Internal Spin Research Articles

Yang-Mills field from fuzzy sphere quantum Kaluza-Klein model

Using the framework of quantum Riemannian geometry, we show that gravity on the product of spacetime and a fuzzy sphere is equivalent under minimal assumptions to gravity on spacetime, an su2-valued Yang-Mills field Aμi and a real-symmetric-matrix valued Liouville-sigma model field hij for gravity on the fuzzy sphere. Moreover, a massless real scalar field on the product appears as a tower of scalar fields on spacetime, with one for each internal integer spin l representation of SU(2), minimally coupled to Aμi and with mass depending on l and the fuzzy sphere size. For discrete values of the deformation parameter, the fuzzy spheres can be reduced to matrix algebras M2j+1(ℂ) for j any non-negative half-integer, and in this case only integer spins 0 ≤ l ≤ 2j appear in the multiplet. Thus, for j = 1 a massless field on the product appears as a massless SU(2) internal spin 0 field, a massive internal spin 1 field and a massive internal spin 2 field, in mass ratio 0, 1,3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{3} $$\\end{document} respectively, which we conjecture could arise in connection with an approximate SU(2) flavour symmetry.

Westerfit: A new program for spin–torsion–rotation spectra

A new program, westerfit, has been developed to treat Cs molecules with internal rotation and spin angular momentum. It implements a single diagonalization Rho Axis Method approach for the torsion–rotation alongside a complete treatment of nuclear quadrupole interaction and spin–rotation coupling. Unlike other programs designed for internal rotation with spin effects, westerfit includes matrix elements off-diagonal in the rotational angular momentum quantum number, N, rather than the perturbative treatment of the spin–rotation and quadrupole interactions. This full combined approach allows fitting of all symmetrically allowed terms in both the spin–rotation and the quadrupole tensors as well as inclusion of higher order terms coupling the large amplitude motion to the spin angular momentum. The program was benchmarked against other published programs to test molecular cases of torsion–rotation, spin–rotation, and spin–torsion-rotation. All three tests produced a lower RMS. westerfit paves a way forward for complete treatment of spin–torsion–rotation problems regardless of barrier height or quadrupole moment.

Towards a holistic magnetic braking model – II: explaining several long-term internal- and surface-spin properties of solar-like stars and the Sun

ABSTRACT We extend our model of magnetic braking (MB), driven by an α–Ω dynamo mechanism, from fully convective M-dwarfs (FCMDs) to explain the surface and internal spin $P_\mathrm{spin}$ evolution of partly convective dwarfs (PCDs) starting from the disc-dispersal stage to the main-sequence turn-off. In our model, the spin of the core is governed by shear at the core-envelope boundary while the spin of the envelope is governed by MB and shear. We show that (1) the most massive FCMDs experience a stronger spin-down than PCDs and less massive FCMDs, (2) the stalled spin-down and enhanced activity of K-dwarfs and the pile-up of G-dwarfs older than a few Gyr are stellar-structure and MB-dependent, and weakly dependent on core-envelope coupling effects, (3) our expression of the core-envelope convergence time-scale $\tau _{\text{converge}}(M_\ast , P_{\text{spin}})$ between a few 10 to 100 Myr strongly depends on stellar structure but weakly on MB strength and shear, such that fast and massive rotators achieve corotation earlier, (4) our estimates of the surface magnetic fields are in general agreement with observations and our wind mass loss evolution explains the weak winds from the solar analog $\pi ^1$ UMa, and (5) with our model the massive young Sun hypothesis as a solution to the faint young Sun problem can likely be ruled out, because the maximum mass lost by winds from our Sun with our model is about an order of magnitude smaller than required to solve the problem.

Tracer dynamics in the active random average process

We investigate the dynamics of tracer particles in the random average process (RAP), a single-file system in one dimension. In addition to the position, every particle possesses an internal spin variable σ(t) that can alternate between two values, ±1, at a constant rate γ. Physically, the value of σ(t) dictates the direction of motion of the corresponding particle and, for finite γ, every particle performs non-Markovian active dynamics. Herein, we study the effect of this non-Markovian behavior in the fluctuations and correlations of the positions of tracer particles. We analytically show that the variance of the position of a tagged particle grows sub-diffusively as ∼ζqt at large times for the quenched uniform initial conditions. While this sub-diffusive growth is identical to that of the Markovian/non-persistent RAP, the coefficient ζq is rather different and bears the signature of the persistent motion of active particles through higher-point correlations (unlike in the Markovian case). Similarly, for the annealed (steady-state) initial conditions, we find that the variance scales as ∼ζat at large times, with the coefficient ζa once again different from the non-persistent case. Although both ζ q and ζa individually depart from their Markovian counterparts, their ratio ζa/ζq is still equal to 2 , a condition observed for other diffusive single-file systems. This condition turns out to be true even in the strongly active regimes, as corroborated by extensive simulations and calculations. Finally, we study the correlation between the positions of two tagged particles in both quenched uniform and annealed initial conditions. We verify all our analytical results using extensive numerical simulations.

