Independent high-purity photons created in domain-engineered crystals

Advanced photonic quantum technology relies on multi-photon interference which requires bright sources of high-purity single photons. Here, we implement a novel domain-engineering technique for tailoring the nonlinearity of a parametric down-conversion crystal. We create pairs of independently-heralded telecom-wavelength photons and achieve high heralding, brightness and spectral purities without filtering.Comment: 8 pages, 5 figures Imprecise comparison with the experimental results in [28] has been remove

Advanced data acquisition for multi-photon experiments

The overarching theme of this thesis was to develop a state-of-the-art multi-photon experiment at telecom wavelengths. With this platform the following experiments in quantum information processing were performed: testing of local observer independence [1], multiqubit phase estimation [2], measurement-device-independent verification of quantum channels [3], assisted macroscopic quantumness [4] and experimental quantum conference key agreement [5]. My focus has been primarily on the signal processing / data analysis required in particular for the required engineering for the used single-photon sources [6] developed by our group and most prominently for the “big data” produced in measurement of the joint spectra such as our demonstration of time-frequency modes from engineered nonlinearites [7]. The analysis required for our source engineering efforts has resulted in the my development of a pair of models to determine accurate multi-photon detection rates and signal-to-noise ratios of each single-photon source. In order to extract the joint spectra from the measured “big data” I have developed a time-correlated single-photon counting toolkit. In this thesis I will outline the following, the requirements for building a high performance single-photon source, develop a pair of models for analysing the signal-to-noise ratio for a number of sources along with exploring the benefits that can be seen via multiplexing. Further, the design of time-correlated single-photon-counting hardware is discussed along with the methods needed to produced meaningful analytics from the data output from said hardware. Finally the joint spectra of a number of down-conversion based single-photon sources are reconstructed via dispersive spectroscopy allowing for the spectral purity to be estimated in each case, this is then extended by use of image processing techniques in order to determine whether our estimates can be improved. In all, this thesis discusses what we need from a single-photon source, how to optimise the experimental configuration for high detection rates and signal-to-noise ratios, how to analyse the resulting signals and then finally combining these into measurement of spectral purity resulting in a broad investigation of single-photon source performance with a view to multi-photon experiments

Enhanced Multi-Qubit Phase Estimation in Noisy Environments by Local Encoding

The first generation of multi-qubit quantum technologies will consist of noisy, intermediate-scale devices for which active error correction remains out of reach. To exploit such devices, it is thus imperative to use passive error protection that meets a careful trade-off between noise protection and resource overhead. Here, we experimentally demonstrate that single-qubit encoding can significantly enhance the robustness of entanglement and coherence of four-qubit graph states against local noise with a preferred direction. In particular, we explicitly show that local encoding provides a significant practical advantage for phase estimation in noisy environments. This demonstrates the efficacy of local unitary encoding under realistic conditions, with potential applications in multi-qubit quantum technologies for metrology, multi-partite secrecy and error correction.Comment: 7 figure

In-situ fabricated 3D micro-lenses for photonic integrated circuits

Aspheric astigmatic polymer micro-lenses were fabricated directly onto photonic integrated circuits using two-photon lithography. We observed a 12.6 dB improvement in the free space coupling efficiency between integrated ridge laser pairs with micro-lenses to those without

