Session Q11: V: Precision Measurements

Imaging Charged Particle Beams With Atomic Magnetometry

We present the results of 2-dimensional imaging of a charged particle beam using an atomic magnetometer. By propagating a beam of electrons through a low-pressure rubidium vapor, the alkali atoms experience a shift in their atomic states. A probe laser monitoring the $D_2$ transition of rubidium reacts with a rotation in its polarization angle directly proportional to the sensed magnetic field of the electron beam. The spatial dependence of the magnetic field can then be inferred using the CCD images of the probe laser polarization components. The obtained magnetic field distribution allows us to reconstruct the current density of the particle beam. As a proof of concept, we are able to image 1.5 mm diameter electron beams down to 20 $mu$A currents. These results are achieved through collaboration with Thomas Jefferson National Accelerator Facility to develop a non-invasive diagnostic tool for charged particle beams.   

Miniature Planar Self-Shielded Coil for Suppressing Crosstalk of Optically Pumped Magnetometer Arrays

The multi-channel optically pumped magnetometer (OPM) array has been considered as a new generation of equipment used in the magnetoencephalography (MEG), due to its high sensitivity, flexibility, no cryogenic cooling required, and multi-axis measurement capability. Reducing the volume of the magnetometer probe and increasing the spatial density of the array can improve the measurement spatial resolution of the whole-head MEG system, which is the future development trend. However, due to the need for magnetic field modulation and compensation based on the coils inside the OPM probe, reducing the probe spacing will exacerbate the adverse effect of the magnetic field outside the coil on adjacent probes, resulting in a magnetic field crosstalk. Here, we present a design method for planar self-shielded uniform magnetic field coils suitable for commonly used miniaturized triaxial atomic magnetometers. The proposed method constructs the multiple coil pairs with the same number of turns in a square planar configuration facilitating the process into flexible printed circuits and the installation on six faces of the cubic structure. The coil structure parameters and current directions are optimized based on the Taylor expansion method and magnetic field characteristics of the target field points to ensure the required uniform interior and rapidly decaying exterior magnetic field. The coils designed by the proposed method can effectively improve the crosstalk problem and support probe spacing reduced in magnetometer arrays.   

Measurement of Rb-Xe S­­­pin-Exchange Rate Coefficients for NMR Gyroscopes

Determination of the spin-exchange rate coefficients between Xe nuclei and alkali-metal atoms is complicated due to various mechanisms of spin-exchange as formation and destruction of van der Waals molecules and binary collisions. There are a variety of conflicting measurements in the literature, recently reviewed by Kelley and Branca [1].  Measurements that rely on temperature dependences are potentially ambiguous due to the difficulty of isolating wall relaxation from the other processes.  We will summarize different methods for measuring spin-exchange rate coefficient without making assumptions about wall relaxation and we will present preliminary measurements of the Rb-Xe spin-exchange rate coefficient under typical conditions used in NMR gyroscopes [2].

 

1. M. Kelley and R. T. Branca, J. Appl. Phys. 129, 154901 (2021)

2. S. S. Sorensen, D. A. Thrasher, T. G. Walker, Appl. Sci. 10, 7099 (2020)   

Optimal Control of a Sagnac Tractor Atom Interferometer

Atom interferometers are powerful tools for the precise measurement of gravitational fields, acceleration, and rotation, with numerous applications in fundamental physics, metrology, and inertial sensing. Rotation can be measured with unprecedented sensitivity from the Sagnac phase arising between wavepackets counter-rotating around an enclosed area. We consider here the implementation of a rotating tractor atom interferometer based on uninterrupted three-dimensional confinement and guidance. Ideally, the wavepacket components adiabatically follow  pre-programmed trapping potentials. Minimizing the amplitude of the trapping potential reduces harmful photon scattering, while maximizing the average acceleration during splitting and recombination maximizes interferometric area for improved phase accumulation. However, weak trapping potentials and fast separation challenge adiabatic wavepacket evolution, and ultimately lead to a breakdown in fidelity. In the work presented here, we numerically map out the achievable fidelity versus trap depth and separation time. We show how the use of optimal control theory can counteract nonadiabatic defects. By dynamically tuning both amplitude and  rotational acceleration of the trapping potentials during splitting and recombination, we can operate the rotating tractor interferometer at a limit of low power and yet high speed, leading to high fidelity under challenging conditions.

Reconfigurable Continuous-Variable Distributed Quantum Metrology

Distributed Quantum Metrology is the study of quantum metrological techniques to enhance measurements that are spatially distributed for applications such as phase imaging and global-scale clock synchronization. Recent studies have both theoretically investigated and experimentally demonstrated some interesting schemes using a linear network with nonclassical states of light. Yet, a truly reconfigurable scheme of distributed quantum metrology with arbitrary weights using continuous-variable states has not been studied. In this talk, I will present our recent study on the topic and show our results in designing a reconfigurable distributed quantum metrology scheme with continuous-variable inputs. The ultimate sensitivity in distributed quantum metrology and the conditions for achieving the Heisenberg limit will be discussed.   

Proving the rotational motion of the photon using the photon energy equation

The motion of the photon is affected by the motion of its source, Electron, and must include all types of motion of its source. So, the photon has a three-dimensional motion, including a transition movement and a rotary motion. And it traverses in a helical trajectory. By using this definition, we have proved wave-particle duality at the same time and introduce a new equation for the photon energy.

Using this energy equation, we conclude that this equation is always valid, so the photon must have rotational motion.