Homodyne versus photon-counting quantum trajectories for dissipative Kerr resonators with two-photon driving

We investigate two different kinds of quantum trajectories for a nonlinear photon resonator subject to two-photon pumping, a configuration recently studied for the generation of photonic Schroedinger cat states. In the absence of feedback control and in the strong-driving limit, the steady-state density matrix is a statistical mixture of two states with equal weight. While along a single photon-counting trajectory the systems intermittently switches between an odd and an even cat state, we show that upon homodyne detection the situation is different. Indeed, homodyne quantum trajectories reveal switches between coherent states of opposite phase.Comment: To appear on Eur. Phys. J. Special Topics, Quantum Gases and Quantum Coherence; 8 pages, 2 composed figures (5 panels

Violence, Paratexts, and Fandoms: The Walking Dead as a Societal Mirror

This project is a critical textual analysis of fan discourse surrounding the season seven premiere of The Walking Dead “The Day Will Come When You Won’t Be” that aired on AMC on October 23rd, 2016. Focusing on paratexts, fandoms, and the violence/horror genre as the theoretical framework, the project highlights fans role in the contemporary age of television and provides insight into how much violence and gore is acceptable for fans of the genre. This project also highlights how the premiere can be read as a societal mirror for violence’s representation in society. The artifact to be analyzed is fan comments on Reddit and Twitter as those sites provided a thread of posts in which fans engaged in dialogue with each other. In the analysis, examples from the episode are used to provide context for the fan comments and to connect the feedback to the episode itself. As a case study, this episode serves as a catalyst demonstrating that fans of the genre have a boundary for acceptable violence and that the episode can be read as a mirror for violence’s representation in society

Photon-Number Resolving by Superconductive Devices

Strong interests on optical quantum based metrology, quantum information and particularly in quantum cryptography are continuously growing. The main limitations to the developments in these fields are due to non-ideal devices: both single photon sources and single photon detectors. In these field of applications, detectors require to be able to resolve the number of photons in a light pulse. Presently state of the art indicates that classical semiconductor light detectors (i.e. avalanche photodiode or single photon avalanche diode) are not able to discriminate the number of photon arriving at the same time. In the meanwhile, superconducting devices have shown the possibility to resolve single photon pulses. One of the most promising superconducting detectors is the Transition-Edge Sensor (TES): a microcalorimeter that takes advantage of the sharp transition (few millikelvin) from the superconducting to the normal phase; for this reason it is sometimes called Superconductive Phase Thermometer (SPT). In the ultraviolet (UV) to infrared (IR) wavelength range, the photons are absorbed directly by the superconductive thin film and the absorbed energy induces an increase of the TES resistance. Thanks to the applied bias voltage, which maintains the device in the transition region the photon absorption induces a decrease of the TES current, measured by a dc-SQUID amplifier, and the pulse integral of the bias power reduction corresponds to the absorbed energy. This means that TESs have the very interesting properties to be able to detect single photons with an intrinsic energy resolution, without filters or gratings, that limit the quantum efficiency. By contrary of classical detectors, if monochromatic light irradiates TESs, as usually happens in communication systems, they show the photon-number resolving (PNR) capability and due to the good signal to noise ratio TESs are almost free from dark counts. Moreover, in the superconducting detector family, TESs are the only true photon-number resolving detectors operating in the VIS-NIR range. Together with quantum information science, the PNR property results useful even for optical radiometry too. In the optical community, the candela - the International System (SI) unit for the luminous intensity - has not a common consensus whether its present definition fully satisfies the current and future needs of growing associated technology. Furthermore, actually there are substantial efforts directed toward a new definitions of four base SI units: the proposal wants to link the SI units to fundamental constants, leaving f.i. material artifact. Considering the recent advances in optical radiometry and in quantum technologies, for the candela world it means redefine its unit linking to the Planck constant and consequently expressing the luminous intensity unit in terms of photon number rather than optical power. This challenge has been accepted by several national metrology institutes to demonstrate the feasibility of redefining the candela. Inside this research project called `qu-candela', the TES PNR capability has been considered to build the bridge between the quantum and classical world of radiometry: i.e. the detector possibility to measure optical powers from one single photon per second to the lower limits of cryogenic radiometry, 104 photons per second. The theme of this work of thesis is to investigate both optical and electrical characterization of different kind of TESs based on a titanium/gold multilayer film, produced and developed at the National Institute of Metrological Research (INRIM) of Torino. Thanks to the proximity effect, the multilayer allows to lower with continuity the critical temperature from that of the Ti bulk (Tc ~ 390 mK) to those of interest: ~ 300 mK and ~ 100 mK. Detectors with higher Tc have shown a faster response pulse with a relaxing time constant of the order of 200 ns, while for the lower Tc sensors, the time constant is about 10 µs. By contrary to the response time, the detector intrinsic energy resolution is proportional to its film critical temperature. Our sensors work to discriminate incident photon from UV wavelengths to those typical of the telecommunications, 1310 nm and 1550 nm. Irradiating a TES with an active area of 10x10 µm^2 by incident photons of 0.79 eV (corresponds to a wavelength 1570 nm), the best energy resolution obtained has been 0.18 eV. Detectors with higher active area 20x20 µm^2 have a worse energy resolution, because it is also proportional to the material film heat capacity. In the meanwhile due to the same reason these kind of sensors present a bigger saturation energy. This has allowed to investigate on the TES capability to discriminate up to 29 incident photons simultaneously. Until now, such count represents the bigger amount of photons discriminated by single photon detectors, without reaching the device saturation, with a linear behaviour. From this count it has been estimated 12 photons on average, per pulse, at 9 kHz repetition rate; this results in a photon flux of about 105 photons/s, demonstrating the possibility of having a detector able to work from low flux regime to 1 photon/s to flux measurable by conventional semiconductor device (f.i. single photon avalanche detector SPAD). An innovative absolute calibration technique for PNR detector has been demonstrated. The absolute technique is based on the Klyshko's efficient solution to measure detection efficiency in photon counting rate and well know for common click-no-click detector. In fact, exploiting the recent developments in quantum state world, it is possible to work with quasi single photon state, by using a parametric down conversion heralded single photon source, and calibrate PNR detectors without requiring reference standards. The best detection efficiency, of ca. 50%, has been reached by coupling the smaller active area detectors with a 9 µm core optical fiber, single mode at telecom wavelength

