1,721,288 research outputs found
Surpassing the Energy Resolution Limit with ferromagnetic torque sensors
No full textWe discuss the fundamental noise limitations of a ferromagnetic torque sensor based on a levitated magnet in the tipping regime. We evaluate the optimal magnetic field resolution taking into account the thermomechanical noise and the mechanical detection noise at the standard quantum limit (SQL). We find that the Energy Resolution Limit (ERL), pointed out in recent literature as a relevant benchmark for most classes of magnetometers, can be surpassed by many orders of magnitude. Moreover, similarly to the case of a ferromagnetic gyroscope, it is also possible to surpass the standard quantum limit for magnetometry with independent spins, arising from spin-projection noise. Our finding indicates that magneto mechanical systems optimized for magnetometry can achieve a magnetic field resolution per unit volume several orders of magnitude better than any conventional magnetometer. We discuss possible implications, focusing on fundamental physics problems such as the search for exotic interactions beyond the standard model
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Modeling Nonlinear Magneto-optical Effects in Atomic Vapors
Full text linkNonlinear magneto-optical processes are a rich source of interesting and useful phenomena, with both practical and fundamental-physics applications. Theoretical modeling is helpful for understanding and visualizing the mechanisms for nonlinear magneto-optical effects (NMOE), and for analyzing and optimizing devices based on these effects. Part I of this Thesis describes Bloch-equation methods and visualization techniques that can be used to model a wide variety of NMOE in atomic vapors. Part II presents several applications of the methods, including the investigation and visualization of a specific effect involving radio-frequency fields, a study of the general consequences of hyperfine structure on NMOE, and modeling and optimization of systems for laser guide stars. Appendices present additional mathematical material and describe a Mathematica package used for density-matrix calculations
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Optical Magnetometry with Nitrogen-Vacancy Centers in Diamond
Full text linkPrecision measurement of magnetic fields is at the heart of many important analytic techniques in materials, geology, biology, medicine, security, space, and the physical sciences. These applications require operation under a wide range of specifications regarding sensitivity, spatial resolution, bandwidth, scalability, and temperature. In this work we have developed the enabling technology for magnetometers based on nitrogen-vacancy (NV) defects in diamond which promise to cover a wider portion of this parameter space than existing sensors. We have studied how to prepare diamond material optimized for magnetometry, and we observed the basic optical and spin properties of the NV centers. Using a novel scheme inspired by new information about NV centers gathered from these studies, we constructed a sensor which improved on the state-of-the-art in a number of areas. Finally, we outline a plan for improving these sensors to study micro- and nano-scale magnetic phenomena currently inaccessible using existing technology
Levitated Ferromagnetic Magnetometer with Energy Resolution Well Below ħ
No full textA quantum limit on the measurement of magnetic fields has been recently pointed out, stating that the so-called energy resolution ER is bounded to ER≳ħ. This limit indeed holds true for the vast majority of existing quantum magnetometers, including superconducting quantum interference devices and solid state spin and optically pumped atomic magnetometers. However, it can be surpassed by highly correlated spin systems, as recently demonstrated with a single-domain spinor BEC. Here, we show that similar and potentially much better resolution can be achieved with a hard ferromagnet levitated above a superconductor at cryogenic temperature. We demonstrate ER=(0.064±0.010) ħ and anticipate that ER<10−3 ħ is within reach with near-future improvements. This finding opens the way to new applications in condensed matter, biophysics, and fundamental science. In particular, we propose an experiment to search for axionlike dark matter and project a sensitivity that is orders of magnitude better than in previous searches
A journey through nonlinear magneto-optics
Full text linkThis thesis contributes to the research on nonlinear magneto-optical effects, specifically focusing on atomic magnetometry based on nonlinear magneto-optical rotation and mirrorless lasing (based on amplified spontaneous emission) – while encountering also other nonlinear effects, such as the Kerr effect.
Measuring magnetic fields has been of great importance since the bronze age and has been crucial to the development of the human civilization: the first magnetometer was the compass, a magnetometer that measures only the direction of the earth’s magnetic field and is so important that it has a place amongst the four great inventions of ancient China. Measuring the magnitude of a magnetic field is a more modern story that starts with Carl Friedrich Gauss measuring the Earth’s magnetic field in 1833.
