Single-crystalline diamond (SCD) films exhibit outstanding thermal, optical, and electronic properties, making them ideal for advanced applications. However, achieving uniform film quality via microwave plasma chemical vapor deposition (MPCVD) remains challenging due to spatial variations in plasma characteristics. In this work, we systematically investigate the effects of microwave power and chamber pressure on SCD growth, with a focus on center-to-edge variations in film quality. Using a recessed Mo substrate holder, we observe clear radial differences in pit density, roughness, and Raman signatures, which could be related to radial CH3*/H imbalance in MPCVD reactors. Under optimized conditions, the films exhibit low surface roughness (R-q similar to 2.0 nm) and a sharp sp(3) Raman peak at 1332.2 cm(-1), comparable to those of the HPHT substrate. Cross-sectional TEM analysis further confirms a uniform (100)-oriented single-crystal lattice across the entire 3 x 3 mm substrate. These findings provide insight into the interplay between deposition parameters and film quality and offer practical guidelines for optimizing MPCVD processes toward large-area, high-purity diamond fabrication.

The nitrogen-vacancy (NV) centers in diamond have the ability to sense alternating-current (AC) magnetic fields with high spatial resolution. However, the frequency range of AC sensing protocols based on dynamical decoupling (DD) sequences has not been thoroughly explored experimentally. In this work, we aimed to determine the sensitivity of the ac magnetic field as a function of frequency using the sequential readout method. The upper limit at high frequency is clearly determined by Rabi frequency, in line with the expected effect of finite DD-pulse width. In contrast, the lower frequency limit is primarily governed by the duration of optical repolarization rather than the decoherence time (T2) of NV spins. This becomes particularly crucial when the repetition (dwell) time of the sequential readout is fixed to maintain the acquisition bandwidth. The equation we provide successfully describes the tendency in the frequency dependence. In addition, at the near-optimal frequency of 1 MHz, we reached a maximum sensitivity of 229 pT/Hz by employing the XY4-(4) DD sequence.

Quantum diamond magnetometers using lock-in detection have successfully detected weak bio-magnetic fields from neurons, a live mammalian muscle, and a live mouse heart. This opens up the possibility of quantum diamond magnetometers visualizing microscopic distributions of the bio-magnetic fields. Here, we demonstrate a lock-in-based widefield quantum diamond microscopy, achieving a mean volume-normalized per-pixel sensitivity of 43.9 nT mu m(1:5) /Hz(0:5). We optimize the sensitivity by implementing a double resonance with hyperfine driving and magnetic field alignment along the < 001 > orientation of the diamond. Additionally, we show that sub-ms temporal resolution (similar to 0:4 ms) can be achieved while keeping the per-pixel sensitivity at a few tens of nanotesla per second using quantum diamond microscopy. This lock-in-based diamond quantum microscopy could be a step forward in mapping functional activity in neuronal networks in micrometer spatial resolution.

Low-field nuclear magnetic resonance (NMR) spectroscopy, conducted at or below a few millitesla, provides only limited spectral information due to its inability to resolve chemical shifts. Thus, chemical analysis based on this technique remains challenging. One potential solution to overcome this limitation is the use of isotopically labeled molecules. However, such compounds, particularly their use in two-dimensional (2D) NMR techniques, have rarely been studied. This study presents the results of both experimental and simulated correlation spectroscopy (COSY) on 1-13C-ethanol at 34.38 μT. The strong heteronuclear coupling in this molecule breaks the magnetic equivalence, causing all J-couplings, including homonuclear coupling, to split the 1H spectrum. The obtained COSY spectrum clearly shows the spectral details. Furthermore, we observed that homonuclear coupling between 1H spins generated cross-peaks only when the associated 1H spins were coupled to identical 13C spin states. Our findings demonstrate that a low-field 2D spectrum, even with a moderate spectral line width, can reveal the J-coupling networks of isotopically labeled molecules.

