Exact Time Evolution of Genuine Multipartite Correlations for N-Qubit Systems in a Common Thermal Reservoir

We investigate the dynamical evolution of genuine multipartite correlations for N-qubits in a common reservoir considering a non-dissipative qubits-reservoir model. We derive an exact expression for the time-evolved density matrix by modeling the reservoir as a set of infinite harmonic oscillators with a bilinear form of interaction Hamiltonian. Interestingly, we find that the choice of two-level systems corresponding to an initially correlated multipartite state plays a significant role in potential robustness against environmental decoherence. In particular, the generalized W-class Werner state shows robustness against the decoherence for an equivalent set of qubits, whereas a certain generalized GHZ-class Werner state shows robustness for inequivalent sets of qubits. It is shown that the genuine multipartite concurrence (GMC), a measure of multipartite entanglement of an initially correlated multipartite state, experiences an irreversible decay of correlations in the presence of a thermal reservoir. For the GHZ-class Werner state, the region of mixing parameters for which there exists GMC, shrinks with time and with increase in the temperature of the thermal reservoir. Furthermore, we study the dynamical evolution of the relative entropy of coherence and von-Neumann entropy for the W-class Werner state.

Teleportation of the entangled state of two superconducting qubits

An efficient scheme is proposed to teleport an entangled state of two superconducting (SC) qubits from Alice's to Bob's lab. This type of two-level systems has recently attracted a lot of attention due to the possible tunability of the coupling strength of the qubits with each other. To achieve the purpose, we first generate the GHZ state as the necessary teleportation channel. Then, appropriate interactions are performed in two processes between two of the five qubits, each with a certain frequency modulative external magnetic field which is applied on specific one of the qubits. Next, via applying proper gates and measurements in each lab, we observe that the teleportation can be successfully performed with maximum possible values of fidelity and success probability. At last, to make the protocol close to reality, decay rates of SC qubits are also taken into account, showing that our protocol still works well, satisfactorily.

Strain-spectroscopy of strongly interacting defects in superconducting qubits

The proper functioning of some micro-fabricated novel quantum devices, such as superconducting resonators and qubits, is severely affected by the presence of parasitic structural material defects known as tunneling two-level-systems (TLS). Recent experiments have reported unambiguous evidence of the strong interaction between individual (coherent) TLS using strain-assisted spectroscopy. This work provides an alternative and simple theoretical insight that illustrates how to obtain the spectral response of such strongly interacting defects residing inside the amorphous tunnel barrier of a qubit's Josephson junction. Moreover, the corresponding spectral signatures obtained here may serve to quickly and efficiently elucidate the actual state of these interacting TLS in experiments based on strain- or electric-field spectroscopy.

Experimental demonstration of efficient high-dimensional quantum gates with orbital angular momentum

Quantum gates are essential for the realization of quantum computer and have been implemented in various types of two-level systems. However, high-dimensional quantum gates are rarely investigated both theoretically and experimentally even that high-dimensional quantum systems exhibit remarkable advantages over two-level systems for some quantum information and quantum computing tasks. Here we experimentally demonstrate the four-dimensional X gate and its unique higher orders with the average conversion efficiency 93\%. All these gates are based on orbital-angular-momentum degree of freedom of single photons. Besides, a set of controlled quantum gates is implemented by use of polarization degree of freedom. Our work is an important step towards the goal of achieving arbitrary high-dimensional quantum circuit and paves a way for the implementation of high-dimensional quantum communication and computation.

Absence of Thermodynamic Uncertainty Relations with Asymmetric Dynamic Protocols

Many versions of Thermodynamic Uncertainty Relations (TUR) have recently been discovered, which impose lower bounds on relative fluctuations of integrated currents in irreversible dissipative processes, and suggest that there may be fundamental limitations on the precision of small scale machines and heat engines. In this work we rigorously demonstrate that TUR can be evaded by using dynamic protocols that are asymmetric under time-reversal. We illustrate our results using a model heat engine using two-level systems, and also discuss heuristically the fundamental connections between TUR and time-reversal symmetry.

Supremacy of theoretical thought over practical thought in Plato's political philosophy

Based on the example of Plato’s political philosophy, this article explores the phenomenon of supremacy of theoretical thought over practical thought, which is a universal trait of the classical Ancient Greek philosophical systems. The first part of the articled indicates the conceptual similarity of the two-level systems of knowledge of Plato and Aristotle in the role that theory plays in relation to practical thought. The second part of the article reconstructs the concept of Plato's philosophy of politics, outlines the key political strategies he dealt with, and provides analytical reconstruction of the democratic theory of politics, oligarchic and civil-political, where the latter is the reflection of Plato’s original political views. The final part is dedicated to the method of Plato's political philosophy. Analysis of the context of using the term “theory” by Plato allows reconstructing the key methodological characteristic of Plato's model of theoretical philosophy. The article also provides the typology of practical knowledge, and substantiates the reasons according to which the political philosophy, as one of the types of practical knowledge, had to adhere to the theoretical prescriptions that fully determined the content of political reflection. The paper reveals the central practical task of philosophical theory, which by Plato's plan was intended to cease the political strife in Athens using true knowledge. The thesis is substantiated that using theory, Plato sought to complete the history of practical politics and subsequently shift towards building the “ideal state” based on the laws that are mandatory for all citizens of the polis. The article also discloses the principles of complex interrelation of the three Socratic methods: irony, dialectics and maieutics, which in Plato's political philosophy manifested as a single complex method. It is demonstrated that the method fulfills a bonding function between theory and practice, which allows transferring the theoretical truth to the sphere of practical problems of politics.