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Biexcitons have been considered as one of the fundamental building blocks for quantum technology because of its overwhelming advantages in generating entangled photon pairs. Although many-body complexes have been demonstrated recently in mono-layer transition metal dichalcogenides (TMDs), the low emission efficiency and scale up capability hinder their applications. Colloidal nanomaterials, with high quantum efficiency and ease of synthesis/processing, are regarded to be an appealing complement to TMDs for biexciton sources. However, a progress towards biexciton emission in colloidal nanomaterials has been challenging largely by small binding energy and ultrafast non-radiative multiexciton recombination. Here, we demonstrate room-temperature biexciton emission in Cu-doped CdSe colloidal quantum wells (CQWs) under continuous-wave excitation with intensity as low as ~10 W/cm2. The characteristics of radiative biexciton states are investigated by their super linear emission with respect to excitation power, thermal stability and transient photophysics. The interaction between the quantum confined host carriers and the dopant ions increases biexciton binding energy by two folds compared to the undoped CQWs. Such strong binding energy together with suppressed Auger recombination and efficient, spectrally narrow photoluminescence in a quasi-2D semiconductor enables sustained biexciton emission at room temperature, providing a potential solution for efficient, scalable and stand-alone quantum devices., Comment: 11 pages, 5 Figures

We develop a new model of laser-matter interaction based on Optical Bloch Equations, which includes photo-ionization, impact ionization, and various relaxation processes typical of dielectric materials. This approach is able to describe the temporal evolution of the electron dynamics in the conduction band driven by few-cycle laser pulses of any wavelength. Moreover, the nonlinear polarization response of both centrosymmetric and non-centrosymmetric materials can be described while ensuring the proper selection rules for the harmonics emission.

The existence and properties of an exact universal excitation waveform for optimal enhancement of directed ratchet transport are deduced from the criticality scenario giving rise to ratchet universality, and confirmed by numerical experiments in the context of a driven overdamped Brownian particle subjected to a vibrating periodic potential. While the universality scenario holds regardless of the waveform of the periodic vibratory excitations involved, it is shown that the enhancement of directed ratchet transport is optimal when the impulse transmitted by those excitations (time integral over a half-period) is maximum. Additionally, the existence of a frequency-dependent optimal value of the relative amplitude of the two excitations involved is illustrated in the simple case of harmonic excitations., Comment: Enlarged version, 8 figures

We have recently presented a geometry dual to a Schwinger-Keldysh closed time contour, with two equal $\beta/2$ length Euclidean sections, which can be thought of as dual to the Thermo Field Dynamics formulation of the boundary CFT. In this work we study non-perturbative holographic excitations of the thermal vacuum by turning on asymptotic Euclidean sources. In the large-$N$ approximation the states are found to be thermal coherent state and we manage to compute its eigenvalues. We pay special attention to the high temperature regime where the manifold is built from pieces of Euclidean and Lorentzian black hole geometries. In this case, the real time segments of the Schwinger-Keldysh contour get connected by an Einstein-Rosen wormhole through the bulk, which we identify as the exterior of a single maximally extended black hole. The Thermal-AdS case is also considered but, the Lorentzian regions become disconnected, its results mostly follows from the zero temperature case., Comment: 23 pages, 14 figures, corrections in Sec. 3 and 4, comments added. Version accepted in JHEP

We present a spherically symmetric aAdS gravity solution with Schwinger-Keldysh boundary condition dual to a CFT at finite temperature defined on a complex time contour. The geometry is built by gluing the exterior of a two-sided AdS Black Hole, the (aAdS) Einstein-Rosen wormhole, with two Euclidean black hole halves. These pieces are interpreted as the gravity duals of the two Euclidean $\beta/2$ segments in the SK path, each coinciding with a Hartle-Hawking-Maldacena (TFD) vacuum state, while the Lorentzian regions naturally describes the real-time evolution of the TFD doubled system. Within the context of Skenderis and van Rees real-time holographic prescription, the new solution should be compared to the Thermal AdS spacetime since both contribute to the gravitational path integral. In this framework, we compute the time ordered 2-pt functions of scalar CFT operators via a non-back-reacting Klein-Gordon field for both backgrounds and confront the results. When solving for the field we find that the gluing leads to a geometric realization of the Unruh trick via a completely holographic prescription. Interesting observations follow from $\langle {\cal O}_L{\cal O}_R\rangle$, which capture details of the entanglement of the (ground) state and the connectivity of the spacetime., Comment: 20 pages, 6 figures

Taming chaos arising from dissipative non-autonomous nonlinear systems by applying additional harmonic excitations is a reliable and widely used procedure nowadays. But the suppressory effectiveness of generic non-harmonic periodic excitations continues to be a significant challenge both to our theoretical understanding and in practical applications. Here we show how the effectiveness of generic suppressory excitations is optimally enhanced when the impulse transmitted by them (time integral over two consecutive zeros) is judiciously controlled in a not obvious way. This is demonstrated experimentally by means of an analog version of a universal model, and confirmed numerically by simulations of such a damped driven system including the presence of noise. Our theoretical analysis shows that the controlling effect of varying the impulse is due to a correlative variation of the energy transmitted by the suppressory excitation., Comment: Main text (6 figs and 5 pages) and Supplemental material (9 figs and 12 pages)

We establish upper bounds for the convolution operator acting between interpolation spaces. This will provide several examples of Young Inequalities in different families of function spaces. We use this result to prove a bilinear interpolation theorem and we show applications to the study of bilinear multipliers.

