Non-Gaussian low-frequency noise, such as random telegraph noise (RTN), is widely present in quantum sensing systems and is usually regarded as the main perturbation limiting sensitivity and stability. However, whether it can be transformed into a usable spectroscopic resource still lacks systematic experimental verification. We demonstrate Ξ - and Λ -type noise-induced transparency (NIT) effects in an optically pumped atomic magnetometer coupled to non-Gaussian RTN reservoirs, showing that NIT arises from interference between stochastic transition channels in spins, both theoretically and experimentally. In the Ξ -type configuration, the spectral splitting driven by RTN exhibits a significant change in the transparency window, and the relationship between dynamic criticality and observable spectral structure is elucidated by the correlation between the Liouvillian exceptional point and the resolvable spectral-splitting threshold. In the Λ -type configuration, the interference effect of amplitude-dependent noise enables the transparency effect to be stably manifested under weak noise, providing a calibrable noise-amplitude readout mechanism. These results extend magnetometer spectra from noise suppression to probing noise with noise, providing a new approach for non-Gaussian noise measurement and adaptive background-noise sensing.
Non-Gaussian low-frequency noise, such as random telegraph noise (RTN), is widely present in quantum sensing systems and is usually regarded as the main perturbation limiting sensitivity and stability. However, whether it can be transformed into a usable spectroscopic resource still lacks systematic experimental verification. We demonstrate Ξ - and Λ -type noise-induced transparency (NIT) effects in an optically pumped atomic magnetometer coupled to non-Gaussian RTN reservoirs, showing that NIT arises from interference between stochastic transition channels in spins, both theoretically and experimentally. In the Ξ -type configuration, the spectral splitting driven by RTN exhibits a significant change in the transparency window, and the relationship between dynamic criticality and observable spectral structure is elucidated by the correlation between the Liouvillian exceptional point and the resolvable spectral-splitting threshold. In the Λ -type configuration, the interference effect of amplitude-dependent noise enables the transparency effect to be stably manifested under weak noise, providing a calibrable noise-amplitude readout mechanism. These results extend magnetometer spectra from noise suppression to probing noise with noise, providing a new approach for non-Gaussian noise measurement and adaptive background-noise sensing.
Optically pumped atomic magnetometer (OPAM), as a highly sensitive quantum sensor, is often significantly disturbed by low-frequency random noise, which seriously limits its measurement robustness. Motivated by this problem, we systematically studied the influence of various parameters of the statistical field related to random telegraph noise (RTN) on the dynamics and spectral characteristics of the OPAM, both theoretically and experimentally. The investigation revealed that the OPAM output spectrum shows a phase sensitivity similar to that induced by the squeezed vacuum field to the relative phase ϕ between the statistical field and the coherent driving field, and its physical essence originates from the phase-dependent reservoir formed by the statistical field. Specifically, the system spectrum is periodically modulated to ϕ , showing complementary regulation behavior of spectral peak and linewidth: when ϕ =90 ∘ , the system is almost insensitive to the RTN noise parameters, showing good robustness; however, when ϕ =0 ∘ , the system is highly responsive to the RTN parameters, showing obvious spectral broadening effect. Our results not only provide what we believe to be a new phase control strategy for the optimization of the OPAM under the background of low-frequency noise, but also provide theoretical and experimental path for the development of noise spectrum precision measurement and dynamical decoupling technology based on OPAM.
Abstract Non-Gaussian noise is usually regarded as a limitation for precision measurements, something to be shielded against or eliminated. We take the opposite approach by injecting controllable random telegraph noise (RTN) into an optically pumped atomic magnetometer (OPAM), demonstrating that controlled colored noise can serve as a spectroscopic probe of spin-environment coupling. By independently tuning the RTN amplitude, switching rate, and carrier detuning, we resolve a stochastic-response crossover from fast-switching motional averaging to a slow-switching, configuration-resolved regime. Beyond noise-induced broadening, the spectral envelope reflects the finite residence time of the two values of the same RTN process. These results establish controlled RTN as a spectroscopic probe of spin-environment coupling in an OPAM. The measured spectra vary systematically with the applied RTN amplitude, switching rate, and carrier detuning.
