Levels Of Ground State Research Articles

Electromagnetically Induced Transparency Cooling of High-Nuclear-Spin Ions.

We report the electromagnetically induced transparency (EIT) cooling of ^{137}Ba^{+} ions with a nuclear spin of I=3/2, which are a good candidate of qubits for future large-scale trapped-ion quantum computing. EIT cooling of atoms or ions with a complex ground-state level structure is challenging due to the lack of an isolated Λ system, as the population can escape from the Λ system to reduce the cooling efficiency. We overcome this issue by leveraging an EIT pumping laser to repopulate the cooling subspace, ensuring continuous and effective EIT cooling. We cool the two radial modes of a single ^{137}Ba^{+} ion to average motional occupations of 0.08(5) and 0.15(7), respectively. Using the same laser parameters, we also cool all the ten radial modes of a five-ion chain to near their ground states. Our approach can be adapted to atomic species possessing similar level structures. It allows engineering of the EIT Fano-like spectrum, which can be useful for simultaneous cooling of modes across a wide frequency range, aiding in large-scale trapped-ion quantum information processing.

Robust Nuclear Spin Polarization via Ground-State Level Anticrossing of Boron Vacancy Defects in Hexagonal Boron Nitride.

Nuclear spin polarization plays a crucial role in quantum information processing and quantum sensing. In this work, we demonstrate a robust and efficient method for nuclear spin polarization with boron vacancy (V_{B}^{-}) defects in hexagonal boron nitride (h-BN) using ground-state level anticrossing (GSLAC). We show that GSLAC-assisted nuclear polarization can be achieved with significantly lower laser power than excited-state level anticrossing, making the process experimentally more viable. Furthermore, we have demonstrated direct optical readout of nuclear spins for V_{B}^{-} in h-BN. Our findings suggest that GSLAC is a promising technique for the precise control and manipulation of nuclear spins in V_{B}^{-} defects in h-BN.

Quantum Magnetism of the Iron Core in Ferritin Proteins-A Re-Evaluation of the Giant-Spin Model.

The electron-electron, or zero-field interaction (ZFI) in the electron paramagnetic resonance (EPR) of high-spin transition ions in metalloproteins and coordination complexes, is commonly described by a simple spin Hamiltonian that is second-order in the spin S: H=D[Sz2-SS+1/3+E(Sx2-Sy2). Symmetry considerations, however, allow for fourth-order terms when S ≥ 2. In metalloprotein EPR studies, these terms have rarely been explored. Metal ions can cluster via non-metal bridges, as, for example, in iron-sulfur clusters, in which exchange interaction can result in higher system spin, and this would allow for sixth- and higher-order ZFI terms. For metalloproteins, these have thus far been completely ignored. Single-molecule magnets (SMMs) are multi-metal ion high spin complexes, in which the ZFI usually has a negative sign, thus affording a ground state level pair with maximal spin quantum number mS = ±S, giving rise to unusual magnetic properties at low temperatures. The description of EPR from SMMs is commonly cast in terms of the 'giant-spin model', which assumes a magnetically isolated system spin, and in which fourth-order, and recently, even sixth-order ZFI terms have been found to be required. A special version of the giant-spin model, adopted for scaling-up to system spins of order S ≈ 103-104, has been applied to the ubiquitous iron-storage protein ferritin, which has an internal core containing Fe3+ ions whose individual high spins couple in a way to create a superparamagnet at ambient temperature with very high system spin reminiscent to that of ferromagnetic nanoparticles. This scaled giant-spin model is critically evaluated; limitations and future possibilities are explicitly formulated.

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.

