Hyperfine Research Articles

Continuous cold rubidium atomic beam with enhanced flux and tunable velocity.

We present a cold atomic beam source based on a two-dimensional (2D)+ magneto-optical trap (MOT), capable of generating a continuous cold beam of 87Rb atoms with a flux up to 4.3 × 109 s-1, a mean velocity of 10.96(2.20) m/s, and a transverse temperature of 16.90(1.56) µK. Investigating the influence of high cooling laser intensity, we observe a significant population loss of atoms to hyperfine-level dark states. To account for this, we employ a multiple hyperfine level model to calculate the cooling efficiency associated with the population in dark states, subsequently modifying the scattering force. Simulations of beam flux at different cooling and repumping laser intensities using the modified scattering force are in agreement with experimental results. Optimizing repumping and cooling intensities enhances the flux by 50%. The influence of phase modulation on both the pushing and cooling lasers is experimentally studied, revealing that the mean velocity of cold atoms can be tuned from 9.5 m/s to 14.6 m/s with a phase-modulated pushing laser. The versatility of this continuous beam source, featuring high flux, controlled velocity, and narrow transverse temperature, renders it valuable for applications in atom interferometers and clocks, ultimately enhancing bandwidth, sensitivity, and signal contrast in these devices.

Spin-Symmetry Breaking and Hyperfine Couplings in Transition-Metal Complexes Revisited Using Density Functionals Based on the Exact-Exchange Energy Density.

A small set of mononuclear manganese complexes evaluated previously for their Mn hyperfine couplings (HFCs) has been analyzed using density functionals based on the exact-exchange energy density─in particular, the spin symmetry breaking (SSB) found previously when using hybrid functionals. Employing various strong-correlation corrected local hybrids (scLHs) and strong-correlation corrected range-separated local hybrids (scRSLHs) with or without additional corrections to their local mixing functions (LMFs) to mitigate delocalization errors (DE), the SSB and the associated dipolar HFCs of [Mn(CN)4]2-, MnO3, [Mn(CN)4N]-, and [Mn(CN)5NO]2- (the latter with cluster embedding) have been examined. Both strong-correlation (sc)-correction and DE-correction terms help to diminish SSB and correct the dipolar HFCs. The DE corrections are more effective, and the effects of the sc corrections depend on their damping factors. Interestingly, the DE-corrections reduce valence-shell spin polarization (VSSP) and thus SSB by locally enhancing exact-exchange (EXX) admixture near the metal center and thereby diminishing spin-density delocalization onto the ligand atoms. In contrast, sc corrections diminish EXX admixture locally, mostly on specific ligand atoms. This then reduces VSSP and SSB as well. The performance of scLHs and scRSLHs for the isotropic Mn HFCs has also been analyzed, with particular attention to core-shell spin-polarization contributions. Further sc-corrected functionals, such as the KP16/B13 construction and the DM21 deep-neural-network functional, have been examined.

Qudit-Based Spectroscopy for Measurement and Control of Nuclear-Spin Qubits in Silicon Carbide.

Nuclear spins with hyperfine coupling to single electron spins are highly valuable quantum bits. Here we probe and characterize the particularly rich nuclear-spin environment around single silicon vacancy color centers (V2) in 4H-SiC. By using the electron spin-3/2 qudit as a four level sensor, we identify several sets of ^{29}Si and ^{13}C nuclear spins through their hyperfine interaction. We extract the major components of their hyperfine coupling via optical detected nuclear magnetic resonance, and assign them to shells in the crystal via the density function theory simulations. We utilize the ground-state level anticrossing of the electron spin for dynamic nuclear polarization and achieve a nuclear-spin polarization of up to 98±6%. We show that this scheme can be used to detect the nuclear magnetic resonance signal of individual spins and demonstrate their coherent control. Our work provides a detailed set of parameters and first steps for future use of SiC as a multiqubit memory and quantum computing platform.

The quest for harnessing nuclear effects in graphene-based devices

The recent successes of superconducting qubits and the demonstration of quantum supremacy over classical bits herald a new era for information processing. Yet, the field is still in its infancy and there exist viable alternative candidates that can also store quantum information. In this review, we will highlight ideas, attempts, and the experimental progress to address nuclear spins in graphene, a readily available Dirac semimetal that consists of a single layer of carbon atoms. Carbon isotopes with a nuclear spin are rare in natural graphene. However, it is possible to enrich the spin-bearing 13C isotopes to produce large-scale graphene sheets, which constitute the testbed to store, transport, and retrieve spin information, or to engineer nanostructures. Here, the hyperfine interaction between the electron spins and the nuclear spins serves as an experimental control knob and mediator to address nuclear polarization and nuclear spin coherence times through electrical measurements. The exploitation of nuclear spins in graphene is thus an alluring perspective. We will discuss methods to synthesize 13C graphene and show experimental approaches and challenges to exploit the relatively weak hyperfine interaction in two-dimensional 13C graphene devices. The ultimate purpose, i.e., the exploitation of nuclear spins in graphene for information processing, is not within reach, but its potential for future applications merits a revisit of the current state-of-the-art.

