Annalen der Physik最新文献

The open quantum dynamics of a two-qubit quantum dot system is investigated initially prepared as thermal state and exposed to an Ohmic bosonic reservoir, modeling it as a prototype quantum processor. By integrating local and interaction Hamiltonians, field-induced couplings, and thermal effects, we derive the system's thermal state and analyze its evolution using quantum measures: concurrence, Bell nonlocality, energy fluctuations, and quantum speed limit (QSL) time. Results reveal that strong field-induced coupling enhances and preserves quantum correlations, which otherwise vanish abruptly beyond a critical coupling strength. Conversely, energy fluctuations and the QSL time are suppressed for weak coupling but increase significantly in the strong coupling regime. Higher temperatures are shown to uniformly accelerate the dissipation of quantum correlations. Furthermore, it is found that while weak splitting strength allows for tunable correlations, strong splitting enhances initial correlations and energy fluctuations at the cost of suppressing the QSL. These findings demonstrate the potential of coupled quantum dots as tunable two-qubit processors, providing a guide for precise control over their quantum and thermal properties.

Topological Heusler ferromagnets have emerged as a promising material platform for realizing a large anomalous Nernst effect (ANE) due to their intrinsic Berry curvature. This work reports a significantly enhanced ANE in polycrystalline bulk Co₂MnAl_1-xSi_x, enabled by synergistic tuning of atomic ordering and Fermi level via Si substitution. A large anomalous Nernst thermopower of 4.9 µV K⁻¹ and an anomalous Nernst conductivity of 1.46 A m⁻¹ K⁻¹ at 300 K are obtained in Co₂MnAl_0.69Si_0.31. Furthermore, A centimeter-sized bulk Nernst thermoelectric generator has been developed using Co₂MnAl_0.69Si_0.31 as the legs, which delivers an output voltage of 2.2 mV and a maximum power of 7.7 µW under a temperature difference of 15 K. These results highlight the potential of scalable, high-performance polycrystalline topological magnets for transverse thermoelectric applications and pave the way for practical integration of ANE-based devices.

Topological modes are well-known for their robust and directional wave transportation. However, the symmetric Lamb and shear horizontal waves are precious in topological wave systems. These guided waves in a plate are promising in fields like wave communications and nondestructive testing. In this work, a valley topological phononic crystal plate that supports symmetric plate modes, e.g., zero-order symmetric Lamb (S0) and fundamental shear horizontal (SH0) waves, is constructed. The proposed structure is efficient for controlling the mode conversion between S0 and SH0 modes. The mode conversion is governed by the weight ratio of displacement components of the topological edge states (TES) branches. The remarkable feature, i.e., robustness, of TES of symmetric plate modes is also demonstrated. These results provide an efficient way to control the wave components feasibly.

Quantum batteries (QBs), as emerging quantum devices for energy storage and transfer, have attracted significant attention due to their potential to surpass classical batteries in charging efficiency and energy density. However, interactions between a QB and its environment result in decoherence, which significantly reduces its operational lifespan. In this work, the aging of QBs is proposed to be suppressed by introducing the electromagnetically-induced transparency (EIT). Specifically, a four-level atom is modeled as a QB with an effective two-level system enabled by the EIT, while the photons in the cavity serve as the energy charger. By comparing the energy and extractable work of the QB with and without the EIT effect, it is demonstrated that the QBs incorporating the EIT exhibit enhanced resistance to spontaneous decay as compared to their counterparts without the EIT. It is believed that the findings may provide valuable insights and shed the light on the design principles for mitigating the degradation of the QBs.

In the present study, a trade off of sharing of entanglement between subsystems of a higher dimensional quantum state is derived. It is presented in terms of an inequality which is analogous to the Coffman–Kundu–Wootters inequality that succinctly describes monogamy of entanglement in $��C^2�\otimes �C^2�\otimes �C^2�$ dimensional pure state. To derive the monogamy inequality in $��C^d�\otimes �C^d�\otimes �C^d�$ dimension, G-concurrence measure of entanglement is considered as a measure of entanglement of maximal dimension. The approach of the present study incidentally points toward a rigorous framework which enables to obtain an upper bound of G-concurrence of a bipartite qudit mixed state. Obtained upper bound of G-concurrence is then shown to satisfy a monogamy relation.

A scheme is proposed for generating controllable quantum correlations in a cavity-magnomechanical system comprising a microwave cavity and two yttrium iron garnet (YIG) spheres. A single-mode squeezed vacuum field drives the cavity, while a red-detuned field excites the magnon modes within the YIG spheres. Activating the magnetostrictive effect in the spheres introduces phonon modes through geometric deformation. By linearizing the system dynamics and introducing slowly moving operators to neglect high-frequency oscillatory terms, the correlated noise from the single-mode squeezed vacuum field can be effectively transferred between the two magnon modes and the phonon modes. Control of the cavity-magnon coupling rate breaks the system's symmetry, enabling the generation of tunable quantum squeezing, entanglement, and one-way quantum steering. This tunability facilitates the development of quantum information processing platforms, offering a promising framework for advancing quantum information technologies.

The use of high-quality factor resonators is of undoubted interest for high-precision measurements and for applications in quantum technologies. Novel types of microwave sensors can be realized by coupling a first resonator acting as a stable frequency reference with a second resonator that is sensitive to a particular physical quantity. Here, a coupled cavity configuration is reported in which a high quality ($�Q$) factor elliptical TESLA-shaped superconducting cavity is coupled with a high permittivity ($�{\epsilon }_r$) $�{\mathrm{SrTiO}}_3$ puck, whose resonant frequency varies as a function of temperature due to the temperature dependence of the permittivity that reaches values higher than 30 000 below 1 K. Extensive electromagnetic simulations are used to test different coupling configurations, showing great versatility in tuning the coupling in the weak or strong regime, depending on the puck's position within the cavity. Moreover, for the coupled system, they allow investigation of the dependence of the zero transmission frequency (notch frequency) on changes in permittivity $�{\epsilon }_r$, obtaining a maximum value of 2.8 MHz per unit change of $�{\epsilon }_r$, for $��{\epsilon }_r�\approx �230�$. Finally, the use of the coupled system as a sensor that operates in different temperature ranges is discussed.

The statistics of sequential measurements of two non-commuting observables typically depends on the order in which they are measured. However, if a system evolves unitarily between sequential measurements of dichotomic observables (i.e., observables whose measurement outcomes are labeled by $��\pm �1�$), then the expectation value of the product of the sequential measurements is in fact independent of the order of the measurements, provided that one uses the inverse unitary for the opposite order. In this work, a quantum Bayes' rule is used to show that the aforementioned time symmetry for sequential measurements of dichotomic observables extends to open quantum systems that evolve according to a general quantum channel between measurements. Such results are quite striking in light of the standard view that open quantum systems—which may lose information to their environment—are not reversible in any operational sense. An example of such time-symmetric correlations is given for the amplitude-damping channel, where it is observed that the symmetry is realized by a reverse channel that is a combination of the Petz recovery map together with a dephasing channel.