Symmetric Spin Orbit Research Articles

Phonon and maxon instability in Bose–Einstein condensates with parity-time symmetric spin–orbit coupling

Parity-time () symmetry has drawn great research interest in non-Hermitian physics. Recently, there is an emerging model of -symmetric spin–orbit coupling (SOC) which could be realized with spin-1/2 atomic Bose–Einstein condensates (BECs) when the two spin components are respectively subjected to momentum-dependent gain and loss (Qin et al 2022 New J. Phys. 24 063025). In this model, inter-atom interaction has no influence on the -symmetric plane waves. Thus, collective excitation playing the role of fingerprint of inter-atom interaction is investigated in this paper. For the phonon excitation, it is shown that the repulsive interaction between atoms in different spin states, which tends to drive the atoms to populate in only one spin component, can break the -symmetry, and leads to a phonon instability. Whereas, for the case of the phonon-maxon-roton collective excitation spectrum, the repulsive interaction between atoms in different spin states can lead to a maxon instability, which does not occur in Hermitian BEC systems (dipolar BECs or BECs with Raman induced SOC). Simulation of the time evolution of the plane wave solution against small noise shows that the maxon instability can result in the formation of a supersolid-like stripe pattern at the initial stage, but the non-Hermitian nature of the system finally destroys the pattern. The phase diagram of stability shows that the Rabi coupling and repulsive interaction between the atoms in the same spin state can stabilize the system.

Intrinsic decoherence effects on nonclassical correlations in a symmetric spin–orbit model

Nonclassical correlations dynamics of local quantum Fisher information, trace-norm measurement-induced nonlocality, and log-negativity are investigated in a symmetric spin–orbit model. This model is described by a Heisenberg XYZ two-spin system exposed to the magnetic field and Kaplan–Shekhtman–Entin-Wohlman–Aharony (KSEA) interaction under the intrinsic decoherence effects. To evaluate the resourcefulness of this model for the generation and preservation of quantum correlations, we consider two qubits that are initially prepared in two different states, namely uncorrelated and maximally correlated states. The magnetic field is discovered to be effective at generating and preserving nonclassical correlations. Besides, we find that the KSEA interaction can alter the generation, preservation, and revival features of nonclassical correlations in the two-qubit system. However, the bipartite nonclassical correlations become extremely fragile when intrinsic decoherence effects appear.

High-purity orbital angular momentum states from a visible metasurface laser

Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin and opposite helicity OAM states (±l) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching l = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δl = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light. A metasurface laser generates orbital angular momentum states with quantum numbers reaching l = 100. Simultaneous output vortex beams, with Δl as great as 90, are demonstrated in the visible regime.

Symmetric spin–orbit interaction in triple quantum dot and minimisation of spin–orbit leakage in CNOT gate

We analyse spin–orbit interaction in triple quantum dots and show that a symmetric spin–orbit Hamiltonian does not follow the standard form used in double quantum dots, as a consequence of the presence of the third dot in the setup. Furthermore, CNOT implementation schemes based on the exchange interaction were studied. It was shown that an antisymmetric Dzyaloshinsky–Moriya term is the dominant source of spin–orbit leakage from the computational space. We present a simple scheme for the minimisation of leakage that can be implemented in cases where interacting spins enclose parallelogram or equilateral triangle loops.

Critical temperature of pair condensation in a dilute Bose gas with spin–orbit coupling

We study the Bardeen–Cooper–Shrieffer (BCS) pairing state of a two-component Bose gas with a symmetric spin–orbit coupling (SOC). In the dilute limit at low temperature, this system is essentially a dilute gas of diatomic molecules. We compute the effective mass of the molecule and find that it is anisotropic in momentum space. The critical temperature of the pairing state is about eight times smaller than the Bose–Einstein condensation (BEC) transition temperature of an ideal Bose gas with the same density.

