[8][9][10][11] . Here, we demonstrate on- as schematized in Fig. 1. In particular, we used a spectrally-filtered mode-locked laser to excite a single resonance of the microring at ~1550 nm wavelength, in turn producing pairs of correlated signal and idler photons spectrally-symmetric to the excitation field and which cover multiple resonances, see Fig. 1. The individual photons were intrinsically generated in a superposition of multiple frequency modes and owing the energy conservation of SFWM, this approach leads to the realization of a two-photon high-dimensional frequency-entangled state.We performed two experiments to characterize the dimensionality of the generated state. The large free spectral range (FSR) of the ring cavity (~200 GHz), i.e. the spectral separation between adjacent resonance modes, enabled us to use a commercially available telecommunications programmable filter (see Methods) for individually selecting and manipulating the states in these modes (given the filter's operational bandwidth of 1527.4 to 1567.5 nm, we were able to access 10 signal and 10 idler resonances). We measured the joint spectral intensity, describing the twophoton state's frequency distribution, see Methods. Specifically, we routed different frequency 4 modes of the signal and idler photons to two single photon detectors and counted photon coincidences for all sets of mode combinations. As shown in Fig. 2a, photon coincidences were measured only for mode combinations spectrally-symmetric to the excitation, a characteristic of frequency-entangled states. In addition, we evaluate the Schmidt number of our source. This parameter describes the lowest number of significant orthogonal modes in a bipartite system, and therefore describes its effective dimension. Through a Schmidt mode decomposition of the correlation matrix (see Methods), we extracted the lower bound for the Schmidt number to be 9.4, see Fig. 2b.Due to the narrow spectral linewidth of the photons (~800 MHz) and the related long coherence time (~0.6 ns), the effective time resolution of our full detection system (~100 ps) was sufficient to perform time-domain measurements and extract the maximal dimensionality of the state, seeMethods. Specifically, we measured the second-order coherence of the signal and idler fields using These measurements confirmed that one photon pair simultaneously spans multiple frequency modes, forming a high-dimensional entangled state of the form, with ∑| | 2 = 1 (Eq. 1).Here | ⟩ s and | ⟩ i are pure, single-frequency quantum states of the signal (s) and idler (i) photons, and k=1,2,…,D is the mode number, as indicated in Fig. 3 In general, the exploitation of quDit states for quantum information processing motivates the need for high-dimensional operations that enable access to multiple modes with a minimum number of components. While the individual elements (phase shifters and beam splitters) employed in the framework of spatial-mode quantum information processing usually operate on only one or two modes at a time 1 , the frequency...

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Integrated Microwave photonics (IMWP) signal processing using Photonic Integrated Circuits (PICs) has attracted a great deal of attention in recent years as an enabling technology for a number of functionalities not attainable by purely microwave solutions. In this context, integrated waveguide Bragg grating (WBG) devices constitute a particularly attractive approach thanks to their compactness and flexibility in producing arbitrarily defined amplitude and phase responses, by directly acting on coupling coefficient and perturbations of the grating profile. In this article, we review recent advances in the field of integrated WBGs applied to MWP, analyzing the advantages leveraged by an integrated realization. We provide a perspective on the exciting possibilities offered by the silicon photonics platform in the field of MWP, potentially enabling integration of highly-complex active and passive functionalities with high yield on a single chip, with a particular focus on the use of WBGs as basic building blocks for linear filtering operations. We demonstrate the versatility of WBG-based devices by proposing and experimentally demonstrating a novel, continuously-tunable, integrated true-time-delay (TTD) line based on a very simple dual phase-shifted WBG (DPS-WBG).

