Symmetry-breaking inelastic wave-mixing atomic magnetometry

Inelastic two-wave mixing induced high-efficiency transfer of optical vortices

A scheme for high-efficiency transfer of optical vortices is proposed by an inelastic two-wave mixing (ITWM) process in an inverted-Y four-level atomic medium, which is originally prepared in a coherent superposition of two ground states. The orbital angular momentum (OAM) information in the incident vortex probe field can be transferred to the generated signal field through the ITWM process. Choosing reasonable experimentally realizable parameters, we find that the presence of the off-resonance control field can greatly improve the conversion efficiency of optical vortices, rather than in the absence of a control field. This is caused by the broken of the destructive interference between two one-photon excitation pathways. Furthermore, we also extend our model to an inelastic multi-wave mixing process and demonstrate that the transfer efficiency between multiple optical vortices strongly depends on the superposition of the ground states. Finally, we explore the composite vortex beam generated by collinear superposition of the incident vortex probe and signal fields. It is obvious that the intensity and phase profiles of the composite vortex can be effectively controlled via adjusting the intensity of the control field. Potential applications of our scheme may exist in OAM-based optical communications and optical information processing.

Theory of colliding-probe atomic magnetometry: breaking the symmetry-enforced magneto-optical rotation blockade

We show theoretically the presence of an optical field polarization rotation blocking mechanism in single-probe-based magnetic field sensing schemes, revealing the root cause for extremely small nonlinear magneto-optical rotation (NMOR) signal in single-probe-based atomic magnetometers. We present a colliding-probe atomic magnetometer theory, analytically describing the principle of the first nonlinear-optical atomic magnetometer. This new atomic magnetometry technique breaks the NMOR blockade in single-probe atomic magnetometers, enabling an energy circulation that results in larger than 20-dB enhancement in NMOR signal as well as better than 6-dB improvement of magnetic field detection sensitivity. Remarkably, all experimental observations reported to date can be qualitatively well-explained using this colliding-probe atomic magnetometry theory without numerical computations. This colliding-probe atomic magnetometry technique may have broad applications in scientific and technological fields ranging from micro-Tesla magnetic resonance imaging to cosmic particle detection.

Magneto-optical rotation: accurate approximated analytical solutions for single-probe atomic magnetometers

We report an approximated analytical solution for a single-probe four-state atomic magnetometer where no analytical solution exists. This approximated analytical solution demonstrates excellent accuracy in broad probe power and detuning ranges when compared with the numerical solution obtained using a 4th order Runge-Kutta differential equation solver on MATLAB. The theoretical framework and results also encompass widely applied single-probe three-state atomic magnetometers for which no analytical solution, even approximated, is available to date in small detuning regions.

Improvement in the signal amplitude and bandwidth of an optical atomic magnetometer via alignment-to-orientation conversion

We evaluated the alignment-to-orientation conversion (AOC) at the cesium D1 line to improve a nonlinear magneto-optical rotation (NMOR) optical atomic magnetometer's signal amplitude and bandwidth. For the 6 ²S_1/2 F = 3 → 6 ²P_1/2 F' = 4 transition, the AOC-related NMOR achieves a 1.7-fold enhancement in signal amplitude compared to the conventional NMOR, benefiting from narrow linewidth and ultraweak power broadening. Therefore, an effective amplitude-to-linewidth ratio is maintained in the high-laser-power region. This method is beneficial for detecting high-frequency magnetic signals in nuclear magnetic resonance and biomagnetism, as the NMOR magnetometer bandwidth increases with laser power.

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.

Artificial modulation-free Pound-Drever-Hall method for laser frequency stabilization

We have proposed an artificial modulation-free Pound-Drever-Hall (PDH) method for laser frequency stabilization and demonstrated it via two-color polarization spectroscopy of Rydberg electromagnetically induced transparency (EIT) resonance in a room-temperature rubidium vapor. Due to the unique error signal profile, the conventional PDH method owns a large capture range in laser frequency locking. Here we manually construct a PDH error signal via a linear combination of polarization spectroscopies of the Rydberg EIT resonances without and with a magnetic field applied. The artificial modulation-free PDH error signal owns a subnatural linewidth dispersion curve as well as a large capture range with which we successfully stabilize the laser to an absolute atomic frequency reference in a long running time, immune to environmental fluctuation and even manmade impulse perturbation. This method can provide an absolute frequency reference based on atomic transition while keeping similar locking ability to provide corrections for frequency fluctuations over a broad bandwidth as the conventional PDH.

Analytical design of axial magnetic coils with systematically improved uniformity for miniature quantum devices

We describe an analytical design method of shielding-coupled uniform magnetic coils for miniature quantum devices. The theoretical and simulation results point out that the 99% range along the symmetrical axis and the 50% range along the radius of the proposed m = 3 coils are uniform, and more important is that both the uniformity and the uniform region for these kinds of coils can be systematically improved only by adding more loops at specific places obtained from our analytical formula. A relevant experiment demonstrates the feasibility of this method and realizes the m = 3 coils with the inhomogeneity below 2.6 × 10^-3 along nearly the whole symmetrical axis. In addition, a practical technology to remove the influence of the shielding's nonideal gaps and openings is proposed and realized. All of these results are crucial for the miniaturization and high performance of quantum devices.

Breaking the Energy-Symmetry-Based Propagation Growth Blockade in Magneto-Optical Rotation

The magneto-optical polarization rotation effect has myriad applications in many research areas spanning the scientific spectrum, including space and interstellar research, nanotechnology, material science, biomedical imaging, and subatomic particle research. In the nonlinear magneto-optical rotation (NMOR) effect, the angle of rotation of a linearly polarized optical field in a magnetized medium is dependent upon its intensity. However, typical NMOR signals of conventional single-beam Λ -scheme atomic magnetometers are peculiarly small, requiring sophisticated magnetic shielding and high-frequency phase-sensitive detection. Here, we show the presence of an energy-symmetry-based propagation growth blockade that undermines the NMOR effect in conventional single-beam Λ -scheme atomic magnetometers. We further demonstrate, both experimentally and theoretically, an inelastic wave-mixing technique that breaks this NMOR blockade, resulting in more-than-2-orders-of-magnitude enhancement of the NMOR signal power amplitude that cannot be achieved with conventional single-beam Λ -scheme atomic magnetometers. This technique, demonstrated here with substantially reduced light intensities at near-room temperatures, may lead to many applications, especially in the field of biomagnetism and high-resolution low-field magnetic imaging.