Anomalous correlation-induced dynamical phase transitions

The nonanalyticity of the Loschmidt echo is termed as the dynamical quantum phase transitions. It extends the notion of quantum criticality to a nonequilibrium scenario, corresponding to the singular behaviour of the Loschmidt echo at critical times in quantum quenched systems. Here, we establish a new paradigm of dynamical phase transitions driven by a sudden change in the internal spatial correlations of the disorder potential in a low-dimensional disordered system. The Loschmidt echo characterizes the quantum quench dynamics and shows a distinctly different behaviour for different correlation exponents in the time scale. Our results indicate the existence of anomalous dynamical phase transitions triggered by the spatial correlations of the random potential. The physical origin of the anomalous transitions is the overlap between two distinctly different extended states. Furthermore, the quench dynamics show a clear signature of the delocalization phase transition in the correlated Anderson model.Comment: 8 pages, 8 figure

Study of Parrondo's paradox regions in one-dimensional quantum walks

The well-known counterintuitive phenomenon, where the combination of unfavorable situations can establish favorable ones, is called Parrondo's paradox. Here, we study one-dimensional discrete-time quantum walks, manipulating two different coins (two-state) operators representing two losing games A and B, respectively, to create the Parrondo effect in the quantum domain. We exhibit that games A and B are losing games when played individually but could produce a winning expectation when played alternatively for a particular sequence of the different periods. Moreover, we also analyze the relationships between Parrondo's games and quantum entanglement in our scheme. Along with the applications of different kinds of quantum walks, our outcomes potentially encourage the development of new quantum algorithms.Comment: 9 pages, 10 figure

Measuring a dynamical topological order parameter in quantum walks

Quantum processes of inherent dynamical nature, such as quantum walks, defy a description in terms of an equilibrium statistical physics ensemble. Until now, identifying the general principles behind the underlying unitary quantum dynamics has remained a key challenge. Here, we show and experimentally observe that split-step quantum walks admit a characterization in terms of a dynamical topological order parameter (DTOP). This integer-quantized DTOP measures, at a given time, the winding of the geometric phase accumulated by the wavefunction during a quantum walk. We observe distinct dynamical regimes in our experimentally realized quantum walks, and each regime can be attributed to a qualitatively different temporal behavior of the DTOP. Upon identifying an equivalent many-body problem, we reveal an intriguing connection between the nonanalytic changes of the DTOP in quantum walks and the occurrence of dynamical quantum phase transitions. Taking stock of a quantum walk A model describing the random walks of quantum particles has been developed by researchers in China and Germany. Classical phenomena such as molecules moving in gases or animals foraging for food can be described by random walks, where every step is chosen through processes like tossing a coin. For quantum particles, randomness arises from the transitions and entanglement of quantum states, but it is difficult to describe the emerging statistical patterns in these quantum walks. Chuan-Feng Li at the University of Science and Technology of China, Hefei, and co-workers used an experimental setup for observing the quantum walks of single photons. They found that the walks could be characterized by a so-called dynamical topological order parameter that describes the behavior of the particle's wavefunction during the walk, thereby linking quantum effects to physical spatial measurements

A structural analysis of self-gravitating anisotropic stars via equation of state in modified teleparallel gravity

This work aims to explore spherically symmetric anisotropic solutions describing compact stellar objects in the extended teleparallel theory of gravity with matter coupling. For this purpose, we use the Adler Finch Skea geometry for both the off-diagonal and diagonal tetrads. We explore the complete matching of the tetrad fields for two different choices of the function f(T,T), i.e., linear and nonlinear models. We obtain complete solutions to the stellar models by taking the strange quark matter distribution after defining the MIT bag model equation of state, pr=13(ρ−4BG). By using the proper choice of the tetrad forms, we incorporate the generic model f(T,T)=αTn(r)+βT(r), which can be treated as linear and nonlinear models depending upon the value of parameter n. After obtaining the field equations, we investigate different physical parameters showing the stability and physical acceptability of the stellar models by using the observational data like mass and radius of PSRJ1416−2230, 4U1608−52, CenX−3, EXO1785−248, and SMCX−1 models

Photonic realization of erasure-based nonlocal measurements

Relativity theory severely restricts the ability to perform nonlocal measurements in quantum mechanics. Studying such nonlocal schemes may thus reveal insights regarding the relations between these two fundamental theories. Therefore, for the last several decades, nonlocal measurements have stimulated considerable interest. However, the experimental implementation of nonlocal measurements imposes profound restrictions because the interaction Hamiltonian cannot contain, in general, nonlocal observables such as the product of local observables belonging to different particles at spacelike-separated regions. In this work, we experimentally realize a scheme for nonlocal measurements with the aid of probabilistic quantum erasure. We apply this scheme to the tasks of performing high-accuracy nonlocal measurements of the parity, as well as measurements in the Bell basis, which do not necessitate classical communication between the parties. Unlike other techniques, the nonlocal measurement outcomes are available locally (upon successful postselection). The state reconstructed via performing quantum tomography on the system after the nonlocal measurement indicates the success of the scheme in retrieving nonlocal information while erasing any local data previously acquired by the parties. This measurement scheme allows to realize any controlled-controlled-gate with any coupling strength. Hence, our results are expected to have conceptual and practical applications to quantum communication and quantum computation