Abstract Measurement sensitivity is one of the critical indicators for Rydberg atomic radio receivers. This work quantitatively studies the relationship between the atomic superheterodyne receiver's sensitivity and the number of atoms involved in the measurement. The atom number is changed by adjusting the length of the interaction area. The results show that for the ideal case, the sensitivity of the atomic superheterodyne receiver exhibits a quantum scaling: the amplitude of its output signal is proportional to the atom number, and the amplitude of its read-out noise is proportional to the square root of the atom number. Hence, its sensitivity is inversely proportional to the square root of the atom number. This work also gives a detailed discussion of the properties of transit noise in atomic receivers and the influence of some non-ideal factors on sensitivity scaling. This work is significant in the field of atom-based quantum precision measurements.
Abstract Measurement sensitivity is one of the critical indicators for Rydberg atomic radio receivers. This work quantitatively studies the relationship between the atomic superheterodyne receiver's sensitivity and the number of atoms involved in the measurement. The atom number is changed by adjusting the length of the interaction area. The results show that for the ideal case, the sensitivity of the atomic superheterodyne receiver exhibits a quantum scaling: the amplitude of its output signal is proportional to the atom number, and the amplitude of its read-out noise is proportional to the square root of the atom number. Hence, its sensitivity is inversely proportional to the square root of the atom number. This work also gives a detailed discussion of the properties of transit noise in atomic receivers and the influence of some non-ideal factors on sensitivity scaling. This work is significant in the field of atom-based quantum precision measurements.
Since its theoretical sensitivity is limited by quantum noise, radio wave sensing based on Rydberg atoms has the potential to replace its traditional counterparts with higher sensitivity and has developed rapidly in recent years. However, as the most sensitive atomic radio wave sensor, the atomic superheterodyne receiver lacks a detailed noise analysis to pave its way to achieve theoretical sensitivity. In this work, we quantitatively study the noise power spectrum of the atomic receiver versus the number of atoms, where the number of atoms is precisely controlled by changing the diameters of flat-top excitation laser beams. The results show that under the experimental conditions that the diameters of excitation beams are less than or equal to 2 mm and the read-out frequency is larger than 70 kHz, the sensitivity of the atomic receiver is limited only by the quantum noise and, in the other conditions, limited by classical noise. However, the experimental quantum-projection-noise-limited sensitivity this atomic receiver reaches is far from the theoretical sensitivity. This is because all atoms involved in light-atom interaction will contribute to noise, but only a fraction of them participating in the radio wave transition can provide valuable signals. At the same time, the calculation of the theoretical sensitivity considers both the noise and signal are contributed by the same amount of atoms. This work is essential in making the sensitivity of the atomic receiver reach its ultimate limit and is significant in quantum precision measurement.
In recent years, electric field measurement techniques based on Rydberg atoms have shown unique advantages in high sensitivity and wideband applications and miniaturization. The Rydberg atom receiver senses the electromagnetic signal using the quantum coherence effect, which overcomes the inherent defects of traditional electronic receivers in terms of thermal noise, insertion loss of microwave devices, and the use of wavelength-dependent antennas, thus providing the Rydberg atomic receivers the potential to become the next generation of microwave receivers. For some particular application scenarios such as radar and communication, superheterodyne reception is a critical technical approach, and the linear dynamic range is an essential factor in evaluating the performance of the superheterodyne receivers. It is challenging to promote the Rydberg atomic receiver without figuring out the influence of system parameters on the linear dynamic range. This paper starts with the response mechanism of the Rydberg atomic superheterodyne receiver, and a theoretical model is established to simulate the atom-microwave responses. Then the harmonics' generation mechanism is discussed, and the atomic linear dynamic range under different probe light Rabi frequencies is studied further. Furthermore, a method to evaluate the antiblocking performance of the system is proposed. This work is expected to provide theoretical guidance for the design and performance optimization of the Rydberg atomic superheterodyne receiver.
