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arXiv:2305.19221 · Communications Physics

Microwave-to-optical conversion in a room-temperature 87Rb vapor for frequency-division multiplexing control

Benjamin D. Smith, Bahar Babaei, Andal Narayanan, Lindsay J. LeBlanc

Published Nov 24, 2023• 6 citations
arXivHTMLPDF

Abstract

Abstract Coherent microwave-to-optical conversion is crucial for transferring quantum information generated in the microwave domain to optical frequencies, where propagation losses can be minimized. Coherent, atom-based transducers have shown rapid progress in recent years. This paper reports an experimental demonstration of coherent microwave-to-optical conversion that maps a microwave signal to a large, tunable 550(30) MHz range of optical frequencies using room-temperature 87Rb atoms. The inhomogeneous Doppler broadening of the atomic vapor advantageously supports the tunability of an input microwave channel to any optical frequency channel within the Doppler width, along with the simultaneous conversion of a multi-channel input microwave field to corresponding optical channels. In addition, we demonstrate phase-correlated amplitude control of select channels, providing an analog to a frequency domain beam splitter across five orders of magnitude in frequency. With these capabilities, neutral atomic systems may also be effective quantum processors for quantum information encoded in frequency-bin qubits.

DOI
10.1038/s42005-023-01455-y

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Abstract Coherent microwave-to-optical conversion is crucial for transferring quantum information generated in the microwave domain to optical frequencies, where propagation losses can be minimized. Coherent, atom-based transducers have shown rapid progress in recent years. This paper reports an experimental demonstration of coherent microwave-to-optical conversion that maps a microwave signal to a large, tunable 550(30) MHz range of optical frequencies using room-temperature 87Rb atoms. The inhomogeneous Doppler broadening of the atomic vapor advantageously supports the tunability of an input microwave channel to any optical frequency channel within the Doppler width, along with the simultaneous conversion of a multi-channel input microwave field to corresponding optical channels. In addition, we demonstrate phase-correlated amplitude control of select channels, providing an analog to a frequency domain beam splitter across five orders of magnitude in frequency. With these capabilities, neutral atomic systems may also be effective quantum processors for quantum information encoded in frequency-bin qubits.
Microwave-to-optical frequency conversion is a key enabling technology for quantum sensing of microwave fields and for hybrid quantum networks connecting superconducting processors with optical channels. Here, we demonstrate coherent microwave-to-optical conversion using four-wave mixing in a room-temperature cesium vapor. The system achieves an internal photon conversion efficiency close to 0.003 , a dynamic range exceeding 17 dB, and a wide bandwidth of 25 MHz despite using reduced powers of the auxiliary fields. Experimental results are qualitatively reproduced by a Maxwell–Bloch model incorporating Doppler averaging. Numerical analysis indicates that the conversion efficiency can potentially reach several percent by increasing the powers of the auxiliary lasers. These findings establish an experimental and theoretical framework for developing efficient, coherent, and broadband frequency conversion with cesium vapors.
Quantum information encoded in optical photons can be transmitted over long distances with very high information density, and suffers from negligible thermal noise at room temperature. On the other hand, microwave photons at cryogenic temperatures can be confined in high quality resonators and strongly coupled to solid-state qubits, providing a quantum bus to connect qubits and a route to deterministic photonic non-linearities. The coherent interconversion of microwave and optical photons has therefore recently emerged as a highly desirable capability that would enable freely-scalable networks of optically-linked qubits, or large-scale photonic information processing with multi-photon interactions mediated by microwaves. Here, we propose a route to efficient and coherent microwave-optical conversion based on frequency mixing in Rydberg atoms. The interaction requires no microfabricated components or cavities, and is tunable, broadband, and both spatially and spectrally multimode.
Photons at microwave and optical frequencies are principal carriers for quantum information. While microwave photons can be effectively controlled at the local circuit level, optical photons can propagate over long distances. High-fidelity conversion between microwave and optical photons will allow the distribution of quantum states across different quantum technology nodes and enhance the scalability of hybrid quantum systems toward a future “Quantum Internet.” Despite a frequency difference of five orders of magnitude, there has been significant progress recently toward the transfer between microwave and optical photons with steadily improved efficiency in a coherent and bidirectional manner. In this review, we summarize this progress, emphasizing integrated device approaches, and provide a perspective for device implementation that enables quantum state transfer and entanglement distribution across microwave and optical domains.
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Microwave-to-optics conversion is a core technology for hybrid quantum networks, enabling the integration of microwave and optical frequency domains essential for quantum communication and quantum information processing. However, the Doppler broadening effect in thermal atomic ensembles often severely limits the conversion efficiency. This study aims to propose a novel mechanism for microwave-to-optics conversion using four-wave mixing (FWM) in room-temperature Rydberg atoms, addressing the challenges posed by Doppler broadening and providing a theoretical framework for practical applications. We develop a theoretical model based on the coupled Maxwell-Bloch equations to describe the FWM process in a symmetric double-ladder four-level system. The density matrix method and perturbation method combined with Maxwell’s equations are used to derive an analytical expression for the coherence coefficient between the microwave field and the optical field. This coherence coefficient characterizes the energy transfer between the microwave and optical fields and is used to obtain an analytical expression for the FWM conversion efficiency. We use cesium vapor as a medium to analyze the propagation characteristics of the FWM efficiency and explore the effects of laser field intensity and the Doppler effect on the conversion efficiency. Our analysis reveals that the detuning effect caused by the thermal motion of atoms significantly reduces the resonance coupling efficiency. Specifically, when the Doppler frequency is lower than the natural linewidth, the conversion efficiency can be notably improved. In a Doppler-free environment, the conversion efficiency approaches unity at an optimal propagation distance. In contrast, in room-temperature cesium vapor (300 K), the conversion efficiency is significantly reduced due to Doppler broadening. However, by cooling the atoms to microkelvin temperatures, the Doppler broadening can be minimized, leading to a substantial increase in conversion efficiency. This study provides new theoretical guidance and experimental schemes for microwave-to-optics conversion at room temperature. The proposed mechanism based on Rydberg atoms provides a promising approach to overcoming the limitations imposed by Doppler broadening. Our findings are of great significance for advancing quantum information technology, especially in the context of developing efficient quantum networks.
Abstract Information conversion from microwave to optical domains represents a frontier field in communication, imaging, and quantum science. As an essential property of electromagnetic waves, polarization enables higher-dimensional information acquisition and enhanced robustness in complex environments. While established conversion methodologies typically target intensity and phase, coherent microwave-to-optical polarization conversion remains challenging. Here, we propose atom-enabled holographic quantum sensing that can achieve a definite one-to-one mapping of polarization states between microwave and optical fields. A vectorial atomic hologram is demonstrated based on photoinduced circular dichroism and birefringence in a four-level atomic system excited by holographic polarization patterns. It is found that the polarization state of the reconstructed holographic diffracted light field is dependent on that of the incident microwave through the vectorial atomic hologram, which is analyzed in terms of Jones theory and density matrix formalism. Moreover, broadband microwave-to-optical polarization conversion with the preservation of phase information is demonstrated experimentally for 31.467 and 2.925 GHz microwaves. The maximum polarization conversion efficiency is up to 10.42%. Our work could provide an effective strategy for coherent polarization-information transfer across disparate frequency bands.