Tuning of end-groups in diketopyrrolopyrrole-based acceptors molecules for organic photovoltaics

In this computational approach, four small novel acceptor molecules of A2-D-A1-D-A2 type have been designed (S1-S4) by the replacement of terminal acceptor groups (A2) of R molecule with four different types of electron accepting-units. The photovoltaic aspects of molecules have been studied by using DFT based method i.e. B3LYP/6–31 G (d, p). The energy level of ground and excited state, bandgap (Egap), excitation energy, transition density matrix (TDM), absorption maxima (λmax), light-harvesting efficiency (LHE), the density of states (DOS), open circuit voltage (VOC) and many other optoelectronic properties of molecules have been investigated in this research. Out of all the newly suggested molecules, S2 has exhibited the highest red-shift in λmax (815 nm), the lowest excitation energy (1.52 eV), small band gap and ionization potential, and the highest oscillator strength (1.97). The VOC of the studied acceptor molecules was calculated with regard to the PTB7-Th donor, and the findings showed that all of the newly suggested molecules displayed a higher VOC and a greater FF than that of R molecule. Consequently, the findings of these calculations show that our computational investigations give profound insights to support a realistic implementation of OSCs with the accepted acceptor molecules examined.

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(III) coordination polymer.

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4- tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc2- dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K-1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.

Properties of the least action level and the existence of ground state solution to fractional elliptic equation with harmonic potential

In this article we consider the following fractional semilinear elliptic equation \[(-\Delta)^su+|x|^2u =\omega u+|u|^{2\sigma}u \quad \text{ in } \mathbb{R}^N,\] where \(s\in (0,1)\), \(N\gt 2s\), \(\sigma\in (0,\frac{2s}{N-2s})\) and \(\omega\in (0, \lambda_1)\). By using variational methods we show the existence of a symmetric decreasing ground state solution of this equation. Moreover, we study some continuity and differentiability properties of the ground state level. Finally, we consider a bifurcation type result.

Combined Experimental and Theoretical Insights: Spectroscopic and Molecular Investigation of Polyphenols from Fagonia indica via DFT, UV-vis, and FT-IR Approaches.

This review deals with computational study of polyphenolic compounds of medicinal importance and interest for drug development. Herein, four polyphenolic compounds comprising catechol (1), caffeic acid (II), gallic acid (III), and pyrogallol (IV) have been isolated from a medicinal specie, Fagonia indica, by applying silica gel column chromatography. These compounds were identified by using gas chromatography-mass spectrometry (GC-MS) analysis and confirmed by geometric computational analysis. According to computational results, caffeic acid has shown the highest biological activation due to higher chemical softness, electronegativity (χ (eV) = -648.644), and electrostatic potential value (-8.424 × 10-2 to +8.424 × 10-2), while smaller values of chemical potential (-0.269), ELUMO (-0.080), and energy gap (ΔE = 0.149). The Mulliken atomic charges were calculated by using DFT/B3LYP with basis set 6-311G for the determination of active sites. The oxygen atom of catechol showed highest nucleophilic characteristic with a more negative charge (08 = -0.695), and pyrogallol indicated a strong electrophilic center at C14 = 0.415 with a higher positive charge. Moreover, UV-visible absorption spectra and a detailed study of vibrational frequencies for all phenolic compounds by employing the DFT approach with 3-21G, 6-31G, and 6-311G basis sets at the ground-state level showed the great agreement with experimental results. ANOVA has been applied to validate the theoretical data. Results suggest that compounds I-IV are suitable in diverse fields.

Hyperfine transition induced by atomic motion above a paraffin-coated magnetic film

We measured transitions between the hyperfine levels of the electronic ground state of potassium-39 atoms (transition frequency: 460 MHz) as the atoms moved through a periodic magneto-static field produced above the magnetic-stripe domains of a magnetic film. The period length of the magnetic field was 3.8 µm. The atoms were incident to the field as an impinging beam with the most probable velocity of 550 m s−1 and experienced a peak oscillating field of 20 mT. Unwanted spin relaxation caused by the collisions of the atoms with the film surface was suppressed by the paraffin coating on the film. We observed increasing hyperfine transition probabilities as the frequency of the field oscillations experienced by the atoms increased from 0 to 140 MHz for the atomic velocity of 550 m s−1, by changing the incident angle of the atomic beam with respect to the stripe domains. Numerical calculation of the time evolution of the hyperfine states revealed that the oscillating magnetic field experienced by the atoms induced the hyperfine transitions, and the main process was not a single-quantum transition but rather multi-quanta transitions.

