Abstract
 

The field of hybrid optical-microwave technology is advancing rapidly, driven by goals such as integrating telecom wavelength optical fiber networks with superconducting circuit-based quantum technology. We present a new protocol for generating entanglement between microwave and optical modes, with an inbuilt quantum memory. The protocol, hybrid Rephased Amplified Spontaneous Emission (RASE) [1-3], first creates entanglement between a spontaneously emitted photonic mode and an atomic ensemble. The atomic coherence is then mapped to a long-lived nuclear spin transition before being rephased to generate a second photonic mode.

We analyse the performance of the protocol for erbium ensembles in crystals, which exhibit narrow transitions at both microwave and optical frequencies. Such materials also possess nuclear-spin coherence times among the longest in the solid state [4]. We describe the theoretical framework to optimise the time-separated, hybrid two-mode squeezed state toward efficient, high bandwidth, and high rate entanglement generation. We further compare our approach with hybrid two-mode squeezing generated through direct three-wave mixing by extending the theoretical framework developed in Ref. [5]. We will also discuss initial steps

toward realising this protocol experimentally, such as on-chip superconducting resonators for coupling to ensembles of erbium electron spins.

Bio
 

Gargi Tyagi is a final-year PhD student at the University of Sydney, working in the Quantum Integration Laboratory under the supervision of A/Prof. John Bartholomew. Her research focuses on hybrid quantum systems, particularly the generation of two-mode entanglement between optical and microwave fields using rare-earth ions for future quantum networking applications. Her work combines theoretical modelling with experimental development, including the design, fabrication, and measurement of superconducting microwave resonators.