Catálogo de publicaciones - revistas

<jats:p>We construct a two-dimensional, discrete-time quantum walk, exhibiting non-Hermitian skin effects under open-boundary conditions. As a confirmation of the non-Hermitian bulk-boundary correspondence, we show that the emergence of topological edge states is consistent with the Floquet winding number, calculated using a non-Bloch band theory, invoking time-dependent generalized Brillouin zones. Further, the non-Bloch topological invariants associated with quasienergy bands are captured by a non-Hermitian local Chern marker in real space, defined via the local biorthogonal eigenwave functions of a non-unitary Floquet operator. Our work aims to stimulate further studies of non-Hermitian Floquet topological phases where skin effects play a key role.</jats:p>

<jats:p>The quantum-classical hybrid algorithm is a promising algorithm with respect to demonstrating the quantum advantage in noisy-intermediate-scale quantum (NISQ) devices. When running such algorithms, effects due to quantum noise are inevitable. In our work, we consider a well-known hybrid algorithm, the quantum approximate optimization algorithm (QAOA). We study the effects on QAOA from typical quantum noise channels, and produce several numerical results. Our research indicates that the output state fidelity, i.e., the cost function obtained from QAOA, decreases exponentially with respect to the number of gates and noise strength. Moreover, we find that when noise is not serious, the optimized parameters will not deviate from their ideal values. Our result provides evidence for the effectiveness of hybrid algorithms running on NISQ devices.</jats:p>

<jats:p>Molecular qubits are promising as they can benefit from tailoring and versatile design of chemistry. It is essential to reduce the decoherence of molecular qubits caused by their interactions with the environment. Herein the dynamical decoupling (DD) technique is utilized to combat such decoherence. The coherence time for a transition-metal complex (PPh<jats:sub>4</jats:sub>)<jats:sub>2</jats:sub>[Cu(mnt)<jats:sub>2</jats:sub>] is prolonged from 6.8 μs to 1.4 ms. The ratio of the coherence time and the length of <jats:italic>π</jats:italic>/2 pulse, defined as the single qubit figure of merit (<jats:italic>Q</jats:italic> <jats:sub>M</jats:sub>), reaches 1.4 × 10<jats:sup>5</jats:sup>, which is 40 times greater than what previously reported for this molecule. Our results show that molecular qubits, with milliseconds coherence time, are promising candidates for quantum information processing.</jats:p>

<jats:p>We present a quantum algorithm for approximating maximum independent sets of a graph based on quantum non-Abelian adiabatic mixing in the sub-Hilbert space of degenerate ground states, which generates quantum annealing in a secondary Hamiltonian. For both sparse and dense random graphs <jats:italic>G</jats:italic>, numerical simulation suggests that our algorithm on average finds an independent set of size close to the maximum size <jats:italic>α</jats:italic>(<jats:italic>G</jats:italic>) in low polynomial time. The best classical algorithms, by contrast, produce independent sets of size about half of <jats:italic>α</jats:italic>(<jats:italic>G</jats:italic>) in polynomial time.</jats:p>

<jats:p>We prove that under the condition of closed boundary to mass flux, pure advection is not a valid mechanism to make a practical thermal diode. Among the various designs of thermal diodes, many of them involve circulating fluid flow, such as in thermosyphons. However, those designs often employ natural convection, which is basically a nonlinear process. It thus remains unclear how the pure advection of temperature field induced by a decoupled velocity field influences the symmetry of heat transfer. Here we study three typical models with pure advection: one with open boundary, one with closed boundary at unsteady state, and one with closed boundary at steady state. It is shown that only the last model is practical, while it cannot become a thermal diode. Finally, a general proof is given for our claim by analyzing the diffusive reciprocity.</jats:p>

<jats:p>Ehrenfest time depends differently on the Planck constant in integrable motion and chaotic motion. We study how its dependence on the Planck constant changes when there is a continuous transition from regular motion to chaotic motion. We find that the dependence is a weighted compromise between its two distinct dependences in regular and chaotic motions. The study is carried out with the system of periodically driven anharmonic oscillator. As the system is quite typical, the result may apply generally.</jats:p>

<jats:p>The acceleration of decay induced by frequency measurements, namely the quantum anti-Zeno effect (AZE), was first predicted by Kofman and Kurizki [Nature 405 (2000) 546]. The effect of the frequency measurements on nuclear <jats:italic>β</jats:italic> decay rate is analyzed based on the time-dependent perturbation theory. We present a detailed calculation of the decay rates of <jats:sup>3</jats:sup>H, <jats:sup>60</jats:sup>Co (<jats:italic>β</jats:italic> <jats:sup>−</jats:sup> type), <jats:sup>22</jats:sup>Na, <jats:sup>106</jats:sup>Ag (<jats:italic>β</jats:italic> <jats:sup>+</jats:sup> type) and <jats:sup>18</jats:sup>F, <jats:sup>57</jats:sup>Co and <jats:sup>111</jats:sup>Sn (EC type) under frequency measurements. It is found that the effects of frequency measurements on the decay rates of <jats:italic>β</jats:italic> <jats:sup>+</jats:sup> and <jats:italic>β</jats:italic> <jats:sup>−</jats:sup> cases are different from the case of EC, and the smaller the <jats:italic>β</jats:italic> decay energy is, the more favorable it is to observe the AZE in experiment. Based on our analysis, it is suggested that possible experimental candidates should have a small decay energy and a reasonable half life (such as <jats:sup>3</jats:sup>H) for observing the AZE in <jats:italic>β</jats:italic> decay.</jats:p>

<jats:p>Classical electrodynamics foresees that the effective interaction force between a moving charge and a magnetic dipole is modified by the time-varying total momentum of the interaction fields. We derive the equations of motion of the particles from the total stress-energy tensor, assuming the validity of Maxwell’s equations and the total momentum conservation law. Applications to the effects of Aharonov–Bohm type show that the observed phase shift may be due to the relative lag between interfering particles caused by the effective local force.</jats:p>

<jats:p>Infrared metamaterial absorber (MMA) based on metal-insulator-metal (MIM) configuration with flexible design, perfect and selective absorption, has attracted much attention recently for passive radiative cooling applications. To cool objects passively, broadband infrared absorption (i.e. 8–14 μm) is desirable to emit thermal energy through atmosphere window. We present a novel MMA composed of multilayer MIM resonators periodically arranged on a PbTe/MgF<jats:sub>2</jats:sub> bilayer substrate. Verified by the rigorous coupled-wave analysis method, the proposed MMA shows a relative bandwidth of about 45% (from 8.3 to 13.1 μm with the absorption intensity over 0.8). The broadband absorption performs stably over a wide incident angle range (below 50°) and predicts 12 K cooling below ambient temperature at nighttime. Compared with the previous passive radiative coolers, our design gets rid of the continuous metal substrate and provides an almost ideal transparency window (close to 100%) for millimeter waves over 1 mm. The structure is expected to have potential applications in thermal control of integrated devices, where millimeter wave signal compatibility is also required.</jats:p>