Stepwise Stiffening Chromophore Strategy Realizes a Series of Ultralong Blue Room-Temperature Phosphorescent Materials.

Ultralong room-temperature phosphorescent (URTP) materials have attracted wide attention in anti-counterfeiting, optoelectronic display, and bio-imaging due to their special optical properties. However, room-temperature blue phosphorescent materials are very scarce during applications because of the need to simultaneously populate and stabilize high-energy excited states. In this work, a stepwise stiffening chromophore strategy is proposed to suppress non-radiative jump by continuously reducing the internal spin of the chromophore, and successfully developing a series of blue phosphorescent materials. Phosphorescence lifetimes of more than 3 s are achieved, with the longest lifetime reaching 5.44 s and lasting more than 70 s in the naked eye. As far as is know, this is the best result that has been reported. By adjusting the chromophore conjugation, multicolor phosphorescences from cyan to green have been realized. In addition, these chromophores exhibit the same excellent optical properties in urea and polyvinyl alcohmance (PVA). Finally, these materials are successfully applied to luminescent displays.

Dynamic control of optical skyrmions in cylindrical waveguide

In recent times, the optical skyrmions have received an increasing amount of interest owing to its applications in optical manipulation, super-resolution imaging and microscopy, quantum technologies. However, few studies are focused on the dynamic control of optical skyrmions. It is found that Neel-type photonic skyrmions were discovered in evanescent electromagnetic waves. Here, we find the Bloch-type skyrmions in a three-dimensional cylindrical waveguide. By modulating the amplitude ratio of two incident vortex beams, the new types of skyrmions such as Twisted-type skyrmions and Planar-type skyrmions can be found. Further more, we have also achieved arbitrary modulation ratios of internal spin components. It is believed that our findings greatly enrich the types of photonic skyrmions and provide a method to freely control the photonic skyrmions.

Quantum control and Berry phase of electron spins in rotating levitated diamonds in high vacuum

Levitated diamond particles in high vacuum with internal spin qubits have been proposed for exploring macroscopic quantum mechanics, quantum gravity, and precision measurements. The coupling between spins and particle rotation can be utilized to study quantum geometric phase, create gyroscopes and rotational matter-wave interferometers. However, previous efforts in levitated diamonds struggled with vacuum level or spin state readouts. To address these gaps, we fabricate an integrated surface ion trap with multiple stabilization electrodes. This facilitates on-chip levitation and, for the first time, optically detected magnetic resonance measurements of a nanodiamond levitated in high vacuum. The internal temperature of our levitated nanodiamond remains moderate at pressures below 10−5 Torr. We have driven a nanodiamond to rotate up to 20 MHz (1.2 × 109 rpm), surpassing typical nitrogen-vacancy (NV) center electron spin dephasing rates. Using these NV spins, we observe the effect of the Berry phase arising from particle rotation. In addition, we demonstrate quantum control of spins in a rotating nanodiamond. These results mark an important development in interfacing mechanical rotation with spin qubits, expanding our capacity to study quantum phenomena.

Beating the Standard Quantum Limit Electronic Field Sensing by Simultaneously Using Quantum Entanglement and Squeezing.

Quantum entanglement and quantum squeezing are two typical approaches to beat the standard quantum limit (SQL) for the sensitive phase estimations in quantum metrology. Each of them has already been utilized individually and sequentially to improve the sensitivity of electric field sensing with the trapped ion platform. However, the upper bound of the demonstrated sensitivity gain is still limited, i.e., the theoretical 6dB and experimental 3dB over the corresponding SQL, for electric field sensing. By simultaneously using the internal (spin)-external (oscillator) state entanglement and the oscillator squeezing to effectively amplify the accumulation phase, we show here that such a theoretical sensitivity gain upper bound can be significantly surpassed. The proposal provides a novel approach to implement the stronger beat of the SQL and even approach the Heisenberg limit, for the sensitive sensings of the desired electric field and also the other metrologies.

