Electrically detected magnetic resonance using radio-frequency reflectometry

The authors demonstrate readout of electrically detected magnetic resonance at radio frequencies by means of an LCR tank circuit. Applied to a silicon field-effect transistor at milli-kelvin temperatures, this method shows a 25-fold increased signal-to-noise ratio of the conduction band electron spin resonance and a higher operational bandwidth of > 300 kHz compared to the kHz bandwidth of conventional readout techniques. This increase in temporal resolution provides a method for future direct observations of spin dynamics in the electrical device characteristics.Comment: 9 pages, 3 figure

Development and operation of the twin radio frequency single electron transistor for solid state qubit readout

Ultra-sensitive detectors and readout devices based on the radio frequency single electron transistor (rf-SET) combine near quantum-limited sensitivity with fast operation. Here we describe a twin rf-SET detector that uses two superconducting rf-SETs to perform fast, real-time cross-correlated measurements in order to distinguish sub-electron signals from charge noise on microsecond time-scales. The twin rf-SET makes use of two tuned resonance circuits to simultaneously and independently address both rf-SETs using wavelength division multiplexing (WDM) and a single cryogenic amplifier. We focus on the operation of the twin rf-SET as a charge detector and evaluate the cross-talk between the two resonance circuits. Real time suppression of charge noise is demonstrated by cross correlating the signals from the two rf-SETs. For the case of simultaneous operation, the rf-SETs had charge sensitivities of $\delta q_{SET1} = 7.5 \mu e/\sqrt{Hz}$ and $\delta q_{SET2} = 4.4 \mu e/\sqrt{Hz}$.Comment: Updated version, including new content. Comments most welcome: [email protected] or [email protected]

Observing sub-microsecond telegraph noise with the radio frequency single electron transistor

Telegraph noise, which originates from the switching of charge between meta-stable trapping sites, becomes increasingly important as device sizes approach the nano-scale. For charge-based quantum computing, this noise may lead to decoherence and loss of read out fidelity. Here we use a radio frequency single electron transistor (rf-SET) to probe the telegraph noise present in a typical semiconductor-based quantum computer architecture. We frequently observe micro-second telegraph noise, which is a strong function of the local electrostatic potential defined by surface gate biases. We present a method for studying telegraph noise using the rf-SET and show results for a charge trap in which the capture and emission of a single electron is controlled by the bias applied to a surface gate.Comment: Accepted for publication in Journal of Applied Physics. Comments always welcome, email [email protected], [email protected]

Excited States in Warm and Hot Dense Matter

Accurate modeling of warm and hot dense matter is challenging in part due to the multitude of excited states that must be considered. In thermal density functional theory, these excited states are averaged over to produce a single, averaged, thermal ground state. Here we present a variational framework and model that includes explicit excited states. In this framework an excited state is defined by a set of effective one-electron occupation factors and the corresponding energy is defined by the effective one-body energy with an exchange and correlation term. The variational framework is applied to an atom-in-plasma model (a generalization of the so-called average atom model). Comparisons with a density functional theory based average atom model generally reveal good agreement in the calculated pressure, but the new model also gives access to the excitation energies and charge state distributions

Bias spectroscopy and simultaneous SET charge state detection of Si:P double dots

We report a detailed study of low-temperature (mK) transport properties of a silicon double-dot system fabricated by phosphorous ion implantation. The device under study consists of two phosphorous nanoscale islands doped to above the metal-insulator transition, separated from each other and the source and drain reservoirs by nominally undoped (intrinsic) silicon tunnel barriers. Metallic control gates, together with an Al-AlOx single-electron transistor, were positioned on the substrate surface, capacitively coupled to the buried dots. The individual double-dot charge states were probed using source-drain bias spectroscopy combined with non-invasive SET charge sensing. The system was measured in linear (VSD = 0) and non-linear (VSD 0) regimes allowing calculations of the relevant capacitances. Simultaneous detection using both SET sensing and source-drain current measurements was demonstrated, providing a valuable combination for the analysis of the system. Evolution of the triple points with applied bias was observed using both charge and current sensing. Coulomb diamonds, showing the interplay between the Coulomb charging effects of the two dots, were measured using simultaneous detection and compared with numerical simulations.Comment: 7 pages, 6 figure