Observation of Coherent Charge-State Mixing in Asymmetric Bloch Transistors

TL;DR

This paper demonstrates how microwave spectroscopy can reveal charge-state mixing in asymmetric Bloch transistors by observing gap-splitting at the electrostatic degeneracy point, highlighting the effects of junction asymmetry.

Contribution

It provides experimental evidence of coherent charge-state mixing in asymmetric Bloch transistors through spectroscopic measurements.

Findings

Observation of finite gap-splitting at degeneracy point

Demonstration of charge-state mixing due to junction asymmetry

Spectroscopic method to probe interband transitions

Abstract

The reduced switching current of an excited energy-band in a Bloch transistor can be used to detect microwave-induced interband transitions. Spectroscopic measurements of the band-gap are performed by mapping the frequency dependence of the excitation threshold where the microwave photon energy and band-gap are equal. This excitation threshold also provides a probe of charge-state mixing on the island of the transistor. Any asymmetry in the junctions of the transistor makes the coherent mixing of charge-states appear as a finite gap-splitting at the electrostatic degeneracy point between states differing by one excess Cooper-pair on the island. The measured gap-splitting in an asymmetric transistor clearly demonstrates the effect.