Parity Conservation Research Articles

Simultaneous analysis of matter radii, transition probabilities, and excitation energies of Mg isotopes by angular-momentum-projected configuration-mixing calculations

We perform simultaneous analysis of (1) matter radii, (2) $B(E2; 0^+ \rightarrow 2^+ )$ transition probabilities, and (3) excitation energies, $E(2^+)$ and $E(4^+)$, for $^{24-40}$Mg by using the beyond mean-field (BMF) framework with angular-momentum-projected configuration mixing with respect to the axially symmetric $\beta_2$ deformation with infinitesimal cranking. The BMF calculations successfully reproduce all of the data for $r_{\rm m}$, $B(E2)$, and $E(2^+)$ and $E(4^+)$, indicating that it is quite useful for data analysis, particularly for low-lying states. We also discuss the absolute value of the deformation parameter $\beta_2$ deduced from measured values of $B(E2)$ and $r_{\rm m}$. This framework makes it possible to investigate the effects of $\beta_2$ deformation, the change in $\beta_2$ due to restoration of rotational symmetry, $\beta_2$ configuration mixing, and the inclusion of time-odd components by infinitesimal cranking. Under the assumption of axial deformation and parity conservation, we clarify which effect is important for each of the three measurements, and propose the kinds of BMF calculations that are practical for each of the three kinds of observables.

Influence of an embedded quantum dot on the Josephson effect in the topological superconducting junction with Majorana doublets

One Majorana doublet can be realized at each end of the time-reversal-invariant Majorana nanowires. We investigate the Josephson effect in the Majorana-doublet-presented junction modified by different inter-doublet coupling manners. It is found that when the Majorana doublets couple indirectly via a non-magnetic quantum dot, only the normal Josephson effect occurs, and the fermion parity in the system just affects the current direction and amplitude. However, one magnetic field applied on the dot can induce the fractional Josephson effect in the odd-parity case. Next if the direct and indirect couplings between the Majorana doublets coexist, no fractional Josephson effect takes place, regardless of the presence of magnetic field. Instead, there almost appears the π-period-like current in some special cases. All the results are clarified by analyzing the influence of the fermion occupation in the quantum dot on the parity conservation in the whole system. We ascertain that this work will be helpful for describing the dot-assisted Josephson effect between the Majorana doublets.

Reprint of : Flux sensitivity of quantum spin Hall rings

We analyze the periodicity of persistent currents in quantum spin Hall loops, partly covered with an s-wave superconductor, in the presence of a flux tube. Much like in normal (non-helical) metals, the periodicity of the single-particle spectrum goes from Φ0=h/e to Φ0/2 as the length of the superconductor is increased past the coherence length of the superconductor. We further analyze the periodicity of the persistent current, which is a many-body effect. Interestingly, time reversal symmetry and parity conservation can significantly change the period. We find a 2Φ0-periodic persistent current in two distinct regimes, where one corresponds to a Josephson junction and the other one to an Aharonov–Bohm setup.

Entanglement storage by classical fixed points in the two-axis countertwisting model

We analyze a scheme for storage of entanglement quantified by the quantum Fisher information in the two-axis countertwisting model. A characteristic feature of the two-axis countertwisting Hamiltonian is the existence of the four stable center and two unstable saddle fixed points in the mean-field phase portrait. The entangled state is generated dynamically from an initial spin coherent state located around an unstable saddle fixed point. At an optimal moment of time the state is shifted to a position around stable center fixed points by a single rotation, where its dynamics and properties are approximately frozen. We also discuss evolution with noise. In some cases the effect of noise turns out to be relatively weak, which is explained by parity conservation.

