| 1. |
- Almlof, Jonas, et al.
(författare)
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Creating and detecting specious randomness
- 2023
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Ingår i: EPJ QUANTUM TECHNOLOGY. - : Springer Nature. - 2662-4400 .- 2196-0763. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a new test of non-randomness that tests both the lower and the upper critical limit of a chi 2-statistic. While checking the upper critical value has been employed by other tests, we argue that also the lower critical value should be examined for non-randomness. To this end, we prepare a binary sequence where all possible bit strings of a certain length occurs the same number of times and demonstrate that such sequences pass a well-known suite of tests for non-randomness. We show that such sequences can be compressed, and therefore are somewhat predictable and thus not fully random. The presented test can detect such non-randomness, and its novelty rests on analysing fixed-length bit string frequencies that lie closer to the a priori probabilities than could be expected by chance alone.
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| 2. |
- Almlöf, Jonas, et al.
(författare)
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Creating and detecting specious randomness
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a new test of non-randomness that tests both the lower and the upper critical limit of aχ2-statistic. While checking the upper critical value has been employed by other tests, we argue that also the lower critical value should be examined for non-randomness. To this end, we prepare a binary sequence where all possible bit strings of a certain length occurs the same number of times and demonstrate that such sequences pass a well-known suite of tests for non-randomness. We show that such sequences can be compressed, and therefore are somewhat predictable and thus not fully random. The presented test can detect such non-randomness, and its novelty rests on analysing fixed-length bit string frequencies that lie closer to the a priori probabilities than could be expected by chance
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| 3. |
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| 4. |
- Feyer, Vitaliy, et al.
(författare)
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Tautomerism in Cytosine and Uracil : An Experimental and Theoretical Core Level Spectroscopic Study
- 2009
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 113:19, s. 5736-5742
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Tidskriftsartikel (refereegranskat)abstract
- The O, N, and C 1s core level photoemission spectra of the nucleobases cytosine and uracil have been measured in the vapor phase, and the results have been interpreted via theoretical calculations. Our calculations accurately predict the relative binding energies of the core level features observed in the experimental photoemission results and provide a full assignment. In agreement with previous work, a single tautomer of uracil is populated at 405 K, giving rise to relatively simple spectra. At 450 K, three tautomers of cytosine, one of which may consist of two rotamers, are identified, and their populations are determined. This resolves inconsistencies between recent laser studies of this molecule in which the rare imino-oxo tautomer was not observed and older microwave spectra in which it was reported.
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| 5. |
- Gyger, Samuel, et al.
(författare)
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Metropolitan single-photon distribution at 1550 nm for random number generation
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:19, s. 194003-
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Tidskriftsartikel (refereegranskat)abstract
- Quantum communication networks will connect future generations of quantum processors, enable metrological applications, and provide security through quantum key distribution. We present a testbed that is part of the municipal fiber network in the greater Stockholm metropolitan area for quantum resource distribution through a 20 km long fiber based on semiconductor quantum dots emitting in the telecom C-band. We utilize the service to generate random numbers passing the NIST test suite SP800-22 at a subscriber 8 km outside of the city with a bit rate of 23.4 kbit/s.
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| 6. |
- Gyger, Samuel, et al.
(författare)
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Metropolitan Single-Photon Distribution at 1550 nm for Random Number Generation
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics, CLEO 2023. - : Institute of Electrical and Electronics Engineers Inc..
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Konferensbidrag (refereegranskat)abstract
- Quantum communication networks are used for QKD and metrological applications. We present research connecting two nodes ≈ 20 kilometers apart over the municipal fiber network using semiconductor quantum dots emitting at 1550 nm.
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| 7. |
- Jakubowska, Katarzyna, et al.
(författare)
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Lyman and Balmer emission following core excitations in methane and ammonia molecules
- 2007
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:8, s. 1489-1500
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Tidskriftsartikel (refereegranskat)abstract
- The intensities of hydrogen Lyman-alpha and Balmer series emission lines as a result of photoexcitation of free CH4 and NH3 molecules at the C 1s and N 1s edges have been measured. For methane, the total fluorescence yield in the visible region ( 300 - 650 nm) was also recorded. Excitation functions of the Balmer lines show relative intensity enhancement of Balmer-beta emission in comparison with Balmer-alpha at higher core- to- Rydberg excitations. The Lyman-alpha emission intensity, in general, follows the relations observed in the corresponding total ion yield measurements. Additionally, the Balmer-gamma and -delta yields were measured for ammonia molecules and they show intensity maxima at photon energies shifted closer to the N 1s threshold than Balmer-alpha and -beta. A quantum defect analysis is performed to find out which core excitations are responsible for this enhanced intensity. Dissociation pathways leading to the emission in H atoms are discussed.
