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.

Counting statistics for electron capture in a dynamic quantum dot.

We report noninvasive single-charge detection of the full probability distribution P(n) of the initialization of a quantum dot with n electrons for rapid decoupling from an electron reservoir. We analyze the data in the context of a model for sequential tunneling pinch-off, which has generic solutions corresponding to two opposing mechanisms. One limit considers sequential "freeze-out" of an adiabatically evolving grand canonical distribution, the other one is an athermal limit equivalent to the solution of a generalized decay cascade model.

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.

An improved method for the prolonged maintenance of Pneumocystis carinii in vitro.

A culture system for rat-derived Pneumocystis carinii was developed that allows the long-term maintenance of viable organisms in vitro. Organisms were derived from the lungs of immunosuppressed rats infected with P. carinii.

Cloning of a fresh isolate of Plasmodium falciparum and drug sensitivity of the clones.

A freshly isolated strain of Plasmodium falciparum was cloned by limited dilution using a co-culture of infected erythrocytes on monolayers of functionally active rodent hepatocytes. 15 clones were isolated, and the anti-malarial activity of chloroquine, quinine, mefloquine and halofantrine against the clones, the original isolate, and a culture-adapted isolate was determined using a 48 h radioisotope microdilution method. The multiplication rates of all clones and the culture-adapted isolate were estimated by counting the number of parasitized cells on Giemsa-stained thin smears.