# Quantum transistor realized with a single $\Lambda$-level atom coupled to the microtoroidal cavity

## TL;DR

This paper proposes a quantum transistor using a single Lambda-level atom coupled to a microtoroidal cavity, enabling control over light transmission and quantum state generation with easier experimental tuning.

## Contribution

It introduces a novel quantum transistor design that operates in both strong and bad cavity limits, emphasizing control via external field amplitude rather than cavity-atom coupling.

## Key findings

- System can switch from transparent to reflective by adjusting control field amplitude.
- Control of input light statistics enables quantum state engineering.
- Design is experimentally feasible with simpler tuning methods.

## Abstract

We propose a realization of the quantum transistor for coherent light fields for the fibre-coupled microdisk cavities. We demonstrate by combining numerical and analytical methods that both in strong coupling and bad cavity limits it is possible to change system's behaviour from being fully transparent to being fully reflective by varying the amplitude of the external control field. We remark that tuning the amplitude of the control field is significantly easier in the experimental setting than tuning cavity-atom coupling strength which was suggested in [Phys. Rev. A 90, 053822 (2014)] for two-level atoms and works only in the strong coupling limit. We also demonstrate the possibility of controlling the statistics of the input coherent field with the control field which opens the venue for obtaining quantum states of light.