CCNY researchers demonstrated coherent microwave-to-optical signal conversion in chromium sulfide bromide (CrSBr), a layered antiferromagnetic semiconductor. Microwave-driven magnetic excitations called magnons modulated the material’s optical response, producing light sidebands that tracked the microwave signal. It is a promising materials result for future quantum-network interfaces—not a demonstration of transferring an individual quantum state between a processor and an optical network.
How the microwave signal becomes light
The experiment uses two kinds of excitations in CrSBr. First, microwaves drive the crystal’s antiferromagnetic resonance, causing its magnetic moments to move collectively. Those collective motions are called magnons. The magnons then couple to excitons—bound pairs of electrons and holes that interact with light—and modulate the material’s resonant optical response.
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That modulation produces coherent optical sidebands: additional light components linked to the microwave drive. The team detected them with homodyne interferometry. In practical terms, reflected laser light carried an optical signal that followed the applied microwave signal. The mechanism and measurements are described in the Nature Materials paper and in CCNY’s announcement.
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- Material: CrSBr, a layered antiferromagnetic semiconductor.
- Output: Coherent optical sidebands tracking the microwave drive.
- Frequency range: The conversion worked over an approximately 300 MHz microwave window, according to CCNY.
- Tuning: Applying a magnetic field changed the operating frequency.
- Setup: The effect was observed in a bulk crystal without an optical or microwave resonator boosting the interaction.
The paper, “Microwave-to-optical transduction using magnon–exciton coupling,” was published in Nature Materials on September 14, 2026. CCNY announced the result on September 17, 2026. The work was led by Pratap Chandra Adak, a postdoctoral researcher in Vinod M. Menon’s group. Collaborators included researchers from the CUNY Advanced Science Research Center, Columbia University, the University of Chemistry and Technology Prague, the University of Chicago, and RPTU Kaiserslautern-Landau in Germany.
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Why a microwave-to-optical converter matters
Many quantum processors use microwave signals, while optical fiber can carry information over long distances. A transducer that links those frequency regimes could eventually help connect quantum devices to optical networks. To serve that purpose, however, a converter must transfer information efficiently while introducing very little noise.
CrSBr brings microwave-frequency magnetism and strong optical interactions together in one layered material. Its structure also makes thin flakes and compact device designs conceivable. Those features make it worth investigating as a platform; they do not by themselves establish a practical network link.
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Why this is not yet quantum-state transfer
The reported result is coherent signal conversion, not evidence that an individual quantum state traveled from a microwave circuit into an optical network. CCNY describes individual-state transfer as a longer-term goal that will require substantial improvements in efficiency and careful control of added noise. The university announcement does not give a conversion-efficiency figure or a measured added-noise value, so the demonstrated signal should not be interpreted as proof of a usable quantum-network transducer.
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CCNY identifies several possible development directions: using thinner CrSBr flakes, adding microwave resonators or high-quality optical cavities to strengthen interactions, and engineering exciton–polaritons as a possible way to manage optical loss. These are proposed routes for future work, not performance improvements established by this experiment.
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Adak said CrSBr’s layered structure offers “considerable freedom in device design and integration,” and that thinning the material could open opportunities to strengthen interactions and build more compact devices. Menon described the result as a starting point for exploring other layered magnetic materials and engineering opto-magnonic devices. Whether any of these approaches can deliver the efficiency and noise performance needed for quantum-state transfer remains an open technical challenge.
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