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Localization of a particle in the wells of an asymmetric double-well (DW)

potential is investigated here. Information entropy-based uncertainty measures,

such as Shannon entropy, Fisher information, Onicescu energy, etc., and

phasespace area, are utilized to explain the contrasting effect of

localization-delocalization and role of asymmetric term in such two-well

potentials. In asymmetric situation, two wells behaves like two different

potentials. A general rule has been proposed for arrangement of

The resonant absorption of light by an ensemble of absorbers decreases when

the resonance is inhomogeneously broadened, as only a fraction of the ensemble

contributes to the absorption at any given optical frequency. Recovering the

lost absorption cross-section is of great importance for various applications

of light-matter interactions, particularly in quantum optics and for few-photon

nonlinearities. However, no recovery mechanism has yet been identified and

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for

analyzing the structure and function of molecules, and for performing

three-dimensional imaging of the spin density. At the heart of NMR

spectrometers is the detection of electromagnetic radiation, in the form of a

free induction decay (FID) signal, generated by nuclei precessing around an

applied magnetic field. While conventional NMR requires signals from 1e12 or

more nuclei, recent advances in sensitive magnetometry have dramatically

We study nanomachines whose relevant (effective) degrees of freedom N >> 1

but smaller than N of proteins. In these machines, both the entropic effect and

the quantum effect over the whole system play the essential roles in producing

nontrivial functions. We therefore call them thermal quantum machines (TQMs).

We propose a systematic protocol for designing the TQMs, which enables the

rough sketch, accurate design of equilibrium states, and accurate estimate of

We compute the minimal energy cost for extracting entanglement from the

ground state of a bosonic or fermionic quadratic system. Specifically, we find

the minimal energy increase in the system resulting from replacing an entangled

pair of modes, sharing entanglement entropy $\Delta S$, by a product state, and

we show how to construct modes achieving this minimal energy cost. Thus, we

obtain a protocol independent lower bound on the extraction of pure state

Irreversibility is a fundamental concept with important implications at many

levels. It pinpoints the fundamental difference between the intrinsically

reversible microscopic equations of motion and the unidirectional arrow of time

that emerges at the macroscopic level. More pragmatically, a full

quantification of the degree of irreversibility of a given process can help in

the characterisation of the performance of thermo-machines operating at the

quantum level. Here, we review the concept of entropy production, which is

We explore the different meanings of "quantum uncertainty" contained in

Heisenberg's seminal paper from 1927, and also some of the precise definitions

that were explored later. We recount the controversy about "Anschaulichkeit",

visualizability of the theory, which Heisenberg claims to resolve. Moreover, we

consider Heisenberg's programme of operational analysis of concepts, in which

he sees himself as following Einstein. Heisenberg's work is marked by the

tensions between semiclassical arguments and the emerging modern quantum

Which theories lead to a contradiction between simple reasoning principles

and modelling observers' memories as physical systems? Frauchiger and Renner

have shown that this is the case for quantum theory, with a thought experiment

that leads to a multi-agent paradox. Here we generalize the conditions of the

Frauchiger-Renner result so that they can be applied to arbitrary physical

theories, and in particular to those expressed as generalized probabilistic

Numerous quantum many-body systems are characterized by either fundamental or

emergent constraints---such as gauge symmetries or parity superselection for

fermions---which effectively limit the accessible observables and realizable

operations. Moreover, these constraints combine non-trivially with the

potential requirement that operations be performed locally. The combination of

symmetry and locality constraints influence our ability to perform quantum

Realisation of experiments even on small and medium-scale quantum computers

requires an optimisation of several parameters to achieve high-fidelity

operations. As the size of the quantum register increases, the characterisation

of quantum states becomes more difficult since the number of parameters to be

measured grows as well and finding efficient observables in order to estimate

the parameters of the model becomes a crucial task. Here we propose a method