arXiv subjects

Aleksandra Sierant

Publications and source records attributed to Aleksandra Sierant.

9 recordsLinked to original sources

arXiv2026

Optimal and efficient inference tools for field tracking with precessing spins

Precise, real-time monitoring of magnetic field evolution is important in applications including magnetic navigation and searches for physics beyond the standard model. One main field-monitoring technique, the spin-precession magnetometer (SPM), observes electron, nucleus, colour centre, or muon spins as they precess in response to their local magnetic field. Here, we study Bayesian signal-recovery methods for SPMs in the free-induction decay (FID) mode. In particular, we study tracking of field changes well within the coherence time of the spin system, and thus well beyond the response bandwidth, as in [R. Jiménez-Martínez et al., Phys. Rev. Lett. 120, 040503 (2018)]. We derive the Bayesian Cramér-Rao bound that dictates the ultimate precision in estimating the Larmor frequency, which we show to be attained by the computationally expensive prediction error method (PEM). Relative to this benchmark, we show that the extended Kalman filter (EKF) and cubature Kalman filter (CKF) offer near-optimal tracking that is also computationally efficient, with the use of the latter giving better results only for a large spin number. Focusing thus on the EKF, we show that it is sufficient to accurately track fluctuating and unknown transient signals. Our methods can be easily adapted to other types of sensors undergoing nonlinear dissipative dynamics and experiencing intrinsic Gaussian-like stochastic noises.

quant-ph↗

arXiv2026

Fast, powerful, low-noise optical pumping of an atomic vapor with semiconductor optical amplifiers

We use a $^{87}\text{Rb}$ atomic vapor, suitable for an optically-pumped magnetometer (OPM) in Earth-field conditions, to study the noise properties of three strategies for generating pulsed optical pumping. We compare a frequency-modulated (FM) laser, amplitude modulation (AM) via an acousto-optic modulator (AOM), and amplitude modulation via a semiconductor optical amplifier (SOA). Pumping the ensemble to operate as a Bell-Bloom OPM, and with an equal degree of spin polarization, the three methods give nearly identical sensitivity, showing that the SOA, despite being an active device, can introduce negligible additional noise. Pumping the ensemble to operate as a free-induction-decay OPM, we observe longer unpumped coherence times with the SOA-AM method than with the FM method. Finally, using the higher power available from the SOA, we demonstrate an environment-limited sensitivity of $80\text{fT}/\sqrt{\text{Hz}}$ at $600\text{Hz}$ and 200fT$200\text{fT}/\sqrt{\text{Hz}}$ at $4\text{kHz}$, one to two orders of magnitude beyond what was achievable with the other pumping methods.

physics.atom-ph↗

arXiv2026

Quantum noise in a squeezed-light-enhanced multiparameter quantum sensor

We study quantum enhancement of sensitivity using squeezed light in a multi-parameter quantum sensor, the hybrid dc-rf optically pumped magnetometer (hOPM) [Phys. Rev. Applied 21, 034054, (2024)]. Using a single spin ensemble, the hOPM acquires both the dc field strength (scalar magnetometry), and resonantly detects one quadrature of the ac magnetic field at a chosen frequency (rf magnetometry). In contrast to the Bell-Bloom scalar magnetometer [Phys. Rev. Lett. 127, 193601 (2021)], the back-action evasion in the hOPM is incomplete, leading to a nontrivial interplay of the three quantum noise sources in this system: photon shot noise, spin projection noise, and measurement back-action noise. We observe these interactions using squeezed light as a tool to control the distribution of optical quantum noise between $S_2$ and $S_3$ polarization Stokes components, and the resulting effect on readout quantum noise and measurement back-action. These results demonstrate quantum-enhanced sensitivity in a continuously operating multi-parameter sensor and reveal fundamental trade-offs between sensitivity, back-action, and bandwidth.

quant-ph↗

arXiv2026

Quantum noise scaling in continuously operating multiparameter sensors

We experimentally investigate the quantum noise mechanisms that limit continuously operating multiparameter quantum sensors. Using a hybrid rf-dc optically pumped magnetometer, we map the photon shot noise, spin projection noise, and measurement back-action noise over an order of magnitude in probe power and a factor of three in pump power while remaining quantum-noise-limited. We observe linear, quadratic, and cubic scaling of the respective total noise powers with probe photon flux, together with a quadratic dependence of back-action on pump photon flux, in quantitative agreement with a stochastic Bloch-equation model. At higher probe powers, additional probe-induced relaxation modifies the spin-noise spectrum while preserving the integrated noise scaling. Our results reveal fundamental, resource-dependent trade-offs unique to continuously monitored multiparameter sensors and establish experimentally the quantum limits governing their optimal operation.

