查看更多>>摘要：Abstract Phase and amplitude modulation of propagating terahertz (THz) waves in free space is essential for many rapidly developing THz technologies. Herein, an all‐optical, high‐performance, and ultra‐broadband THz phase shifter is demonstrated. Tunable phase shift is achieved by the photothermal effect of plasmonic gold nanoparticles in toluene, which can induce variations in the THz refractive index of toluene as the temperature increases. A phase shift of 270° at 1 THz can be achieved under a laser irradiation of 2.5 W (3.9 W cm?2) on the mixture solution. Constructive and destructive interference of THz waves can be achieved by tuning the relative phase of two split THz waves, which can be controlled by the power of the irradiation laser. This is the first broadband THz phase modulator in free space driven by optical stimuli, and it provides a new solution for tuning the phase shift of THz waves.
查看更多>>摘要：Abstract A theoretical scheme for a single‐magnon generator based on a hybrid cavity‐magnonic system, in which a microwave cavity is coupled to the magnetostatic mode through the magnetic dipole interaction and coupled to a superconducting qubit (transmon) through electric dipole interaction, and the virtual excitation of microwave photons mediates the interaction between the magnon mode and the transmon qubit, is proposed. The magnon blockade effect is studied based on the coexistence mechanism of anharmonicity of energy levels and multipath interference, and a global optimal condition of magnon blockade is obtained. The numerical results with accessible experimental parameters demonstrate that under this global optimal condition, a perfect single‐magnon generator with a second‐order correlation function tends to zero and a higher single‐magnon number can be achieved even at ambient temperature up to 25 mK. The current scheme is proposed based on the lithographically scalable and superconducting circuit compatible design, which provides convenience for precisely and flexibly engineering in experiments. It is expected to be used as an integrated single‐quanta generator in quantum?network.
查看更多>>摘要：Abstract For a quantum system prepared probabilistically on two or more non‐orthogonal states, the observer cannot discriminate the initial preparation perfectly. Kurt Jacobs [Quantum Inf. Comput. 2007, 7, 127] introduced a measurement operator that could increase the rate of information obtained using a continuous measurement scheme. However, the better effect happens at the expense of reducing the total information from the quantum system. To address this problem, an optimal operator that could yield the maximal value of mutual information for a long‐time measurement is found. Particularly, it turns out that the error probability is minimized for any measurement moment by measuring the optimal operator. Furthermore, for a given finite measurement time, a measurement scheme to maximize the obtained mutual information is presented. It is shown that while the Jacobs' operator should be used for a short‐time case, for a long‐time limit, the proposed optimal operator should be employed. For a given finite duration, the proposal could determine the optimal measurement operator that maximizes the final value of mutual?information.
查看更多>>摘要：Abstract The process of dispersive waves (DWs) emitted from unique Pearcey Gaussian (PG) pulses with both temporal and spectral asymmetric shapes in the anomalous dispersion region of optical fiber is investigated. In contrast to symmetric pulses such as fundamental soliton (Sech) or Gaussian, the radiation amplitude and energy conversion efficiency of DWs are significantly improved by adjusting the asymmetry of the spectral distribution and the temporal oscillation structure of PG pulses. It is shown that, for the case of PG pulses, the minimum value of third‐order dispersion parameter required for the emergence of DWs emission is nearly reduced 50% compared with the case of symmetric pulses. It is also shown that the radiation frequency of DWs emitted from PG pulses can be predicted by a modified phase matching condition. The theoretical predictions are in good agreement with the numerical simulations. The impact of Raman scattering effects on the DWs emission is also disclosed. The results of this study clearly reveal the impact of the inherent behaviors of PG pulses on the DWs emission, which should be relevant for applications requiring broadband light sources based on the mechanism of DWs emission.