We have investigated some possibilities to use effect of Electromagnetically Induced Transparency (EIT), which is based on quantum interference, for measuring magnetic fields. Multi-frequency laser light is driving atomic transitions (e.g. in a Λ-type excitation scheme), and the atoms are decaying into a super positional dark state, in which the population is trapped, if the frequencies of the applied light fulfills certain conditions. Then the atomic medium becomes transparent for the exciting electromagnetic fields. The observed line width of this "transparency window" is not limited by the natural line width of the involved optical transitions and can be decreased down to a few hundredths of Hertz. As a consequence, this narrow feature can be used as a sensitive probe if the frequencies fulfill the required conditions, which are dependent on the energy positions of the involved atomic levels. These energy positions are influenced by external magnetic fields, thus the observation of EIT can be used to determine external magnetic fields strengths. In our approach a so called Hanle-configuration is used, where only one laser frequency is used to simultaneously excite σ+- and σ--transitions within a single hyperfine transition of the Rb87 Dl-line. In this configuration a resonant Λ-system is formed at zero magnetic field. The detuning from two-photon resonance is caused by a magnetic field scanned in laser propagation direction. Any additional probe magnetic field characteristically changes the width and shape of the EIT transparency window resonance; hence the probe magnetic field can be determined directly from the shape of this resonance.
For spin-polarized ensembles of alkali-metal atoms with hyperfine structure and spin greater than 1/2, the interplay between spin dynamics and quantum noise mechanisms remains largely unexplored, especially in the spin-exchange-relaxation-free (SERF) regime. In particular, the theoretical understanding of the dynamics for the mean values of the spin operators was established shortly after the advent of optical pumping. In contrast, a corresponding theory for spin fluctuations has not yet been developed, and is addressed in this work. Here, we develop such a first-principles theory of spin fluctuations in alkalimetal vapors. The nonlinearity bottleneck of spin-exchange collisions, which dominate the physics of such vapors, is overcome by linearizing the dynamics around the equilibrium density matrix. The result is a precise calculation of the absolute magnetic sensing limit of optically pumped atomic magnetometers, which can precisely benchmark quantum limited and quantum enhanced protocols, in contrast to the traditional approach shown to be adequate only within a factor of 2. Further, we elucidate how signal and noise in atomic magnetometers are distributed among the spin eigenmodes defined under continuous optical pumping and probing via the paramagnetic Faraday rotation. Notably, in the SERF regime, alongside the magnetic resonance narrowing, we find a reduction of spin noise at the spin-precession frequency as a consequence of strong hyperfine correlations redistributing spin noise, when both hyperfine manifolds are simultaneously probed. These insights can lead to improved quantum devices utilizing alkali-metal atoms or similar spin-based sensing platforms.
Optically pumped magnetometers (OPMs) are revolutionizing the task of magnetic-field sensing due to their extremely high sensitivity combined with technological improvements in miniaturization which have led to compact and portable devices. OPMs can be based on spin-oriented or spin-aligned atomic ensembles which are spin polarized through optical pumping with circular or linear polarized light, respectively. Characterization of OPMs and the dynamical properties of their noise is important for applications in real-time sensing tasks. In our work, we experimentally perform spin noise spectroscopy of an alignment-based magnetometer. Moreover, we propose a stochastic model that predicts the noise power spectra exhibited by the device when, apart from the strong magnetic field responsible for the Larmor precession of the spin, white noise is applied in the perpendicular direction aligned with the pumping-probing beam. By varying the strength of the noise applied as well as the linear-polarization angle of incoming light, we verify the model to accurately predict the heights of the Larmor-induced spectral peaks and their corresponding linewidths. Our work paves the way for alignment-based magnetometers to become operational in real-time sensing tasks. Published by the American Physical Society 2024
The quantum noise of squeezed probe light passing through an atomic system with different electromagnetically induced transparency and Autler—Townes splitting effects is investigated theoretically. It is found that the optimal squeezing preservation of the outgoing probe beam occurs in the strong-coupling-field regime rather than in the weak-coupling-field regime. In the weak-coupling-field regime, which was recently recognized as the electromagnetically induced transparency regime (Abi-Salloum T Y 2010 Phys. Rev. A 81 053836 ), the output amplitude noise is affected mainly by the atomic noise originating from the random decay process of atoms. While in the strong-coupling-field regime, defined as the Autler—Townes splitting regime, the output amplitude noise is affected mainly by the phase-to-amplitude conversion noise. This is useful in improving the quality of the experiment for efficient quantum memory, and hence has an application in quantum information processing.