A magneto-optic platform, comprising magnetic waves inside a layered semiconductor, could enable more efficient use of optical signals for quantum networks. The new platform converts microwave signals to optical signals by coupling magnetic wave particles — also known as magnons — with excitons.
The work was led by the City College of New York (CCNY) and included researchers from the City University of New York (CUNY) Advanced Science Research Center, Columbia University, the University of Chemistry and Technology Prague, the University of Chicago, and RPTU Kaiserslautern-Landau.
Optical signals are more suitable for carrying information over long-distance networks than microwave signals. However, because many quantum processors operate using microwave signals, quantum networks require transducers to convert signals from one frequency range to another. Also, quantum networks must be able to send signals through long-distance optical fibers without losing or corrupting any of the transmission. Existing microwave-to-optical transducers often achieve high conversion efficiency, but it’s at the expense of added noise, reduced bandwidth, or ease of integration into practical devices.
To realize coherent microwave-to-optical transduction, the researchers used chromium sulfide bromide (CrSBr), a layered, antiferromagnetic semiconductor, for magnon-exciton coupling. They also took advantage of the especially strong light-matter interactions near exciton resonances.
The team found that, when the atomic magnetic moments in the CrSBr crystal were driven by microwaves, they moved collectively, producing magnons (magnetic waves). The magnons shifted the energy of the excitons. The laser light reflected from the crystal picked up a coherent optical signal that tracked the microwave drive. Driving the antiferromagnetic resonance with microwaves modulated the resonant excitonic susceptibility and generated coherent optical sidebands.
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