Spontaneous-emission rates in finite photonic crystals of plane scatterers

The concept of a plane scatterer that was developed earlier for scalar waves is generalized so that polarization of light is included. Starting from a Lippmann-Schwinger formalism for vector waves, we show that the Green function has to be regularized before T-matrices can be defined in a consistent way. After the regularization, optical modes and Green functions are determined exactly for finite structures built up of an arbitrary number of parallel planes, at arbitrary positions, and where each plane can have different optical properties. The model is applied to the special case of finite crystals consisting of regularly spaced identical planes, where analytical methods can be taken further and only light numerical tasks remain. The formalism is used to calculate position- and orientation-dependent spontaneous-emission rates inside and near the finite photonic crystals. The results show that emission rates and reflection properties can differ strongly for scalar and for vector waves. The finite size of the crystal influences the emission rates. For parallel dipoles close to a plane, emission into guided modes gives rise to a peak in the frequency-dependent emission rate.Comment: 18 pages, 6 figures, to be published in Phys. Rev.

Size-dependent nonlocal effects in plasmonic semiconductor particles

Localized surface plasmons (LSP) in semiconductor particles are expected to exhibit spatial nonlocal response effects as the geometry enters the nanometer scale. To investigate these nonlocal effects, we apply the hydrodynamic model to nanospheres of two different semiconductor materials: intrinsic InSb and $n$-doped GaAs. Our results show that the semiconductors indeed display nonlocal effects, and that these effects are even more pronounced than in metals. In a $150\mathrm{\,nm}$ InSb particle at $300\mathrm{\,K}$, the LSP frequency is blueshifted 35%, which is orders of magnitude larger than the blueshift in a metal particle of the same size. This property, together with their tunability, makes semiconductors a promising platform for experiments in nonlocal effects.Comment: 7 pages, 3 figures, 1 table, corrected typos in text and figure

Quantum state preparation in circuit QED via Landau-Zener tunneling

We study a qubit undergoing Landau-Zener transitions enabled by the coupling to a circuit-QED mode. Summing an infinite-order perturbation series, we determine the exact nonadiabatic transition probability for the qubit, being independent of the frequency of the QED mode. Possible applications are single-photon generation and the controllable creation of qubit-oscillator entanglement.Comment: 7 pages, 3 figure

Coupling Nitrogen Vacancy Centers in Diamond to Superconducting Flux Qubits

We propose a method to achieve coherent coupling between Nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the magnetic coupling can be used to achieve a coherent transfer of quantum information between the flux qubit and an ensemble of NV centers. This enables a long-term memory for a SC quantum processor and possibly an interface between SC qubits and light.Comment: Accepted in Phys. Rev. Lett. Updated text and Supplementary Material adde

Quantum optical effective-medium theory for loss-compensated metamaterials

A central aim in metamaterial research is to engineer sub-wavelength unit cells that give rise to desired effective-medium properties and parameters, such as a negative refractive index. Ideally one can disregard the details of the unit cell and employ the effective description instead. A popular strategy to compensate for the inevitable losses in metallic components of metamaterials is to add optical gain material. Here we study the quantum optics of such loss-compensated metamaterials at frequencies for which effective parameters can be unambiguously determined. We demonstrate that the usual effective parameters are insufficient to describe the propagation of quantum states of light. Furthermore, we propose a quantum-optical effective-medium theory instead and show that it correctly predicts the properties of the light emerging from loss-compensated metamaterials.Comment: 6 pages, 3 figures. Accepted for Physical Review Letter

Limitation of entanglement due to spatial qubit separation

We consider spatially separated qubits coupled to a thermal bosonic field that causes pure dephasing. Our focus is on the entanglement of two Bell states which for vanishing separation are known as robust and fragile entangled states. The reduced two-qubit dynamics is solved exactly and explicitly. Our results allow us to gain information about the robustness of two-qubit decoherence-free subspaces with respect to physical parameters such as temperature, qubit-bath coupling strength and spatial separation of the qubits. Moreover, we clarify the relation between single-qubit coherence and two-qubit entanglement and identify parameter regimes in which the terms robust and fragile are no longer appropriate.Comment: 7 pages, 3 figures; revised version, accepted for publication in Europhys. Let