Spin-orbit coupling and spin relaxation in phosphorene: Intrinsic versus extrinsic effects

First-principles calculations of the essential spin-orbit and spin relaxation properties of phosphorene are performed. Intrinsic spin-orbit coupling induces spin mixing with the probability of $b^2 \approx 10^{-4}$, exhibiting a large anisotropy, following the anisotropic crystalline structure of phosphorene. For realistic values of the momentum relaxation times, the intrinsic (Elliott--Yafet) spin relaxation times are hundreds of picoseconds to nanoseconds. Applying a transverse electric field (simulating gating and substrates) generates extrinsic $C_{2v}$ symmetric spin-orbit fields in phosphorene, which activate the D'yakonov--Perel' mechanism for spin relaxation. It is shown that this extrinsic spin relaxation also has a strong anisotropy, and can dominate over the Elliott-Yafet one for strong enough electric fields. Phosphorene on substrates can thus exhibit an interesting interplay of both spin relaxation mechanisms, whose individual roles could be deciphered using our results.

Electrical and dielectric properties of co-precipitated nanocrystalline tin oxide

Nanocrystalline tin oxide (SnO 2) powders were synthesized by chemical co-precipitation method using stannic chloride pentahydrate (SnCl 4·5H 2O) precursor in aqueous medium. The influence of sintering temperatures on the crystalline structure, morphological, electrical, dielectric and XPS properties has been studied. X-ray diffraction study reveals that sintered powder which exhibits tetragonal crystal structure and both crystallinity as well as crystal size increase with increase in temperature. The nature of species of various absorption bonds viz. Sn–O, O–Sn–O and O–H involved in sintered SnO 2 samples has been studied using FTIR technique. The morphological studies reveal randomly arranged grains with compact nature and grain size increases with sintering temperature. Measurements of electrical properties show relatively lower resistivity (≈10 2–10 3 Ω cm) and higher dielectric constant at 400 °C than other sintering temperatures. The compositional analysis and electronic behavior of SnO 2 nanoparticles is studied using X-ray photoelectron spectroscopy. The symmetric spin orbit splitting of Sn 3d 5/2 ground state and Sn 3d 3/2 excited states is observed with sintering temperature while O 1s is recognized with O 2 − state.

Influence of Spin–Orbit Force on Nucleon–Nucleon Scattering in the Quark Delocalization Colour Screening Model

The symmetric spin–orbit interactions of one-gluon-exchange and confinement are included in the nucleon—nucleon phase shift calculation in the framework of quark delocalization colour screening model. The spin–orbit interaction has little influence on D wave phase shift. For the triplet P waves, 3PT is in good agreement with the experimental data and 3PLS is attractive but not strong enough, whereas 3PC is too strongly repulsive. Our results indicate that the symmetric spin–orbit interaction of one-gluon-exchange and confinement potential cannot give a good description of the triplet P wave phase shifts. More sophisticated considerations, the delocalization depending on the relative orientation between two cluster, might be needed to improve the description of P-wave NN interaction.

Lower symmetric generalization of the SU(4) spin–orbit model

We numerically study several lower symmetric spin–orbit coupled models in one dimension as the generalization of the mostly simplified SU(4) model. First, the SU(4) model under uni-axial magnetic fields is investigated to observe the crossover phenomena between the SU(4) and SU(2) symmetric limits, which correspond to zero and fully polarized magnetizations, respectively. As another example, we study the SU(2)⊗SU(2) symmetric model, deviating from the SU(4) symmetric condition. We show the existence of the new critical phases around the SU(4) symmetric point, spreading both sides of the previously known gapless line.

Numerical Study of the One-Dimensional Spin-Orbit Coupled System with SU(2) ⊗SU(2) Symmetry

We numerically study the SU(2)$\otimes$SU(2) symmetric spin-orbit coupled model as a lower symmetric generalization of the SU(4) exchange model. On the symmetric line with respect to the spin and orbit, our result shows the essentially singular gap formation in consistent with the analytic approach, which is different from the previous numerical calculation. Furthermore, we find new critical phases around the SU(4) point, surrounding the previously known gapless symmetric line. In these novel phases either spin or orbital excitations around momentum $q=\pi$ form massless continua which split from the excitations belonging to the $[2^2]$ irreducible representation at the SU(4) point. On the critical symmetric line, the additional coupled spin-orbit excitations around $q=\pi/2$ originating from [$2^11^2$] become critical, too.