Differences of up-conversion and temperature sensing behaviors of NaYF4: 2 mol % Er3+, 20 mol % Yb3+ Phosphors with cubic and hexagonal phases

In this work, NaYF4: 2 mol % Er3+, 20 mol % Yb3+ phosphors with cubic and hexagonal phases were prepared by co-precipitation method with different reaction temperature. The multi-photon up-conversion processes and optical temperature sensing properties are discussed. The emission spectra of hexagonal phase show higher emission intensity and lower red-to-green ratio (R/G), which are attributed to the decrease of local symmetric. And the number of photons (n), participated in the up-conversion processes, declines as the phase changes from cubic to hexagonal. This can be originated to the exhaustion of electrons on ground state level: 4I15/2 in hexagonal phase. And the fitting n of green emissions decline more obviously than red emission with temperature increasing. The temperature dependent FIR is fitted and the fitted function implies that the energy gap ∆E increases as the phase changes to hexagonal. And the max relative sensitivity reaches 0.012 K−1 at 300 K. Thus, NaYF4: 2 mol % Er3+, 20 mol % Yb3+ phosphors with hexagonal phase have higher SR and can be promising in FIR-based temperature sensing.

Multi-frequency Doppler-free spectroscopy of cesium using an external cavity diode laser

We employed a different approach to develop multi-frequency saturated-absorption spectroscopy (SAS) involving both cesium hyperfine ground state levels using a multimode external cavity diode laser (ECDL), which could operate with neither another independent laser nor a modulator. The multi-frequency SAS is formed by atomic velocity groups on resonance with both of the laser modes from an ECDL in multimode operation, which are counterpropagated through the vapor cell as a quasicoherent pair of laser beams. A sign reversal of the sub-Doppler resonance under special pump–probe polarization with and without applied magnetic fields is observed. Simultaneously, the optical microwave generation of the multimode ECDL is also investigated experimentally. The free-running linewidth of the beat note spectra between two modes is about 475 Hz, which indicates a high coherence between them. This oscillator- and modulator-free approach provides a complementary scheme for existing optical microwave generation and has potential for improvements.

Mixed-field effect at the hyperfine level of 127I79Br in its rovibronic ground state: Toward field manipulation of cold molecules

The mixed-field effect at the hyperfine level of the rovibronic ground state of the 127I79Br (X1Σ, v = 0, J = 0) molecule is computed on the J–I uncoupled basis of |JMJI 1 M 1 I 2 M 2〉, where J is the molecular total angular momentum excluding nuclear spin, MJ is the projection number of J, I 1 and I 2 are the nuclear spins of the iodine and bromine atoms, and M 1 and M 2 are the projection numbers of I 1 and I 2, respectively. When the two applied electric and magnetic fields are parallel, the perturbations are rare and only one perturbation is observed in a relatively large field regime in our computation range. However, when the two fields are off-parallel, the perturbations increase significantly and some sublevels show the Feshbach-like resonance phenomenon. Therefore, such sublevels transit between weak-field seeking and strong-field seeking repeatedly, which can be utilized to enhance or suppress cold molecular collision and chemical reaction rates. Such behavior of the molecular hyperfine structure in the mixed off-parallel fields may also be utilized to construct an electric-field-assisted anti-Helmholtz magnetic trap for cold molecules and to realize evaporative cooling of cold molecules (sub-mK) into the ultracold regime (μK).

DNA Origami Assembled Nanoantennas for Manipulating Single-Molecule Spectral Emission.

The emission spectrum of a dye is given by the energy of all of the possible radiative transitions weighted by their probability. This spectrum can be altered with optical nanoantennas that are able to manipulate the decay rate of nearby emitters by modifying the local density of photonic states. Here, we make use of DNA origami to precisely place an individual dye at different positions around a gold nanorod and show how this affects the emission spectrum of the dye. In particular, we observe a strong suppression or enhancement of the transitions to different vibrational levels of the excitonic ground state, depending on the spectral overlap with the nanorod resonance. This reshaping can be used to experimentally extract the spectral dependence of the radiative decay rate enhancement. Furthermore, for some cases, we argue that the drastic alteration of the fluorescence spectrum could arise from the violation of Kasha's rule.