Investigations of pure and derivatized fullerenes by mass spectrometry

The following thesis represents an investigation into the gas-phase behavior of fullerenes and fullerene derivatives, using mass spectrometry as an analytical method. This thesis encompasses the formation and structure elucidation of carbon-based clusters which have been formed through the ablation of fullerene derivatives, the formation of fullerenes from non-fullerene precursor material, an evaluation of the stability of solid C60, the delayed ionization of pure fullerenes, and the assessment of an alternative ionization method for the direct analysis of fullerenes and fullerene derivatives. The coalescence reactivities of C60H36, oxides of C60, and C70, metallofullerenes, fluorinated fullerenes, and three fullerene derivatives of the formula C60[C(COOEt)2]n (where n = 1,2, and 3) have been studied. Analogously, an organometallic compound of the formula [Cp5CpMn(CO)3] has been evaluated as a possible precursor for fullerene formation using laser ablation. The stability of Q under ambient conditions, in the presence of light and air, has been studied, revealing that dimerization reactions occur following oxidation. Following analysis of the structures of coalesced species, it became apparent that time-of-flight instruments of a particular design may be prone to artifact signals originating from the delayed ionization of fullerenes; a subsequent study led to the development of a new method for examining this behavior and the findings have far reaching consequences for studies using similar instrumentation. Laser desorption/ionization and matrix-assisted laser desorption/ionization are not always suitable ionization methods due to the observation of high degrees of fragmentation or reactions with the matrix. Electrospray ionization represents an obvious solution, but an investigation into the suitability of this method was required due to the lack of successful analyses in the literature. Though the topics involved and the samples used are diverse, each investigation thus represents a mass spectrometric study into the gas-phase behavior of fullerenes and their derivatives, along one of several themes

Direct Generation of Tailored Pulse-Mode Entanglement

Photonic quantum technology increasingly uses frequency encoding to enable higher quantum information density and noise resilience. Pulsed time-frequency modes (TFM) represent a unique class of spectrally encoded quantum states of light that enable a complete framework for quantum information processing. Here, we demonstrate a technique for direct generation of entangled TFM-encoded states in single-pass, tailored downconversion processes. We achieve unprecedented quality in state generation---high rates, heralding efficiency and state fidelity---as characterised via highly resolved time-of-flight fibre spectroscopy and two-photon interference. We employ this technique in a four-photon entanglement swapping scheme as a primitive for TFM-encoded quantum protocols.Comment: 5 pages, 4 figures, 3 pages supplemental materia

A dynamical system approach to higher order gravity

The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review the main results and I give brief comments on the perspectives for further developments.Comment: 6 pages, 1 figure, 2 tables, talk given at IRGAC 2006, July 200

Use of top-down and bottom-up fourier transform ion cyclotron resonance mass spectrometry for mapping calmodulin sites modified by platinum anticancer drugs

Calmodulin (CaM) is a highly conserved, ubiquitous, calcium-binding protein; it binds to and regulates many different protein targets, thereby functioning as a calcium sensor and signal transducer. CaM contains 9 methionine (Met), 1 histidine (His), 17 aspartic acid (Asp), and 23 glutamine acid (Glu) residues, all of which can potentially react with platinum compounds; thus, one-third of the CaM sequence is a possible binding target of platinum anticancer drugs, which represents a major challenge for identification of specific platinum modification sites. Here, top-down electron capture dissociation (ECD) was used to elucidate the transition metal–platinum(II) modification sites. By using a combination of top-down and bottom-up mass spectrometric (MS) approaches, 10 specific binding sites for mononuclear complexes, cisplatin and [Pt(dien)Cl]Cl, and dinuclear complex [{cis-PtCl2(NH3)}2(μ-NH2(CH2)4NH2)] on CaM were identified. High resolution MS of cisplatin-modified CaM revealed that cisplatin mainly targets Met residues in solution at low molar ratios of cisplatin–CaM (2:1), by cross-linking Met residues. At a high molar ratio of cisplatin:CaM (8:1), up to 10 platinum(II) bind to Met, Asp, and Glu residues. [{cis-PtCl2(NH3)}2(μ-NH2(CH2)4NH2)] forms mononuclear adducts with CaM. The alkanediamine linker between the two platinum centers dissociates due to a trans-labilization effect. [Pt(dien)Cl]Cl forms {Pt(dien)}2+ adducts with CaM, and the preferential binding sites were identified as Met51, Met71, Met72, His107, Met109, Met124, Met144, Met145, Glu45 or Glu47, and Asp122 or Glu123. The binding of these complexes to CaM, particularly when binding involves loss of all four original ligands, is largely irreversible which could result in their failure to reach the target DNA or be responsible for unwanted side-effects during chemotherapy. Additionally, the cross-linking of cisplatin to CaM might lead to the loss of the biological function of CaM or CaM–Ca2+ due to limiting the flexibility of the CaM or CaM–Ca2+ complex to recognize target proteins or blocking the binding region of target proteins to CaM