Among the techniques existing nowadays, for precisely measuring magnetic fields, optically pumped magnetometry (OPM) stands out for its sensitivity, size, robustness and low cost. After the pioneers set the foundations more than half a century ago, diode laser technology allowed optical magnetometers to become a workhorse for magnetometry. OPM magnetometers are potentially as sensitive as SQUIDs (Superconducting Quantum Interference Device) and do not require cryogenics. Applications span over a wide range of fields: geophysics, bio-magnetic measurements and fundamental physics. OPM research in recent years has shifted from working in the laboratory to applications in the field and a useful step towards commercialization is the self-oscillating configuration. The basic operation principle is based on using the detected signal to sustain continuous oscillation at the resonant frequency. Such systems have a broad dynamic range, can follow field fluctuations and are simple.
Although OPMs and especially SERF (spin exchange relaxation-free) type magnetometers are highly sensitive, they need to operate in low fields and hence require magnetic shielding from the Earth’s field and other noise sources. Being able to measure in the geophysical field range or earth field with high sensitivity could open the path to low-cost bio-magnetic measurements, space-magnetometry, non-destructive testing and imaging and magnetometry on rapidly moving platforms.
This thesis focuses on Earth-field optical magnetometry and addresses challenges arising from the Earth’s magnetic field by using techniques like spin locking or creating a device free of classic Earth-field magnetometry issues, such as heading error.
The second part of this thesis is dedicated to mirrorless lasing. Since their invention in the 60s, lasers (light amplification by stimulated emission of radiation) have played a huge role in many areas of scientific research, industry, and everyday life and continue to grow. There are three principal components usually attributed to a laser: a gain medium, a pumping process and a feedback loop, although there is a debate over whether a feedback loop is always required. Lasing is often distinguished from processes such as Amplified Spontaneous Emission (ASE), Superradiance (SR) and Superflouorescence (SF), but this is not the case for the work presented here. Typically, lasers follow a conventional structure that includes an optical resonator setup. This setup uses mirrors to amplify light over multiple round trips in the gain medium. In mirrorless laser setups, the gain
medium serves as the resonator, and the feedback loop would typically happen through multiple scattering processes in systems with varying degrees of disorder. Optical feedback through scattering can also create random lasers. The system we are studying does not involve scattering mechanisms and we use the term lasing interchangeably with Amplified Spontaneous Emission (ASE). We define mirrorless lasing as as directed monochromatic emission from an ensemble of atoms or molecules
pumped with a laser light. Experiments in alkali metal vapor have shown gain through the
phenomenon of amplified spontaneous emission (ASE). This thesis focuses on the phenomenon of amplification of spontaneous emission and degenerate mirrorless lasing in alkali atoms with magnetically degenerate hyperfine states.xvii, 153 Seiten ; Illustrationen, Diagramm
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Magnetometry and Imaging with Nitrogen Vacancy Centers in Diamond
Full text linkAfter a brief introduction to nitrogen vacancy (NV) centers and related physics, a description is presented of the principles and methodology of the diamond-based imaging magnetometer using an ensemble of NV centers. The diamond-based magnetic imaging platform is used to realize a force-induced remnant magnetization spectroscopy technique in which specific biomolecular binding is measured and detection is performed with wide-field optical and diamond-based magnetometry. This diamond-based technique that has both optical and magnetic detection modalities may be adapted for massively parallel screening of arrays of nanoscale samples. In a separate, but similarly inspired experiment, a description is given of the methods used to analyze the motion of a microscopic ferromagnetic particle levitated above a superconducting niobium surface
New applications of nitrogen-vacancy centers in diamond
Full text linkMagnetometry is widely used industry, science and everyday life. Applications include navigation,
geology, chemical analysis and magnetic resonance imaging (MRI), among many others.
The different types of magnetic-field sensors, depending on the application, may differ in sensitivity,
bandwidth, operational conditions (e.g. temperature and pressure), spatial resolution
and price.
