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Computational models are an essential tool for the design, characterization, and discovery of novel materials. Hard computational tasks in materials science stretch the limits of existing high-performance supercomputing centers, consuming much of their simulation, analysis, and data resources. Quantum computing, on the other hand, is an emerging technology with the potential to accelerate many of the computational tasks needed for materials science. In order to do that, the quantum technology must interact with conventional high-performance computing in several ways: approximate results validation, identification of hard problems, and synergies in quantum-centric supercomputing. In this paper, we provide a perspective on how quantum-centric supercomputing can help address critical computational problems in materials science, the challenges to face in order to solve representative use cases, and new suggested directions., Comment: 65 pages, 15 figures; comments welcome

The helimagnetic order describes a non-collinear spin texture of antiferromagnets, arising from competing exchange interactions. Although collinear antiferromagnets are elemental building blocks of antiferromagnetic (AFM) spintronics, the potential of implementing spintronic functionality in non-collinear antiferromagnets has not been clarified thus far. Here, we propose an AFM helimagnet of EuCo2As2 as a novel single-phase spintronic material that exhibits a remarkable sign reversal of anisotropic magnetoresistance (AMR). The contrast in the AMR arises from two electrically distinctive magnetic phases with spin reorientation driven by magnetic field lying on the easy-plane, which switches the sign of the AMR from positive to negative. Further, various AFM memory states associated with the evolution of the spin structure under magnetic fields were identified theoretically, based on an easy-plane anisotropic spin model. These results reveal that non-collinear antiferromagnets hold potential for developing spintronic devices.

A spin valve is a prototype of spin-based electronic devices found on ferromagnets, in which an antiferromagnet plays a supporting role. Recent findings in antiferromagnetic spintronics show that an antiferromagnetic order in single-phase materials solely governs dynamic transport, and antiferromagnets are considered promising candidates for spintronic technology. In this work, we demonstrated antiferromagnet-based spintronic functionality on an itinerant Ising antiferromagnet of Ca0.9Sr0.1Co2As2 by integrating nanoscale spin-valve-type structure and investigating anisotropic magnetic properties driven by spin-flips. Multiple stacks of 1 nm thick spin-valve-like unit are intrinsically embedded in the antiferromagnetic spin structure. In the presence of a rotating magnetic field, a new type of the spin-valve-like operation was observed for large anomalous Hall conductivity and anisotropic magnetoresistance, whose effects are maximized above the spin-flip transition. In addition, a joint experimental and theoretical study provides an efficient tool to read out various spin states, which scheme can be useful for implementing extensive spintronic applications.

We theoretically propose a circuit QED system implemented with triple-leg stripline resonator (TSR). Unlikely from linear stripline resonator, the fundamental intra-cavity microwave modes of the TSR are two-fold degenerate. When a superconducting qubit is placed near one of the TSR legs, one fundamental mode is directly coupled to the qubit, while the other one remains uncoupled. Our system closely resembles an optical cavity QED system, where an atom in a cavity couples only to the incident photon with a specific polarization by placing a polarization beamsplitter in front of the optical cavity. Using our circuit QED system, we have theoretically studied a two-qubit quantum gate operation in a hybrid qubit composed of flying microwave qubit and superconducting qubit. We have demonstrated that for the hybrid qubit, the quantum controlled phase flip (CPF) gate can be reliably implemented for the experimentally available set of parameters., Comment: 13 pages, 4 figures

We have theoretically studied a graphene-based plasmonic waveguide, which can gate the transmission of a surface plasmon polariton (SPP) localized at the graphene-semiconductor interface. When a gate voltage is applied above a certain critical value, the charge density modulation in the quasi two-dimensional electron gas formed in the inversion layer can induce a local plasma resonance. Since the local plasma resonance is strongly coupled to the SPP, it can suppress the transmission of the SPP. By calculating the propagation length of the SPP with varying gate voltage, we have obtained the sharp switching line shape. We have demonstrated that the wavelength of the SPP can be reduced below ~1/100 of that of an incident light and the propagation length of the SPP can be significantly reduced by a factor of ~15 upon switching. This ensures that our plasmonic waveguide can operate effectively as a plasmonic switch for the SPP., Comment: 10 pages, 9 figures