Mono-jet, -photon and -Z signals of a supersymmetric (B − L) model at the Large Hadron Collider

Search for invisible final states produced at the Large Hadron Collider (LHC) by new physics scenarios are normally carried out resorting to a variety of probes emerging from the initial state, in the form of single-jet, -photon and -$Z$ boson signatures. These are particularly effective for models of Supersymmetry (SUSY) in presence of $R$-parity conservation, owing to the presence in their spectra of a stable neutralino as dark matter candidate. We assume here as theoretical framework Supersymmetric ($B-L$) extension of the Standard Model (BLSSM), wherein a mediator for invisible decays can be $Z'$ boson. The peculiarity of the signal is thus that the final state objects carry a very large (transverse) missing energy, since the $Z'$ is naturally massive and constrained by direct searches and electro-weak precision tests to be at least in TeV scale region. Under these circumstances the efficiency in accessing the invisible final state and rejecting the standard model background is very high. This somehow compensates the rather meagre production rates. Another special feature of this invisible BLSSM signal is its composition, which is often dominated by sneutrino decays (alongside the more traditional neutrino and neutralino modes). Sensitivity of the CERN machine to these two features can therefore help disentangling the BLSSM from more popular SUSY models. We assess in this analysis the scope of the LHC in establishing the aforementioned invisible signals through a sophisticated signal-to-background simulation carried out in presence of parton shower, hadronisation and detector effects. We find that significant sensitivity exists already after 300 fb$^{-1}$ during Run 2. We find that mono-jet events can be readily accessible at the LHC, so as to enable one to claim a prompt discovery, while mono-photon and -$Z$ signals can be used as diagnostic tools of the underlying scenario.

Braiding properties of Majorana Kramers pairs

We consider the braiding of Kramers pairs of Majorana bound states. We derive the most general transformation on the many-body ground state that is applied as the result of such a braiding process. The result is derived in the context of a simple toy model, but we will show that it has the most general form that is compatible with local and global conservation of electron parity. In accordance with earlier work the resulting transformation turns out to be path dependent, which shows that Kramers pairs of Majorana bound states cannot be used for topological quantum computation. We also discuss under which conditions the result is path independent and corresponds to two independent exchanges of pairs of Majorana bound states.

Helical Spin Texture and Interference of Majorana Bound States in One-Dimensional Topological Superconductor

We investigate one-dimensional (1D) Majorana bound states (MBSs) realized in terms of the helical edge states of a 2D quantum spin-Hall insulator (QSHI) in a heterostructure with a superconducting substrate and two ferromagnetic insulators (FIs). By means of Bogoliubov-de Gennes approach we demonstrate that there is a helical spin texture in the MBS wave function with a pitch proportional to the Fermi momentum of the helical edge states of QSHI. Moreover, simultaneous detection on local density of states by scanning tunneling microscopy and spectroscopy at a position close to one FI edge and at the midpoint between two FIs can not only map out the energy spectrum $\pm E \cos(\phi/2)$, but also prove experimentally that the two quasiparticle excitations do not mix with each other as protected by the parity conservation associated with the MBSs.

Helicity Amplitudes for Photoproduction of Baryons with J = 1/2 and JP = 3/2+**Supported by the Chinese Scholarship Council (CSC)

We derive the separate helicity amplitudes using the partial wave analysis in the process of pseudo-scalar meson photoproduction. For JP = 3/2+, we find the amplitude is model independent. According to parity conservation, the general amplitude in the case of JP = 1/2− is obtained. We prove this general amplitude corresponds to the situation of λ = −1 when adopting the circular polarization. Finally, the formulas of scattering amplitudes involving the meson photoproduction with JP = 3/2+ are obtained from the chiral quark model.

Flux sensitivity of quantum spin Hall rings

We analyze the periodicity of persistent currents in quantum spin Hall loops, partly covered with an s-wave superconductor, in the presence of a flux tube. Much like in normal (non-helical) metals, the periodicity of the single-particle spectrum goes from Φ0=h/e to Φ0/2 as the length of the superconductor is increased past the coherence length of the superconductor. We further analyze the periodicity of the persistent current, which is a many-body effect. Interestingly, time reversal symmetry and parity conservation can significantly change the period. We find a 2Φ0-periodic persistent current in two distinct regimes, where one corresponds to a Josephson junction and the other one to an Aharonov–Bohm setup.

Conservation laws, radiative decay rates, and excited state localization in organometallic complexes with strong spin-orbit coupling.

