Tomographic analysis demonstrates that the polarization state of pairs photons emitted from a biexciton decay cascade becomes entangled when spectral filtering is applied. The measured density matrix photon pair satisfies Peres criterion for entanglement by more than 3 standard deviations experimental uncertainty and violates Bell's inequality. We show erases "which path" information contained in photons' color remanent quantum dot degrees freedom negligible.

We have succeeded in fabricating a two-dimensional electron gas (2DEG) on the cleaved (110) edge of GaAs wafer by molecular beam epitaxy (MBE). A (100) previously prepared MBE growth is reinstalled chamber so that an situ cleave exposes fresh for further overgrowth. sequence Si-doped AlGaAs layers completes modulation-doped structure at edge. Mobilities as high 6.1×105 cm2/V s are measured 2DEG interface.

Weaving an entangled cluster Entanglement is a powerful resource for quantum computation and information processing. One requirement the ability to entangle multiple particles reliably. Schwartz et al. created on-demand state of several photons by addressing dot with sequence laser pulses (see Perspective Briegel). They used internal dot, dark exciton, its association another state, biexciton, weave successive into cluster, generating entanglement between up five photons. Science , this...

Abstract Entanglement between particles is a basic concept of quantum sciences. The ability to produce entangled in controllable manner essential for any technology. light (photons) particularly crucial communication due light’s non-interactive nature and long-lasting coherence. Resources producing multiphoton cluster states will enable remote nodes, as the inbuilt redundancy photons allows repeated local measurements—compensating losses probabilistic Bell measurements. For feasible...

We apply low temperature confocal optical microscopy to spatially resolve, and spectroscopically study a single self assembled quantum dot. By comparing the emission spectra obtained at various excitation levels theoretical many body model, we show that: Single exciton radiative recombination is very weak. Sharp spectral lines are due transitions between confined multiexcitonic states among which excitons thermalize within their lifetime. Once these few fully occupied, broad bands appear...

We present a comprehensive examination of optical pumping spins in individual GaAs quantum dots as we change the net charge from positive to neutral negative with charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by ground state electron spins, which prove first measurements Hanle effect on an dot. use Overhauser high longitudinal magnetic field demonstrate efficient nuclear for all three states

A method for calculating the electronic states and optical properties of multidimensional semiconductor quantum structures is described. The applicable to heterostructures with confinement in any number dimensions: e.g. bulk, wells, wires dots. It applied here model bulk multiquantum well (MQW) InGaAsP active layer quaternary lasers. band parameters system required modeling are interpolated from available literature. We compare versus MQW performance, effects compressive tensile strain, room...

Bulk $^{13}\mathrm{C}$ polarization can be strongly enhanced in diamond at room temperature based on the optical pumping of nitrogen-vacancy color centers. This effect was confirmed by irradiating single crystals a $\ensuremath{\sim}50\text{ }\text{ }\mathrm{mT}$ field promoting anticrossings between electronic excited-state levels, followed shuttling sample into an NMR setup and subsequent detection. A nuclear $\ensuremath{\sim}0.5%$---equivalent to achievable thermal fields...

Polarizing nuclear spins is of fundamental importance in biology, chemistry and physics. Methods for hyperpolarizing 13C nuclei from free electrons bulk, usually demand operation at cryogenic temperatures. Room-temperature approaches targeting diamonds with nitrogen-vacancy (NV) centers could alleviate this need, but hitherto proposed strategies lack generality as they stringent conditions on the strength and/or alignment magnetic field. We report here an approach achieving efficient...

Nanometer-scale quantum wires have been directly produced using an epitaxial-growth technique. Modulation of the in-plane lattice constant a GaAs/GaAlAs well, grown over InGaAs/GaAs strained-layer superlattice, laterally confines carriers to one dimension. These novel structures are studied by luminescence and luminescence-excitation spectroscopies transmission electron microscopy. Large energy shifts polarization anisotropy observed. The results compare very well with theoretical model...

We present a method of formulating the multiband-envelope-function equations for quantum structure whose internal interfaces are perpendicular planes. The can be used wells, wires, or dots (one-, two-, three-dimensional confinement electronic wave function), as well periodic repetitions (superlattices) these elementary structures. technique is expansion multiband envelope functions in Fourier series each coordinates x, y, and z. Special attention paid to interface-matching conditions that...