quant-ph↗

arXiv2025

Sequential analysis in a continuous spin-noise quantum sensor

Many control and detection applications require real-time analysis of signals from sensors, in order to quickly and accurately act upon events revealed by the sensors. Such signal analysis benefits from statistical models of signal and sensor behavior. This creates a need for data analysis methods that are simultaneously model-based, computationally efficient and causal, in the sense that they employ only sensor data available prior to a specific point in time. In this work, we implement sequential data analysis techniques on a spin-noise-based quantum sensor, to perform two key tasks: hypothesis testing and quickest change-point detection. These online protocols allow us to detect weak magnetic fields by adaptively collecting measurement data until a predefined confidence threshold is reached. We demonstrate these methods in a realistic experimental setting and derive performance bounds for the achievable precision and response time. Our approach has potential utility when detecting small perturbations to the magnetic field, in both applied and fundamental contexts including biomagnetism, geophysical surveys, detection of concealed materials, searches for dark matter candidates and exotic spin interactions. Our results demonstrate that sequential techniques enable faster and more sensitive detection, making them a powerful tool for quantum sensing.

quant-ph↗

arXiv2024

Multiparameter quantum sensing and magnetic communications with a hybrid dc and rf optically pumped magnetometer

We introduce and demonstrate a hybrid optically pumped magnetometer (HOPM) that simultaneously measures one dc field component and one rf field component quadrature with a single atomic spin ensemble. The HOPM achieves sub-pT/$\sqrt{\mathrm{Hz}}$ sensitivity for both dc and rf fields, and is limited in sensitivity by spin projection noise at low frequencies and by photon shot noise at high frequencies. We demonstrate with the HOPM a new application of multiparameter quantum sensing: background-cancelling spread spectrum magnetic communication. We encode a digital message as rf amplitude, spread among sixteen channels from \SI{29}{\kilo\hertz} to \SI{33}{\kilo\hertz} in a noisy magnetic environment, and observe quantum-noise-limited rf magnetic signal recovery enabled by quantum-noise-limited dc noise cancellation, reaching noise rejection of \SI{15}{\decibel} at \SI{100}{\hertz} and more than \SI{20}{\decibel} at \SI{60}{\hertz} and below. We measure signal fidelity versus signal strength and extrinsic noise in communication of a short text message. The combination of high sensitivity, quantum-noise-limited performance, and real-world application potential makes the HOPM ideally suited for study of high-performance multiparameter quantum sensing.

quant-ph↗

arXiv2023

Tailoring population transfer between two hyperfine ground states of Rb87

In this paper, we investigate the coherent control over a complex multi-level atomic system using the stimulated Raman adiabatic passage (STIRAP). Based on the example of rubidium-87 atoms, excited with circularly-polarized light at the D1 line, we demonstrate the ability to decompose the system into three- and four-level subsystems independently interacting with light beams. Focusing on the four-level system, we demonstrate that the presence of an additional excited state significantly affects the dynamics of the system evolution. Specifically, it is shown that, through the appropriate tuning of the light beams, some of the transfer channels can be blocked, which leads to better control over the system. We also demonstrate that this effect is most significant in media free from inhomogeneous broadening (e.g., Doppler effect) and deteriorates if such broadening is present. For instance, motion of atoms affects both the efficiency and selectivity of the transfer.

physics.atom-ph↗

arXiv2021

Auto-heterodyne characterization of narrow-band photon pairs

We describe a technique to measure photon pair joint spectra by detecting the time-correlation beat note when non-degenerate photon pairs interfere at a beamsplitter. The technique implements a temporal analog of the Ghosh-Mandel effect with one photon counter and a time-resolved Hong-Ou-Mandel interference with two. It is well suited to characterize pairs of photons, each of which can interact with a single atomic species, as required to study recently predicted photon-photon interaction in sub-wavelength atomic arrays. With this technique, we characterize photon pairs from cavity-enhanced parametric downconversion with a bandwidth $\approx$ 5 MHz and frequency separation of $\sim$ 200 MHz near the D$_1$ line of atomic Rb.

quant-ph↗

arXiv2020

Quantitative near-field characterization of Surface Plasmon Polaritons on nanofabricated transmission structure

The tailoring of plasmonic near-fields is central to the field of nanophotonics. The detailed knowledge of the field distribution is crucial for a design and fabrication of plasmonic sensors, detectors, photovoltaics, plasmon-based cicuits, nanomanipulators, electrooptic plasmonic modulators and atomic devices. We report on a fully quantitative comparison between near field observation and numerical calculations, considering the intensity distribution for TM and TE polarisations, necessary for the construction of devices in all these areas. We present the near field scanning microscopy (NSOM) results of Surface Plasmon Polaritons (SPPs), excited by linearly polarized illumination on a gold, nanofabricated transmission grating. The optimization process is performed for infrared light, for future applications in cold atoms trapping and plasmonic sensing. We show the in situ processes of build up and propagation of SPPs and confirm that the out of plane component is not coupled to the aperture-type NSOM probe.

physics.optics↗