There is longstanding fundamental interest in 6-fold coordinated d6 () transition metal complexes such as [Ru(bpy)3]2+ and Ir(ppy)3, particularly their phosphorescence. This interest has increased with the growing realisation that many of these complexes have potential uses in applications including photovoltaics, imaging, sensing, and light-emitting diodes. In order to design new complexes with properties tailored for specific applications a detailed understanding of the low-energy excited states, particularly the lowest energy triplet state, T1, is required. Here we describe a model of pseudo-octahedral complexes based on a pseudo-angular momentum representation and show that the predictions of this model are in excellent agreement with experiment - even when the deviations from octahedral symmetry are large. This model gives a natural explanation of zero-field splitting of T1 and of the relative radiative rates of the three sublevels in terms of the conservation of time-reversal parity and total angular momentum modulo two. We show that the broad parameter regime consistent with the experimental data implies significant localization of the excited state.

Search for two body muon decay signals

Lepton family number violation is tested by searching for $\mu^+\to e^+X^0$ decays among the 5.8$\times 10^8$ positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive $X^0$ bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic $\mu^+\to e^+X^0$ decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order $10^{-5}$ are obtained for bosons with masses of 13 - 80 MeV/c$^2$ and with different decay asymmetries. For bosons with masses less than 13 MeV/c$^{2}$ the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to $5.8 \times 10^{-5}$. This is the first study that explicitly evaluates the limits for anisotropic two body muon decays.

Tunable fractional Josephson effect in the topological superconducting junction with embedded quantum dots

We investigate the fractional Josephson effect in the junction of two Majorana zero modes contributed by the topological superconducting wires. It shows that when the Majorana zero modes couple indirectly via one quantum dot, shifting the dot level does not change the phase of the Josephson current. However, if the junction is a double-channel geometry, abundant Josephson phase transitions can be observed. Such a result arises from the fermion parity conservation which is related to the quantum interference. Moreover, in the presence of appropriate structural parameters, destructive interference will occur between the two channels, which induces the appearance of the normal Josephson effect. These results will be helpful for describing the fractional Josephson effect modulated by quantum dots.

Jackiw-Rebbi-type bound state carrying fractional fermion parity

We find the coexistence of two kinds of fractionalized modes, Majorana modes at the geometric ends and Jackiw–Rebbi-type bound state (JRBS) at a domain-wall, in a new topological superconducting phase in one-dimensional (1D) systems. Each localized JRBS carries a new fractional quantity, half of the parity of the fermion number. This induces a topological protected crossing at the zero energy for its eigenenergy. For a chain embedded with a JRBS, it is possible to switch between the occupied and the empty states of the Majorana zero energy state (MZES) by varying the strength of the external magnetic field across that crossing point. This enables a way to encode a quantum qubit into one MZES without breaking parity conservation. We propose that such JRBS and Majorana fermions may appear in two 1D models. One may be implemented in an artificial lattice with staggered hopping, staggered spin-orbital interaction and staggered superconducting pairing in cold fermion atoms. The other is a 1D semiconductor chain sandwiched between s-wave superconductor and antiferromagnet.

Order parameters of non-centrosymmetric superconductors

The non-centrosymmetric (NCS) superconductors (SCs), a class of novel superconducting materials, have recently attracted considerable interests. As a result of antisymmetric spin-orbital coupling (ASOC) arising from the absence of inversion symmetry, the superconducting pairing state of these compounds allows the admixture of spin-singlet and spin-triplet components. This is in contrast to other previously studied superconductors, which usually possess an inversion symmetry in their crystal structure, and therefore their pairing state is of either spin-singlet/even parity or the spin-triplet/odd parity due to the restrictions of the Pauli principles and parity conservation.#br#Determination of the gap structure is crucial for unveiling the pairing state of NCS SCs. In this article, we first describe a method of measuring the precise temperature dependence of the changes in the London penetration depth using the tunnel-diode-oscillator (TDO), which provides an important evidence for the superconducting gap structures. Then the pairing states of NCS SCs are briefly reviewed, putting the emphasis on a few compounds with different ASOC strengths. It is proposed that the ASOC may tune the ratio of the spin-triplet to the spin-singlet component and, therefore, the spin-triplet state may become dominant while the ASOC effect is sufficiently strong in NCS SCs. However, our investigations demonstrate that the actual case is more complicated and there is no simple correspondence between the ASOC size and the pairing states. Instead, it is found that the band splitting due to the ASOC effect divided by the superconducting transition temperature Tc may better characterize of the superconducting pairing states in NCS SCs.

