Journal of Low Temperature Physics最新文献

Graphene networks are a privileged platform for investigating quantum information processes due to their unique electronic structure and the unconventional diffusion behavior of electrons near Dirac points. In this work, we examine the impact of an external electromagnetic field on quantum teleportation and on the degree of thermal entanglement of two identical qubits in the ground state of a graphene network. These qubits are modeled based on the electronic states localized near the Dirac points (K and (K')) of the Brillouin zone. The interaction between qubits is described by an elastic collision process, resulting in the derivation of an effective Hamiltonian and the corresponding density matrix. In this context, we examine the teleportation performance and the entanglement degree of the two-qubit system using three main indicators: the average teleportation fidelity (F_A), the concurrence C, and the entanglement of formation (E_f). Our results show that an electromagnetic field significantly enhances quantum teleportation and the degree of entanglement, even as the temperature increases. Furthermore, it is demonstrated that linear polarization of the field outperforms circular and elliptical polarizations in optimizing these phenomena. These results show how important electromagnetic fields are for maintaining quantum correlations in graphene networks. They also open up exciting possibilities for using advanced quantum communication protocols and developing quantum computing devices based on solid-state systems such as graphene.

Non-Hermitian (NH) quantum systems host exceptional points (EPs), where eigenstates and eigenvalues coalesce, leading to unconventional many-body phenomena absent in Hermitian systems. While NH fermionic systems with complex interactions exhibit superfluid (SF) breakdown with EPs, spin-dependent asymmetric hopping can stabilize a NH superfluid (NH-SF) that coexists with EPs. In this work, we investigate the quasi-one-dimensional NH attractive Fermi-Hubbard model by using NH-BCS theory. We demonstrate that, when the system is regarded as weakly-coupled chains, the exceptional SF phase becomes unstable and metastable (exceptional) SF state appears between the stable SF and normal states. In the one-dimensional limit, the exceptional SFs disappear entirely and EPs only appear on the phase boundary between the normal and SF states. These results reveal how dimensional crossover governs the stability of the exceptional SF, providing the insights into the interplay between dimensionality and dissipation, with potential relevance for experimental implications in ultracold atoms.

Hyperuniform patterns present enhanced physical properties that make them the new generation of cutting-edge technological devices. Synthesizing devices with tens of thousands of components arranged in a hyperuniform fashion has thus become a breakthrough to achieve in order to implement these technologies. Here we provide evidence that extended two-dimensional hyperuniform patterns spanning tens of thousands of components can be nucleated using as a template the low-temperature vortex structure obtained in pristine Bi(_{2})Sr(_{2})CaCu(_{2})O(_{8}) samples after following a field-cooling protocol.

We study the effect of an external magnetic field on superconducting properties within a mean-field theoretical framework motivated by iron-based superconductors. Inclusion of the magnetic field is introduced solely by Zeeman splitting of quasi-particle energies, corresponding to the Pauli-limited regime, valid in orbital magnetic effects being neglected. Based on the Zubarev Green’s function formalism, the self-consistent equations of the superconducting (SC) order parameter, quasi-particle spectrum, and density of states (DOS) are found. The issue of dependence of the SC gap, DOS and transition temperature on the degree of magnetic field and temperature is analysed in the framework. The findings indicate that the superconductivity was suppressed monotonically with magnetic field and the quasi-particle DOS was subject to Zeeman splitting and its associated changes. The current methodology is not meant to give a quantitative and material-specific description of iron-based superconductors; instead, it provides a qualitative description of the superconducting behaviour of Pauli-limited systems at the mean-field level.

Recently, novel phenomena have been discovered in a superfluid (^4)He pendant droplet, such as a large amplitude undamped oscillatory motion and a translational motion known as the Noether mode, as well as discretization of the dripping period. In the present paper, we report on an anomalous feature of the [2, 0] mode that the oscillation period is almost independent of the droplet volume, in contrast to the case for classical pendant droplets, whose oscillation period becomes longer as the droplet volume increases. This anomaly is another instance of novel dynamics in a superfluid pendant droplet that differ drastically from the classical case.

