Self-referenced single-electron quantized current source.

The future redefinition of the international system of units in terms of natural constants requires a robust, high-precision quantum standard for the electrical base unit ampere. However, the reliability of any single-electron current source generating a nominally quantized output current I=ef by delivering single electrons with charge e at a frequency f is eventually limited by the stochastic nature of the underlying quantum mechanical tunneling process. We experimentally explore a path to overcome this fundamental limitation by serially connecting clocked single-electron emitters with multiple in situ single-electron detectors.

Semiconductor quantized voltage source.

We realize and investigate an all-semiconductor quantized voltage source which generates quantized output voltages V(out) = f(h/e) linked only to two fundamental constants, the electron's charge e and Planck's constant h, and to an applied excitation frequency f. The device is based on an integrated quantized circuit of a single-electron pump operated at pumping frequency f and a quantum Hall device monolithically integrated in series. Robust output voltages up to several μV are generated, which are expected to be scalable by orders of magnitude using present technology.

Quantitative measurement of the magnetic moment of individual magnetic nanoparticles by magnetic force microscopy.

The quantitative measurement of the magnetization of individual magnetic nanoparticles (MNPs) using magnetic force microscopy (MFM) is described. Quantitative measurement is realized by calibration of the MFM signal using an MNP reference sample with traceably determined magnetization. A resolution of the magnetic moment of the order of 10(-18) A m(2) under ambient conditions is demonstrated, which is presently limited by the tip's magnetic moment and the noise level of the instrument.

Reversal of coherently controlled ultrafast photocurrents by band mixing in undoped GaAs quantum wells.

It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed.

Coherent control of ultrafast shift currents in GaAs with chirped optical pulses.

We demonstrate the coherent control of ultrafast shift currents in GaAs with two orthogonally polarized linearly chirped laser pulses. By varying the chirp and phase delay between the pulses, we achieve the control of the shape of the shift current transients in a wide range from a monopolar shape to different bipolar shapes (alternating currents). Moreover, the terahertz emission patterns resulting from the ultrafast shift currents allow one to determine the sign of the chirp of the laser pulses.