Identification of an X-Band Clock Transition in Cp'3Pr- Enabled by a 4f25d1 Configuration.

Molecular qubits offer an attractive basis for quantum information processing, but challenges remain with regard to sustained coherence. Qubits based on clock transitions offer a method to improve the coherence times. We propose a general strategy for identifying molecules with high-frequency clock transitions in systems where a d electron is coupled to a crystal-field singlet state of an f configuration, resulting in an MJ = ±1/2 ground state with strong hyperfine coupling. Using this approach, a 9.834 GHz clock transition was identified in a molecular Pr complex, [K(crypt)][Cp'3PrII], leading to 3-fold enhancements in T2 relative to other transitions in the spectrum. This result indicates the promise of the design principles outlined here for the further development of f-element systems for quantum information applications.

Photonic comb: a stabilized single-mode fiber etalon for wavelength calibration

We present a low-cost alternative to more complex laser metrology systems that uses a single-mode fiber Fabry–Perot etalon to generate an emission spectrum of evenly spaced lines with similar intensities, ideal for calibrating spectrographs (both in terms of wavelength and image quality). The system uses the hyperfine transition lines of 87Rb near 780.24 nm as an absolute reference. By controlling the cavity dimensions by small changes in temperature, we can tune and thus stabilize the transmission spectrum. A 20 Hz PID loop controls the etalon temperature and locks it to the 87Rb transitions. Through this method, we achieve a centroid error/precision of <1m/s (2.6 fm or 1.3 MHz) for 1 s integrations and 1 cm/s (0.026 fm or 13 kHz) for 30 min integrations of the reference line. We also show that a solution can be found to mathematically describe the spectrum. With the correct calibration and environmental controls in place, we show that this setup has the potential to be competitive with the best existing methods based on expensive and cumbersome laser combs.

Room‐Temperature Macroscopic Ferromagnetism in Multilayered Graphene Oxide

AbstractGraphene has a long spin lifetime and hyperfine interactions, favoring its potential application as spintronics. Despite the recent discoveries of spin‐containing graphene materials, graphene‐based materials with room‐temperature macroscopic ferromagnetism are extremely rare. In this article, room‐temperature ferromagnetic amorphous graphene oxide (GO) is synthesized by introducing abundant oxygen‐containing functional groups and C defects into single‐layered graphene, followed by a self‐assembly process under supercritical CO2 (SC CO2). Such amorphous GO exhibits the highest saturation magnetization (1.71 emu g−1) and remanent magnetization (0.251 emu g−1) compared to the rest of metal‐free graphene‐based materials at room temperature. Experimental and theoretical investigations attribute such strong ferromagnetism to the bridging of the adjacent graphene layers though the out‐of‐plane oxygen‐containing groups, which leads to asymmetric lattices with large net magnetic moments.

Fast coherent control of nitrogen-14 spins associated with nitrogen-vacancy centers in diamonds using dynamical decoupling

Abstract A nitrogen-vacancy (NV) center in a diamond enables the access to an electron spin, which is expected to present highly sensitive quantum sensors. Although exploiting a nitrogen nuclear spin improves the sensitivity, manipulating it using a resonant pulse requires a long gate time owing to its small gyromagnetic ratio. Another technique to control nuclear spins is a conditional rotation gate based on dynamical decoupling, which is faster but unavailable for nitrogen spins owing to the lack of transverse hyperfine coupling with the electron spin. In this study, we generated effective transverse coupling by applying a weak off-axis magnetic field. An effective coupling depends on the off-axis field; the conditional rotation gate on the nitrogen-14 spins of an NV center was demonstrated within 4.2 μs under an 1.8% off-axis field and a longitudinal field of approximately 280 mT. We estimated that a population transfer from the electron to nitrogen spins can be implemented with 8.7 μs. Our method is applicable to an ensemble of NV centers, in addition to a single NV center.

