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In this paper, we study a non-Hermitian (NH) ladder subjected to a variety of driving protocols. The driven system looses chiral symmetry (CS) whose presence is indispensable for its topological characterization. Further, the bulk boundary correspondence (BBC) gets adversely affected due to the presence of non-Hermitian skin effect (NHSE). Here, we present a formalism that not only retrieves the lost CS, but also restores the BBC via the construction of a generalized Brillouin zone (GBZ). Specifically, we employ delta and step drives to compare and contrast between them with regard to their impact on NHSE. Further, a widely studied harmonic drive is invoked in this context, not only for the sake of completeness, but its distinct computational framework offers valuable insights on the properties of out-of-equilibrium systems. While the delta and the harmonic drives exhibit unidirectional skin effect in the system, the step drive may show bi-directional skin effect. Also, there are specific points in the parameter space that are devoid of skin effect. These act as critical points that distinguish the skin modes to be localized at one boundary or the other. Moreover, for the computation of the non-Bloch invariants, we employ GBZ via a pair of symmetric time frames corresponding to the delta and the step drives, while a high-frequency expansion was carried out to deal with the harmonic drive. Finally, we present phase boundary diagrams that demarcate distinct NH phases obtained via tracking the trajectories of the exceptional points. These diagrams demonstrate a co-existence of the zero and $\pi$ energy modes in the strong NH limit and thus may be relevant for studies of Floquet time crystals.

We perform systematic analyses of single and multi-frequency driving protocols on a Rashba nanowire with superconducting correlations induced by proximity effects. The results for the single-mode drive reveal interesting frequency dependencies of the Majorana modes, in the sense that the parameters corresponding to the trivial and topological limits of the undriven (static) case host Majorana zero modes, respectively at low and high frequencies. Further, emergence of long-range interactions are noted that give rise to multiple gap-closing scenarios, which imply occurrence of multiple Majorana modes. On the other hand, the multi-frequency driving protocol, sub-grouped into commensurate and incommensurate ratios of the frequencies, demonstrates intriguing consequences. The commensurate case yields dynamical control over the stability of the edge modes. Moreover, complex driving protocols harm the Majoranas by pushing them into the bulk. Finally, the incommensurate case yields independent Majorana modes occurring at low-symmetry points in the Brillouin zone. While the single and the commensurate multi-frequency driving protocols admit the usage of symmetric time frames for the computation of the topological invariants, the incommensurate case relies on the framework of many-mode Floquet theory, where the topological properties are ascertained via calculating the Berry phase. We present band structure and phase diagrams to substantiate all our results. The robustness and concurrent existence of these unique Majorana modes, even amidst a very dense energy spectrum along with a lack of global time-periodicity, hold promise for applications in quantum computing and the development of Floquet time crystals.

The interplay of topology and disorder in non-equilibrium quantum systems is an intriguing subject. Here, we look for a suitable platform that enables an in-depth exploration of the topic. To this end, We analyze the topological and localization properties of a dimerized one-dimensional Kitaev chain in the presence of an onsite quasiperiodic potential with its amplitude being modulated periodically in time. The topological features have been explored via computing the real-space winding numbers corresponding to both the Majorana zero and the $\pi$ energy modes. We enumerate the scenario at different driving frequencies. In particular, at some intermediate frequency regime, the phase diagram concerning the zero mode involves two distinct phase transitions, one from a topologically trivial to a non-trivial phase, and another from a topological phase to an Anderson localized phase. On the other hand, the study of the $\pi$ modes reveals the emergence of a unique topological phase, with the bulk and the edges being fully localized, which may be called as the Floquet topological Anderson phase. Furthermore, we study the localization properties of the bulk states by computing the inverse and normalized participation ratios, while the critical phase is ascertained by computing the fractal dimension. We have observed extended, critical, and localized phases at intermediate frequencies, which are further confirmed via a finite-size scaling analysis. Finally, fully extended and localized phases are respectively observed at lower and higher frequencies.

We have investigated a periodically driven Creutz ladder in presence of two different driving protocols, namely, a sinusoidal drive and a $\delta$-kick imparted to the ladder at regular intervals of time. Specifically, we have studied the topological properties corresponding to the trivial and the non-trivial limits of the static (undriven) case via computing suitable topological invariants. Corresponding to the case where the chiral symmetry is intact, in addition to the zero energy modes, $\pi$ energy modes appear in both these cases. Further, two different frequency regimes of the driving protocol emerge, where Floquet-Magnus expansion is particularly employed to study the high frequency regime for the sinusoidal drive. Apart from the physics being identical in the high frequency and the static scenarios, the zero energy modes show distinctive features at low and high frequencies. For the sinusoidal drive, there exists a sharp frequency threshold beyond which the zero energy mode only exists in the topological limit, while in the trivial limit, it exists only upto the threshold frequency. In presence of the $\delta$-kick, the Creutz ladder demonstrates higher values of the topological invariant, and as a consequence the system possesses large number of edge modes., Comment: 10 pages, 19 figures

Purpose-This paper is based on design of a quadruped robot and manufacturing it with 3-D printer followed by its detailed analysis. It focuses on the advantages of additive manufacturing rather than conventional manufacturing techniques and also highlights its limitations. The consequences of choice of different materials for 3-D printing are evaluated in this report. Design/methodology/Approach- The parts were designed in CAD software and made into Stereo lithography files, which were fed into the 3-D printing software. They were printed with the selection of ABS material. Low torque servos were employed in the beginning of the assembly and were controlled with the Arduino Uno micro controller. Findings- The versatility of legged robots require materials with high strength to weight ratio, where 3003 aluminium alloy sheets proved to be a better choice than conventional ABS. The ABS legs buckled under load and proved to be an inferior material choice for fabrication. The aluminium sheet fabricated legs not only imparted structural stability to the robot but also allowed in selection of more powerful servos for added strength.The bot could now achieve significant level of stability. Research Limitations/Implications- The power supply used for powering the bot was of SMPS type of power supply which made it less mobile. Due to the huge demand of current by the high torque servos used later, the power supply became a huge limitation which can be overcome by applying Lithium ion batteries. Practical Implications- The bot can be used for SLAM and autonomous navigation in areas where it is almost impossible for humans to access into. Originality/Value- This paper shows a concrete study on efficacy of quick CAD designing and rapid fabrication.