Ultimate charge sensitivity and efficiency of a quantum point contact with a superposed input state

TL;DR

This paper demonstrates that using a superposed input state in a quantum point contact enhances charge detection sensitivity and efficiency, reaching the fundamental quantum limits through controlled interference.

Contribution

It introduces a scheme utilizing superposed input states and output interference control to achieve ultimate charge sensitivity and quantum-limited detection in quantum point contacts.

Findings

Superposed input states improve charge sensitivity.

Interference control enables quantum-limited detection.

The scheme reaches fundamental quantum limits.

Abstract

We address the ultimate charge detection scheme with a quantum point contact. It is shown that a superposed input state is necessary to exploit the full sensitivity of a quantum point contact detector. The coherence of the input state provides an improvement in charge sensitivity, and this improvement is a result of the fundamental property of the scattering matrix. Further, a quantum-limited (maximally efficient) detection is possible by controlling the interference between the two output waves. Our scheme provides the ultimate sensitivity and efficiency of charge detection with a generic quantum point contact.