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| 8. |
- Kivimaki, A., et al.
(författare)
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Fluorescence emission at core-to-Rydberg excitations in the N-2 molecule
- 2009
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 42:18
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence emission at the N 1s edge of the N-2 molecule has been studied with synchrotron radiation excitation. The partial fluorescence yields in the ultraviolet (250-320 nm) and visible (300-650 nm) wavelengths were collected by scanning the photon energy across the core-to-Rydberg excitations and the N 1s ionization potential (IP). When compared to the total ion yield, both fluorescence yields are most enhanced at the excitations to high Rydberg orbitals. A discrete structure appears just below the N 1s IP only in the UV yield and is assigned to core-valence doubly excited states. Dispersed fluorescence spectra in selected wavelength windows were measured at several photon energies in order to find out which fragments are responsible for the enhancement of fluorescence emission just below the N 1s IP. The excitation functions determined and considerations on de-excitation pathways indicate that the main responsible is the N+ ion.
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| 9. |
- Kivimaki, A., et al.
(författare)
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Line shape narrowing in the ultraviolet yield at the N 1s -> pi* resonance of the N-2 molecule
- 2009
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 42:7
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Tidskriftsartikel (refereegranskat)abstract
- The intensity of fluorescence emission in the wavelength region of 250-320 nm has been measured across the N 1s -> pi* resonance of the N-2 molecule. It displays a narrower line shape than the total ion yield recorded simultaneously. We explain the finding by the particularities of the resonant Auger transitions from the N 1s(-1) pi* state to the D-2 Pi(g) state in N-2(+) and by the subsequent D-2 Pi(g) -> A(2)Pi(u) emission.
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| 10. |
- Kivimäki, Antti, et al.
(författare)
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Fluorescence emission following core excitations in the water molecule
- 2006
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:5, s. 1101-1112
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Tidskriftsartikel (refereegranskat)abstract
- Photon-induced fluorescence spectroscopy has been used to study the fragmentation of the water molecule at the O 1s is edge. Fluorescence emission has been observed from the neutral fragments H, O and OH as well as from the ionic fragments O+ and OH+. The extracted fluorescence yields of the H Lyman-alpha emission and O 2p(3)(S-4)3p(P-3) -> 2p(3)(S-4)3s(S-3) transitions show the same structures as the total ion yield spectrum but with different relative intensities. The most intense fluorescence emission is restricted to the region of the core excitations, while above the O 1s ionization limit the signal is much weaker (in the case of H) or below the detection limit (O, OH and OH+). The fluorescence emission is concluded to follow from the following general cascade: the core-excited states decay by resonant Auger transitions, the final states reached undergo dissociation into ionic and neutral fragments, and fluorescence occurs from excited fragments. In the case of the OH (A(2)Sigma(+) -> X-2 Pi) emission, the decay of core-excited states through soft x-ray emission may also be responsible for the observed fluorescence.
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| 11. |
- Plekan, Oksana, et al.
(författare)
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An Experimental and Theoretical Core-Level Study of Tautomerism in Guanine
- 2009
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 113:33, s. 9376-9385
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Tidskriftsartikel (refereegranskat)abstract
- The core level photoemission and near edge X-ray photoabsorption spectra of guanine in the gas phase have been measured and the results interpreted with the aid of high level ab initio calculations. Tautomers are clearly identified spectroscopically, and their relative free energies and Boltzmann populations at the temperature of the experiment (600 K) have been calculated and compared with the experimental results and with previous calculations. We obtain good agreement between experiment and the Boltzmann weighted theoretical photoemission spectra, which allows a quantitative determination of the ratio of oxo to hydroxy tautomer populations. For the photoabsorption spectra, good agreement is found for the C 1s and I 1s spectra but only fair agreement for the N 1s edge.
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| 12. |
- Urban, Patryk, et al.
(författare)
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Detection of Fiber Faults in Passive Optical Networks
- 2013
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Ingår i: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 5:11, s. 1111-1121
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Tidskriftsartikel (refereegranskat)abstract
- Wider deployment of fiber in the last mile is driven by increased customer needs for broadband communication services. This deployment requires solutions that reduce operational expenditures for the operator. A cost-efficient fully reliable and accurate monitoring solution supporting fault detection, identification, and localization in different fiber access architectures will be essential. In this article, we present a fast, automatic, and precise monitoring method applicable to both power-splitter- and wavelength-router-based passive optical networks through the combined techniques of optical time domain reflectometry and optical transceiver monitoring. The description of the architecture, components, and process flow is followed by tests on setups with live data transmission.
