A linear-optics quantum computer 5 requires hundreds to thousands of single-photon components including sources, detectors and interferometers, which is obviously only feasible in an integrated circuit.Even the small-scale circuits needed in quantum repeaters 2 would greatly benefit from monolithic integration in view of the improved stability and coupling efficiency attainable in a chip. A very large experimental research activity has been dedicated to the development of single-photon sources based on III-V semiconductors 10 , in view of large-scale integration, and to passive quantum circuits based on silica-onsilicon 6 and on laser-micromachined glass 8,9 , but a clear approach towards a fully integrated photonic network including sources and detectors has not been proposed. This is in large part due to the complexity of most single-photon detector technologies -for example, the complex device structures associated to avalanche photodiodes are not easily compatible with the integration of low-loss waveguides and even less of sources. Transition-edge sensors may be suited for integration 11 , but they are plagued by very slow response times (leading to maximum counting rates in the tens of kHz range) and require cooling down to <100 mK temperatures. Here we propose a platform for the full integration of quantum photonic components on the same chip. It is based on the mature III-V semiconductor technology and comprises ( Fig. 1(a) ) waveguide single-photon sources based on InAs quantum dots (QDs), GaAs/AlGaAs ridge waveguides, Mach-Zehnder interferometers using directional couplers or multimode-interference couplers, and 3 waveguide detectors based on superconducting nanowires. Efficient single-photon emission from QDs in a waveguide can be obtained by using photonic crystals (PhCs), e.g. in a cavity side-coupled to a waveguide 12 or using the slow-light regime in PhC waveguides 13 , and the photons can then be transferred to ridge waveguides using tapers. Photons emitted by distinct QDs can be made indistinguishable by using electric fields to control the exciton energy 14 . The high index contrast available in the GaAs/AlGaAs system allows circuits with short bending radii, therefore more compact than in the silica platform 6 , while the large electrooptic coefficient of GaAs enables compact modulators operating at GHz frequencies. In this letter we report the key missing component, a single-photon detector integrated with GaAs waveguides. Our waveguide single-photon detectors (WSPDs) are based on the principle of photon-induced hot-spot creation in ultranarrow superconducting NbN wires, which is also used in nanowire superconducting single-photon detectors 15 (SSPDs) and can provide ultrahigh sensitivity at telecommunication wavelengths, high counting rates, broad spectral response and high temporal resolution due to low jitter values. In our design (see Fig. 1(b)), the wires are deposited and patterned on top of a GaAs ridge waveguide, in order to sense the evanescent field on the surface. Four NbN nanowi...

(v , 0) Werner bands for v = 0-4, using a narrow-band tunable extreme UV laser source at wavelengths λ = 92-105 nm in conjunction with the technique of 1 + 1 two-photon ionization. The measurements can be divided into three categories for which varying absolute accuracies were obtained. Special focus was on the B, v = 2-5 bands, where an accuracy of 0.004 cm −1 or δν/ν = 4 × 10 −8 is achieved. For transitions to B, v ≤ 13 and C, v ≤ 3 states the accuracy is 0.005 cm −1 or δν/ν = 5 × 10 −8 . Due to a different frequency mixing scheme uncertainties for B, v ≥ 13 and C, v = 4 are at the level of 0.011 cm −1 or δν/ν = 1.1 × 10 −7 . Inspection of combination differences between R(J ) and P(J + 2) lines shows that the accuracies are even better than estimated in the error budget. Based on the measurements of 138 spectral lines and the known combination differences, transition frequencies of 60 P-lines could be calculated as well, so that a data base of 198 accurately calibrated lines results for the Lyman and Werner bands of H 2 .Key words: vacuum UV, molecular spectroscopy, hydrogen, precision metrology. . Un examen des différences des combinaisons entre les raies R(J ) et P(J + 2) montre que les précisions sont meilleures que celles évaluées dans le budget des erreurs. Sur la base de mesures de 138 raies spectrales et de différences de combinaison connues, on a pu aussi calculer les fréquences de transition de 60 raies P et il en résulte qu'une base de données de 198 raies bien calibrées est disponible pour les bandes de Lyman et de Werner du H 2 .

