Any amplifier requires coupling to its internal degrees of freedom for energy gain. This coupling introduces extra quantum noise to the output. On the other hand, if the internal degree of the amplifier can be accessed and manipulated, we can manage and even reduce the quantum noise of the amplifier’s output. In this Letter, we present an experiment to reduce the quantum noise of a Raman amplifier by preparing the atomic medium in a correlated state with the Stokes light field. We report an observation of quantum noise reduction of more than 3.5 dB in the atomic Raman amplification process. From another perspective, the Raman amplifier at high gain in turn serves as a measurement tool for the quantum correlation between the atom and light. Furthermore, such a scheme, when viewed as a whole, also forms a quantum-entangled atom-light hybrid interferometer that can lead to quantum-enhanced sensors.
Read more at Physical Review Letters:
https://journals.aps.org/prl/abstract/10.1103/425s-ydl9
Photo caption:
Conceptual schemes for (a) quantum noise reduction of an amplifier by correlating internal degree with the input field; (b) measurement of quantum correlation between atomic spin wave and Stokes light field by a Raman amplifier; (c) formation of a hybrid atom-light SU(1,1) interferometer using Raman amplifiers (RA) as beam splitters for the input Stokes field.
13 Nov 2025