Measurement sensitivity is crucial for the practical application of Rydberg atomic microwave superheterodyne receiver systems in communication, radar, and navigation. Based on laser-atom-microwave interaction mechanisms, the influence of laser powers and local-oscillator (LO) microwave field intensity on measurement sensitivity is systematically studied in this paper. Measurement sensitivity is analyzed through electromagnetically induced transparency (EIT) spectral characteristics, specifically EIT amplitude and full-width-half-maximum (FWHM),larger amplitudes and narrower FWHM indicate improved signal-to-noise ratios. For a 60D-state Rydberg atomic system with fixed probe and coupling laser beam waists (800 µm and 875 µm), optimal parameters are determined: probe laser power of 60 µW(Rabi frequency: 2π×7.02 MHz), coupling laser power of 40 mW (Rabi frequency: 2π×0.66 MHz), and LO microwave Rabi frequency of 2π×8.34 MHz. Experimental results demonstrate a 4.6 dB sensitivity enhancement, advancing from −137.5dBm/Hz to −142.1 dBm/Hz at 3.21 GHz microwave field. This improvement is attributed to precise alignment of laser-atom and microwave-atom interactions, bridging the gap toward quantum sensitivity limits.
High-sensitivity measurements of the microwave electric field are important in applications of communication and metrology. The sensitivity of traditional Rydberg superheterodyne receivers in free space is effectively determined by the signal-to-noise ratio (SNR), which is often considered equivalent to sensitivity in practical sensing applications. In this work, we demonstrate a cavity-enhanced receiver, where an optical cavity significantly amplifies the interaction between the probe light and cesium atoms, which substantially improves the signal-to-noise ratio via enhancing the expansion coefficient κ . Here, κ is the edge slope of the single peak obtained by fitting the double-peak EIT-AT spectrum, characterizing the response of the probe light to the frequency detuning of the coupling laser. The sensitivity is thus boosted by a factor of approximately 19 dB. This study highlights the pivotal role of optical cavities in advancing Rydberg-based detection systems, offering a promising approach for high-sensitivity microwave electric field measurements.
Quantum microwave measurement techniques based on Rydberg atoms exhibit exceptional potential in microwave communication, sub-wavelength imaging and quantum metrology, due to the inherent advantages of self-calibration, minimal interference with external electric fields, and a broadband range of measurable frequencies. However, the current measurement sensitivity is not yet comparable to that of classical receivers. One contributing factor is the low utilization of atoms within the vapor cell, which remains a significant challenge to enhance substantially. To address this problem, scholars have proposed a variety of optical domain methods to enhance sensitivity. For example, increasing vapor cell length, utilizing multi-photons excitation or repump lasers. Despite these advancements, the study of the influence of laser beam diameter on the sensitivity is insufficient, and the lack of a comprehensive experimental investigation is not conducive to the practical application and optimization of the receiver. In this study, we investigate the impact of varying probe laser diameters on receiver sensitivity using a beam expander to adjust the diameter from 600 μm to 3 mm. Modifying the beam diameter could alter the light-atom interaction area in the vapor cell, offering a feasible approach to adjust the utilization of the atoms. Our findings indicate that under the experimental conditions, the sensitivity could be enhanced by expanding the beam diameter, where the sensitivity is changed from 299 nV cm-1 Hz-1/2 to 127 nV cm-1 Hz-1/2. These results could provide valuable insights for designing and optimizing ultrahigh-sensitivity Rydberg atomic receivers and facilitating applications in meteorology, communication, and quantum precision measurement.
The highly-excited Rydberg states are with a unique property of radio-frequency (RF) resonance, and Rydberg atoms at room temperature are promising for developing a broadband RF electric field sensor and relevant metrology standards. In this paper, the working mechanism of an atomic amplitude-modulation(AM) radio receiver is investigated in detail, and various factors affecting the communication quality are discussed. The modulation RF signal can be directly retrieved by measuring the transmission of a probe laser at resonance of rubidium D2 transition using a fast photo-diode detector, without any conventional demodulation process. Various communication experiments are tested at a 10.22 GHz carrier, and a modulation bandwidth of 1 MHz and an acceptable data transfer rate of about 1 Mbps have been achieved using current detection techniques. Owing to a potential high sensitivity and ultra-broadband capability of free-space RF field sensing, the quantum receiver has great significance compared with conventional electronics-based receivers, including but not limited to a weak signal, long-distance, and broadband communication in free space or via a fiber link.