Blackbody thermalization and vibrational lifetimes of trapped polyatomic molecules

We study the internal state dynamics of optically trapped polyatomic molecules subject to room-temperature blackbody radiation. Using rate equations that account for radiative decay and blackbody excitation between rovibrational levels of the electronic ground state, we model the microscopic behavior of the molecules' thermalization with their environment. As an application of the model, we describe in detail the procedure used to determine the blackbody and radiative lifetimes of low-lying vibrational states in ultracold CaOH molecules, the values of which were reported in previous work [C. Hallas et al., Phys. Rev. Lett. 130, 153202 (2023)]. Ab initio calculations are performed and are found to agree with the measured values. Vibrational-state lifetimes for several other laser-coolable molecules, including SrOH and YbOH, are also calculated.

Observation of Narrow Optical Homogeneous Linewidth and Long Nuclear Spin Lifetimes in a Prototypical [Eu(trensal)] Complex

Coherent light–matter interfaces are key elements for many quantum information processing architectures. Rare-earth ion (REI)-containing systems featuring narrow inter-configurational f–f transitions are suitable for creating such interfaces. Recently, narrow homogeneous linewidths (Γh) and long nuclear spin lifetimes (T1spin) associated with two Eu3+ complexes featuring the 5D0 → 7F0 f–f transition have been reported, elucidating that REI-molecule-based coherent light–matter interfaces can be obtained. In this study, we report a homogeneous linewidth of 2.8 MHz at 4.2 K, corresponding to an optical coherence lifetime (T2opt) of 114 ns (0.11 μs), associated with the 5D0 → 7F0 transition of the prototypical charge neutral Eu3+ complex─[Eu(trensal)]. Moreover, we have observed long nuclear spin lifetimes (T1spin) up to 460 ± 80 s at 4.2 K for the complex and efficient optical pumping of hyperfine levels of the 5D0 ground state. The results presented in this study indicate that narrow homogeneous linewidths and long nuclear spin lifetimes could be a generic property of molecular Eu3+ complexes featuring the 5D0 → 7F0 transition.

First-principles calculations of electronic and optical properties of Ce3+-activated phosphors toward evaluating valence stability of Eu ions

The valence stability of activator ions with multiple stable valence states has always been a major concern in the field of luminescent materials. Here we present a computational protocol that is able to predict the valence stability of the europium (Eu) ion in its activated phosphors, in terms of the energy difference between the ground-state level of Eu2+ and the Fermi level of the host. The protocol is based on hybrid density functional theory (DFT) and wavefunction-based multiconfigurational ab initio calculations of the dopant Ce3+, in conjunction with the established relationship between energy levels of Ce3+ and Eu2+. The predictions are in good agreements with experimental findings. It is demonstrated that across the study set consisting of five borate-containing phosphors, the valence stability of the dopant Eu2+ is positively correlated with the host band gap, and this positive correlation is more significant than the negative correlation with the energy level of Eu2+ within the host band gap. Microscopic analysis reveals that a strong bonding of electrons within the anion groups together with a large dopant site is beneficial for the reduction of Eu3+ into Eu2+. The influence of hybrid DFT functional on the predicted valence stability of a given compound was found be negligible due to cancellation of changes in the host band gap and the Eu2+ ground level. This study clarifies the reasons for the stabilization of Eu2+ in phosphors synthesized in air at high temperature and is expected to help to screen out the host compounds that could stabilize Eu2+ activators for diverse optical applications.