High-frequency magnetic response of superparamagnetic composites of spherical Fe and Fe3O4 nanoparticles

The response of arrays of magnetic nanoparticles (MNPs) of cubic anisotropy materials (magnetite or iron) to high-frequency (sub-GHz) field is investigated utilizing micromagnetic simulations. Composites of MNPs embedded in dielectric media are of interest as core materials for high-frequency power microconverters with low eddy-current losses. Going beyond the macrospin approximation for MNPs (including internal spin structure), we simulate the magnetization dynamics of arrays of spherical and periodically arranged MNPs under periodic boundary conditions and in the presence of thermal fluctuations of the magnetization within the stochastic thermal field. Analyzing the dependence of the dynamical response on the size of the MNPs, we find the size to be crucial for exciting regular magnetization oscillations at room temperature and reducing hysteresis loss. The efficiency of the dynamical response of composites of high-magnetization-metal (iron) MNPs is compared to that of magnetite nanocomposites. We find the sub-GHz susceptibility of magnetite-containing nanocomposite to be comparable to that of the iron MNPs despite the lower saturation magnetization of Fe3O4, (at the volumetric ratio of the magnetic phase of 0.13, susceptibility is χ≈1.6 for 5 nm Fe and ≈1.4 for 12 nm Fe3O4 MNPs at T=300 K and frequency of 0.1 GHz).

Spinning protons and gluons in the η′

The proton spin puzzle has inspired a vast programme of experiments and theoretical work challenging our understanding of QCD and its role in the structure of hadrons. The proton’s internal spin structure is connected to chiral symmetry and, through gluon degrees of freedom in the flavor singlet channel, to the physics of the [Formula: see text] meson. Why do quarks contribute just about one third of the proton’s spin? Why are [Formula: see text] mesons and their interactions so sensitive to gluonic degrees of freedom? We review the status of these topics and some key observables for forthcoming experiments.

Polarization losses from the nonadiabatic passage of hyperpolarized solutions through metallic components

From complex-mixture analysis to in vivo molecular imaging, applications of liquid-state nuclear spin hyperpolarization have expanded widely over recent years. In most cases, hyperpolarized solutions are generated ex situ and transported from the polarization instrument to the measurement device. The sample hyperpolarization usually survives this transport, since the changes in magnetic fields that are external to the sample are typically adiabatic (slow) with respect to the internal nuclear spin dynamics. The passage of polarized samples through weakly magnetic components such as stainless steel syringe needles and ferrules is not always adiabatic, which can lead to near-complete destruction of the magnetization. To avoid this effect becoming “folklore” in the field of hyperpolarized NMR, we present a systematic investigation to highlight the problem and investigate possible solutions. Experiments were carried out on: (i) dissolution-DNP-polarized [1-13C]pyruvate with NMR detection at 1.4T, and (ii) 1.5-T-polarized H2O with NMR detection at 2.5μT. We show that the degree of adiabaticity of solutions passing through metal parts is intrinsically unpredictable, likely depending on many factors such as solution flow rate, degree of remanent ferromagnetism in the metal, and nuclear spin species. However, the magnetization destruction effects can be suppressed by application of an external field on the order of 0.1–10mT.

Exploring the spin structure of the nucleon at STAR

Understanding the internal spin structure of the nucleon remains a challenge in strong interaction physics. The unique capability of RHIC opened new avenues in studying the internal structure of the proton with unprecedented depth and precision. Significant progress has been made in the last few years through various measurements at STAR. The longitudinal spin measurements have contributed significantly to our understanding of the quark and gluon helicity distributions inside the proton. The longitudinal double-spin asymmetry, ALL, from STAR inclusive jet and dijet measurements provides the first evidence of a positive gluon polarization with partonic momentum fraction x > 0.05. The reconstruction of W±/Z in longitudinally polarized proton-proton collisions indicates that there is a flavor separation of the light sea quark helicity distributions. In transversely polarized proton collisions, W±/Z-bosons provide the first constraint on the sea-quark Sivers function and contributes to the tests of the predicted sign change. The tilt of the dijet opening angle provides a direct access to the first Mellin momentum of the Sivers function and avoids the spin-correlated fragmentation contributions. The novel measurements of the azimuthal distributions of identified hadrons in jets and spin-dependent dihadron correlations directly probe the collinear quark transversity in the proton, with the former coupled to the transverse momentum dependent (TMD) Collins fragmentation function and the latter to the dihadron interference fragmentation function. These measurements shed lights on Sivers function, quark transversity and spin-dependent fragmentation functions in both collinear and TMD formalism. In this proceeding, recent jet results on both the longitudinal and transverse spin structure of the proton from STAR are presented.

