A new device can freely and efficiently change the frequency of microwave signals, enabling communication between otherwise incompatible quantum systems.
A quantum network that distributes and processes entanglement would enable powerful new computers and sensors. Optical photons with a frequency of a few hundred terahertz are perhaps the only way to distribute quantum information over long distances. Superconducting qubits on the other hand, which are one of the most promising approaches for realizing large-scale quantum machines, operate naturally on microwave photons that have roughly 40,000 times less energy. To network these quantum machines across appreciable distances, we must bridge this frequency gap and learn how to generate entanglement across widely disparate parts of the electromagnetic spectrum. Here we implement and demonstrate a transducer device that can generate entanglement between optical and microwave photons, and use it to show that by detecting an optical photon we add a single photon to the microwave field. We achieve this by using a gigahertz nanomechanical resonance as an intermediary, and efficiently coupling it to optical and microwave channels through strong optomechanical and piezoelectric interactions. We show continuous operation of the transducer with 5% frequency conversion efficiency, and pulsed microwave photon generation at a heralding rate of 15 hertz. Optical absorption in the device generates thermal noise of less than two microwave photons. Joint measurements on optical photons from a pair of transducers would realize entanglement generation between distant microwave-frequency quantum nodes. Improvements of the system efficiency and device performance, necessary to realize a high rate of entanglement generation in such networks are within reach.
Discrete energy-level dynamics in quantum systems provide a fundamental framework for understanding particle manipulation. The two-level system, as the archetypal model, demonstrates how energy levels evolve under an external driving field, manifesting phenomena such as Rabi oscillations. Recent advances in microwave photonics enable the emulation of quantum effects through optical-RF signal coupling, prompting exploration of analogous quantum-inspired phenomena in microwave photonic platforms. Here, we propose and experimentally demonstrate a microwave photonic scheme for coherent optical-RF signal coupling based on a dual-fiber-loop configuration. In this system, electro-optic modulation facilitates coherent energy-level coupling analogous to quantum systems. We show that the output oscillation frequency can be precisely controlled by varying the power of an input RF signal, attributed to modulation-induced sideband coupling. This behavior exhibits remarkable consistency with Rabi oscillations observed in atomic systems. Our work establishes a novel method for RF signal generation in microwave photonics, with potential applications in signal processing, photonics-assisted communications, and high-performance frequency control devices, thereby offering a new bridge between quantum and classical domains.
Discrete energy-level dynamics in quantum systems provide a fundamental framework for understanding particle manipulation. The two-level system, as the archetypal model, demonstrates how energy levels evolve under an external driving field, manifesting phenomena such as Rabi oscillations. Recent advances in microwave photonics enable the emulation of quantum effects through optical-RF signal coupling, prompting exploration of analogous quantum-inspired phenomena in microwave photonic platforms. Here, we propose and experimentally demonstrate a microwave photonic scheme for coherent optical-RF signal coupling based on a dual-fiber-loop configuration. In this system, electro-optic modulation facilitates coherent energy-level coupling analogous to quantum systems. We show that the output oscillation frequency can be precisely controlled by varying the power of an input RF signal, attributed to modulation-induced sideband coupling. This behavior exhibits remarkable consistency with Rabi oscillations observed in atomic systems. Our work establishes a novel method for RF signal generation in microwave photonics, with potential applications in signal processing, photonics-assisted communications, and high-performance frequency control devices, thereby offering a new bridge between quantum and classical domains.