Nanoplasmonics beyond Ohm's law

In tiny metallic nanostructures, quantum confinement and nonlocal response change the collective plasmonic behavior with important consequences for e.g. field-enhancement and extinction cross sections. We report on our most recent developments of a real-space formulation of an equation-of-motion that goes beyond the common local-response approximation and use of Ohm's law as the central constitutive equation. The electron gas is treated within a semi-classical hydrodynamic model with the emergence of a new intrinsic length scale. We briefly review the new governing wave equations and give examples of applying the nonlocal framework to calculation of extinction cross sections and field enhancement in isolated particles, dimers, and corrugated surfaces.Comment: Invited paper for TaCoNa-Photonics 2012 (www.tacona-photonics.org), to appear in AIP Conf. Pro

Letter from the Editors: The Past and Present of Fashion Cities

In the past decade or so, discussion has increasingly addressed the need to rip apart the idea of a single fashion history stemming from Europe and North America which opened up with the outsourcing of the postwar period (Ling, Lorusso, and Segre Reinach 2019). Research has presented an open perspective, engaging with fashion beyond the boundaries of the traditional fashion capitals, considering skills, specialisms and placemaking strategies, fostered in diverse locations across the globe (Breward and Gilbert 2006; Skov 2011; Brydges, Hracs, and Lavanga 2018). Fashion affects elites and non-elites; cities in core and periphery areas alike. Furthermore, the structure of the fashion industry has varied from historical period to historical period and between cities, regions, and nations (Breward and Gilbert 2006; Rantisi 2004). The industry is composed of complex transnational supply chains which encompass textile and clothing manufacturing, the organization of temporary clusters like trade shows and fashion weeks, and (digital) media management (Skov 2006; Rocamora 2017; Wubs and Maillet 2017; Blaszczyk and Wubs 2018; Lavanga 2018; Huang and Janssens 2019). While scholars across the globe have enriched the geography of fashion by studying locations beyond the “big four,” there remains a need for better understanding of fashion centers from global and evolutionary perspectives. Employing an interdisciplinary approach, combining business history, economic history, fashion studies and economic geography, this special issue aims to present a burgeoning perspective. It focuses on the spatial and transnational dimensions of the industry, taking a long-term historical perspective—from Paris in the late nineteenth century to Turin and London in the early-mid twentieth century—while also providing provocations addressing how we could define and study fashion cities. As business historians and economic geographers, we are cautious to predict the future, but clearly, the rise of China as an economic superpower may create a cultural shift that could affect the power structure of the fashion industry. China is no longer the global sweatshop. It has become the largest consumer market of the world with a significant interest in fashion and luxury, complemented by an increasing number of domestic fashion designers and brands (Ling and Segre Reinach 2018). Chinese brands excel in their domestic market but often have not expanded fully in the West, likely as it is not necessary. Shanghai’s recent endeavors to become one of the fashion capitals of the world are closely linked to the global shifts of the industry, and the rise of China’s star. Perhaps the re-bundling of the symbolic and material aspects of fashion, along with the restructuring of unsustainable global production networks would create new chances for old and new fashion capitals alike. This, in turn, begs the question of whether we should still think in terms of fashion capitals and cities. Should we rather explore the interrelation of diverse fashion systems and digital spaces, which may, in turn, change our understanding of not just fashion places, but also of fashion itself

Mode expansions in the quantum electrodynamics of photonic media with disorder

We address two issues in the quantum electrodynamical description of photonic media with some disorder, neglecting material dispersion. When choosing a gauge in which the static potential vanishes, the normal modes of the medium with disorder satisfy another transversality condition than the modes of the ideal medium. Our first result is an integral equation for optical modes such that all perturbation-theory solutions automatically satisfy the desired transversality condition. Secondly, when expanding the vector potential for the medium with disorder in terms of the normal modes of the ideal structure, we find the gauge transformation that makes the static potential zero, thereby generalizing work by Glauber and Lewenstein [Phys. Rev. A 43, 467 (1991)]. Our results are relevant for the quantum optics of disordered photonic crystals.Comment: 7 pages; accepted in Photonics and Nanostructure