Large dynamics of a phase separating arginine-glycine-rich domain revealed via nuclear and electron spins

Liquid-liquid phase separation is the key process underlying formation of membrane-less compartments in cells. A highly dynamic cellular body with rapid component exchange is Cajal body (CB), which supports the extensive compositional dynamics of the RNA splicing machinery, spliceosome. Here, we select an arginine-glycine (RG)-rich segment of coilin, the major component of CB, establish its RNA-induced phase separation, and through combined use of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) probes, interrogate its dynamics within the crowded interior of formed droplets. Taking advantage of glycine-based singlet-states, we show that glycines retain a large level of sub-nanoseconds dynamics inside the coilin droplets. Furthermore, the continuous-wave (CW) and electron-electron dipolar (PELDOR) and electron-nucleus hyperfine coupling EPR data (HYSCORE) support the RNA-induced formation of dynamic coilin droplets with high coilin peptide concentrations. The combined NMR and EPR data reveal the high dynamics of the RG-rich coilin within droplets and suggest its potential role in the large dynamics of CBs.

Role of Protons in and around Strongly Coupled Nitroxide Biradicals for Cross-Effect Dynamic Nuclear Polarization.

In magic angle spinning dynamic nuclear polarization (DNP), biradicals such as bis-nitroxides are used to hyperpolarize protons under microwave irradiation through the cross-effect mechanism. This mechanism relies on electron-electron spin interactions (dipolar coupling and exchange interaction) and electron-nuclear spin interactions (hyperfine coupling) to hyperpolarize the protons surrounding the biradical. This hyperpolarization is then transferred to the bulk sample via nuclear spin diffusion. However, the involvement of the protons in the biradical in the cross-effect DNP process has been under debate. In this work, we address this question by exploring the hyperpolarization pathways in and around bis-nitroxides. We demonstrate that for biradicals with strong electron-electron interactions, as in the case of the AsymPols, the protons on the biradical may not be necessary to quickly generate hyperpolarization. Instead, such biradicals can efficiently, and directly, polarize the surrounding protons of the solvent. The findings should impact the design of the next generation of biradicals.

Spin Light Emitting Diode Based on Exciton Fine Structure Tuning in Quantum Dots.

We propose a concept of quantum dot based light emitting diode that produces circularly polarized light without magnetic contacts due to the hyperfine interaction at the crossing of the exciton levels in a weak magnetic field. The electroluminescence circular polarization degree can reach 100%. The concept is compatible with the micropillar cavities, which allows for the generation of single circularly polarized photons. Second order photon correlation function includes information about the nuclear spin dynamics in the quantum dot, and the nuclear spin state can be purified by the quantum measurement backaction.

Hyperfine-resolved rotational spectroscopy of HCNH.

The rotational spectrum of the molecular ion HCNH+ is revisited using double-resonance spectroscopy in an ion trap apparatus, with six transitions measured between 74 and 445GHz. Due to the cryogenic temperature of the trap, the hyperfine splittings caused by the 14N quadrupolar nucleus were resolved for transitions up to J = 4 ← 3, allowing for a refinement of the spectroscopic parameters previously reported, especially the quadrupole coupling constant eQq.

Constraining cosmic reionization by combining the kinetic Sunyaev–Zel’dovich and the 21 cm power spectra

ABSTRACT During the Epoch of Reionization (EoR), the ultraviolet radiation from the first stars and galaxies ionized the neutral hydrogen of the intergalactic medium, which can emit radiation through its 21 cm hyperfine transition. Measuring the 21 cm power spectrum is a key science goal for the future Square Kilometre Array (SKA); however, observing and interpreting it is a challenging task. Another high-potential probe of the EoR is the patchy kinetic Sunyaev–Zel’dovich (pkSZ) effect, observed as a foreground to the cosmic microwave background temperature anisotropies on small scales. Despite recent promising measurements, placing constraints on reionization from pkSZ observations is a non-trivial task, subject to strong model dependence. We propose to alleviate the difficulties in observing and interpreting the 21 cm and pkSZ power spectra by combining them. With a simple yet effective parametric model that establishes a formal connection between them, we can jointly fit mock 21 cm and pkSZ data points. We confirm that these observables provide complementary information on reionization, leading to significantly improved constraints when combined. We demonstrate that with as few as two measurements of the 21 cm power spectrum with 100 h of observations with the SKA, as well as a single ℓ = 3000 pkSZ data point, we can reconstruct the reionization history of the universe and its morphology. We find that the reionization history (morphology) is better constrained with two 21 cm measurements at different redshifts (scales). Therefore, a combined analysis of the two probes will give access to tighter constraints on cosmic reionization even in the early stages of 21 cm detections.

