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This study presents bounds on transient variations of fundamental constants, with typical timescales ranging from minutes to months, using clocks in space. The underlying phenomenology describing such transient variations relies on models for Dark Matter (DM) which suggest possible encounters of macroscopic compact objects with the Earth, due to the motion of the solar system in the galactic halo. If such compact objects possess an effective feeble interaction with the ordinary matter beyond the gravitational one, it may result in effective transient variations of fundamental constants. Such variations leave signatures on clocks onboard GNSS satellites. In this paper, we introduce a phenomenological study dedicated to the search for such DM transient objects using the network of passive hydrogen masers (H-Masers) onboard Galileo satellites. We first model the signature of transient variations of fundamental constants as a frequency modulation in the difference between two satellite clocks, considering the satellite trajectories relative to the transient event. Then, we present first results based on a fast analysis method, the maximum reach analysis. The main result is a significant extension of the discovery range for DM transients, with a sensitivity never achieved before. We investigate indeed the range of transient sizes from $10^5$ to $10^9$ kilometres, which, apart from indirect and model-dependent non-transient effects, has never been explored previously., Comment: 13 pages, 11 figures, version accepted for publication in Advances in Space Research

The optically trapped ensembles of atoms provide a versatile platform for storing and coherent manipulation of quantum information. However, efficient realization of quantum information processing requires long-lived quantum states protected from the decoherence e.g. via spontaneous emission. Here, we theoretically study collective dipolar oscillations in finite planar arrays of quantum emitters in free space and analyze mechanisms that govern the emergence of strongly subradiant collective states. We demonstrate that the external coupling between the collective states associated with the symmetry of the array and with the quasi-flat dispersion of the corresponding infinite lattice plays a crucial role in the boost of their radiative lifetime. We show that among different regular arrangements of the atoms the square atomic arrays support eigenstates with minimal radiative losses that scale with the total number of atoms $N_{tot}$ as $\propto N_{tot}^{-5}$.

Arrays of coupled dipole emitters support collective single- and multiphoton states that can preserve quantum excitations. One of the crucial characteristics of these states is the lifetime, which is fundamentally limited due to spontaneous emission. Here, we present a mechanism of external coupling of two states via the radiation continuum, which allows for an increase in the lifetime of both single and double excitations. As an illustrative example, we consider a ring-like ensemble of quantum emitters, demonstrating that upon slight optimization of the structure geometry, one can increase the lifetime of singly and doubly excited states with non-zero orbital momentum by several orders of magnitude.

This review describes the emerging field of waveguide quantum electrodynamics (WQED) concerned with the interaction of photons propagating in a waveguide with localized quantum emitters. The collective emitter-photon interactions can lead to both enhanced and suppressed coupling compared to the case of independent emitters. Here, we focus on guided photons and ordered arrays, leading to super- and sub-radiant states, bound photon states and quantum correlations with promising quantum information applications. We highlight recent groundbreaking experiments performed with different quantum platforms, including cold atoms, superconducting qubits, semiconductor quantum dots, quantum solid-state defects, and we provide a comprehensive introduction to theoretical techniques to study the interactions and dynamics of these emitters and the photons in the waveguide., Comment: 64 pages, 36 figures, 2 tables. Significant update with respect to v2

We investigate optimal conditions for the quantum interface between a signal photon pulse and one-dimensional chain consisting of a varied number of atoms. The tested object is physically designed as an atomic array of tripod-type atoms confined with a nanoscale dielectric waveguide and experiencing its fundamental HE11 mode. The efficiency of interaction is mainly limited by achieved overlap and coupling of the waveguide evanescent field with the trapped atoms. We verify those physical conditions when the coupling within the main scattering channels would be sufficient for further providing various elementary interface protocols such as light storage, light-matter entanglement, preparation of a few photon states on demand, etc., Comment: 15 pages, 11 figures, accepted for publication in Physical Review A

We develop a multiple scattering theory for the absorption of waves in disordered media. Based on a general expression of the average absorbed power, we discuss the possibility to maximize absorption by using structural correlations of disorder as a degree of freedom. In a model system made of absorbing scatterers in a transparent background, we show that a stealth hyperuniform distribution of the scatterers allows the average absorbed power to reach its maximum value. This study provides a theoretical framework for the design of efficient non-resonant absorbers made of dilute disordered materials, for broadband and omnidirectional light, and other kinds of waves.

We develop the theoretical formalism to calculate second-order correlations in dissipative exciton-polariton system and we propose intensity-intensity correlation experiments to reveal the physics of exciton-light coupling in semiconductor microcavities in the Rabi oscillation regime. We predict a counter intuitive behaviour of the correlator between upper and lower polariton branches: due to the decoherence caused by stochastic exciton-photon conversions this correlator is expected to decrease below 1, while the individual second-order coherence of upper and lower polaritons exhibits non-monotonous bunching., Comment: 4 pages, 3 figures

We present here a microscopic analysis of the cooperative light scattering on an atomic system consisting of \Lambda-type configured atoms with the spin-degenerate ground state. The results are compared with a similar system consisting of standard "two-level" atoms of the Dicke model. We discuss advantages of the considered system in context of its possible implications for light storage in a macroscopic ensemble of dense and ultracold atoms.

We consider a quantum memory scheme based on the conversion of a signal pulse into a long-lived spin coherence via stimulated off-resonant Raman process. For a storing medium consisting of alkali atoms, we have calculated the Autler-Townes resonance structure created by a strong control field. By taking into account the upper hyperfine states of the D1 optical transition, we show important deviations from the predictions of the usual three-level Lambda-scheme approximation and we demonstrate an enhancement of the process for particular detunings of the control. We estimate the memory efficiency one can obtain using this configuration., Comment: 8 pages, 6 figures