiative decay in time-resolved photoluminescence. Post-growth thermal annealing of the dot structures leads to a considerable increase of the homogeneous linewidth, while a strong reduction of the exchange splitting is simultaneously observed. The annealing can be tailored such that δ1 and γ become comparable, whereupon the carriers are still well confined. This opens the possibility to observe polarization entangled photon pairs through the biexciton decay cascade.PACS numbers: 71.36.+c, 73.20.Dx, 78.47.+p, Entangled photon pairs are a key requirement for the implementation of quantum teleportation schemes.[1] Typically, such photon pairs are created by parametric down conversion of a strongly attenuated laser beam in a non-linear optical crystal, with limited efficiency. Recently, the decay of a biexciton complex confined in a quantum dot (QD) has been suggested as an efficient source for polarization entangled photon pairs.[2] This concept was based on the assumption of an idealistic QD structure for which the valence band ground state has pure heavy hole character with angular momentum projections J h,z = ±3/2 along the heterostructure growth direction. When an electron-hole pair is injected, the momenta of the carriers become coupled by the exchange interaction. If the dot has perfect D 2d -symmetry, angular momentum is a good quantum number: the optically active states with momenta M = ±1 are degenerate, and their decay leads to emission of σ ± -circularly polarized photons.If the dot ground states are occupied by two electrons and two holes, each with opposite spin orientations, a spin singlet biexciton X 2 is formed, for whose decay two channels exist, as shown in Fig. 1 (upper panel left). The first photon is emitted with either σ + or σ − -polarization, and then the second photon with opposite polarization, as long as no spin flip occurs after the first process. Unless a polarization measurement is performed, the two photon polarization state is therefore described by2, forming an entangled state. A key requirement is that the photons emitted at each stage of the cascade are quasi-degenerate within their homogeneous linewidth, such that they cannot be distinguished by an energy measurement.Experiments have failed up to now to demonstrate such an entanglement, as only classical correlations were observed.[3] While some of the idealizations of the original proposal are well fulfilled, for example, for strongly confined self-assembled (In,Ga)As/GaAs quantum dots (such as the long exciton spin relaxation time as com- pared to the radiative lifetime [4], or the almost pure heavy-hole character of the valence band ground state [6]), a fundamental problem arises from the broken D 2d symmetry, which is reduced to at least C 2v or even lower symmetry in realistic dot structures. [7,8,...

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Tailored quantum dots for entangled photon pair creation

et al. 2006

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confidence: 69%

“…Hyperfine interactions of confined carriers with nuclear spins of host lattice atoms within QDs [2,3] and carrier-carrier exchange interaction [4] become the dominant spin relaxation mechanisms at low temperatures. The expected extended carrier spin lifetimes have been confirmed experimentally [5][6][7][8], and efficient room-temperature spin detection has also recently been demonstrated [9], which is encouraging for proposals of QDs in applications of quantum computing [10] and spintronic devices such as spin light-emitting devices [11]. Multiple QD structures have been proposed for creating entangled photon pairs, due to their separated biexciton state [12], which may simplify separate extraction of the two entangled photons.…”

Section: Introductionmentioning

confidence: 93%

Effects of a longitudinal magnetic field on spin injection and detection in InAs/GaAs quantum dot structures

Beyer¹,

Wang²,

Buyanova³

et al. 2012

J. Phys.: Condens. Matter

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Abstract. Effects of a longitudinal magnetic field on optical spin injection and detection in InAs/GaAs quantum dot (QD) structures are investigated by optical orientation spectroscopy. An increase in optical and spin polarization of the QDs is observed with increasing magnetic field in the range of 0-2 T, and is attributed to suppression of exciton spin depolarization within the QDs that is promoted by hyperfine interaction and anisotropic electron-hole exchange interaction. This leads to a corresponding enhancement in spin detection efficiency of the QDs by a factor of up to 2.5. At higher magnetic fields when these spin depolarization processes are quenched, electron spin polarization in anisotropic QD structures (such as double QDs that are preferably aligned along a specific crystallographic axis) still exhibits rather strong field dependence under non-resonant excitation. In contrast, such field dependence is practically absent in more "isotropic" QD structures (e.g. single QDs). We attribute the observed effect to stronger electron spin relaxation in the spin injectors (i.e. wetting layer and GaAs barriers) of the lower-symmetry QD structures, which also explains the lower spin injection efficiency observed in these structures.PACS numbers: 73.21. La, 78.67.Hc, 72.25.Fe, 72.25.Rb IntroductionSemiconductor quantum dot (QD) structures are currently under intense investigations in view of their potential applications in spin-based quantum information technology and nanospintronics, as the three-dimensional carrier confinement in these structures promises suppression of many spin relaxation mechanisms that are predominant in semiconductors of higher dimensionality [1]. In threeand two-dimensional structures, the most important spin relaxation mechanisms such as the D'yakonov-Perel and Elliott-Yafet mechanisms are promoted by the motion of carriers. For confined carriers in QDs, the lack of carrier motion efficiently deactivates these spin relaxation mechanisms. Furthermore, their atomic-like, discrete energy level structure restricts efficiency of phonon-induced inelastic scattering processes. Hyperfine interactions of confined carriers with nuclear spins of host lattice atoms within QDs [2,3] and carrier-carrier exchange interaction [4] become the dominant spin relaxation mechanisms at low temperatures. The expected extended carrier spin lifetimes have been confirmed experimentally [5][6][7][8], and efficient room-temperature spin detection has also recently been demonstrated [9], which is encouraging for proposals of QDs in applications of quantum computing

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“…Two further exciton states with angular momenta ±2 can be formed from the lowest single particle states, which are usually referred to as dark excitons as they cannot be excited directly by the laser field. A relaxation into these dark states requires spin flip processes that take place on a time scale of typically longer than a nanosecond [28,29,30] or relaxation from energetically higher excited states [31]. Therefore, they are not relevant for state preparation schemes occurring on a time scale of at most a few tens of picoseconds and will not be considered in this review.…”

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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Spin Relaxation Quenching in Semiconductor Quantum Dots

Cited by 412 publications

References 25 publications

Tailored quantum dots for entangled photon pair creation

Tailored quantum dots for entangled photon pair creation

Effects of a longitudinal magnetic field on spin injection and detection in InAs/GaAs quantum dot structures

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

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