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| 13. |
- Vall-Llosera, Gemma
(författare)
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Flourescence properties of trendy molecules studied with synchrotron radiation
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis summarises the experimental results on molecular spectroscopy of gas phase molecules using synchrotron radiation in the UV- VUV and soft-X rays regions. The results of applying Photon Induced Fluorescence Spectroscopy (PIFS) to D2, H2S, H2O and pyrimidine are presented and discussed. Both inner and outer shell excitations of free molecules lead to different relaxation processes. However, a common result is that when the molecule breaks and the resulting neutral fragments are left in an excited state, they might fluoresce in the UV- Vis range. PIFS technique has two main advantages, it permits to detect neutral fragments and to identify the fluorescing species. From this fact, we can infer dissociation channels and trace back the electronic processes that led to the fluorescence. For these molecules we have analysed and interpreted both dispersed and undispersed fluorescence. What motivates our work is the lack of fluorescence studies and in a more general sense, to contribute to the knowledge of important molecules for life such as water and pyrimidine.
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| 14. |
- Vall-llosera, Gemma, et al.
(författare)
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Fluorescence emission from photo-fragments after resonant S 2p excitations in H2S
- 2007
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 9:3, s. 389-395
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Tidskriftsartikel (refereegranskat)abstract
- Visible-UV fluorescence emission of gas-phase hydrogen sulfide, H2S, has been studied at the S 2p edge with synchrotron radiation excitation. Dispersed fluorescence measurements in the wavelength range 300 - 900 nm were taken at several photon energies corresponding to the excitations of the S 2p electrons to the unoccupied molecular and Rydberg orbitals. The spectra reveal fluorescence from the H, S, S+, HS and HS+ photo-fragments. H is found to be the strongest emitter at Rydberg excitations, while the emission from S+ is dominant at the molecular resonances and above the S 2p ionization thresholds. The intensities of hydrogen Lyman-alpha (122 nm), Balmer-alpha (656 nm), Balmer-beta (486 nm) transitions as well as the visible-UV total fluorescence yield (300 - 900 nm) and the total ion yield were measured by scanning the photon energy in small steps across the S 2p edge. The different Balmer lines show some sensitivity to the specific core excitations, which is, however, not so strong as that recently observed in the water molecule.
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| 15. |
- Vall-llosera, Gemma, et al.
(författare)
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Photofragmentation of 2-deoxy-D-ribose molecules in the gas phase
- 2008
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 9:7, s. 1020-1029
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the synchrotron-induced photofragmentation of isolated 2-deoxy-D-ribose molecules (C5H10O4) at four photon energies, namely, 23.0, 15.7, 14.6, and 13.8 eV At all photon energies above the molecule's ionization threshold, we observe the formation of a large variety of molecular cation fragments, including CH3+, OH+, H3O+, C2H3+, C2H4+, CHxO+ (x=1,2,3), C2HxO+ (x=1-5), C3HxO+ (x=3-5), C2H4O2+, C3HxO2+ (x=1,2,4-6), C4H5O2+, C4HxO3+ (x=6,7), C5H7O3+, and C5H8O3+. The formation of these fragments shows a strong propensity of the DNA sugar to dissociate upon absorption of vacuum ultraviolet photons. The yields of particular fragments at various excitation photon energies in the range between 10 and 28 eV are also measured and their appearance thresholds determined. At all photon energies, the most intense relative yield is recorded for the m/q = 57 fragment (C3H5O+), whereas a general intensity decrease is observed for all other fragments- relative to the m/q=57 fragment-with decreasing excitation energy. Thus, bond cleavage depends on the photon energy deposited in the molecule. All fragments up to m/q=75 are observed at all photon energies above their respective threshold values. Most notably, several fragmentation products, for example, CH3+, H3O+, C2H4+, CH3O+, and C2H5O+, involve significant bond rearrangements and nuclear motion during the dissociation time. Multibond fragmentation of the sugar moiety in the sugar-phosphate backbone of DNA results in complex strand lesions and, most likely, in subsequent reactions of the neutral or charged fragments with the surrounding DNA molecules.
