Quantum-efficient charge detection using a single-electron transistor

We evaluate the detector nonideality (and energy sensitivity) of a normal-state single-electron transistor (SET) in the cotunneling regime in a two-charge-state approximation. For small conductances and at zero temperature, the SET's performance as a charge-qubit readout device is characterized by a universal one-parameter function. The result shows that near-ideal, quantum-limited measurement is possible for a wide range of small bias voltages. However, near the threshold voltage for crossover to sequential tunneling, the device becomes strongly nonideal. The (symmetrized) current-charge cross-correlation vanishes for low frequencies, causing two different definitions of detector nonideality to agree. Interpretations of these findings are discussed.Comment: REVTeX, 4 pages, no figures; discussion expanded, $\epsilon$-$\eta$ relation corrected below (10); subm. to PR

Temperature relaxation and the Kapitza boundary resistance paradox

The calculation of the Kapitza boundary resistance between dissimilar harmonic solids has since long (Little [Can. J. Phys. 37, 334 (1959)]) suffered from a paradox: this resistance erroneously tends to a finite value in the limit of identical solids. We resolve this paradox by calculating temperature differences in the final heat-transporting state, rather than with respect to the initial state of local equilibrium. For a one-dimensional model we thus derive an exact, paradox-free formula for the boundary resistance. The analogy to ballistic electron transport is explained.Comment: 10 p., REVTeX 3.0 with LaTeX 2.09, ITFA-94-2