Young-Jin Kim

Development of a SQUID-Based

A discovery of a permanent electric dipole moment (EDM) of the neutron would provide one of the most important low energy tests of the discrete symmetries beyond the Standard Model of particle physics. A new search of neutron EDM, to be conducted at the spallation neutron source at Oak Ridge National Laboratory, is designed to improve the present experimental limit of ~10-26 e·cm by two orders of magnitude. The experiment is based on the magnetic-resonance technique in which polarized neutrons precess at the Larmor frequency when placed in a static magnetic field; a nonzero EDM would be evident as a difference in precession frequency when a strong external electric field is applied parallel versus antiparallel to the magnetic field. In addition to its role as neutron spin-analyser via the spin-dependent n+3He nuclear capture reaction, polarized helium-3 (which has negligible EDM) will serve as co-magnetometer to correct for drifts in the magnetic field. In one of the two methods that will be built into the apparatus, the helium-3 precession signal is read out by SQUID-based gradiometers. We present a design study of a SQUID system suitable for the neutron EDM apparatus, and discuss using very long leads between the pickup loop and the SQUID.

{}^{3}\hbox{He}

We propose a novel experimental approach to explore exotic spin-dependent interactions using a spin-exchange relaxation-free (SERF) magnetometer, the most sensitive noncryogenic magnetic-field sensor. This approach studies the interactions between optically polarized electron spins located inside a vapor cell of the SERF magnetometer and unpolarized or polarized particles of external solid-state objects. The coupling of spin-dependent interactions to the polarized electron spins of the magnetometer induces the tilt of the electron spins, which can be detected with high sensitivity by a probe laser beam similarly as an external magnetic field. We estimate that by moving unpolarized or polarized objects next to the SERF Rb vapor cell, the experimental limit to the spin-dependent interactions can be significantly improved over existing experiments, and new limits on the coupling strengths can be set in the interaction range below

Co-Magnetometer Readout for a Neutron Electric Dipole Moment Experiment

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Search for exotic spin-dependent interactions with a spin-exchange relaxation-free magnetometer

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Magnetic microscopic imaging with an optically pumped magnetometer and flux guides

By combining an optically pumped magnetometer (OPM) with flux guides (FGs) and by installing a sample platform on automated translation stages, we have implemented an ultra-sensitive FG-OPM scanning magnetic imaging system that is capable of detecting magnetic fields of ∼20 pT with spatial resolution better than 300u2009μm (expected to reach ∼10 pT sensitivity and ∼100u2009μm spatial resolution with optimized FGs). As a demonstration of one possible application of the FG-OPM device, we conducted magnetic imaging of micron-size magnetic particles. Magnetic imaging of such particles, including nano-particles and clusters, is very important for many fields, especially for medical cancer diagnostics and biophysics applications. For rapid, precise magnetic imaging, we constructed an automatic scanning system, which holds and moves a target sample containing magnetic particles at a given stand-off distance from the FG tips. We show that the device was able to produce clear microscopic magnetic images of 10u2009μm-size magn...

High-resolution magnetic imaging with an array of flux guides

Potential applications in neuroscience, such as recordings of neural electrical activity at a microscopic scale, set demanding requirements on both high-resolution and high-sensitivity magnetic imaging. Optically pumped magnetometers (OPMs) based on lasers and alkali-metal vapor cells are the most sensitive magnetic field sensors that do not require cryogenic cooling. Recently, we constructed and tested an ultra-sensitive magnetic microscope by combining a cm-size spin-exchange relaxation-free (SERF) OPM with a pair of flux guides (FGs). The FGs served to direct the magnetic flux from a microscopic source of magnetic field to the OPM to improve simultaneously the spatial resolution and the magnetic field sensitivity. The specific demonstrated performance of the FG-OPM device was resolution 250 μm and sensitivity 23 pT/ Hz1/2, with potential for further improvement according to numerical simulations to the level that a single neuron could be detected. Our previous demonstration and simulations were done for a single pair of FGs. In this work, we numerically investigated the performance of a parallel multi-FG system and show that similar high resolution and high sensitivity are feasible. Many applications such as the neuronal direct magnetic imaging, non-destructive tests, and detection of magnetic particles with high throughput are anticipated.

Tests of a SQUID-Based Co-Magnetometer Readout for a Neutron EDM Experiment

In a new experimental search for an electric dipole moment (EDM) of the neutron, polarized 3He will occupy the same volume as the neutrons under study to serve as a co-magnetometer, enabling precise corrections for ambient magnetic field drifts that would otherwise severely limit the reach of the experiment. One of the two methods that will be built into the apparatus is to directly detect the 3He magnetization signal using superconducting quantum interference device (SQUID)-based gradiometers. In a previous work in this Transactions, we proposed a candidate design for a SQUID system consistent with experimental requirements and the planned neutron EDM apparatus. Because the 3He precession signal is at approximately 100 Hz, signal contamination from low-frequency magnetic noise could adversely affect the co-magnetometer readout precision; the addition of reference magnetometer channels to the SQUID system could mitigate this risk. In this paper, we present noise studies of the candidate SQUID system in a test apparatus and demonstrate effective ambient magnetic field noise cancelation with the implementation of reference channels. In addition, we report a demonstration of low-noise SQUID operation while a nearby photomultiplier tube and its high-voltage power supply are operating.