Nested SU(2) symmetry of photonic orbital angular momentum

The polarization state is described by a quantum mechanical two-level system, which is known as special unitary group of degree 2 [SU(2)]. Polarization is attributed to an internal spin degree of freedom inherent to photons, while photons also possess an orbital degree of freedom. A fundamental understanding of the nature of spin and orbital angular momentum of photons is significant to utilize the degrees of freedom for various applications in optical communications, computations, sensing, and laser-patterning. Here, we show that the orbital angular momentum of coherent photons emitted from a laser diode can be incremented using a vortex lens, and the magnitude of orbital angular momentum increases with an increase in the topological charge inside the mode. The superposition state of the left and right vortices is described by the SU(2) state, similar to polarization; however, the radius of the corresponding Poincaré sphere depends on the topological charge. Consequently, we expect a nested SU(2) structure to describe various states with different magnitudes in orbital angular momentum. We have experimentally developed a simple system to realize an arbitrary SU(2) state of orbital angular momentum by controlling both amplitudes and phases of the left and right vortices using a spin degree of freedom, whose interplays were confirmed by expected far-field images of dipoles and quadruples.

Optically controlled single-valley exciton doublet states with tunable internal spin structures and spin magnetization generation

Manipulating quantum states through light-matter interactions has been actively pursued in two-dimensional materials research. Significant progress has been made toward the optical control of the valley degrees of freedom in semiconducting monolayer transition-metal dichalcogenides, based on doubly degenerate excitons from their two distinct valleys in reciprocal space. Here, we introduce a type of optically controllable doubly degenerate exciton states that come from a single valley, dubbed as single-valley exciton doublet (SVXD) states. They are unique in that their constituent holes originate from the same valence band, making possible the direct optical control of the spin structure of the excited constituent electrons. Combining ab initio GW plus Bethe-Salpeter equation (GW-BSE) calculations and a theoretical analysis method, we demonstrate such SVXD in substrate-supported monolayer bismuthene-which has been successfully grown using molecular beam epitaxy. In each of the two distinct valleys in the Brillouin zone, strong spin-orbit coupling and [Formula: see text] symmetry lead to a pair of degenerate 1s exciton states (the SVXD states) with opposite spin configurations. Any coherent linear combinations of the SVXD in a single valley can be excited by light with a specific polarization, enabling full manipulation of their internal spin configurations. In particular, a controllable net spin magnetization can be generated through light excitation. Our findings open routes to control quantum degrees of freedom, paving the way for applications in spintronics and quantum information science.

Effect of internal magnetic flux on a relativistic spin-1 oscillator in the spinning point source-generated spacetime

In this paper, we consider a charged relativistic spin-1 oscillator under the influence of an internal magnetic flux in a [Formula: see text]-dimensional spacetime induced by a spinning point source. In order to analyze the effects of the internal magnetic flux and spin of the point source on the relativistic dynamics of such a vector field, we seek a non-perturbative solution of the associated spin-1 equation derived as an excited state of Zitterbewegung. By performing an analytical solution of the resulting equation, we determine exact results for the system in question. Accordingly, we analyze the effects of spin of the point source and internal magnetic flux on the relativistic dynamics of the considered test field. We see that the spin of such a field can be altered by the magnetic flux and this means that the considered system may behave as a fermion or boson according to the varying values of the magnetic flux, in principle. We observe that the internal magnetic flux and the spin of the point source impact on the relativistic energy levels and probability density functions. Also, our results indicate that the spin of the point source breaks the symmetry of the energy levels corresponding to particle–antiparticle states.

Geodesic angular momentum

Translational symmetry gives rise to rotational symmetry in general relativistic symmetry. This is an inconceivable fact according to conventional common sense, but the proof is given. Could the converse also be true? No, a counter-example is given. There is rotational symmetry that does not require translational symmetry, which does not give rise to translational symmetry even in general relativistic symmetry. The latter fact of course does not defy conventional common sense. Rotational symmetry conserves angular momentum. Antisymmetric tensor that vanishes by covariant differentiation is here defined geodesic angular momentum tensor. Killing vector due to rotational symmetry exists. We show a vierbein formalism for discussing translational symmetry and rotational symmetry in the same footing. We present a simple model that reveals how the internal spin of a Dirac particle contributes to the momentum tensor as vorticity, and how this vorticity is transformed into spin by the integration of the geodesic angular momentum tensor.