查看更多>>摘要：Abstract Leggett–Garg inequalities (LGIs) test the incompatibility between the notion of macrorealism and quantum theory. For unitary dynamics, the optimal quantum violation of a Leggett–Garg inequality is constrained by the Lüders bound. However, the LGIs do not provide the necessary and sufficient condition of macrorealism. A suitably formulated set of no‐signaling in time conditions along with the arrow‐of‐time condition provides the same. In this paper, two formulations in the three‐time Leggett–Garg scenario, are studied namely, the standard LGIs and the recently formulated variant of LGIs when the system evolves under PT‐symmetric Hamiltonian. It is first demonstrated that the quantum violations of both forms of LGIs exceed their respective Lüders bounds and can even reach their algebraic maximum. It is further shown that for the case of standard Leggett–Garg inequality, the violation of Lüders bound can be obtained when both no‐signaling in time and arrow‐of‐time conditions are violated. Interestingly, for the case of a variant of LGIs, for suitable choices of relevant parameters, the quantum violation can even be obtained when only the arrow‐of‐time is violated. However, all no‐signaling in time conditions are satisfied. Such a feature is hitherto unexplored.
查看更多>>摘要：Abstract In this work a quantum sorting algorithm with adaptable requirements of memory and circuit depth is introduced, and is used to develop a new quantum version of the classical machine learning algorithm known as k‐nearest neighbors (k‐NN). Both the efficiency and performance of this new quantum version of the k‐NN algorithm are compared to those of the classical k‐NN and another quantum version proposed by Schuld et?al. Results show that the efficiency of both quantum algorithms is similar to each other and superior to that of the classical algorithm. On the other hand, the performance of the proposed quantum k‐NN algorithm is superior to the one proposed by Schuld et?al. and similar to that of the classical?k‐NN.
查看更多>>摘要：Abstract The temperature‐dependent behavior emerging in the vicinity of the superfluid (SF) to Mott‐insulator (MI) transition of interacting bosons in a 2D optical lattice, described by the Bose–Hubbard model is investigated. The equilibrium phase diagram at finite‐temperature is computed using the cluster mean‐field (CMF) theory including a finite‐cluster‐size‐scaling. The SF, MI, and normal fluid (NF) phases are characterized as well as the transition or crossover temperatures between them are estimated by computing physical quantities such as the superfluid fraction, compressibility and sound velocity using the CMF method. It is found that the nonlocal correlations included in a finite cluster, when extrapolated to infinite size, leads to quantitative agreement of the phase boundaries with quantum Monte Carlo (QMC) results as well as with experiments. Moreover, it is shown that the von Neumann entanglement entropy within a cluster corresponds to the system's entropy density and that it is enhanced near the SF–MI quantum critical point (QCP) and at the SF–NF boundary. The behavior of the transition lines near this QCP, at and away from the particle‐hole (p–h) symmetric point located at the Mott‐tip, is also discussed. The results obtained by using the CMF theory can be tested experimentally using the quantum gas microscopy?method.
Megandhren GovenderSudan HansrajFarook RahamanKsh. Newton Singh...
11页
查看更多>>摘要：Abstract An exact anisotropic star model with a linear barotropic equation?of state and with Finch‐Skea potential is constructed within the framework of pure Lovelock gravity. A comparison with the corresponding Einstein model in a suitable limit is easily deduced. Evidently higher curvature effects induced by the Lovelock contributions generate lower densities, pressures, surface tensions, and anisotropy factors when compared to its Einstein counterpart. The maximum moment of inertia is attained for the Einstein case and hence it may be inferred that Lovelock effects soften the equation?of state. The model satisfies various stability?tests.
查看更多>>摘要：Abstract It is well known that one can extract all the information of an unknown quantum channel by means of quantum process tomography, such as standard quantum‐process tomography and ancilla‐assisted quantum process tomography (AAQPT). Furthermore, it is shown that entanglement is not necessary for AAQPT; there exist separable states that are also useful for it. Surprisingly, in this work we find that not all entangled states are useful for AAQPT; there also exist some entangled states that are useless. The realignment operation used in entanglement detection can be related to the question whether a bipartite state is useful for AAQPT. The relationship between them is derived and the process of extracting the complete information of an unknown channel by the realignment operation shown. Based on this relationship, examples of a two‐qutrit entangled state and a two‐qutrit bound entangled state are presented. Both of these two examples are entangled but they cannot be used for AAQPT. Last but not the least, experimental verification is been performed on the IBM?platform.
NSTL
Wiley