We investigate first- and second-order quantum phase transitions of the anisotropic Rabi model, in which rotating- counter-rotating terms are allowed to have different coupling strength. The model interpolates between two known limits with distinct universal properties. Through a combination analytic numerical approaches we extract diagram, scaling functions, critical exponents, allows us establish that universality class at finite? anisotropy is same as isotropic limit. also reveal other...

Spin waves traveling in certain directions within antiferromagnetic materials appear to be unstable and likely split up into spinons. New simulations show that, actually, these abnormal spin aren't unstable, but rather fluctuate between

We provide analytic insight into the generation of stationary itinerant photon entanglement in a 3-mode optomechanical system. identify parameter regime maximal entanglement, and show that strong is possible even for weak many-photon couplings. also tripartite generated between photonic phononic output fields; unlike bipartite photon-photon this diverges as one approaches boundary system stability.

In recent years, hole-spin qubits based on semiconductor quantum dots have advanced at a rapid pace. We first review the main potential advantages of these with respect to their electron-spin counterparts, and give general theoretical framework describing them. The basic features spin-orbit coupling hyperfine interaction in valence band are discussed, together consequences coherence spin manipulation. second part article we provide survey experimental realizations, which spans relatively...

We study the energy-transfer process in quantum battery systems consisting of multiple central spins and bath spins. Here with ``quantum battery'' we refer to spins, whereas serves as ``charger.'' For single-central-spin battery, analytically derive time evolutions energy transfer charging power arbitrary number case find scaling-law relation between maximum ${P}_{\mathrm{max}}$ ${N}_{B}$. It approximately satisfies a scaling law...

We investigate the exact solution of honeycomb model proposed by Kitaev and derive an explicit formula for projector onto physical subspace. The states are simply characterized parity total occupation fermionic eigenmodes. consider a general lattice on torus show that fermion depends in nontrivial way vortex configuration choice boundary conditions. In vortex-free case with constant gauge field we able to obtain analytical expression parity. For can be easily evaluated numerically, which...

We propose a one-step scheme to generate Greenberger-Horne-Zeilinger (GHZ) states for superconducting flux qubits or charge in circuit QED setup. The GHZ state can be produced within the coherence time of multiqubit system. Our is independent initial transmission line resonator and works presence higher harmonic modes. analysis also shows that robust various operation errors environmental noise.

The ability to store information is of fundamental importance any computer, be it classical or quantum. To identify systems for quantum memories which rely, analogously memories, on passive error protection (`self-correction') greatest interest in science. While with topological ground states have been considered promising candidates, a large class them was recently proven unstable against thermal fluctuations. Here, we propose two-dimensional (2D) spin models unaffected by this result....

We obtain analytically close forms of benchmark quantum dynamics the collapse and revival (CR), reduced density matrix, Von Neumann entropy, fidelity for XXZ central spin problem. These quantities characterize decoherence entanglement system with few to many bath spins, a short infinitely long time evolution. For homogeneous problem, effective magnetic field $B$, coupling constant $A$ longitudinal interaction $\Delta$ significantly influence scales bath, providing tunable resource metrology....

We study how strong mechanical squeezing (beyond 3 dB) can be achieved through reservoir engineering in an optomechanical system which is far from the resolved-sideband regime. In our proposed setup, effect of unwanted counter-rotating terms suppressed by quantum interference two auxiliary cavities. weak coupling regime, we develop analytical treatment based on effective master equation approach, allows us to obtain explicitly condition maximum squeezing.

Understanding (and controlling) hyperfine interactions in semiconductor nanostructures is important for fundamental studies of material properties as well quantum information processing with electron, hole, and nuclear-spin states. Through a combination first-principles density-functional theory (DFT) $\mathbf{k}\cdot\mathbf{p}$ theory, we have calculated tensors electrons holes GaAs crystalline silicon. Accounting relativistic effects near the nuclear core, find contact that are consistent...

We discuss and review several thermodynamic criteria that have been introduced to characterize the thermal stability of a self-correcting quantum memory. first examine use symmetry-breaking fields in analyzing properties memories limit: we show expectation values all logical operators vanish for any stabilizer subsystem code spatial dimension. On positive side, generalize results [R. Alicki et al., arXiv:0811.0033] obtain general upper bound on relaxation rate memory at nonzero temperature,...

Spin-orbit-coupled two-dimensional electron gases (2DEGs) are a textbook example of helical Fermi liquids, i.e., quantum liquids in which spin (or pseudospin) and momentum degrees freedom at the surface have well-defined correlation. Here we study long-wavelength plasmon dispersion Drude weight archetypical spin-orbit-coupled 2DEGs. We first show that these measurable quantities sensitive to electron-electron interactions due broken Galilean invariance then discuss detail why popular random...