We have studied a random walk model based on majority rule. At a given instant, the moving direction of a cargo is determined by motor coordination mediated by a tug-of-war mechanism between two kinds of competing motor proteins. We have demonstrated that the probability distribution $P(t)$ for unidirectional run time $t$ of a cargo can be remarkably described by Levy walk for $t<\gamma_u^{-1}$ as $P(t)\propto t^{-3/2} e^{-\gamma_u t}$ with $\gamma_u$ being the unbinding rate of a motor protein from microtubule. The mean squared displacement of a cargo changes from super-diffusive behavior $\langle X^2\rangle\propto t^2$ for $t<\gamma_u^{-1}$ to normal diffusion $\langle X^2\rangle\propto t$ for $t>\gamma_u^{-1}$. By considering the correlation effect in binding of a motor protein to microtubule, we have shown that Levy walk behavior of $P(t)\propto t^{-{3/2}}$ persists robustly against correlations only adding an effective cutoff time $\gamma_b/\gamma_c^2$ with $\gamma_c$ representing the amount of correlations.

We theoretically propose an efficient way to generate and detect squeezed light by a single qubit in circuit QED. By tuning the qubit energy splitting close to the fundamental frequency of the first harmonic mode (FHM) in a transmission line resonator and placing the qubit at the nodal point of the third harmonic mode, one can generate the resonantly enhanced squeezing of the FHM upon pumping with the second harmonic mode. In order to investigate the photon number splitting for the squeezed FHM, we have numerically calculated the qubit absorption spectrum, which exhibits regularly spaced peaks at frequencies separated by twice the effective dispersive shift. It is also shown that adding a small pump field for the FHM makes additional peaks develop in between the dominant ones as well.

There has been tremendous recent progress in realizing topological insulator initiated by the proposal of Kane and Mele for the graphene system. They have suggested that the odd $Z_2$ index for the graphene manifests the spin filtered edge states for the graphene nanoribbons, which lead to the quantum spin Hall effect(QSHE). Here we investigate the role of the spin-orbit interaction both for the zigzag and armchair nanoribbons with special care in the edge geometry. For the pristine zigzag nanoribbons, we have shown that one of the $\sigma$ edge bands located near E=0 lifts up the energy of the spin filtered chiral edge states at the zone boundary by warping the $\pi$-edge bands, and hence the QSHE does not occur. Upon increasing the carrier density above a certain critical value, the spin filtered edge states are formed leading to the QSHE. We suggest that the hydrogen passivation on the edge can recover the original feature of the QSHE. For the armchair nanoribbon, the QSHE is shown to be stable. We have also derived the real space effective hamiltonian, which demonstrates that the on-site energy and the effective spin orbit coupling strength are strongly enhanced near the ribbon edges. We have shown that the steep rise of the confinement potential thus obtained is responsible for the warping of the $\pi$-edge bands., Comment: 20 pages, 6 figures

Electronic structures of the zigzag bilayer graphite nanoribbons(Z-BGNR) with various ribbon width $N$ are studied within the tight binding approximation. Neglecting the inter-layer hopping amplitude $\gamma_4$, which is an order of magnitude smaller than the other inter-layer hopping parameters $\gamma_1$ and $\gamma_3$, there exist two fixed Fermi points $\pm k^*$ independent of the ribbon width with the peculiar energy dispersion near $k^*$ as $\ve (k) \sim \pm (k-k^*)^N$. By investigating the edge states of the Z-BGNR, we notice that the trigonal warping of the bilayer graphene sheets are reflected on in the edge state structure. With the inclusion of $\gamma_4$, the above two Fermi points are not fixed, but drift toward the vicinity of the Dirac point with the increase of the width $N$ as shown by the finite scaling method and the peculiar dispersions change to the parabolic ones. The edge magnetism of the Z-BGNR is also examined by solving the half-filled Hubbard Hamiltonian for the ribbon using the Hartree-Fock approximation. We have shown that within the same side of the edges, the edge spins are aligned ferromagnetically for the experimentally relevant set of parameters., Comment: 22 pages, 7 figures; Corrections are added concerning the edge magnetism

We investigate the non-commutative (NC) field theory approach to the vortex liquid system restricted to the lowest Landau level (LLL) approximation. NC field theory effectively takes care of the phase space reduction of the LLL physics in a $\star$-product form and introduces a new gauge invariant form of a quartic potential of the order parameter in the Ginzburg-Landau (GL) free energy. This new quartic interaction coupling term has a non-trivial equivalence relation with that obtained by Br\'ezin, Nelson and Thiaville in the usual GL framework. The consequence of the equivalence is discussed., Comment: Add vortex lattice formation, more references, and one author

