Determination of gold,palladium and copper by flame atomic absorption spectrometry after preconcentration on silica gel modified with 3-(2-aminoethylamino)propyl group

A preconcentration method of gold, palladium and copper based on the sorption of Au (III), Pd (II) and Cu (II) ions on a column packed with 3-(2-aminoethylamino)propyl bonded silica gel is described. The modified silica gel was synthesized and characterized by FT-IR and C, H, N elemental analysis. At column preconcentration, the effects of parameters such as pH, volume, flow rate, matrix constituents of solutions and type of eluent on preconcentration of gold, palladium and copper were studied. The recoveries of Au (III), Pd (II) and Cu (II) were 98.93±0.51, 98.81±0.36 and 99.21±0.42 % at 95 % confidence level, respectively. The detection limits (δ) of the elements were 0.032, 0.016 and 0.012 μg ml⁻¹, respectively. The preconcentration method was applied for determination of gold and palladium in certified reference material SARM 7B and copper in river and synthetic seawater by FAAS. Gold, palladium and copper were determined with relative error lower than 10 %.     

Nuclear spin cooling using Overhauser-field selective coherent population trapping

We show that a quantum interference effect in optical absorption from two electronic spin states of a solid-state emitter can be used to prepare the surrounding environment of nuclear spins in well-defined states, thereby suppressing electronic spin dephasing. The coupled electron-nuclei system evolves into a coherent population trapping state by optical-excitation-induced nuclear-spin diffusion for a broad range of initial optical detunings. The spectroscopic signature of this evolution where the single-electron strongly modifies its environment is a drastic broadening of the dark resonance in optical absorption experiments. The large difference in electronic and nuclear time scales allows us to verify the preparation of nuclear spins in the desired state.     

Single photon absorption by a single quantum emitter

We show that a three-level lambda quantum emitter with equal spontaneous emission rates on both optically active transitions can absorb an incident single-photon pulse with a probability approaching unity, provided that the focused light profile matches that of the emitter dipole emission. Even with realistic focusing geometries, our results could find applications in long-distance entanglement of spin qubits.     

Strong electron-hole exchange in coherently coupled quantum dots

We have investigated few-body states in vertically stacked quantum dots. Because of a small interdot tunneling rate, the coupling in our system is in a previously unexplored regime where electron-hole exchange plays a prominent role. By tuning the gate bias, we are able to turn this coupling off and study a complementary regime where total electron spin is a good quantum number. The use of differential transmission allows us to obtain unambiguous signatures of the interplay between electron and hole-spin interactions. Small tunnel coupling also enables us to demonstrate all-optical charge sensing, where a conditional exciton energy shift in one dot identifies the charging state of the coupled partner.     

Coulomb effects in spatially separated electron and hole layers in coupled quantum wells

We report on the (magneto-) optical study of many-body effects in spatially separated electron and hole layers in GaAs/Al_xGa_1?x As coupled quantum wells (CQWs) at low temperatures (T = 1.4 K) for a broad range of electron-hole (e-h) densities. Coulomb effects were found to result in an enhancement of the indirect (interwell) photoluminescence (PL) energy with increasing the e-h density both for a zero magnetic field and at high fields for all Landau level transitions; this is in contrast to the electron-hole systems in single QWs where the main features are explained by the band-gap renormalization resulting in a reduction of the PL energy. The observed enhancement of the ground state energy of the system of the spatially separated electron and hole layers with increasing the e-h density indicates that the real space condensation to droplets is energetically unfavorable. At high densities of separated electrons and holes, a new direct (intrawell) PL line has been observed: its relative intensity increased both in PL and in absorption (measured by indirect PL excitation) with increasing density; its energy separation from the direct exciton line fits well to the X ^? and X ⁺ binding energies previously measured in single QWs. The line is therefore attributed to direct multiparticle complexes.     

Enhancement of electron spin coherence by optical preparation of nuclear spins

We study a large ensemble of nuclear spins interacting with a single electron spin in a quantum dot under optical excitation and photon detection. At the two-photon resonance between the two electron-spin states, the detection of light scattering from the intermediate exciton state acts as a weak quantum measurement of the effective magnetic (Overhauser) field due to the nuclear spins. In a coherent population trapping state without light scattering, the nuclear state is projected into an eigenstate of the Overhauser field operator, and electron decoherence due to nuclear spins is suppressed: We show that this limit can be approached by adapting the driving frequencies when a photon is detected. We use a Lindblad equation to describe the driven system under photon emission and detection. Numerically, we find an increase of the electron coherence time from 5 to 500 ns after a preparation time of 10 micros.     

Tea-industry waste activated carbon, as a novel adsorbent, for separation, preconcentration and speciation of chromium

Activated carbon was produced from tea-industry wastes (TIWAC) and employed as a low cost and effective solid phase material for the separation, preconcentration and speciation of chromium species without using a complexing agent, prior to determination by flame atomic absorption spectrometry (FAAS). The characterization of TIWAC was performed by utilizing several techniques such as Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), and elemental analysis. The adsorption experiments were conducted in a batch adsorption technique. Under the experimental conditions, Cr(VI) adsorption amount was nearly equal to zero, however the adsorption percentage of Cr(III) was in the range of 95–100%. Therefore total chromium was determined after the reduction of Cr(VI) to Cr(III) and Cr(VI) was calculated by subtracting Cr(III) concentration from total chromium concentration. The suitable conditions for adsorption and speciation processes were evaluated in terms of pH, eluent type and volume, TIWAC concentration, adsorption and desorption contact time, etc. Adsorption capacity of TIWAC was found to be 61.0 mg g⁻¹. The detection limit for Cr(III) was found to be 0.27 μg L⁻¹ and the preconcentration factor was 50 for 200 mL of sample volume. The procedure was applied to the determination and speciation of chromium in stream, tap and sea water. Also, the proposed method was applied to total chromium preconcentration in microwave digested tobacco and dried eggplant samples with satisfactory results. The method was validated by analyzing certified reference materials (CRM-TMDW-500 Drinking Water and CRM-SA-C Sandy Soil C) and the results were in good agreement with the certified values.     

Nonlinear optics and quantum entanglement of ultraslow single photons

Two light pulses propagating with slow group velocities in a coherently prepared atomic gas exhibit dissipation-free nonlinear coupling of an unprecedented strength. This enables a single-photon pulse to coherently control or manipulate the quantum state of the other. Processes of this kind result in generation of entangled states of radiation field and open up new prospectives for quantum information processing.     

Knight-field-enabled nuclear spin polarization in single quantum dots

We demonstrate dynamical nuclear-spin polarization in the absence of an external magnetic field by resonant circularly polarized optical excitation of a single electron or hole charged quantum dot. Optical pumping of the electron spin induces an effective inhomogeneous magnetic (Knight) field that determines the direction along which nuclear spins could polarize and enables nuclear-spin cooling by suppressing depolarization induced by nuclear dipole-dipole interactions. Our experiments constitute a first step towards a quantum measurement of the Overhauser field.