Evidence is presented for the finite wave vector crossing of two lowest one-dimensional spin-split subbands in quantum point contacts fabricated from two-dimensional hole gases with strong spin-orbit interaction. This phenomenon offers an elegant explanation anomalous sign spin polarization filtered by a contact, as observed magnetic focusing experiments. Anticrossing introduced field parallel to channel or asymmetric potential transverse it. Controlling magnitude splitting affords novel...

We study the semiclassical limit of two-photon Dicke model with both cavity decay and qubit dissipation, extend a recent analysis its stationary points [Garbe et al., Sci. Rep. 10, 13408 (2020)], where large unstable region was found. By considering explicit dynamical evolution, we show that actually hosts rich nonlinear behavior. At variance other types models (without dissipation or one-photon interactions), occurrence chaos does not rely on counterrotating interaction. Furthermore, new...

We propose an inhomogeneous open spin ladder, related to the Kitaev honeycomb model, which can be tuned between topological and nontopological phases. In extension of Lieb's theorem, we show numerically that ground state ladder is either vortex free or full. study robustness Majorana end states (MES) emerge at boundary sections in different phases while MES homogeneous are destroyed by single-body perturbations, presence inhomogeneities least two-body perturbations required destabilize MES....

Abstract We have analyzed magnetic order in the one-dimensional Kondo lattice with classical localized spins. To identify relevant low-energy configurations, we combine exact diagonalization of electronic system a dissipative evolution, described by Landau-Lifshitz-Gilbert equation. find that spiral states always relax into more complex form noncollinear order, characterized periodic modulation relative angles between neighboring A finite-size scaling analysis shows amplitude and gain free...

We study theoretically the statistical properties of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized magnetic moments in a disordered two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit couplings. Averaging over disorder, static spin susceptibility tensor is evaluated diagrammatically mesoscopic (phase-coherent) regime. The disorder-averaged leads to twisted exchange suppressed exponentially distance, whereas second-order correlations, which determine...

We present transport experiments performed in high-quality quantum point contacts embedded a GaAs two-dimensional hole gas. The strong spin-orbit interaction results peculiar phenomena, including the previously observed anisotropic Zeeman splitting and level-dependent effective g factors. Here we find additional effects, namely, crossing anticrossing of spin-split levels depending on subband index magnetic field direction. Our experimental observations are reconciled heavy-hole Hamiltonian...

We develop a theory for the spin-echo dynamics of heavy hole in quantum dot, accounting both hyperfine- and electric-field-induced fluctuations. show that moderate applied magnetic field can drive this system to motional-averaging regime, making hyperfine interaction ineffective as decoherence source. Furthermore, we decay envelope is highly sensitive geometry. In particular, find specific choice initialization π-pulse axes which be used study intrinsic hyperfine-induced hole-spin dynamics,...

The manipulation of single spins in double quantum dots by making use the exchange interaction and a highly inhomogeneous magnetic field was discussed [W. A. Coish D. Loss, Phys. Rev. B 75, 161302 (2007)]. However, such large inhomogeneity is difficult to achieve through slanting micromagnet current designs lateral dots. Therefore, we examine an analogous spin scheme directly applicable realistic GaAs dot setups. We estimate that typical gate times, realized at singlet-triplet anticrossing...

Inspired by spin-electric couplings in molecular magnets, we introduce the Kitaev honeycomb model a linear modification of Ising interactions due to presence quantized cavity fields. This allows control properties low-energy toric code Hamiltonian, which can serve as quantum memory, tuning physical parameters modes, like frequencies, photon occupations, and coupling strengths. We study perturbatively making use Schrieffer-Wolff transformation show that, depending on specific setup, modes be...

The spontaneous breaking of time translation symmetry in periodically driven Floquet systems can lead to a discrete crystal. Here we study the occurrence such dynamical phase driven-dissipative optomechanical system with two membranes middle. We find that, under certain conditions, be mapped an open Dicke model and realizes superradiant-type transition. Furthermore, applying suitable modulated drive, dynamics exhibits robust subharmonic oscillation persistent thermodynamic limit. Published...

We investigate the dissipative phase transitions of anisotropic quantum Rabi model with cavity decay and demonstrate that large spin fluctuations persist in stationary state, having important consequences on diagram critical properties. In second-order transition to superradiant phase, there is a significant suppression order parameter appearance nonuniversal factors, which directly reflect populations. Furthermore, upon entering regime where mean-field theory predicts tricritical we find...