In the last two decades, a new magnetometer type based on nitrogen-vacancy (NV) color
centers in diamond has gained a lot of attention. NV magnetometers are not the most sensitive
compared to superconducting quantum interference devices (SQUIDs) or atomic magnetometers,
but feature remarkable properties such as nanoscale resolutions and the ability to be
operated from cryogenic temperatures up to ~ 700K and under pressures up to 60GPa they
excel in various applications
This work presents several applications and advances in sensor development that show the
strengths of NV-center-based magnetometry.
In particular, micron sized diamond samples which In incorporate a layer with high NVcenter
density are employed to image vortices in a type-II superconductor using a wide-field
configuration.
Furthermore, a setup to image both magnetization of (ferro-)magnetic samples via light
polarization and the generated stray magnetic field via NV magnetic imaging is designed and
constructed. The functionality was demonstrated on a ferromagnetic thin film that shows
stripelike domains upon change of external magnetic field.
In addition to the aforementioned applications, a method to utilize (single-) NV centers at
zero field was developed. This was necessary due to failure of conventional NV magnetometry
protocols because of line crossings at zero field. With the use of circularly polarized microwave
fields, we were able to overcome this issue and extend NV-center magnetometry to applications
that require zero-field conditions, such as zero-field nuclear magnetic resonance or observation
of the domain structure of magnetic samples across the full hysteresis loop.89, 2 Seiten ; Illustrationen, Diagramm
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Search for variation of the fine-structure constant and violation of Lorentz symmetry using atomic dysprosium
Full text linkWe report on the spectroscopy of radio-frequency transitions between nearly-degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant, , owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in Dy and 235-MHz transition in Dy were measured over the span of two years. Linear variation of is found to be ~yr, consistent with zero. The same data are used to constrain the dimensionless parameter , characterizing a possible coupling of to a changing gravitational potential. We find that , essentially consistent with zero and the best constraint to date.The same data are used to report a joint test of local Lorentz invariance and the Einstein Equivalence Principle for electrons. We present many-body calculations which demonstrate that the energy splitting of these states is particularly sensitive to violations of both special and general relativity. Lorentz violation for electrons is limited at the level of , matching or improving the best laboratory and astrophysical limits by up to a factor of 10, and gravitational redshift anomalies for electrons to the level of . With some enhancements, our experiment may be sensitive to Lorentz violation at the level of .We also report measurements of the differential polarizability between the nearly degenerate, opposite parity states. The differential scalar and tensor polarizabilities due to additional states were measured for the sublevels in Dy and Dy and determined to be \overline{\balpha}_{\sss BA}^{(0)} = 180\,(45)_\text{stat}\,(8)_\text{sys} mHz cm/V and \overline{\balpha}_{\sss BA}^{(2)} = -163\,(65)_\text{stat}\,(5)_\text{sys} mHz cm/V, respectively. The average blackbody radiation induced Stark shift of the Zeeman spectrum was measured around 300 K and found to be ~mHz/K and ~mHz/K for the Dy and Dy isotopes, respectively. We conclude that ac-Stark related systematics will not limit the precision of a search for variation of the fine-structure constant, using dysprosium, down to the level of ~yr for a one-year experiment
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Exploring Basic Properties and Applications of Nitrogen-Vacancy Color Centers in Diamond
Full text linkNitrogen-vacancy (NV) defect centers in diamond have generated much interest for their uses in quantum information and sensing. Despite the ongoing improvements in sensitivity and the range of new applications, much about the NV basic physics remains unresolved, which is important to understand in order to fully exploit potential uses. In this work I describe a series of experiments on NV basic properties, applications, and projects in between. First, I describe an NV singlet absorption spectroscopy experiment, which searched for additional NV electronic states and studied the 1A1 phonon modes. Next, I discuss an NV microwave saturation spectroscopy experiment, which is useful for NV thermometry, removes inhomogeneous broadening, and can yield information about diamond magnetic spin bath dynamics. I then describe an NV relaxation experiment that senses GHz-frequency magnetic noise, which we demonstrated using paramagnetic substitutional nitrogen (P1) centers. Finally, I describe open questions on the NV singlet states, saturation spectroscopy, and relaxation (and how to address them), and report on my ongoing work on using NVs for nuclear polarization and rotation sensing
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