Universal detector efficiency of a mesoscopic capacitor

TL;DR

This paper theoretically analyzes a high-frequency quantum detector based on a mesoscopic capacitor, demonstrating near quantum-limited efficiency in reading out a charge qubit at GHz frequencies, with efficiency being universal due to charge relaxation resistance.

Contribution

It introduces a novel high-frequency quantum detector using a mesoscopic capacitor and shows its near quantum-limited efficiency is universal due to charge relaxation resistance.

Findings

Detector operates in GHz regime with high efficiency

Quantum efficiency is universal owing to charge relaxation resistance

Potential for quantum-limited charge qubit readout

Abstract

We investigate theoretically a novel type of high frequency quantum detector based on the mesoscopic capacitor recently realized by Gabelli et al., [Science {\bf 313}, 499 (2006)], which consists of a quantum dot connected via a single channel quantum point contact to a single lead. We show that the state of a double quantum dot charge qubit capacitively coupled to this detector can be read out in the GHz frequency regime with near quantum limited efficiency. To leading order, the quantum efficiency is found to be universal owing to the universality of the charge relaxation resistance of the mesoscopic capacitor.