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| 16. |
- Vall-llosera, Gemma, 1975-
(författare)
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Synchrotron radiation studies of gas phase molecules : from hydrogen to DNA sugars
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis summarises experimental results on the molecular spectroscopy of gas phase molecules excited by synchrotron radiation in the VUV and soft X-ray regions. We have used three different detection techniques, photon induced fluorescence spectroscopy, photoionisation mass spectroscopy and near edge X-ray absorption fine structure spectroscopy to study molecular deuterium, hydrogen sulphide, ammonia, methanol, pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, and 2-deoxy-D-ribose, the last one also known as the DNA sugar. Out of this variety of techniques and molecules we have shown that: (1) high resolution dispersed fluorescence allows us to identify vibrational and rotational bands in molecular deuterium, as well as to estimate the predissociation probability of the same molecule [paper I]; (2) the main species fluorescing after core excitation of methane, ammonia [paper III], hydrogen sulphide [paper II], pyridine, pyrimidine and s-triazine is H Balmer α, followed by fluorescence from ionised species, molecular bands and Balmer β, γ , δ; (3) the Rydberg enhancement seen in fluorescence measurements of water [Melero et al. PRL 96 (2006) 063003], corroborated later in H2S [paper II], NH3 [paper III] and CH4 [paper III] and postulated as general behaviour for molecules formed by low-Z atoms, is also seen in larger organic cyclic molecules, e.g. azabenzenes; (4) when dissociative ionisation of pyridine, pyridazine, pyrimidine, pyrazine, s-triazine and 2-deoxy-D-ribose occurs, concerted bond rearrangement and nuclear motion takes place as opposed to stepwise dissociation [papers V and VI].
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| 17. |
- Vall-llosera, Gemma, et al.
(författare)
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The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4, s. 044316-1-044316-12
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Tidskriftsartikel (refereegranskat)abstract
- Near edge x-ray absorption fine structure spectra have been measured and interpreted by means of density functional theory for five different azabenzenes (pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine) in the gas phase. The experimental and theoretical spectra at the N 1s and C 1s edges show a strong resonance assigned to the transition of the 1s electron in the respective N or C atoms to the lowest unoccupied molecular orbital with pi* symmetry. As opposed to the N 1s edge, at the C 1s edge this resonance is split due to the different environments of the core hole atom in the molecule. The shift in atomic core-level energy due to a specific chemical environment is explained with the higher electronegativity of the N atom compared to the C atom. The remaining resonances below the ionization potential (IP) are assigned to transitions to valence/Rydberg orbitals with mixed pi*/sigma* character. Upon N addition, a reduction of intensity is observed in the Rydberg region at both edges as compared to the intensity in the continuum. Above the IP one or more resonances are seen and ascribed here to transitions to sigma* orbitals. Calculating the experimental and theoretical Delta(pi) term values at both edges, we observe that they are almost the same within +/- 1 eV as expected for isoelectronic bonded pairs. The term values of the pi* and sigma* resonances are discussed in terms of the total Z number of the atoms participating in the bond.
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| 18. |
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| 19. |
- Vall-llosera, Gemma, et al.
(författare)
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The npσ,π to EF emission systems in D2 studied by selective excitation
- 2005
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 38:6, s. 659-664
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Tidskriftsartikel (refereegranskat)abstract
- The np sigma 1 Sigma(u)(+) and np pi (1)Pi(u) states in D-2 have been selectively excited using monoenergetic synchrotron light in the range of 13.97-15.84 eV and the subsequent dispersed emission to the EF (1)Sigma(g)(+) state was observed using a grating spectrometer. In total, 18 emission bands from the levels n = 3-6 were studied and rotationally analysed. The intensities of the P and R branches relative to the Q branch were found to vary strongly in the np pi (1)Pi(u)(+)-EF(1)Sigma(g)(+) bands indicating the existence of predissociations of np pi (1)Pi(u)(+) levels above the dissociation limit D(1s) + D(2l).
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| 20. |
- Vall-llosera, Gemma, et al.
(författare)
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VUV photoionisation of free azabenzenes : pyridine, pyrazine, pyrimidine, pyridazine and s-triazine
- 2008
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 275:1-3, s. 55-63
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Tidskriftsartikel (refereegranskat)abstract
- Photoionisation Mass spectrometry was used to obtain the fragmentation pathways of pyridine, pyridazine, pyrimidine, pyrazine and s-triazine molecules upon absorption of 23.0, 15.7 and 13.8eV synchrotron photons. The ionic fragments observed vary from molecule to molecule, however C2H2+, HCN+ and HCNH+ are common to all five molecules at the three photon energies. Furthermore, the presence of C2H2N2+,C3H3N+ and C4H4+ in the spectra of some of the molecules suggests dissociation pathways via loss of HCN moieties. The respective parent cations, m/q = 79, 80 and 81 have a greater yield at low photon energies when compared to the most intense fragment peak in each spectra. We recorded two of the fragment cation yields, as well as the parent photoion yield Curves of pyridine, pyridazine, and pyrimidine in the 8-30 eV range. The formation of abundant cation fragments show a strong propensity of the molecules for dissociation after the absorption of VUV photons higher than 14eV. The differences in relative fragment yields from molecule to molecule, and when changing the excitation energy, Suggest significant bond rearrangements and nuclear motion during the dissociation time. Thus, bond cleavage is dependent on the photon energy deposited in the molecule and on intramolecular reactivity. With the aid of photoion yield Curves and energy estimations we have assigned major peaks in the spectra and discussed their fragmentation pathways.
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