# All

We address the question whether the super-Heisenberg scaling for quantum

estimation is realizable. We unify the results of two approaches. In the first

one, the original system is compared with its copy rotated by the parameter

dependent dynamics. If the parameter is coupled to the one-body part of the

Hamiltonian the precision of its estimation is known to scale at most as

$N^{-1}$ (Heisenberg scaling) in terms of the number of elementary subsystems

used, $N$. The second approach considers fidelity at criticality often leading

Recently it has been demonstrated that an ensemble of trapped ions may serve

as a quantum annealer for the number-partitioning problem [Nature Comm. DOI:

10.1038/ncomms11524]. This hard computational problem may be addressed

employing a tunable spin glass architecture. Following the proposal of the

trapped ions annealer, we study here its robustness against thermal effects,

that is, we investigate the role played by thermal phonons. For the efficient

description of the system, we use a semiclassical approach, and benchmark it

The nonequilibrium quantum dynamics of few boson ensembles which experience a

spatially modulated interaction strength and are confined in finite optical

lattices is investigated. Performing quenches either on the wavevector or the

phase of the interaction profile an enhanced imbalance of the interatomic

repulsion between distinct spatial regions of the lattice is induced. Following

both quench protocols triggers various tunneling channels and a rich excitation

We study the nonlinear dynamics of trapped-ion models far away from the

Lamb-Dicke regime. This nonlinearity induces a sideband cooling blockade,

stopping the propagation of quantum information along the Hilbert space of the

Jaynes-Cummings and quantum Rabi models. We compare the linear and nonlinear

cases of these models in the ultrastrong and deep strong coupling regimes.

Moreover, we propose a scheme that simulates the nonlinear quantum Rabi model

in all coupling regimes. This can be done via off-resonant nonlinear red and

Stokes phenomenon refers to the fact that the asymptotic expansion of complex

functions can differ in different regions of the complex plane, and that beyond

the so-called Stokes lines has an unphysical divergence. An important special

case is when the Stokes lines emanate from phase space caustics of a complex

trajectory manifold. In this case, symmetry determines that to second order

there is a double coverage of the space, one portion of which is unphysical.

Quantum simulators have the exciting prospect of giving access to real-time

dynamics of lattice gauge theories, in particular in regimes that are difficult

to compute on classical computers. Future progress towards scalable quantum

simulation of lattice gauge theories, however, hinges crucially on the

efficient use of experimental resources. As we argue in this work, due to the

fundamental non-uniqueness of discretizing the relativistic Dirac Hamiltonian,

Quantum effects, prevalent in the microscopic scale, generally elusive in

macroscopic systems due to dissipation and decoherence. Quantum phenomena in

large systems emerge only when particles are strongly correlated as in

superconductors and superfluids. Cooperative interaction of correlated atoms

with electromagnetic fields leads to superradiance, the enhanced quantum

radiation phenomenon, exhibiting novel physics such as quantum Dicke phase and

ultranarrow linewidth for optical clocks. Recent researches to imprint atomic

We analyze the second-order photon autocorrelation function $g^{(2)}$ with

respect to the photon probability distribution and discuss the generic features

of a distribution that result in superthermal photon bunching ($g^{(2)}>2$).

Superthermal photon bunching has been reported for a number of optical

microcavity systems that exhibit processes like superradiance or mode

competition. We show that a superthermal photon number distribution cannot be

constructed from the principle of maximum entropy, if only the intensity and

We report on the coupling of the emission from a single europium-doped

nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first

step, we study the sample properties and observe a strong correlation between

emission lifetime and brightness, as well as a lifetime reduction for

nanocrystals embedded in a polymer film. This is explained by differences in

the local density of states. We furthermore quantify the scattering loss of a

nanocrystal inside the cavity and use this to deduce the crystal size. Finally,

It is shown that a linearized classical gravity wave $\hat{a}$ {\em la}

Einstein can get entangled with an array of test masses in a plane

perpendicular to its direction of propagation. A Bell-CHSH inequality based on

the requirement of noncontextuality for classical realism is derived, and it is

shown that the entangled state produced violates this inequality.