The temperature dependence of the chemical potential in a half-filled Landau subband of a two-dimensional electron gas (2DEG), modeled using a Gaussian density of states (DOS), has been investigated through detailed numerical simulations. A characteristic temperature interval (0-{T}^{*}) is identified, within which the chemical potential remains nearly constant and close to the Fermi energy ({E}_{F}). The variation of ({T}^{*}) with the effective mass, filling factor, and broadening parameter (Gamma) is systematically analyzed. Temperature-dependent filling factors of Landau levels are also calculated, clarifying the mechanism by which asymmetric inter-subband transitions drive the deviation of (mu) from ({E}_{F}). The results show good agreement with available experimental data for 2DEG systems and provide a solid theoretical basis for interpreting magnetization, entropy, and heat capacity measurements in quantizing magnetic fields. These findings deepen the understanding of the thermodynamics of quantized states in two-dimensional electron gases and underlines their significance for contemporary low-temperature physics.

We present a simulation framework for the electro-thermal modeling of AlMn transition-edge sensors (TESs) with large-area absorbers, which are essential for the Wide-band X-ray Polarization Telescope (WXPT) to achieve high quantum efficiency across the 3–60 keV science band. The framework incorporates the two-fluid model for the superconducting transition and a dedicated thermal model for the (textrm{SiN}_{textrm{x}}) membrane. After experimental validation, the model is applied to quantify position-dependent energy broadening. We implemented an efficient sparse-sampling strategy to map the spatial response. Under a fixed heat-capacity budget, the position-induced broadening is contained below (6.97 textrm{eV}) @ (59.5 textrm{keV}). This result is achieved for absorbers with a side length of (sim 1 textrm{mm}) and supporting pillar widths under (50 upmu textrm{m}), further confirming the design’s effectiveness. This work provides a predictive simulation tool and concrete geometrical constraints to guide the design of the WXPT focal-plane array.

The present theoretical analysis is carried out in order to study some aspects of the electron transport in a degenerate two-dimensional electron gas (2DEG) at low lattice temperature, taking into account some particular features. These features, in contrast to the usual practice, include the inelasticity of the interaction of the carriers with the intravalley acoustic phonons, the true phonon distribution function setting aside the equipartition approximation for the same, and the transverse component of the three-dimensional phonon wave vector in the light of Ridley’s momentum conservation approximation. The scattering rate and the corresponding zero-field mobility are evaluated for an ensemble of degenerate carriers, confined in a triangular quantum well at the AlGaAs/GaAs interface, over a range of the lattice temperatures and the degeneracy levels. Numerical results demonstrate that the degeneracy parameter, the inelastic electron–phonon interaction, and the transverse component of phonon wave vector contribute significantly to effect the scattering and mobility characteristics compared to traditional theories, particularly in the low-temperature regime. The results which are obtained here seem to be stimulating and thus call forth more studies in the same framework as that of the present analysis.

It has been shown that a chain of unusual vortices can travel in a Josephson sandwich embedded in a dielectric. The limiting velocity of such vortex chain is greater than the limiting velocity of the usual vortex chain by (coth (L/lambda )), where L is the thickness of the sandwich electrodes, (lambda) is the London penetration depth. This makes it much easier to extract radiation into a dielectric, in which the speed of light (c_m) must be less than the velocity of the vortex chain v. Cherenkov radiation from a chain of unusual vortices in the dielectric surrounding the sandwich has been studied. The radiation spectrum of the chain consists of a discrete number of lines at frequencies that are multiples of (2pi v/Xi), where (Xi) is the period of the chain. In cases where (Xi) is of the order of the size of a solitary vortex or greater, then the main contribution to the radiation occurs at the frequency of the first harmonic. For typical parameters of the sandwich and the chain, the radiation frequency falls in the terahertz range.

The paper presents the theory of planar ballistic SNS junctions with equal Fermi velocities and effective masses in all layers. The theory takes into account phase gradients in superconducting layers commonly ignored in the past. At (T=0), the current-phase relation was derived for any thickness L of the normal layer in the model of the steplike pairing potential model analytically. The obtained current-phase relation is essentially different from that in theory neglecting phase gradients, especially in the limit (Lrightarrow 0) (short junction). The analysis resolves the problem with the charge conservation law in the steplike pairing potential model. The current-phase relation at temperatures exceeding the energy spacing between Andreev levels but less than the critical temperature was also calculated numerically. The current at these temperatures is temperature independent and decreases with growing L as (1/L^4). The previous theory predicted the current exponentially decreasing with growing T and L. Possible implications of the analysis for planar junctions with non-equal Fermi velocities and for non-planar junctions (narrow normal bridge between two bulk superconductors) are also discussed.