Étude par spectroscopie de coulomb d'une boîte quantique latérale contenant de 1 à 12 électrons

Une boîte quantique contenant un nombre discret et variable d'électrons est formée dans un gaz bi-dimensionnel d'électrons. On explique concrètement comment la géométrie des grilles utilisées pour former la boîte permet de contrôler exactement le nombre d'électrons jusqu'à zéro. Ce contrôle nous permet d'obtenir, par transport dans le régime de blocage de Coulomb, les spectres d'addition et d'excitation associés à l'ajout des 12 premiers électrons dans la boîte. On montre que le potentiel de confinement peut être approximé, près de son minimum, par celui d'un oscillateur harmonique dont l'énergie caractéristique est de l'ordre du meV. Ce résultat permet de calibrer l'énergie d'addition du premier électron et d'obtenir la variation en champ magnétique B du niveau de Fermi du gaz électronique bi-dimensionnel (GE2D) utilisé comme réservoir pour le transport à travers la boîte. Le résultat montre une oscillation périodique en 1/ B avec une amplitude beaucoup plus petite que l'énergie cyclotron. On observe ensuite la transition en champ magnétique entre les deux états de plus basse énergie d'une boîte contenant 2 électrons, soient les états singulet et triplet. On montre que l'approximation harmonique cesse d'être valide pour une boîte contenant plus d'un électron. Les résultats montrent que le champ critique de la transition dépend du potentiel appliqué sur les grilles. De plus, on observe une modulation de l'amplitude du courant circulant à travers la boîte lors de la transition. On attribue cette modulation à l'injection partiellement polarisée en spin, causée par la séparation spatiale des états de bords du GE2D de spin «1/2. Finalement, les résultats pour un plus grand nombre d'électrons montrent que l'hypothèse de l'injection partiellement polarisée est en accord avec les transitions en champ magnétique des configurations électroniques de la boîte et qu'elle permet de mesurer, par l'amplitude du courant, le spin total de la boîte

Telegraph Noise in Coupled Quantum Dot Circuits Induced by a Quantum Point Contact

Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed.Comment: 4 pages, 3 figures (as published

Electron spin manipulation and resonator readout in a double quantum dot nano-electromechanical system

Magnetically coupling a nano-mechanical resonator to a double quantum dot confining two electrons can enable the manipulation of a single electron spin and the readout of the resonator's natural frequency. When the Larmor frequency matches the resonator frequency, the electron spin in one of the dots can be selectively flipped by the magnetised resonator. By simultaneously measuring the charge state of the two-electron double quantum dots, this transition can be detected thus enabling the natural frequency of the mechanical resonator to be determined.Comment: 7 pages, fixed typos, updated figures 4 and

Microwave band on-chip coil technique for single electron spin resonance in a quantum dot

Microwave band on-chip microcoils are developed for the application to single electron spin resonance measurement with a single quantum dot. Basic properties such as characteristic impedance and electromagnetic field distribution are examined for various coil designs by means of experiment and simulation. The combined setup operates relevantly in the experiment at dilution temperature. The frequency responses of the return loss and Coulomb blockade current are examined. Capacitive coupling between a coil and a quantum dot causes photon assisted tunneling, whose signal can greatly overlap the electron spin resonance signal. To suppress the photon assisted tunneling effect, a technique for compensating for the microwave electric field is developed. Good performance of this technique is confirmed from measurement of Coulomb blockade oscillations.Comment: 7 pages, 8 figures, Accepted for publication in Rev. Sci. Instrum. The bibliography file is update

Probing a spin transfer controlled magnetic nanowire with a single nitrogen-vacancy spin in bulk diamond

The point-like nature and exquisite magnetic field sensitivity of the nitrogen vacancy (NV) center in diamond can provide information about the inner workings of magnetic nanocircuits in complement with traditional transport techniques. Here we use a single NV in bulk diamond to probe the stray field of a ferromagnetic nanowire controlled by spin transfer (ST) torques. We first report an unambiguous measurement of ST tuned, parametrically driven, large-amplitude magnetic oscillations. At the same time, we demonstrate that such magnetic oscillations alone can directly drive NV spin transitions, providing a potential new means of control. Finally, we use the NV as a local noise thermometer, observing strong ST damping of the stray field noise, consistent with magnetic cooling from room temperature to $\sim$150 K.Comment: 6 pages, 5 figures, plus supplementary informatio

Mapping electron delocalization by charge transport spectroscopy in an artificial molecule

In this letter we present an experimental realization of the quantum mechanics textbook example of two interacting electronic quantum states that hybridize forming a molecular state. In our particular realization, the quantum states themselves are fabricated as quantum dots in a molecule, a carbon nanotube. For sufficient quantum-mechanical interaction (tunnel coupling) between the two quantum states, the molecular wavefunction is a superposition of the two isolated (dot) wavefunctions. As a result, the electron becomes delocalized and a covalent bond forms. In this work, we show that electrical transport can be used as a sensitive probe to measure the relative weight of the two components in the superposition state as a function of the gate-voltages. For the field of carbon nanotube double quantum dots, the findings represent an additional step towards the engineering of quantum states