Electronic and spin-rovibrational spectroscopy of the HPS+ cation

Using post Hartree-Fock multi-configuration interaction ab initio approaches, the six (four) doublet (quartet) lowest electronic states of thioxophosphane cation, HPS+, are treated. These electronic states are mapped along the internal coordinates, including the HP, PS distances and in-plane HPS bending angle. Several potential minima are located where long-lived HPS+ ions can be found. Also, computations show that the (X˜2A', 12A", 22A", 22A', 14A' and 14A") states are bound, for which we generate their 3D-potential energy surfaces (3D-PESs). After nuclear motion treatments, we determine the rotational and vibrational constants of these states and the pattern of their rovibrational levels up to 4000 cm−1 above the corresponding vibrational ground state level. For instance, the RCCSD(T)/aug-cc-pV(5 + d)Z anharmonic frequencies of HPS+(X˜2A') are computed ν1 = 2237.7, ν2 = 543.0, ν3 = 686.8 (in cm−1). For the lowest electronic excited state (HPS+(12A")), these frequencies change to ν1 = 2330.5, ν2 = 254.6 and ν3 = 749.6 (in cm−1). Several anharmonic resonances are identified. Besides, a very accurate adiabatic ionization energy of HPS (= 9.3173 eV) is deduced using the (U)CCSDT(Q)/aug-cc-pV(T + d)Z approach and where the core-valence (ΔCV), scalar relativistic (ΔSR) and zero point vibrational energy (ΔZPE) corrections are included. Our spectroscopic data should be useful for identifying this ion in laboratory and in media where reactive collisions between PS/PS+ + H+/H or HP/HP+ + S+/S are taking place.

Photon-mediated correlated hopping in a synthetic ladder

We propose a new direction in quantum simulation that uses multilevel atoms in an optical cavity as a toolbox to engineer new types of bosonic models featuring correlated hopping processes in a synthetic ladder spanned by atomic ground states. The underlying mechanisms responsible for correlated hopping are collective cavity-mediated interactions that dress a manifold of excited levels in the far detuned limit. By weakly coupling the ground state levels to these dressed states using two laser drives with appropriate detunings, one can engineer correlated hopping processes while suppressing undesired single-particle and collective shifts of the ground state levels. We discuss the rich many-body dynamics that can be realized in the synthetic ladder including pair production processes, chiral transport and light-cone correlation spreading. The latter illustrates that an effective notion of locality can be engineered in a system with fully collective interactions.

Proposal for Zeeman slowing of Rb2 molecules in a supersonic beam, inducing internal cooling

We present a theoretical proposal on Zeeman slowing of a Rb2 supersonic beam, relying on transitions between rovibrational levels of the electronic ground-state and the electronic excited state. Translational cooling is induced by optical transitions from to involving P () and Q () branches. This is achieved by shaping the spectrum of broadband laser sources, in addition to two single-frequency laser sources addressing the transitions. Our Monte–Carlo simulations indicate that the velocity of the molecules can be slowed from 500 m s−1 down to a few m s−1 by a Zeeman slower with a 1.2 m length, after scattering about 150 000 photons. At the end of the slowing process, half of the molecules are internally cooled, predicted to be in the ground-state levels. A final optical pumping step transferring the population to the ground-state level could produce a molecular beam exiting the Zeeman slower which is cold in all the translational, vibrational, and rotational degrees of freedom. Such an approach could potentially be a great interest for cooling down a large class of molecular species.

Low-temperature specific heat and heat transport of Tb2Ti2−xZrxO7 single crystals

We report a study on the specific heat and heat transport of Tb$_2$Ti$_{2-x}$Zr$_x$O$_7$ ($x =$ 0, 0.02, 0.1, 0.2, and 0.4) single crystals at low temperatures and in high magnetic fields. The magnetic specific heat can be described by the Schottky contribution from the crystal-electric-field (CEF) levels of Tb$^{3+}$, with introducing Gaussian distributions of the energy split of the ground-state doublet and the gap between the ground state and first excited level. These crystals has an extremely low phonon thermal conductivity in a broad temperature range that can be attributed to the scattering by the magnetic excitations, which are mainly associated with the CEF levels. There is strong magnetic field dependence of thermal conductivity, which is more likely related to the field-induced changes of phonon scattering by the CEF levels than magnetic transitions or spin excitations. For magnetic field along the [111] direction, there is large thermal Hall conductivity at low temperatures which displays a broad peak around 8 T. At high fields up to 14 T, the thermal Hall conductivity decreases to zero, which supports its origin from either the spinon transport or the phonon skew scattering by CEF levels. The thermal Hall effect is rather robust with Zr doping up to 0.2 but is strongly weakened in higher Zr-doped sample.