We investigate terahertz emission from two-color fs-laser-induced microplasmas. Under strongest focusing conditions, microplasmas are shown to act as point-sources for broadband terahertz-to-far-infrared radiation, where the emission bandwidth is determined by the plasma density. Semi-analytical modeling allows us to identify scaling laws with respect to important laser parameters. In particular, we find that the optical-to-THz conversion efficiency crucially depends on the focusing conditions. We use this insight to demonstrate by means of Maxwell-consistent 3D simulations, that for only 10-$\mu$J laser energy a conversion efficiency well above $10^{-4}$ can be achieved.

It is commonly accepted that states in a conformal field theory correspond to classical spacetimes with Anti-de-Sitter asymptotics. In this work we give a prescription for the CFT states with a dual classical spacetime and, using basic holographic rules, show that they are holographically connected to coherent states in the large-N limit, or by considering linearized perturbations. We also point out implications in the spacetime emergence mechanism, for instance, the (entangled) state dual to the black hole should be properly described as a quantum superposition of products of these states. This also complements the quantum interpretation of the Hawking-Page transition., Comment: 14 pages, 8 figures

We compute time-ordered 2- and 3-pt correlation functions of CFT scalar operators between generic in/out states. The calculation is holographically carried out by considering a non backreacting AdS scalar field with a $\lambda \phi^3$ self-interaction term on a combination of Euclidean and Lorentzian AdS sections following the Skenderis-van Rees prescription. We show that, although working in an essentially different set up, the final result for the 3-pt correlators agree with those of Rastelli et al. for Euclidean AdS. By analyzing the inner product between the in/out excited states in the large $N$ approximation, we argue that a cubic bulk interaction deforms the excited states from coherent into \emph{squeezed}. Finally, a diagrammatic interpretation of the results suggests some general properties for the $n$-point correlation functions between excited states., Comment: 23 pages, 5 figures

The standard techniques of variational calculus are geometrically stated in the ambient of fiber bundles endowed with a (pre)multisymplectic structure. Then, for the corresponding variational equations, conserved quantities (or, what is equivalent, conservation laws), symmetries, Cartan (Noether) symmetries, gauge symmetries and different versions of Noether's theorem are studied in this ambient. In this way, this constitutes a general geometric framework for all these topics that includes, as special cases, first and higher order field theories and (non-autonomous) mechanics., Comment: 16 pp. Some (minor) mistakes and misprints have been corrected, mainly on pages 3, 12, and 14

The aim of this work is to study fiber derivatives associated to Lagrangian and Hamiltonian functions describing the dynamics of a higher-order autonomous dynamical system. More precisely, given a function in $T^*T^{(k-1)}Q$, we find necessary and sufficient conditions for such a function to describe the dynamics of a kth-order autonomous dynamical system, thus being a kth-order Hamiltonian function. Then, we give a suitable definition of (hyper)regularity for these higher-order Hamiltonian functions in terms of their fiber derivative. In addition, we also study an alternative characterization of the dynamics in Lagrangian submanifolds in terms of the solutions of the higher-order Euler-Lagrange equations., Comment: 31 pp. Minor corrections in the revised version

The Skenderis-van Rees prescription, which allows the calculation of time-ordered correlation functions of local operators in CFT's using holographic methods is studied and applied for excited states. Calculation of correlators and matrix elements of local CFT operators between generic in/out states are carried out in global Lorentzian AdS. We find the precise form of such states, obtain an holographic formula to compute the inner product between them, and using the consistency with other known prescriptions, we argue that the in/out excited states built according to the Skenderis-Van Rees prescription correspond to {\it coherent} states in the (large-$N$) AdS-Hilbert space. This is confirmed by explicit holographic computations. The outcome of this study has remarkable implications on generalizing the Hartle-Hawking construction for wave functionals of excited states in AdS quantum gravity., Comment: 16 pages, 6 figures, accepted for publication by JHEP

Optimizing information transmission across a network is an essential task for controlling and manipulating generic information-processing systems. Here, we show how topological amplification effects in scale-free networks of signaling devices are optimally enhanced when the $\it{impulse}$ transmitted by periodic external signals (time integral over two consecutive zeros) is maximum. This is demonstrated theoretically by means of a star-like network of overdamped bistable systems subjected to $\it{generic}$ zero-mean periodic signals, and confirmed numerically by simulations of scale-free networks of such systems. Our results show that the enhancer effect of increasing values of the signal's impulse is due to a correlative increase of the energy transmitted by the periodic signals, while it is found to be resonant-like with respect to the topology-induced amplification mechanism., Comment: arXiv admin note: text overlap with arXiv:1412.3583