Sensitive Atoms

Zheng Wang, Mingyong Jing, Peng Zhang +5 more

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.

S. M. Barnett

Clyde E. Wiegand

Takuya Kawasaki, Sotatsu Otabe, Tomoya Sato +3 more

The sensitivity of an interferometer depends on its readout scheme. However, little attention has been paid to the readout schemes of atom interferometers from the viewpoint of their sensitivity. The difference in sensitivity between readout schemes or their optimization has not been considered in the literature. Herein we analytically calculate the sensitivities of an atom interferometer with typical readout schemes by applying the two-photon formalism, which was developed for optical interferometers to deal with quantum noise. Our calculations reveal that by using sinusoidal phase modulation, the sensitivity can surpass that obtained by the conventional phase sweeping scheme. The superiority of this phase modulation scheme for both cold and thermal atomic beams is demonstrated. In addition, we show that the phase modulation scheme is advantageous for atom-flux fluctuation and resists atom-flux drift. This study performs a general analysis of the sensitivity of atom interferometers and identifies an advantageous readout scheme.

Kwanruthai Sibsiri, Piyachat Wungmool, Phusit Nualpijit +4 more

Abstract An atomic magnetometer (AM) is very sensitive to magnetic fields and useful in many applications. AM works by optical interrogation of orientation of alkali-atom spins in a vapor cell. Since the sensitivity characterizes the performance of AM, it should be optimized. We investigate the effect of the gain of a balanced photodetector on the sensitivity of an RF atomic magnetometer setup. While the amplitude of RF signal (BRF) varies between 0.1-10 nT, the frequency is fixed at 100 kHz. The gain of the balanced photodetector varies between 103 - 107 V/A. the noise density and AM signal are measured to calculate the signal-to-noise ratios (SNR) and the AM sensitivity. The results show that noise density increases with the gain value. The AM signal increases with both BRF as well as the gain value. SNR increases with BRF while the AM sensitivity is independent on BRF. When the gain is increased from 103 - 105 V/A, SNR increases and reaches a maximum while the AM sensitivity decreases and reaches a minimum value of 0.4 pT/√Hz. However, SNR and the AM sensitivity are almost unchanged for the gain value of 105 - 107 V/A. Therefore, the gain of balanced photodetector in our AM setup should be set sufficiently high, at least 105 V/A.