Extreme ultravioletϩultraviolet ͑XUVϩUV͒ two-photon ionization spectra of the b 1 ⌸ u (v ϭ0-9), c 3 1 ⌸ u (vϭ0,1), o 1 ⌸ u (vϭ0,1), c 4 Ј 1 ⌺ u ϩ (vϭ1) and bЈ 1 ⌺ u ϩ (vϭ1,3-6) states of 15 N 2 were recorded with a resolution of 0.3 cm Ϫ1 full-width at half-maximum ͑FWHM͒. In addition, the b 1 ⌸ u (vϭ1,5-7) states of 14 N 15 N were investigated with the same laser source. Furthermore, using an ultranarrow bandwidth XUV laser ͓ϳ250 MHz (ϳ0.01 cm Ϫ1) FWHM͔, XUVϩUV ionization spectra of the b 1 ⌸ u (vϭ0-1,5-7), c 3 1 ⌸ u (vϭ0), o 1 ⌸ u (vϭ0), c 4 Ј 1 ⌺ u ϩ (vϭ0), and bЈ 1 ⌺ u ϩ (v ϭ1) states of 15 N 2 were recorded in order to better resolve the band-head regions. For 14 N 15 N, ultrahigh resolution spectra of the b 1 ⌸ u (vϭ0-1,5-6), c 3 1 ⌸ u (vϭ0), and bЈ 1 ⌺ u ϩ (vϭ1) states were recorded. Rotational analyses were performed for each band, revealing perturbations arising from the effects of Rydberg-valence interactions in the 1 ⌸ u and 1 ⌺ u ϩ states, and rotational coupling between the 1 ⌸ u and 1 ⌺ u ϩ manifolds. Finally, a comprehensive perturbation model, based on the diabatic-potential representation used previously for 14 N 2 , and involving diagonalization of the full interaction matrix for all Rydberg and valence states of 1 ⌺ u ϩ and 1 ⌸ u symmetry in the energy window 100 000-110 000 cm Ϫ1 , was constructed. Term values for 15 N 2 and 14 N 15 N computed using this model were found to be in good agreement with experiment.

High-resolution laser-based one extreme-ultraviolet ͑EUV͒ + one UV two-photon ionization spectroscopy and EUV photoabsorption spectroscopy have been employed to study spin-forbidden 3 ⌸ u -X 1 ⌺ g + ͑v ,0͒ transitions in 14 N 2 and 15 N 2 . Levels of the C 3 ⌸ u valence and 3s g F 3 and 3p u G 3 3 ⌸ u Rydberg states are characterized, either through their direct optical observation, or, indirectly, through their perturbative effects on the 1 ⌸ u and 1 ⌺ u + states, which are accessible in dipole-allowed transitions. Optical observation of the G 3 -X͑0,0͒ and ͑1,0͒ transitions is reported for the first time, together with evidence for six new vibrational levels of the C state. Following the recent observation of the F 3 -X͑0,0͒ transition at rotational resolution ͓J. P. Sprengers et al., J. Chem. Phys. 123, 144315 ͑2005͔͒, the F 3 ͑v =1͒ level is found to be responsible for a local perturbation in the rotational predissociation pattern of the bЈ 1 ⌺ u + ͑v =4͒ state. Despite their somewhat fragmentary nature, these new observations provide a valuable database on the 3 ⌸ u states of N 2 and their interactions which will help elucidate the predissociation mechanisms for the nitrogen molecule.

Lifetime and predissociation yield of N-14(2) b (1)Pi(u)(v=1) revisited: Effects of rotationLewis,

The lifetime of the b 1 ⌸ u (vϭ1) state in 14 N 2 has been determined experimentally using a laser-based pump-probe scheme and an exceptionally long lifetime of 2.61 ns was found. Semiempirical close-coupling calculations of the radiative lifetime, which include Rydberg-valence interactions in the singlet manifold, are consistent with this large value, giving a value of 3.61 ns and suggesting a predissociation yield of ϳ28% for this level of the b state.

N 2 are recorded at ultrahigh resolution, using a narrow band tunable XUV-laser source. Lifetimes are derived from the linewidths of single rotationally resolved spectral lines after deconvolution of the instrument function. The observed lifetimes depend on the vibrational quantum number and are found to be strongly isotope dependent.

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