We describe fabrication and photoluminescence excitation of InGaAs/InP quantum wires with a lateral dimension ∼350 Å. Transverse confinement results in the splitting n=1 heavy hole-electron transition. Three these levels are observed spectrum. The exciton energies agree theoretical predictions based on new method solving two-dimensional effective mass Schrödinger equation.

We apply photoluminescence, photoluminescence excitation, and time-resolved optical spectroscopy for studying a set of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ periodic structures, which were characterized by high-resolution x-ray diffraction including mapping in reciprocal space. found that the energy differences between absorption edge peak (Stokes shift), decay time drastically increase with...

We investigate the intensity correlation properties of single photons emitted from an optically excited semiconductor quantum dot. The second order temporal coherence function at various wavelengths is measured as a excitation power. show experimentally and theoretically that dot not only source nonclassically correlated monochromatic but also multicolor with tunable properties. found photon statistics can be varied by rate sub-Poissonian one, where are temporally antibunched, to...

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable $\mathrm{InAs}/\mathrm{GaAs}$ quantum dots. The spectrum exhibits a $p$-shell resonance with fine structure arising from direct electron spin triplet states. energy splitting arises axially symmetric electron-hole exchange interaction. magnitude and sign polarization are understood character states small amount dot asymmetry, which mixes wave functions through asymmetric...

We demonstrate that the quantum dot-confined dark exciton forms a long-lived integer spin solid state qubit which can be deterministically on-demand initiated in pure by one optical pulse. Moreover, we show this fully controlled using short pulses, are several orders of magnitude shorter than life and coherence times qubit. Our demonstrations do not require an externally applied magnetic field they establish excellent matter with some advantages over half-integer qubits such as confined...

We applied low-temperature diffraction-limited confocal optical microscopy to spatially resolve and spectroscopically study photoluminescence from single self-assembled semiconductor quantum dots. Using selective wavelength imaging we unambiguously demonstrated that a photoexcited dot emits light in few very narrow spectral lines. The measured spectrum its dependence on the power of either cw or pulsed excitation are explained by taking carrier correlations into account. solve numerically...

We resolve spatially, spectroscopically, and temporally the photoluminescence emission from single self-assembled InAs/GaAs quantum dots. The rich spectrum its evolution with time after pulse excitation density of is experimentally measured analyzed using a theoretical multiexciton model. model accounts quantitatively for dynamics small number interacting electrons holes confined in optically excited semiconductor

We report on the observation of photoluminescence from positive, neutral, and negative charge states single semiconductor quantum dots. For this purpose we designed a structure enabling optical injection controlled unequal number electrons positive holes into an isolated InGaAs dot embedded in GaAs matrix. Thereby, optically produced -3, -2, -1, 0, +1, +2. The injected carriers form confined collective ``artificial atoms molecules'' dot. resolve spectrally temporally excited use it to...

We compare binding energies for positive and negative trions in a series of narrow GaAs quantum wells ``natural'' dots defined by well thickness fluctuations. assign photoluminescence features to oppositely charged through combination charging behavior, luminescence polarization, spin fine structure. Negative are found have higher energy than trions. Our observations with path integral Monte Carlo calculations different widths. This comparison provides physical interpretation the observed...

We use a combination of electrical, optical, and structural characterization techniques to determine the critical layer thickness strained Ga1−xInxAs/InP quantum wells. Well compositions covering entire range strain available, from −3.8% (GaAs) +3.2% (InAs), were investigated. find that in this material system is unambiguously described by classical Matthews Blakeslee force balance model [J. Cryst. Growth 27, 118 (1974)]. Reverse leakage current strained-well samples grown p-i-n...

We report measurements of the conduction-band offset in strained-layer superlattices InxGa1−xAs/InP. Admittance spectroscopy was used to measure activation energy for thermionic emission electrons over InP barriers n-type superlattices. Superlattice dimensions and x values were obtained from high-resolution x-ray diffraction transmission electron microscopy studies. For x=0.37, 0.53, 0.69, are 175±25 meV, 210±20 315±25 respectively.