57Fe-Mössbauer spectroscopic study of some double and triple metal oxalates

57Fe-Mössbauer spectra of double MM’(C2O4)2⋅4H2O (M = Fe, M’ = Mg, Co, Zn) and triple metal oxalates MM’M”(C2O4)3⋅6H2O (M = Fe, M’ = Mg, Mn, Co; M” = Zn) were recorded at room temperature and briefly discussed on the basis of their structural characteristics. No changes in the hyperfine interactions at the 57Fe site were detected because of the presence of the other metal ions.

Hyperfine Spectroscopy and Fast, All-Optical Arbitrary State Initialization and Readout of a Single, Ten-Level ^{73}Ge Vacancy Nuclear Spin Qudit in Diamond.

A high-spin nucleus coupled to a color center can act as a long-lived memory qudit in a spin-photon interface. The germanium vacancy (GeV) in diamond has attracted recent attention due to its excellent spectral properties and provides access to the ten-dimensional Hilbert space of the I=9/2 ^{73}Ge nucleus. Here, we observe the ^{73}GeV hyperfine structure, perform nuclear spin readout, and optically initialize the ^{73}Ge spin into any eigenstate on a μs timescale and with a fidelity of up to ∼84%. Our results establish ^{73}GeV as an optically addressable high-spin quantum platform for a high-efficiency spin-photon interface as well as for foundational quantum physics and metrology.

High-fidelity initialization and control of electron and nuclear spins in a four-qubit register

Single electron spins bound to multi-phosphorus nuclear spin registers in silicon have demonstrated fast (0.8 ns) two-qubit SWAP\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{\\mathrm{SWAP}}$$\\end{document} gates and long spin relaxation times (~30 s). In these spin registers, when the donors are ionized, the nuclear spins remain weakly coupled to their environment, allowing exceptionally long coherence times. When the electron is present, the hyperfine interaction allows coupling of the spin and charge degrees of freedom for fast qubit operation and control. Here we demonstrate the use of the hyperfine interaction to enact electric dipole spin resonance to realize high-fidelity (F=100−6+0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F=10{0}_{-6}^{+0}$$\\end{document}%) initialization of all the nuclear spins within a four-qubit nuclear spin register. By controllably initializing the nuclear spins to ⇓⇓⇓\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left\\vert \\Downarrow \\Downarrow \\Downarrow \\right\\rangle$$\\end{document}, we achieve single-electron qubit gate fidelities of F = 99.78 ± 0.07% (Clifford gate fidelities of 99.58 ± 0.14%), above the fault-tolerant threshold for the surface code with a coherence time of T2*=12μs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}^{\\,* }=12\\,\\upmu {{{\\rm{s}}}}$$\\end{document}.

Ammonia observations of Planck cold cores

Single-pointing observations of NH$_ $\,(1,1) and (2,2) were conducted toward 672 Planck Early Cold Cores (ECCs) using the Nanshan 26-m radio telescope. Out of these sources, a detection rate of 37<!PCT!> (249 cores) was achieved, with a $\,(1,1) hyperfine structure detected in 187 cores and $\,(2,2) emission lines detected in 76 of them. The detection rate of $ is positively correlated with the continuum emission fluxes at a frequency of 857\,GHz. Among the observed 672 cores, sim 22<!PCT!> have associated stellar and infrared objects within the beam size (sim 2arcmin ). This suggests that most of the cores in our sample may be starless. The kinetic temperatures of the cores range from 8.9 to 20.7\,K, with an average of 12.3\,K, indicating a coupling between gas and dust temperatures. The ammonia column densities range from 3.6\,times \,1014 to 6.07\,times $, with a median value of 2.04\,times $. The fractional abundances of ammonia range from 0.3 to 9.7\,times $, with an average of 2.7\,times $, which is one order of magnitude larger than that of massive star-forming (MSF) regions and infrared dark clouds (IRDCs). The correlation between thermal and nonthermal velocity dispersion of the NH$_ $\,(1,1) inversion transition indicates the dominance of supersonic nonthermal motions in the dense gas traced by $, and the relationship between these two parameters in Planck cold cores is weaker, with lower values observed for both parameters relative to other samples under our examination. The cumulative distribution shapes of line widths in the Planck cold cores closely resemble those of the dense cores found in regions of Cepheus, in addition to Orion L1630 and L1641, with higher values compared to Ophiuchus.

Laser frequency stabilization by modulation transfer spectroscopy and balanced detection of molecular iodine for laser cooling of 174Yb.