Majority of dynamic nuclear polarization (DNP) experiments have been requiring helium cryogenics and strong magnetic fields for a high degree of nuclear polarization. In this work, we instead demonstrate an optical hyperpolarization of naturally abundant 13C nuclei in a diamond crystal at a low magnetic field and the room temperature. It exploits continuous laser irradiation for polarizing electronic spins of nitrogen vacancy centers and microwave irradiation for transferring the electronic polarization to 13C nuclear spins. We have studied the dependence of 13C polarization on laser and microwave powers. For the first time, a triplet structure corresponding to the 14N hyperfine splitting has been observed in the 13C polarization spectrum. By simultaneously exciting three microwave frequencies at the peaks of the triplet, we have achieved 13C bulk polarization of 0.113 %, leading to an enhancement of 90,000 over the thermal polarization at 17.6 mT. We believe that the multi-tone irradiation can be extended to further enhance the 13C polarization at a low magnetic field.

Nitrogen-vacancy (NV) centers in diamond have been developed into essential hardware units for a wide range of solid-state-based quantum technology applications. While such applications require the long spin coherence times of the NV centers, they are often limited due to decoherence. In this study, we theoretically investigate the decoherence of NV-spin ensembles induced by nitrogen impurities (P1 centers), which are one of the most dominant and inevitable magnetic field noise sources in diamond. We combined cluster correlation expansion and density functional theory to compute the Hahn-echo spin-coherence time of the NV centers for a broad range of P1 concentrations. Results indicate a clear linear dependence of T 2 on P1 concentrations on a log scale with a slope of −1.06, which is in excellent agreement with previous experimental results. The interplay between the Jahn–Teller effect and the hyperfine interaction in the P1 center plays a critical role in determining the bath dynamics and the resulting NV decoherence. Our results provide a theoretical upper bound for the NV-spin T 2 over a wide range of P1 densities, serving as a key reference for materials optimization and spin bath characterization to develop highly coherent NV-based devices for quantum information technology.

1 Korean Research Institute of Standards and Science, Daejeon 34113, Republic of Korea 2 Department of Medical Physics, University of Science and Technology, Daejeon 34113, Republic of Korea 3 Department of Physics, Hanyang University, Seoul 04763, Republic of Korea 4 Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea 5 Department of Physics, University of Maryland, College Park, Maryland 20742, USA 6 Department of Electrical Engineering and Computer Science, University of Maryland, College Park, Maryland 20742, USA 7 Quantum Technology Center, University of Maryland, College Park, Maryland 20742, USA

with multi-tone microwave irradiation Vladimir Vladimirovish Kavtanyuk, Hyun Joon Lee, Sangwon Oh, Keunhong Jeong, and Jeong Hyun Shim 4, a) Quantum Magnetic Imaging Team, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea Radio & Satellite Research Division, Electronics and Telecommunications Research Institute, Daejeon 34129, Republic of Korea Korea Military Academy, Seoul 01805, Republic of Korea Department of Medical Physics, University of Science and Technology, Daejeon 34113, Republic of Korea

Jeong Hyun Shim, 2, ∗ Seong-Joo Lee, Santosh Ghimire, Ju Il Hwang, Kang Geol Lee, Kiwoong Kim, Matthew J. Turner, 6, 7 Connor A. Hart, 6, 7 Ronald L. Walsworth, 6, 7 and Sangwon Oh † Korean Research Institute of Standards and Science, Daejeon 34113, Republic of Korea Department of Medical Physics, University of Science and Technology, Daejeon 34113, Republic of Korea Department of Physics, Hanyang University, Seoul 04763, Republic of Korea Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea Department of Physics, University of Maryland, College Park, Maryland, 20742, USA Department of Electrical Engineering and Computer Science, University of Maryland, College Park, Maryland, 20742, USA Quantum Technology Center, University of Maryland, College Park, Maryland, 20742, USA (Dated: April 27, 2021)

Currently, signal amplification by reversible exchange (SABRE) using para-hydrogen is an attractive method of hyperpolarization for overcoming the sensitivity problems of nuclear magnetic resonance (NMR) spectroscopy. Additionally, SABRE, using the spin order of para-hydrogen, can be applied in reaction monitoring processes for organic chemistry reactions where a small amount of reactant exists. The organic reaction monitoring system created by integrating SABRE and benchtop NMR is the ideal combination for monitoring a reaction and identifying the small amounts of materials in the middle of the reaction. We used a laboratory-built setup, prepared materials by synthesis, and showed that the products obtained by esterification of glycine were also active in SABRE. The products, which were synthesized esterified glycine with nicotinoyl chloride hydrochloride, were observed with a reaction monitoring system. The maximum SABRE enhancement among them (approximately 147-fold) validated the use of this method. This study is the first example of the monitoring of this organic reaction by SABRE and benchtop NMR. It will open new possibilities for applying this system to many other organic reactions and also provide more fruitful future applications such as drug discovery and mechanism study.

