The OAM quantum properties of photons, especially microwave photons, have been extremely attractive for researches. However, the research on the quantum properties of microwave photons has been limited due to the use of superconducting or cryogenic environments. To address this problem, the use of Rydberg Atoms, which can operate at room temperature and pressure, has been proposed as our solution in this paper. Furthermore, we propose an OAM keying encoding method for microwave quantum with the utilization of Rydberg atom detection. The proposed system exhibits excellent noise immunity, which is a crucial factor in maintaining reliable performance. The potential consequence of this advancement is the ability to minimize the size of the quantum characterization device for microwave photons, which may enable it to fit within a compact box.
The OAM quantum properties of photons, especially microwave photons, have been extremely attractive for researches. However, the research on the quantum properties of microwave photons has been limited due to the use of superconducting or cryogenic environments. To address this problem, the use of Rydberg Atoms, which can operate at room temperature and pressure, has been proposed as our solution in this paper. Furthermore, we propose an OAM keying encoding method for microwave quantum with the utilization of Rydberg atom detection. The proposed system exhibits excellent noise immunity, which is a crucial factor in maintaining reliable performance. The potential consequence of this advancement is the ability to minimize the size of the quantum characterization device for microwave photons, which may enable it to fit within a compact box.
The orbital angular momentum (OAM) technology, promising for future communications, radar, and quantum information processing, confronts challenges in OAM detection of the microwave photons, due to the noise and equipment complexity. Conventional detection approaches based on gyrotron systems, which demand vacuum and high-voltage environments, prove impractical for scalable applications. Thus, we introduce a Rydberg-atom-based architecture for OAM detection of vortex microwave photons, which operates in normal pressure and low voltage with miniaturized equipment. Specifically, leveraging the unique dipole-forbidden, quadrupole-allowed transitions of Rydberg atoms, we can receive the vortex microwave photons and identify the corresponding intrinsic OAM (IOAM), with precise frequency alignment by external electrode plates for fine-tuning. Moreover, experimental observations reveal the insight of Autler–Townes splitting, confirming that the OAM of microwave photons can couple to atomic energy levels through electric-quadrupole interactions, inducing a dynamic Stark effect. In contrast, the experiments with plane microwave photons, i.e., the OAM mode is zero, show the result with only static stark broadening rather than the peak splitting, which highlights the critical role of quadrupole transitions in OAM detection. Significantly, this approach overcomes the limitations of conventional techniques requiring high-energy superconducting devices or high-voltage setups, offering a low-cost, scalable solution for efficient vortex microwave photons detection with promising applications, e.g., secure wireless communications and quantum radars.
Rydberg atoms are atoms in their highly excited energy states. The physical properties of Rydberg atoms in the presence of external fields play an important role in quantum precision measurement. In recent years, radio-frequency electric field sensing based on Rydberg atoms has attracted significant interest. It is widely recognized as an electromagnetic sensing system fundamentally different from traditional ones. As a quantum sensor, it is expected to surpass several foundational limitations of traditional receivers, such as sensitivity, dynamic range and frequency bandwidth. It was reported that Rydberg sensing systems can sense microwaves of frequencies from DC up to 1THz. Its quantum nature would possibly avoid internal thermal (Johnson) noise, even at room temperature. Recent demonstrations have also observed high precision for terahertz imaging, strong fields sensing, proof-of-principle communication. However, limitations of this novel system have not been addressed, especially for a practical radar, communication or electronic warfare system. Here in this work, we first compare the architectures of different microwave receivers and then analyze the metrics of Rydberg microwave receivers, such as instantaneous bandwidth and dynamic range based on experimental results. We concluded by pointing out several main obstacles to overcome for realizing a practical state-of-the-art microwave receiver.
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.
Abstract The coupling of microwave and optical systems presents an immense challenge due to the natural incompatibility of energies, but potential applications range from optical interconnects for quantum computers to next-generation quantum microwave sensors, detectors and coherent imagers. Several of the engineered platforms that have emerged are constrained by specific conditions, such as cryogenic environments, impulse protocols or narrowband fields. Here we employ Rydberg atoms that allow the wideband coupling of optical and microwave photons at room temperature with the use of a modest set-up. We present continuous-wave conversion of a 13.9 GHz field to a near-infrared optical signal using an ensemble of Rydberg atoms via a free-space six-wave mixing process designed to minimize noise interference from any nearby frequencies. The Rydberg photonic converter exhibits a conversion dynamic range of 57 dB and a wide conversion bandwidth of 16 MHz. Using photon counting, we demonstrate the readout of photons of free-space 300 K thermal background radiation at 1.59 nV cm −1 rad −1/2 s −1/2 (3.98 nV cm −1 Hz −1/2 ) with a sensitivity down to 3.8 K of noise-equivalent temperature, allowing us to observe Hanbury Brown and Twiss interference of microwave photons.
Rydberg atoms, with one highly excited, nearly ionized electron, have extreme sensitivity to electric fields, including microwave fields ranging from 100 MHz to over 1 THz. Here, we show that room-temperature Rydberg atoms can be used as sensitive, high bandwidth, microwave communication antennas. We demonstrate near photon-shot-noise limited readout of data encoded in amplitude-modulated 17 GHz microwaves, using an electromagnetically induced-transparency (EIT) probing scheme. We measure a photon-shot-noise limited channel capacity of up to 8.2 Mbit s−1 and implement an 8-state phase-shift-keying digital communication protocol. The bandwidth of the EIT probing scheme is found to be limited by the available coupling laser power and the natural linewidth of the rubidium D2 transition. We discuss how atomic communication receivers offer several opportunities to surpass the capabilities of classical antennas.
Extending optical nonlinearity into the extremely weak light regime is at the heart of quantum optics, since it enables the efficient generation of photonic entanglement and implementation of photonic quantum logic gate. Here, we demonstrate the capability for continuously tunable single-photon level nonlinearity, enabled by precise control of Rydberg interaction over two orders of magnitude, through the use of microwave-assisted wave-function engineering. To characterize this nonlinearity, light storage and retrieval protocol utilizing Rydberg electromagnetically induced transparency is employed, and the quantum statistics of the retrieved photons are analyzed. As a first application, we demonstrate our protocol can speed up the preparation of single photons in low-lying Rydberg states by a factor of up to ~ 40. Our work holds the potential to accelerate quantum operations and to improve the circuit depth and connectivity in Rydberg systems, representing a crucial step towards scalable quantum information processing with Rydberg atoms.