Spin noise in Er3+ single-ion magnets surrounded by ferromagnetic microparticles

Ferromagnetic microparticles significantly affect spin relaxation in the Er3+ single-ion magnet sandwiched in a composite material. The balance of thermal spin noise corresponding to Orbach, Raman, quantum tunneling, and direct relaxation channels is shifted in Er3+ complexes under the influence of surrounding ferromagnetic matrix. There are two competing sources of the electron spin noise controlled by ferromagnetic media. First, internal residual magnetic field delays spin relaxation in the Er3+ complexes due to the Zeeman interaction of the Er3+ spin even in the absence of external magnetic field. Second, chemical bonding between the Er 4d shell and the O 1s shell accelerates magnetic relaxation in the Er3+ ions on the surface of microparticles. Significance of these results is that composite media can be sliced into small elements with a variable frequency of spin noise depending on individual magnetization programmed within each element.

Exciton Lifetime and Optical Line Width Profile via Exciton-Phonon Interactions: Theory and First-Principles Calculations for Monolayer MoS2.

Exciton dynamics dictates the evolution of photoexcited carriers in photovoltaic and optoelectronic devices. However, interpreting their experimental signatures is a challenging theoretical problem due to the presence of both electron-phonon and many-electron interactions. We develop and apply here a first-principles approach to exciton dynamics resulting from exciton-phonon coupling in monolayer MoS2 and reveal the highly selective nature of exciton-phonon coupling due to the internal spin structure of excitons, which leads to a surprisingly long lifetime of the lowest-energy bright A exciton. Moreover, we show that optical absorption processes rigorously require a second-order perturbation theory approach, with photon and phonon treated on an equal footing, as proposed by Toyozawa and Hopfield. Such a treatment, thus far neglected in first-principles studies, gives rise to off-diagonal exciton-phonon self-energy, which is critical for the description of dephasing mechanisms and yields exciton line widths in excellent agreement with experiment.

Observation of large spontaneous emission rate enhancement of quantum dots in a broken-symmetry slow-light waveguide

Quantum states of light and matter can be manipulated on the nanoscale to provide a technological resource for aiding the implementation of scalable photonic quantum technologies. Experimental progress relies on the quality and efficiency of the coupling between photons and internal spin states of quantum emitters. Here we demonstrate a nanophotonic waveguide platform with embedded quantum dots (QDs) that enables both Purcell-enhanced emission and strong chiral coupling. The design uses slow-light effects in a glide-plane photonic crystal waveguide with QD tuning to match the emission frequency to the slow-light region. Simulations were used to map the chirality and Purcell enhancement depending on the position of a dipole emitter relative to the air holes. The highest Purcell factors and chirality occur in separate regions, but there is still a significant area where high values of both can be obtained. Based on this, we first demonstrate a record large radiative decay rate of 17 ± 2 ns−1 (60 ± 6 ps lifetime) corresponding to a 20 ± 2 fold Purcell enhancement. This was achieved by electric-field tuning of the QD to the slow-light region and quasi-resonant phonon-side band excitation. We then demonstrate a 5 ± 1 fold Purcell enhancement for a dot with high degree of chiral coupling to waveguide modes, substantially surpassing all previous measurements. Together these demonstrate the excellent prospects for using QDs in scalable implementations of on-chip spin-photonics relying on chiral quantum optics.

Asynchronising five-fold symmetry sequence for better homonuclear polarisation transfer in magic-angle-spinning solid-state NMR

Recoupling, decoupling, and multidimensional correlation experiments in magic-angle-spinning (MAS) solid-state NMR can be designed by exploiting the symmetry of internal spin interactions. One such scheme, namely, C521, and its supercycled version SPC521, notated as a five-fold symmetry sequence, is widely used for double-quantum dipole-dipole recoupling. Such schemes are generally rotor synchronised by design. We demonstrate an asynchronous implementation of the SPC521 sequence leading to higher double-quantum homonuclear polarisation transfer efficiency compared to the normal synchronous implementation. Rotor-synchronisation is broken in two different ways: lengthening the duration of one of the pulses, denoted as pulse-width variation (PWV), and mismatching the MAS frequency denoted as MAS variation (MASV). The application of this asynchronous sequence is shown on three different samples, namely, U–13C-alanine and 1,4-13C-labelled ammonium phthalate which include 13Cα-13Cβ, 13Cα-13Co, and 13Co–13Co spin systems, and adenosine 5′- triphosphate disodium salt trihydrate (ATP⋅3H2O). We show that the asynchronous version performs better for spin pairs with small dipole-dipole couplings and large chemical-shift anisotropies, for example, 13Co–13Co. Simulations and experiments are shown to corroborate the results.