Nitrogen vacancy center (NV center) in diamond has recently been appeared as a promising candidate for hyperpolarization applications due to its optical pumping property by laser. Optically Detected Magnetic Resonance (ODMR) has been used as a conventional method to obtain the resonance spectrum of NV centers. ODMR, however, has a shortcoming of sensitivity and a limitation of subjects, such that the degree of hyperpolarization can hardly be estimated, and that the spins other than NV centers are invisible. In contrast, Electron Spin Resonance (ESR) spectroscopy is known to proportionally reflect the degree of spin polarization. In this work, we successfully observed the optically-induced hyperpolarization of NV spins in diamond through CW-ESR spectroscopy with an X-band system. All the NV peaks were identified by calculating the eigenvalues of NV spin Hamiltonian The intensities of NV peaks were enhanced over 240 times after optical pumping. The enhanced peaks corresponding to the transition from vertical bar m(s)=0> to vertical bar m(s)=-1> revealed inverted phases, while other peaks remained in-phase. The optically-induced hyperpolarization on NV spins can be a useful polarization source, leading to C-13 nuclear hyperpolarization in diamond.

Signal Amplification by Reversible Exchange (SABRE), a hyperpolarization technique, has been harnessed as a powerful tool to achieve useful hyperpolarized materials by polarization transfer from parahydrogen. In this study, we systemically applied SABRE to a series of nitrile compounds, which have been rarely investigated. By performing SABRE in various magnetic fields and concentrations on nitrile compounds, we unveiled its hyperpolarization properties to maximize the spin polarization and its transfer to the next spins. Through this sequential study, we obtained a ~130-fold enhancement for several nitrile compounds, which is the highest number ever reported for the nitrile compounds. Our study revealed that the spin polarization on hydrogens decreases with longer distances from the nitrile group, and its maximum polarization is found to be approximately 70 G with 5 μL of substrates in all structures. Interestingly, more branched structures in the ligand showed less effective polarization transfer mechanisms than the structural isomers of butyronitrile and isobutyronitrile. These first systematic SABRE studies on a series of nitrile compounds will provide new opportunities for further research on the hyperpolarization of various useful nitrile materials.

Magnetic resonance imaging in ultra-low fields is often limited by mediocre signal-to-noise ratio hindering a higher resolution. Overhauser dynamic nuclear polarisation (O-DNP) using nitroxide radicals has been an efficient solution for enhancing the thermal nuclear polarisation. However, the concurrence of positive and negative polarisation enhancements arises in ultra-low fields resulting in a significantly reduced net enhancement, making O-DNP far less attractive. Here, we address this issue by applying circularly polarised RF. O-DNP with circularly polarised RF renders a considerably improved enhancement factor of around 150,000 at 1.2 microtesla. A birdcage coil was adopted into a ultra-low field MRI system to generate the circularly polarised RF field homogeneously over a large volume. We acquired an MR image of a nitroxide radical solution with an average in-plane resolution of 1 mm. De-noising through compressive sensing further improved the image quality.

A former study has shown that the spin-lattice relaxation time (T-1) in cancerous prostate tissue had enhanced contrast at an ultra-low magnetic field, 132 mu T. To study the field dependence and the origin of the contrast we measured T-1 in pairs of ex-vivo prostate tissues at the Earth's magnetic field. A portable and coil-based nuclear magnetic resonance (NMR) system was adopted for T-1 measurements at 40 mu T. The T-1 contrast, delta = 1 - T-1 (more cancer)/T-1(less cancer), was calculated from each pair. Additionally, we performed pathological examinations such as Gleason's score, cell proliferation index, and micro-vessel density (MVD), to quantify correlations between the pathological parameters and T-1 of the cancerous prostate tissues.