We report laser frequency stabilization by the combination of modulation transfer spectroscopy and balanced detection of a relatively weak hyperfine transition of the R(158)25-0 line of molecular iodine (127I2), which is used as a new frequency reference for laser trapping and cooling of 174Yb on the 1S0 - 3P1 transition. The atomic cloud is characterized by time-of-flight measurements, and an on-resonance optical depth of up to 47 is obtained. We show laser noise reduction and characterize the short-term laser frequency instability by the Allan deviation of the laser fractional frequency. The minimum measured value is 3.9 ×10-13 at 0.17 s of averaging time.

ENDOR Spectroscopy Reveals the "Free" 5'-Deoxyadenosyl Radical in a Radical SAM Enzyme Active Site Actually is Chaperoned by Close Interaction with the Methionine-Bound [4Fe-4S]2+ Cluster.

1/2H and 13C hyperfine coupling constants to 5'-deoxyadenosyl (5'-dAdo•) radical trapped within the active site of the radical S-adenosyl-l-methionine (SAM) enzyme, pyruvate formate lyase-activating enzyme (PFL-AE), both in the absence of substrate and the presence of a reactive peptide-model of the PFL substrate, are completely characteristic of a classical organic free radical whose unpaired electron is localized in the 2pπ orbital of the sp2 C5'-carbon (J. Am. Chem. Soc. 2019, 141, 12139-12146). However, prior electron-nuclear double resonance (ENDOR) measurements had indicated that this 5'-dAdo• free radical is never truly "free": tight van der Waals contact with its target partners and active-site residues guide it in carrying out the exquisitely precise, regioselective reactions that are hallmarks of RS enzymes. Here, our understanding of how the active site chaperones 5'-dAdo• is extended through the finding that this apparently unexceptional organic free radical has an anomalous g-tensor and exhibits significant 57Fe, 13C, 15N, and 2H hyperfine couplings to the adjacent, isotopically labeled, methionine-bound [4Fe-4S]2+ cluster cogenerated with 5'-dAdo• during homolytic cleavage of cluster-bound SAM. The origin of the 57Fe couplings through nonbonded radical-cluster contact is illuminated by a formal exchange-coupling model and broken symmetry-density functional theory computations. Incorporation of ENDOR-derived distances from C5'(dAdo•) to labeled-methionine as structural constraints yields a model for active-site positioning of 5'-dAdo• with a short, nonbonded C5'-Fe distance (∼3 Å). This distance involves substantial motion of 5'-dAdo• toward the unique Fe of the [4Fe-4S]2+ cluster upon S-C(5') bond-cleavage, plausibly an initial step toward formation of the Fe-C5' bond of the organometallic complex, Ω, the central intermediate in catalysis by radical-SAM enzymes.

Capturing CO2 in Quadrupolar Binding Pockets: Broadband Microwave Spectroscopy of Pyrimidine-(CO2)n, n = 1,2.

Pyrimidine has two in-plane CH(δ+)/N̈(δ-)/CH(δ+) binding sites that are complementary to the (δ-/2δ+/δ-) quadrupole moment of CO2. We recorded broadband microwave spectra over the 7.5-17.5 GHz range for pyrimidine-(CO2)n with n = 1 and 2 formed in a supersonic expansion. Based on fits of the rotational transitions, including nuclear hyperfine splitting due to the two 14N nuclei, we have assigned 313 hyperfine components across 105 rotational transitions for the n = 1 complex and 208 hyperfine components across 105 rotational transitions for the n = 2 complex. The pyrimidine-CO2 complex is planar, with CO2 occupying one of the quadrupolar binding sites, forming a structure in which the CO2 is stabilized in the plane by interactions with the C-H hydrogens adjacent to the nitrogen atom. This structure is closely analogous to that of the pyridine-CO2 complex studied previously by (Doran, J. L. J. Mol. Struct. 2012, 1019, 191-195). The fit to the n = 2 cluster gives rotational constants consistent with a planar cluster of C2v symmetry in which the second CO2 molecule binds in the second quadrupolar binding pocket on the opposite side of the ring. The calculated total binding energy in pyrimidine-CO2 is -13.7 kJ mol-1, including corrections for basis set superposition error and zero-point energy, at the CCSD(T)/ 6-311++G(3df,2p) level, while that in pyrimidine-(CO2)2 is almost exactly double that size, indicating little interaction between the two CO2 molecules in the two binding sites. The enthalpy, entropy, and free energy of binding are also calculated at 300 K within the harmonic oscillator/rigid-rotor model. This model is shown to lack quantitative accuracy when it is applied to the formation of weakly bound complexes.