Gradiometer improves “magnetic resonance without magnets”

Significance 

Nuclear magnetic resonance (NMR), a technique that is conventionally operated in large magnetic fields, is among common powerful analytical approaches applied in chemistry, biology and medicine. As a complementary tool to conventional high-field NMR, zero- and ultralow-field (ZULF) NMR offers improved spectral resolution and untruncated spin interactions. Specifically, as a complementary analysis tool to conventional high-field nuclear magnetic resonance, ZULF NMR detects nuclear magnetization signals in the submicrotesla regime. Combining with recently developed quantum-control techniques, ZULF NMR has shown to be promising in probing the frontiers of fundamental physics. Presently, ZULF NMR systems are normally equipped with high-quality magnetic shields to ensure that ambient magnetic-field noise does not dwarf the magnetization signal. An alternative approach would be to separate the magnetization signal from the noise based on their differing spatial profiles, as can be achieved using a magnetic gradiometer.

To this note, University of Science and Technology of China scientists: Jiang Min (PhD candidate), Professor Xinhua Peng together with their colleagues Román Picazo Frutos, Dr. Teng Wu, John W. Blanchard and Professor Dmitry Budker at Johannes Guttenberg University in Germany designed a new gradiometric NMR spectrometer based on a two-channel SERF atomic magnetometer. They anticipated that the use of the gradiometric NMR spectrometer would help reduce the sensitivity to the ambient magnetic-field noise. Their work is currently published in the research journal, Physical Review Applied.

The research team considered a gradiometric ZULF NMR spectrometer with a magnetic-field-gradient noise of 17 fT/cm Hz1/2 in the frequency ranging from 100 to 400 Hz, based on a single vapor cell (0.7 × 0.7 × 1.0 cm3). As such, they demonstrated high signal-to-noise ratio (SNR) measurement of liquid state NMR samples under the application of spatially homogeneous white magnetic-field noise, with a noise spectral density of approximately 0.3 pT/Hz1/2, comparable to the noise level in an unshielded environment. The gradiometric spectrometer used in the experimental setup basically comprised to two parts; the NMR sample and the sensor.

With applied white magnetic-field noise, the authors were able to show that the gradiometric spectrometer achieved 13-fold enhancement in the signal-to-noise ratio compared to the single-channel configuration. Overall, by reducing the influence of the common-mode magnetic-field noise, they demonstrated the usability of compact and low-cost magnetic shields.

In summary, the study presented an experimental demonstration of a gradiometric NMR spectrometer with a magnetic-field-gradient noise of 17 fT/cm Hz1/2 and a measurement volume for a single channel of 0.1 cm3. Following detailed investigations as presented, gradiometric detection proves to be beneficial for eliminating systematic errors in ZULF-NMR experiments searching for exotic spin-dependent interactions and molecular parity violation. This opens the possibility of making a robust and portable NMR spectrometer, particularly in an unshielded environment where large common-mode magnetic-field noise is introduced. Altogether, an optimized gradiometric spectrometer reported in this study is promising for sensing such chirality and parity non-conservation effects while remaining robust against background magnetic-field noise.

Magnetic Gradiometer Detection of Zero- to Ultralow-Field Nuclear Magnetic Resonance - Advances in Engineering

About the author

Dmitry Budker received his PhD in 1993 from the University of California, Berkeley. After a two-year postdoctoral appointment at Berkeley, he joined the Berkeley Physics Department as a faculty member, where he is currently Professor of Graduate School. Since 2014, he has been the Matter-Antimatter Section Leader at the Helmholtz Institute and a Professor at the Johannes Guttenberg University in Mainz. He is a Fellow of the American Physical Society and a former chair of its Group on Precision Measurement and Fundamental Constants.

About the author

Jiang Min is a PhD candidate of Department of Modern Physics, University of Science and Technology of China. Since 2013, he joined the CAS Key Laboratory of Microscale Magnetic Resonance. His current research interests are focused on the ultrasensitive atomic magnetometry, quantum control and zero-field nuclear magnetic resonance.

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About the author

Teng Wu received his PhD in Radio Physics in 2016 from the Peking University, China. Then he joined the Helmholtz Institüt Mainz and began to work as a postdoc researcher in Prof. Dmitry Budker’s group. His current research interests are concentrated on zero- and ultralow-field nuclear magnetic resonance, high-sensitivity atomic magnetometer, tests of fundamental symmetries, and experimental searches for new physics beyond the standard model.

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About the author

Dr. Xinhua Peng is the professor of Department of Modern Physics at University of Science and Technology of China. She received her Ph.D. in atomic and molecular physics from Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, in 2003. After that, she arrived at the University of Dortmund, Germany, as an Alexander von Humboldt Fellow. In 2008, she joined in University of Science and Technology of China as full professor from “CAS Hundred Talents program”. She was awarded National Science Fund for Distinguished Young Scholars, the Twelfth Chinese Young Women Scientist Award, Young Yangtze River Scholars Award of the Ministry of Education, and Young Scientific and Technological Innovation Leader etc.

Her research interests include quantum information processing, quantum control, nuclear magnetic resonance spectroscopy, atomic magnetometer and quantum sensing. Her group has extensive expertise in circuit synthesis and experimental implementation of quantum information processing, having carried out varied quantum algorithms using current technology for projects such as quantum simulation, quantum image processing, optimal control, factorisation, database search and quantum metrology. She has published more than 80 papers in reputed journals, such as Nature Physics, Phys. Rev. X, Phys. Rev. Lett. and so on.

About the author

John W. Blanchard received his PhD in Chemistry in 2014 from the University of California, Berkeley, working with Prof. Alexander Pines to develop zero- to ultralow-field nuclear magnetic resonance spectroscopy. He then joined Prof. Dmitry Budker’s group in 2015 at the Helmholtz-Institut Mainz as a Helmholtz Postdoctoral Fellow. His research interests include novel methods and applications of nuclear magnetic resonance, energy materials analysis, fundamental physical chemistry, and searches for physics beyond the Standard Model.

About the author

Román Picazo Frutos completed his Bachelor studies in Physics in the University of Valencia, Spain. He then obtained a Masters degree by the Johannes Gutenberg-Universität, where he did his MSc thesis supervised by Prof. Dmitry Budker. Since 2019 he has joined the Budker group at the Helmholtz Institut Mainz as a PhD student. His current research interests are Zero and Ultra-Low-Field Nuclear Magnetic Resonance (ZULF NMR), optical magnetometry, quantum optics, quantum computing, dynamic spin-decoupling pulses sequences and Dissolution Dynamic Nuclear Polarization(dDNP)-enhanced ZULF NMR.

Reference

Min Jiang, Román Picazo Frutos, Teng Wu, John W. Blanchard, Xinhua Peng, Dmitry Budker. Magnetic Gradiometer for the Detection of Zero- to Ultralow-Field Nuclear Magnetic Resonance. Physical Review Applied 11, 024005 (2019)

Go To Physical Review Applied

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