Mitochondrial calcium (Ca 2ϩ ) dyshomeostasis constitutes a critical step in the metabolic crossroads leading to cell death. Therefore, we have studied here whether 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one (CGP37157; CGP), a blocker of the mitochondrial Na . This drastic cytoprotective effect of CGP could be explained in part through its regulatory actions on the mNCX.In general, it is accepted that a dysregulation of the mechanism that fine tunes the transient or more sustained levels of the cytosolic Ca 2ϩ concentrations ([Ca 2ϩ ] c ), leads to excitotoxic neuronal death (Schanne et al., 1979) and to neurodegeneration (Mattson, 2007). However, Ca 2ϩ may behave as both a cell survival supporter and a cell death inducer. For instance, cell depolarization and subsequent Ca 2ϩ entry into the cytosol helps to sustain the survival of cerebellar granule cells (Gallo et al., 1987) and bovine chromaffin cells (Orozco et al., 2006). However, chronic elevation of [Ca 2ϩ ] c by ionophores induces apoptosis (Martikainen et al., 1991). The opposite is also true, i.e., Ca 2ϩ antagonists that reduce [Ca 2ϩ ] c also cause neuronal death (Koh and Cotman, 1992) and chromaffin cell death (Novalbos et al., 1999). These apparent contradictory findings may be explained in the frame of the hypothesis suggesting that the [Ca 2ϩ ] c changes occurring during cell activation must move within a critical set point; beyond this point a cytoprotective signal might turn into a cytotoxic one (Koike et al., 1989). In this context, the suggestion of Nicholls (1985) and White and Reynolds (1995) that Ca 2ϩ accumulation into mitochondria could play a neuropro- Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.109.154765.ABBREVIATIONS: mNCX, mitochondrial Na ϩ /Ca 2ϩ -exchanger; DMSO, dimethyl sulfoxide; FPL64176, FPL, 2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylic acid methyl ester; 30 K ϩ /FPL, 30 mM K ϩ /0.3 M FPL; MTT formazan, 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan, thiazolyl blue formazan; CGP37157, 7-chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one; TTX, tetrodotoxin citrate, octahydro-12-(hydroxymethyl)-2-imino-5,9:7,10a-dimethan o-10aH- [1,3] dioxocino [6,5-d]pyrimidine

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The investigation of integrated frequency comb sources characterized by equidistant spectral modes was initially driven by considerations towards classical applications, seeking a more practical and miniaturized way to generate stable broadband sources of light. Recently, in the context of scaling the complexity of optical quantum circuits, these on-chip approaches have provided a new framework to address the challenges associated with non-classical state generation and manipulation. For example, multi-photon and high-dimensional states were to date either inaccessible, lacked scalability, or were difficult to manipulate, requiring elaborate approaches. The emerging field of quantum frequency combs studying spectral multimode Manuscript

The development of quantum technologies for quantum information (QI) science demands the realization and precise control of complex (multipartite and high dimensional) entangled systems on practical and scalable platforms. Quantum frequency combs (QFCs) represent a powerful tool towards this goal. They enable the generation of complex photon states within a single spatial mode as well as their manipulation using standard fiber-based telecommunication components. Here, we review recent progress in the development of QFCs, with a focus on results that highlight their importance for the realization of complex quantum states. In particular, we outline recent work on the use of integrated QFCs for the generation of high-dimensional multipartite optical cluster states -lying at the basis of measurement-based quantum computation. These results confirm that the QFC approach can provide a stable, practical, low-cost, and established platform for the development of quantum technologies, paving the way towards the advancement of QI science for out-of-the-lab applications, ranging from practical quantum computing to more secure communications. Index Terms-coherent control of photon states, computing and information science, fiber-based telecommunications, highdimensional multipartite entanglement, photon cluster states, photonic integrated circuits, practical and scalable quantum technology, quantum frequency combs.

Broadband radio-frequency chirped waveforms (RFCWs) with dynamically tunable parameters are of fundamental interest to many practical applications. Recently, photonic-assisted solutions have been demonstrated to overcome the bandwidth and flexibility constraints of electronic RFCW generation techniques. However, state-of-the-art photonic techniques involve broadband mode-locked lasers, complex dual laser systems, or fast electronics, increasing significantly the complexity and cost of the resulting platforms. Here we demonstrate a novel concept for photonic generation of broadband RFCWs using a simple architecture, involving a single CW laser, a recirculating frequency-shifting loop, and standard low-frequency electronics. All the chirp waveform parameters, namely sign and value of the chirp rate, central frequency and bandwidth, duration and repetition rate, are easily reconfigurable. We report the generation of mutually coherent RF chirps, with bandwidth above 28 GHz, and time-bandwidth product exceeding 1000, limited by the available detection bandwidth. The capabilities of this simple platform fulfill the stringent requirements for real-world applications.