Spatio-temporal entanglement of twin photons: an intuitive picture

We draw an intuitive picture of the spatio-temporal properties of the entangled state of twin photons, where they are described as classical wave-packets. This picture predicts a precise relation between their temporal and transverse spatial separations at the crystal output. The space-time coupling described by classical arguments turns out to determine in a precise way the spatio-temporal structure of the quantum entanglement, analysed by means of the biphotonic correlation and of the Schmidt dimensionality of the entanglement.Comment: 12 pages, 3 figure

On-chip Quantum State Generation by Means of Integrated Frequency Combs

Summary form only given. This paper investigates different approaches to generate optical quantum states by means of integrated optical frequency combs. These include the generation of multiplexed heralded single-photons, the first realization of cross-polarized photon-pairs on a photonic chip, the first generation of multiple two-photon entangled states, and the first realizations of multi-photon entangled quantum states on a photonic chip

Changes in quality of life and functional capacity after lung transplantation: A single-center experience

Lung transplantation (LT) increases the life expectancy of patients affected by end stage pulmonary disease; specifically, its ultimate aims are to improve survival and health related quality of life (HRQoL). The aim of the present longitudinal study was to determine the HRQoL trajectory and changes in functional capacity from time of entry in the waiting list for LT to 2 year after LT. The study included sixty-nine outpatients enrolled in a single medical center when they entered the waiting list for LT and who subsequently received it. They were then followed up over 2 years after LT. HRQoL was assessed by the physical and mental component summary (PCS and MCS) scores of the 36-item Short Form Health Survey (SF-36) and Saint George's Respiratory Questionnaire (SGRQ). Psychological distress was evaluated with the General Health Questionnaire (GHQ), and functional capacity was investigated using the six-minute walk test (6MWT) and forced expiratory volume (FEV1). Patients showed low SF-36 PCS (30.5±7.8) and SGRQ total (61.8±17.5) scores at entry in the waiting list, but exhibited significant changes over time after LT (p<0.001). Furthermore, patients who showed an increase of at least 50% in SF36 PCS and SGRQ scores at 6 months survived longer. Both FEV1 and 6MWT distance as well as GHQ scores significantly changed over time, with improvements occurring in the first 6 months after LT but no major changes thereafter. Out of the 69 patients enrolled, 32 died over a median follow-up of 51 months. Although mortality tended to be slightly higher for patients with lower HRQoL at the baseline assessment, this difference was not statistically significant. HRQoL evaluations appear critical in the follow-up of LT candidates, in particularly SGRQ, because of its specificity in targeting respiratory symptoms and functional wellbeing

Generation of Complex Quantum States Via Integrated Frequency Combs

The generation of optical quantum states on an integrated platform will enable low cost and accessible advances for quantum technologies such as secure communications and quantum computation. We demonstrate that integrated quantum frequency combs (based on high-Q microring resonators made from a CMOS-compatible, high refractive-index glass platform) can enable, among others, the generation of heralded single photons, cross-polarized photon pairs, as well as bi- and multi-photon entangled qubit states over a broad frequency comb covering the S, C, L telecommunications band, constituting an important cornerstone for future practical implementations of photonic quantum information processing

Single-frequency optical parametric oscillator intracavity-pumped by a visible VECSEL for low-noise down-conversion to 1.55 µm

We report, to the best of our knowledge, the first optical parametric oscillator (OPO) pumped by a visible AlGaInP-based vertical-external-cavity surface-emitting laser (VECSEL). Tunable emission over 1155–1300 nm in the signal and 1474–1718 nm in the idler are observed by temperature adjustment of a 40 mm-long 5%-MgO:PPLN crystal intracavity-pumped at 690 nm. When optimized for low oscillation threshold, and by implementing resonant idler output-coupling (TOC = 1.7%), extracted output powers of 26.2 mW (signal) and 5.6 mW (idler; one-way) are measured, corresponding to a total down-conversion efficiency and extraction efficiency of 70.2% and 43%, respectively. Further, a total down-conversion efficiency of 72.1% is achieved in the absence of idler output-coupling. Of particular interest for high-precision applications, including quantum optics experiments and squeezed light generation, high stability and single-frequency operation are also demonstrated. We measure RMS stabilities of 0.4%, 1.8% and 2.3% for the VECSEL fundamental, signal and idler, with (resolution-limited) frequency linewidths of 2.5 MHz (VECSEL) and 7.5 MHz (signal and idler)

Integrated sources of photon quantum states based on nonlinear optics

The ability to generate complex optical photon states involving entanglement between multiple optical modes is not only critical to advancing our understanding of quantum mechanics but will play a key role in generating many applications in quantum technologies. These include quantum communications, computation, imaging, microscopy and many other novel technologies that are constantly being proposed. However, approaches to generating parallel multiple, customisable bi- and multi-entangled quantum bits (qubits) on a chip are still in the early stages of development. Here, we review recent developments in the realisation of integrated sources of photonic quantum states, focusing on approaches based on nonlinear optics that are compatible with contemporary optical fibre telecommunications and quantum memory infrastructures as well as with chip-scale semiconductor technology. These new and exciting platforms hold the promise of compact, low-cost, scalable and practical implementations of source s for the generation and manipulation of complex quantum optical states on a chip, which will play a major role in bringing quantum technologies out of the laboratory and into the real world

Measurement of sub-shot-noise spatial correlations without subtraction of background

In this paper we present the first measurement of sub-shot-noise spatial correlations without any subtraction of background, a result opening the way to realize sub-shot-noise imaging of weak objectsComment: 4 pages, 4 figure

Universal N-partite d-level pure-state entanglement witness based on realistic measurement settings

Entanglement witnesses are operators that are crucial for confirming the generation of specific quantum systems, such as multipartite and high-dimensional states. For this reason, many witnesses have been theoretically derived which commonly focus on establishing tight bounds and exhibit mathematical compactness as well as symmetry properties similar to that of the quantum state. However, for increasingly complex quantum systems, established witnesses have lacked experimental achievability, as it has become progressively more challenging to design the corresponding experiments. Here, we present a universal approach to derive entanglement witnesses that are capable of detecting the presence of any targeted complex pure quantum system and that can be customized towards experimental restrictions or accessible measurement settings. Using this technique, we derive experimentally optimized witnesses that are able to detect multipartite d -level cluster states, and that require only two measurement settings. We present explicit examples for customizing the witness operators given different realistic experimental restrictions, including witnesses for high-dimensional entanglement that use only two-dimensional projection measurements. Our work enables us to confirm the presence of probed quantum states using methods that are compatible with practical experimental realizations in different quantum platforms

CCD-based imaging and 3D space--time mapping of terahertz fields via Kerr frequency conversion

We investigate the spatially and temporally resolved four-wave mixing of terahertz (THz) fields and optical pulses in large-bandgap dielectrics, such as diamond. We show that it is possible to perform beam profiling and space–time resolved mapping of THz fields by encoding the spatial information into an optical signal, which can then be recorded by a standard CCD camera