Revealing Topological Superconductivity in Extended Quantum Spin Hall Josephson Junctions

Quantum spin Hall-superconductor hybrids are promising sources of topological superconductivity and Majorana modes, particularly given recent progress on HgTe and InAs/GaSb. We propose a new method of revealing topological superconductivity in extended quantum spin Hall Josephson junctions supporting "fractional Josephson currents." Specifically, we show that as one threads magnetic flux between the superconductors, the critical current traces an interference pattern featuring sharp fingerprints of topological superconductivity-even when noise spoils parity conservation.

Parafermion stabilizer codes

We define and study parafermion stabilizer codes which can be viewed as generalizations of Kitaev's one dimensional model of unpaired Majorana fermions. Parafermion stabilizer codes can protect against low-weight errors acting on a small subset of parafermion modes in analogy to qudit stabilizer codes. Examples of several smallest parafermion stabilizer codes are given. A locality preserving embedding of qudit operators into parafermion operators is established which allows one to map known qudit stabilizer codes to parafermion codes. We also present a local 2D parafermion construction that combines topological protection of Kitaev's toric code with additional protection relying on parity conservation.

Parity conservation in electron-phonon scattering in zigzag graphene nanoribbon

In contrast with carbon nanotubes, the absence of translational symmetry (or periodical boundary condition) in the restricted direction of zigzag graphene nanoribbon removes the selection rule of subband number conservation. However, zigzag graphene nanoribbons with even dimers do have the inversion symmetry. We, therefore, propose a selection rule of parity conservation for electron-phonon interactions. The electron-phonon scattering matrix in zigzag graphene nanoribbons is developed using the tight-binging model within the deformation potential approximation.

Entropic topological invariant for a gapped one-dimensional system

We propose an order parameter for a general one-dimensional gapped system with an open boundary condition. The order parameter can be computed from the ground state entanglement entropy of some regions near one of the boundaries. Hence, it is well-defined even in the presence of arbitrary interaction and disorder. We also show that it is invariant under a finite-depth local quantum circuit, suggesting its stability against an arbitrary local perturbation that does not close the energy gap. Further, it can unambiguously distinguish Majorana chain from a trivial chain under a global fermion parity conservation. We argue that the order parameter can be in principle measured in an optical lattice system.

Madame Wu Chien-Shiung: the first lady of physics research

Childhood in Liuhe A Young Wu Chien-Shiung Became the Favorite Student of Hu Shih Choice of Future A Rising Star in Berkeley Youth and Love Going East From Nuclear Fission to The Manhattan Project A World Authority in Beta Decay Revolution in Parity Conservation Experiment at 2000 Feet Below Ground First Female President of the American Physical Society Love of China The First Lady of Physics Research Wu Chien-Shiung: The Scientist.

Phenomenology of spin observables in the reactions of meson production with the 1 S 0 Diproton pN → {pp} s X

Formalism for spin observables for production of pseudoscalar, scalar, and vectormesons in pN collision with formation of the 1S0 diproton {pp}s in the final state is considered in model-independent way assuming parity and angular momentum conservation. Production of the pseudoscalar mesons (Jπ = 0−) is described by two spin amplitudes and both of them can be completely determined by measurement of unpolarized cross section dσ0, vector analyzing power Ay, and spin-correlation coefficients Cx,x = −Cz,z> and Cx,z. Similar result is obtained for production of scalar mesons (Jπ = 0+). It is shown that measurement of the tensor polarization t20 of the vector meson V (Jπ = 1−) in the reaction pN → {pp}sV in collinear kinematics gives the same information as measurement of the spin-correlation coefficients Cz,z or Cy,y.