We present an Anderson-type model Hamiltonian with exchange coupling between the localized spins and the confined holes in the quantum dots to study the ferromagnetism in diluted magnetic semiconductor (DMS) quantum dot arrays embedded in semiconductors. The hybridization between the quantum-confined holes in the DMS quantum dots and the itinerant holes in the semiconductor valence band makes hole transfer between quantum dots, which can induce the long range ferromagnetic order of the localized spins. In addition, it makes the carrier spins both in the DMS quantum dots and in the semiconductors polarized. The spontaneous magnetization of the localized spins and the spin polarization of the holes are calculated using both the Weiss mean field approximation and the self-consistent spin wave approximation, which are developed for the present model., Comment: 6 pages, 6 figures

We revisit the quantum Hall system with no Zeeman splitting energy using the noncommutative field theory. We analyze the BPS condition for the delta-function interaction near the filling factor $\nu=1$. Multi-skyrmions are shown to saturate the BPS bounds. The dimension of the moduli space of $k$ skyrmions is $4k+2$. Advantage of the noncommutative field description is demonstrated through the derivation of the effective nonlinear $\sigma$ model Lagrangian., Comment: 23 pages, Revtex, more references added in

Using the spin-polarized tunneling model and taking into account the basic physics of ferromagnetic semiconductors, we study the temperature dependence of the tunneling magnetoresistance (TMR) in the diluted magnetic semiconductor (DMS) trilayer heterostructure system (Ga,Mn)As/AlAs/(Ga,Mn)As. The experimentally observed TMR ratio is in reasonable agreement with our result based on the typical material parameters. It is also shown that the TMR ratio has a strong dependence on both the itinerant-carrier density and the magnetic ion density in the DMS electrodes. This can provide a potential way to achieve larger TMR ratio by optimally adjusting the material parameters., Comment: 5 pages (RevTex), 3 figures (eps), submitted to PRB

Starting with a Chern-Simons theory, we derive an effective action for interacting quantum Hall skyrmions that takes into account both large-distance physics and short-distance details as well. We numerically calculate the classical static skyrmion profile from this action and find excellent agreement with other, microscopic calculations over a wide range of skyrmion sizes including the experimentally relevant one. This implies that the essential physics of this regime might be captured by a continuum classical model rather than resorting to more microscopic approaches. We also show that the skyrmion energy closely follows the formula suggested earlier by Sondhi et al. for a broad parameter range of interest as well., Comment: 13 pages (Revtex) + 3 ps-figures

Double-layer quantum Hall systems at total filling factor $\nu_T=1$ can exhibit a commensurate-incommensurate phase transition driven by a magnetic field $B_{\parallel}$ oriented parallel to the layers. Within the commensurate phase, the lowest charge excitations are believed to be linearly-confined Meron pairs, which are energetically favored to align with $B_{\parallel}$. In order to investigate this interesting object, we propose a gated double-layer Hall bar experiment in which $B_{\parallel}$ can be rotated with respect to the direction of a constriction. We demonstrate the strong angle-dependent transport due to the anisotropic nature of linearly-confined Meron pairs and discuss how it would be manifested in experiment., Comment: 4 pages, RevTex, 3 postscript figures

Double-layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel manybody quantum Hall effect due to the strong interlayer coherence. When the layer separation becomes close to the critical value, quantum fluctuations can destroy the interlayer coherence and the quantum Hall effect will disappear. We calculate the renormalized isospin stiffness $\rho_s$ due to quantum fluctuations within the Hartree-Fock-RPA formalism. The activation energy of the topological excitations thus obtained demonstrates a nice qualitative agreement with recent experiment., Comment: 4 pages (Revtex) + 3 ps-figures; Vertex corrections are added in the new version; accepted to Phys. Rev. Lett

We study numerically the motion of vortices in dirty type II superconductors. In two dimensions at strong driving currents, vortices form highly correlated ``static channels''. The static structure factor exhibits convincing scaling behaviour, demonstrating quasi long range translational order in the transverse direction. However order in the longitudinal direction is only short range. We clearly establish the existence of a finite transverse critical current, suggesting strong barriers against small transverse driving forces. These results are most consistently interpreted in terms of the recently proposed moving glass picture, modified to account for the strong anisotropy., Comment: submitted to Physical Review Letters