Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userQuantum state readout of individual quantum dots by electrostatic force detection
180
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Electric charge detection by atomic force microscopy (AFM) with single- electron resolution (e-EFM) is a promising way to investigate the electronic level structure of individual quantum dots (QD). The oscillating AFM tip modulates the energy of the QDs, causing single electrons to tunnel between QDs and an electrode. The resulting oscillating electrostatic force changes the resonant frequency and damping of the AFM cantilever, enabling electrometry with a single-electron sensitivity. Quantitative electronic level spectroscopy is possible by sweeping the bias voltage. Charge stability diagram can be obtained by scanning the AFM tip around the QD. e-EFM technique enables to investigate individual colloidal nanoparticles and self- assembled QDs without nanoscale electrodes. e-EFM is a quantum electromechanical system where the back-action of a tunneling electron is detected by AFM; it can also be considered as a mechanical analog of admittance spectroscopy with a radio frequency resonator, which is emerging as a promising tool for quantum state readout for quantum computing. In combination with the topography imaging capability of the AFM, e-EFM is a powerful tool for investigating new nanoscale material systems which can be used as quantum bits.
rate research
Read More
We describe two different modes for electronically detecting an adsorbed molecule using a nanoscale transistor. The attachment of an ionic molecular target shifts the threshold voltage through modulation of the depletion layer electrostatics. A stronger bonding between the molecule and the channel, involving actual overlap of their quantum mechanical wavefunctions, leads to scattering by the molecular traps that creates characteristic fingerprints when scanned with a backgate. We describe a theoretical approach to model these transport characteristics.
Nuclear polarization dynamics are measured in the nuclear spin bi-stability regime in a single optically pumped InGaAs/GaAs quantum dot. The controlling role of nuclear spin diffusion from the dot into the surrounding material is revealed in pump-probe measurements of the non-linear nuclear spin dynamics. We measure nuclear spin decay times in the range 0.2-5 sec, strongly dependent on the optical pumping time. The long nuclear spin decay arises from polarization of the material surrounding the dot by spin diffusion for long (>5sec) pumping times. The time-resolved methods allow the detection of the unstable nuclear polarization state in the bi-stability regime otherwise undetectable in cw experiments.
Strong confinement of charges in few electron systems such as in atoms, molecules and quantum dots leads to a spectrum of discrete energy levels that are often shared by several degenerate quantum states. Since the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum in the Coulomb blockade regime, resulting from a change in cantilever resonance frequency and dissipation during tunneling events, shows one by one electron charging of a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the first observation of predicted temperature-dependent shifts of Coulomb blockade peaks. Further, by scanning the surface we observe that several quantum dots may reside on what topologically appears to be just one. These images of grouped weakly and strongly coupled dots allow us to estimate their relative coupling strengths.
Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. As already shown, optical control of a spin of a magnetic ion is feasible employing photo-generated carriers confined in a quantum dot. A non-radiative recombination, regarded as a severe problem, limited development of quantum dots with magnetic ions. Our photoluminescence studies on, so far unexplored, individual CdTe dots with single cobalt ions and individual CdSe dots with single manganese ions show, however, that even if energetically allowed, the single ion related non-radiative recombination is negligible in such zero-dimensional structures. This opens solotronics for a wide range of even not yet considered systems. Basing on the results of our single spin relaxation experiments and on the material trends, we identify optimal magnetic ion-quantum dot systems for implementation of a single-ion based spin memory.
Quantum dots are an important model system for thermoelectric phenomena, and may be used to enhance the thermal-to-electric energy conversion efficiency in functional materials. It is therefore important to obtain a detailed understanding of a quantum-dots thermopower as a function of the Fermi energy. However, so far it has proven difficult to take effects of co-tunnelling into account in the interpretation of experimental data. Here we show that a single-electron tunnelling model, using knowledge of the dots electrical conductance which in fact includes all-order co-tunneling effects, predicts the thermopower of quantum dots as a function of the relevant energy scales, in very good agreement with experiment.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