Overhauser dynamic nuclear polarization (O-DNP) can significantly boost the intensity of the nuclear magnetic resonance (NMR) signal in comparison to the thermal magnetization for field strengths in the microtesla range. We demonstrate the development and use of an Overhauser spin-echo magnetometer using a superconducting quantum interference device-based microtesla NMR system and dissolved nitroxide radicals in deoxygenated tetramethylsilane liquid. A spin-echo train with an enhanced signal was successfully obtained with the O-DNP technique. A magnetic field strength of about 0.92 mu T was measured with an uncertainty of 0.7 pT in the presence of a field gradient of 0.038 mu T cm(-1). The Overhauser proton spin-echo magnetometer will be useful for the measurement of low magnetic fields by minimizing the generation of disturbing magnetic fields without the need to compensate for residual field gradients.

Measuring the electrical impedance of biological tissues in a low frequency range is challenging. Here, we have conducted a superconducting quantum interference device-based microtesla magnetic resonance (MR) imaging study. To obtain an MR image caused by an injected alternating current (ac), we utilized the direct resonance method in which the nuclear spins resonate with the ac magnetic field generated by the external ac current. This method requires an adiabatic pulse and non-adiabatic step-down pulse techniques. The experimental and simulation results agree well with each other and show the feasibility of low-frequency magnetic resonance electrical impedance tomography in the kHz range.

Esophageal cancer is the third most common cancer of the gastrointestinal tract. Despite new therapies, the prognosis for patients with these cancers remains poor with 5-year survival rates lower than 15%. Recently, immunotherapy has increasingly gained attention as a novel treatment strategy for advanced esophageal cancer.Recent success of immunotherapy in treating other solid tumors has shed light on the utility of these approaches for esophageal cancers. Here, the authors focus on antibody-based, adoptive-cell-therapy-based, and vaccine-based immunotherapies, and briefly address their rationale, clinical data, and implications.Immunotherapy is now established to be a key treatment modality that can improve the outcomes of many cancer patients and appears to be ushering in a new era in cancer treatment. Checkpoint inhibitor drugs have shown preliminary favorable results in esophageal cancer treatment. Adoptive cell therapy and vaccine studies have also shown some promise in various clinical studies. Future endeavors will need to focus on identifying patients who are likely to benefit from immunotherapy, monitoring and managing immune responses and designing optimal combination strategies where immunotherapy agents are combined with other traditional treatment modalities.

We report here magnetic resonance imaging measurements performed on suspensions with a bulk solid volume fraction (ϕ_{0}) up to 0.55 flowing in a pipe. We visualize and quantify spatial distributions of ϕ and velocity across the pipe at different axial positions. For dense suspensions (ϕ_{0}>0.5), we found a different behavior compared to the known cases of lower ϕ_{0}. Our experimental results demonstrate compaction within the jammed region (characterized by a zero macroscopic shear rate) from the jamming limit ϕ_{m}≈0.58 at its outer boundary to the random close packing limit ϕ_{rcp}≈0.64 at the center. Additionally, we show that ϕ and velocity profiles can be fairly well captured by a frictional rheology accounting for both further compaction of jammed regions as well as normal stress differences.

We describe and analyze the effects of transients within radio-frequency (RF) pulses on multiple-pulse NMR measurements such as the well-known Carr-Purcell-Meiboom-Gill (CPMG) sequence. These transients are functions of the absolute RF phases at the beginning and end of the pulse, and are thus affected by the timing of the pulse sequence with respect to the period of the RF waveform. Changes in transients between refocusing pulses in CPMG-type sequences can result in signal decay, persistent oscillations, changes in echo shape, and other effects. We have explored such effects by performing experiments in two different low-frequency NMR systems. The first uses a conventional tuned-and-matched probe circuit, while the second uses an ultra-broadband un-tuned or non-resonant probe circuit. We show that there are distinct differences between the absolute phase effects in these two systems, and present simple models that explain these differences.