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Krizhanovskii, D. N.; Ebbens, A.; Tartakovskii, A. I.; Pulizzi, Fabio; Wright, T.; Skolnick, M. S.; Hopkinson, M.

doi:10.1103/physrevb.72.161312

Cited by 67 publications

(54 citation statements)

References 27 publications

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“…This allows us to extract for the dot in Fig. 2A η ≈ 0.57 and a strong mixing |β| = 0.25 which lies within the typical range 0.16 < |β| < 0.3 for strain free dots in our samples, compared to 0.2 < |β| < 0.7 reported for strained InAs, CdSe and CdTe dots [11][12][13].…”

supporting

confidence: 69%

Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

Belhadj

Amand

Kunold

et al. 2010

Applied Physics Letters

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We report strong heavy hole-light mixing in GaAs quantum dots grown by droplet epitaxy. Using the neutral and charged exciton emission as a monitor we observe the direct consequence of quantum dot symmetry reduction in this strain free system. By fitting the polar diagram of the emission with simple analytical expressions obtained from k·p theory we are able to extract the mixing that arises from the heavy-light hole coupling due to the geometrical asymmetry of the quantum dot. A large variety of promising applications for self assembled semiconductor quantum dots in photonics and spin electronics are based on the discreteness of the interband transitions [1] and on long carrier spin relaxation times [2,3]. Combining the two characteristics allows electrical tuning of the light polarization of single photon emitters based on quantum dots [4]. Optical preparation, manipulation and read-out of a single spin state [5][6][7][8] are governed by the optical selection rules [9,10]. For excitons based on pure angular momentum eigenstates for electrons (m s = ±1/2) and for heavy holes (m j = ±3/2), a given light polarization can be associated unambiguously with the optical creation of a certain spin state (solid arrows in the inset of Fig. 1). In the common case of [100] growth (defining the quantization axis z) the symmetry of the bulk semiconductor implies that the x and y axis, [110] and [110], are equivalent (D 2d ). The conduction electron is well described as an isotropic particle of spin ±1/2. In contrast, valence hole states are non-isotropic as the x-y equivalence is lifted in realistic dots due to strain and/or shape and in plane anisotropy [11]. Despite being separated in energy by tens of meV (∆ HL in the inset of Fig. 1), substantial mixing between valence heavy hole and light hole (HH-LH) states has been reported in strained II-VI and III-V quantum dots [11][12][13][14][15]. The resulting non pure selection rules in combination with long carrier relaxation times have allowed the implementation of very original, high fidelity (≥ 99%) electron and hole spin initialization schemes [16,17]. In addition, HH-LH mixing has been identified as the key parameter at the origin of the dipole-dipole nuclear spin mediated hole spin dephasing in quantum dots [14,18]. The dominant physical origin of HH-LH mixing has been attributed to lattice strain [11,12,19].This was our motivation to study strain free, individual GaAs/AlGaAs quantum dots by molecular droplet epitaxy [20][21][22][23], see [24] for alternative growth method. We performed detailed, angle dependent polarization analysis of the photoluminescence (PL) emitted parallel to the quantum dot growth direction. We observe, even in the absence of strain, strong evidence for HH-LH mixing revealed in the emission of the positively charged exciton X + (trion: 2 valence holes + 1 conduction electron) and the neutral exciton X 0 (1 hole + 1 electron). Our experiments show that (i) an asymmetry in the confinement potential due to quantum dot elongation (ii) the main axis ...

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supporting

confidence: 69%

Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

Belhadj

Amand

Kunold

et al. 2010

Applied Physics Letters

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“…Heavy-light hole mixing [86][87][88] introduces a smaller off-diagonal part ∝Ŝ h,+Î− +Ŝ h,−Î+ and an even smaller …”

Section: B General Feedback Processes Between Electron Hole and Numentioning

confidence: 99%

General theory of feedback control of a nuclear spin ensemble in quantum dots

Yang

Sham

2013

Phys. Rev. B

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We present a microscopic theory of the nonequilibrium nuclear spin dynamics driven by the electron and/or hole under continuous-wave pumping in a quantum dot. We show the correlated dynamics of the nuclear spin ensemble and the electron and/or hole under optical excitation as a quantum feedback loop and investigate the dynamics of the many nuclear spins as a nonlinear collective motion. This gives rise to three observable effects: (i) hysteresis, (ii) locking (avoidance) of the pump absorption strength to (from) the natural resonance, and (iii) suppression (amplification) of the fluctuation of weakly polarized nuclear spins, leading to prolonged (shortened) electron-spin coherence time. A single nonlinear feedback function is constructed which determines the different outcomes of the three effects listed above depending on the feedback being negative or positive. The general theory also helps to put in perspective the wide range of existing theories on the problem of a single electron spin in a nuclear spin bath.

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“…not prevent heavy-hole-light-hole coupling 20,21 . Heavy-hole-light-hole coupling is an experimental fact [22][23][24][25] , revealed by deviations in the optical selection rules from the heavy-hole limit. For strained InGaAs quantum dots, the light-hole accounts for 5 − 10% of the hole state 22,24,25 .…”

mentioning

confidence: 99%

Decoupling a hole spin qubit from the nuclear spins

Prechtel¹,

Kuhlmann²,

Houel³

et al. 2016

Nature Mater

107

106

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A huge effort is underway to develop semiconductor nanostructures as low noise hosts for qubits. The main source of dephasing of an electron spin qubit in a GaAs-based system is the nuclear spin bath 1-3 . A hole spin may circumvent the nuclear spin noise 4 . In principle, the nuclear spins can be switched off for a pure heavy-hole spin 4-6 . In practice, it is unknown to what extent this ideal limit can be achieved. A major hindrance is that p-type devices are often far too noisy. We investigate here a single hole spin in an InGaAs quantum dot embedded in a new generation of low-noise p-type device. We measure the hole Zeeman energy in a transverse magnetic field with 10 neV resolution by dark state spectroscopy as we create a large transverse nuclear spin polarization. The hole hyperfine interaction is highly anisotropic: the transverse coupling is < 1% of the longitudinal coupling. For unpolarized, randomly fluctuating nuclei, the ideal heavy-hole limit is achieved down to neV energies; equivalently dephasing times up to a µs. The combination of large T * 2 and strong optical dipole 3,7-11 make the single hole spin in a GaAs-based device an attractive quantum platform.A localized, single spin is a small and fast qubit. The exchange interaction between neighbouring spins facilitates two-qubit operations 12 . Implementation in a semiconductor benefits from advanced semiconductor heterostructures and nano-fabrication; implementation in a GaAs-based heterostructure, the cleanest and most versatile semiconductor system, by trapping the spin to a quantum dot also facilitates the creation of a spin-photon interface. A stumbling block is that the nuclear spins in the quantum dot lead to a rapid loss of electron spin coherence (both T 2 and T * 2 processes). This has motivated interest in isotopically-pure silicon, a nuclear spin-free host 13 . However, the large effective mass of a conduction electron in Si demands much smaller structures and lower operating temperatures; the valley degeneracy is an additional complication 14 ; the strong

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Individual neutral and chargedInxGa1−xAs−GaAsquantum dots wit

Cited by 67 publications

References 27 publications

Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

General theory of feedback control of a nuclear spin ensemble in quantum dots

Decoupling a hole spin qubit from the nuclear spins

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