The development of a quantum internet relies on efficiently converting signals between different frequencies, particularly bridging the microwave and optical domains, and storing quantum information for later use. Hai-Tao Tu, Kai-Yu Liao, and Si-Yuan Qiu, alongside colleagues at their respective institutions, now demonstrate a significant step towards this goal with a new method for on-demand conversion between microwave and optical signals, assisted by quantum memory. Their research introduces a system that not only converts these signals but also stores microwave photons within a highly excited atomic ensemble, enabling faithful retrieval and significantly improving efficiency. This innovative approach achieves storage efficiency exceeding 90%, a bandwidth of 2. 1MHz, and remarkably low noise, even without the need for complex cavity structures, thus representing a crucial advancement for building practical quantum repeaters and realising long-distance quantum communication.
Rydberg Atom Converter, Calibration and Theory
This document supplements a research paper detailing a microwave-to-optical converter based on Rydberg atoms, explaining the underlying physics, experimental calibration procedures, and error analysis to validate the results. It clarifies definitions of key metrics, such as Apparent Source Efficiency, ensuring a clear understanding of the research findings. The theoretical model calculates the dephasing of Rydberg states, crucial for understanding conversion efficiency, detailing collisional dephasing, Doppler broadening, and other factors impacting coherence, essential for optimizing experimental parameters. Scientists meticulously calibrated key parameters, including Rabi frequencies, microwave field intensity, and atomic density, using techniques like Autler-Townes splitting and beam waist measurements.
Researchers measured the optical depth of the atomic ensemble to accurately determine atomic density, employing a probe laser and fitting procedures. This precise knowledge is crucial for calculating conversion efficiency and understanding system limitations. The definition of Apparent Source Efficiency is clarified, demonstrating its equivalence to the flux-density method under specific conditions, providing a clear metric for evaluating system performance. Detailed descriptions of calibration procedures, including beam profiling, power measurements, and spectral analysis, ensure the reliability and reproducibility of experimental measurements. A thorough analysis of thermal noise demonstrates its consistency with theoretical predictions, confirming that the experimental results are not significantly affected by noise. This supplementary information provides a rigorous theoretical foundation, detailed experimental calibration, validation of the model, clear definitions of metrics, and a comprehensive error analysis.
Rydberg Ensemble Enables Microwave-Optical Quantum Transduction
Researchers have engineered an on-demand microwave-to-optical quantum transducer that integrates quantum memory and conversion capabilities, essential for advancing quantum networks. This device stores microwave photons and subsequently converts them into optical photons, enabling long-distance quantum communication. The core of the transducer relies on a cascaded electromagnetically induced transparency process within a Rydberg ensemble to effectively store incoming microwave signals. Scientists harnessed the ensemble’s exceptional optical depth, exceeding millions for microwave photons, combined with minimal storage dephasing at the single-photon level, to achieve high-fidelity storage and retrieval.
Experiments employed a five-level ladder-type atomic system, manipulating transitions with precisely controlled laser fields to store and retrieve photons. A storage field initiated the EIT process, trapping the microwave photon, and a read field subsequently triggered the conversion of the stored energy into an optical photon. The team optimized control strategies for both storage and retrieval, resulting in an area-normalized storage efficiency exceeding 90 percent. This high efficiency was maintained alongside a storage time of 0. 56 microseconds, operating within the no-cloning quantum regime, a bandwidth of 2.
1MHz, and a remarkably low noise-equivalent temperature of 26 Kelvin, all achieved without optical cavities. Detailed analysis of noise sources, including blackbody radiation and detector dark counts, allowed for further refinement of the system. Measurements of recalled noise photons over extended periods provided a comprehensive understanding of the system’s limitations and performance characteristics. This innovative approach represents a significant step towards practical quantum repeaters and opens new possibilities for applications in radio astronomy and next-generation microwave sensors operating in the single-photon domain.
Microwave to Optical Conversion with Quantum Memory
Scientists have achieved a breakthrough in quantum microwave-to-optical transduction, demonstrating a memory-enhanced device capable of storing and converting microwave photons into optical photons on demand. This work represents a crucial step towards realizing practical quantum repeaters and advancing quantum internet technology, utilizing a cold 87Rb ensemble within a magneto-optical trap. The team successfully implemented an on-demand microwave-optical quantum transducer that combines quantum memory functionality with efficient signal conversion. Experiments reveal an area-normalized storage efficiency exceeding 90 percent for microwave photons within the Rydberg ensemble, a significant achievement in maintaining signal integrity during storage.
This high efficiency is coupled with a bandwidth of 2. 1MHz, allowing for the transmission of complex quantum signals. Measurements confirm a storage time of 0. 56 microseconds at the threshold efficiency of the no-cloning quantum regime, demonstrating the ability to preserve quantum information for a meaningful duration. The device also exhibits remarkably low noise, with a noise-equivalent temperature as low as 26 Kelvin even without optical cavities.
Detailed analysis of noise sources reveals contributions from blackbody radiation, detector dark counts, and laser fluctuations, all carefully characterized and minimized. The team measured stray noise at 0. 01 per pulse and total noise at 0. 109 per pulse after a 50 nanosecond storage duration. Furthermore, the team demonstrated that the area-normalized storage efficiency remains stable over time, with data collected over 600 seconds confirming consistent performance. These results pave the way for implementing quantum repeaters based on atomic ensembles and open new possibilities for sensitive detection applications, such as radio astronomy and next-generation microwave sensors in the single-photon domain.
Efficient Microwave to Optical Photon Conversion
This research demonstrates a new method for efficiently converting and storing microwave photons using a Rydberg ensemble, a key advancement for building quantum repeaters and ultimately, a quantum internet. By employing a cascaded electromagnetically induced transparency process, the team successfully stored microwave photons in a collective atomic state and then converted them back into photons during retrieval. The resulting transducer achieves a high area-normalized storage efficiency, exceeding 90 percent, alongside a bandwidth of 2. 1MHz and a low noise equivalent temperature of 26K, even without a cavity.
This work distinguishes itself from previous approaches by utilizing adiabatic storage operations and quantum memory-optimized control strategies, suppressing detrimental effects from dark states and achieving efficiencies beyond conventional methods. The integrated design combines quantum storage and microwave-to-optical conversion into a single device, offering advantages for synchronizing and storing quantum information essential for long-distance entanglement. Furthermore, the system operates with a broader bandwidth and requires fewer photons for detectable conversion compared to existing ambient methods. The authors acknowledge that Rydberg dephasing currently limits storage time and propose transferring collective excitations to a hyperfine clock state to extend it. They also suggest incorporating a narrowband etalon to further reduce noise and improve the signal-to-noise ratio, enhancing the transducer’s performance and bringing practical quantum repeaters closer to realization.