Chapter The management of dredged materials: the «long and winding road» from waste to resource

Both the dredging operations and the management of dredged materials may have heavy impacts on coastal and marine ecosystems. Dredged materials, in particular, have been considered for a very long time nothing more than a waste meant for disposal. Now the time has come to move from the ‘disposal approach’ to the ‘waste recovery’ or, even better, to the ‘waste can be a non-waste’ ones. Unfortunately, the management of dredged materials is committed to a congeries of rules, which build up a framework of law that appears plainly fragmentary and incoherent. The road is still long (and winding)

Ti/Au TES as photon-number–resolving detector

One of the most promising detector, able to resolve single photons thanks to their intrinsic energy resolution, is the transition-edge sensor (TES). We present the state of the art on these superconducting single-photon detectors, developed and characterised at the National Institute of Metrological Research (INRIM). We show both the physical properties and the best results obtained on a Ti/Au TES in the spectral range between visible and near infrared

The management of dredged materials: the «long and winding road» from waste to resource

The removal of material from the seabed and from the bottom of brackish bodies of water is necessary to maintain downflow conditions, to ensure navigability and port accessibility, to collect sands for coastal nourishment, to guarantee coastal protection, to help habitat development or enhancement, to pick contaminated sediments up, to promote land reclamation. And examples could go on. However, both the dredging operations and the management of the resulting materials have the potential to cause relevant damages to the environment, especially in coastal and marine contexts, where ecosystems are fragile and vulnerable. Dredged materials, in particular, have been considered for a very long time nothing more than a waste meant for disposal. Now the time has come to move from the ‘disposal approach’ to the ‘waste recovery’ or, even better, to the ‘waste can be a non-waste’ ones. Unfortunately, the management of dredged materials reveals itself as committed to a congeries of rules, which build up a framework of law that appears plainly fragmentary and incoherent. The road is still long (and winding)

Binding to DNA of the RNA-polymerase II C-terminal domain allows discrimination between Cdk7 and Cdk9 phosphorylation

The C-terminal domain (CTD) of RNA polymerase II regulates transcription through spatially and temporally coordinated events. Previous work had established that the CTD binds DNA but the significance of this interaction has not been determined. The present work shows that the CTD binds DNA in its unphosphorylated form, the form in which it is present in the pre-initiation complex. The CTD/DNA complex is recognized by and is phosphorylated by Cdk7 but not by Cdk9. Model-building studies indicate the structural mechanism underlying such specificity involves interaction of Cdk7 with DNA in the context of the CTD/DNA complex. The model has been tested by mutagenesis experiments. CTD dissociates from DNA following phosphorylation by Cdk7, allowing transcription initiation. The CTD then becomes accessible for further phosphorylation by Cdk9 that drives the transition to transcription elongation

Identification of natural product stereochemistry via calculation of ECD spectra

Most commercially available antibiotics are obtained from natural products, secondary metabolites of bacteria or other living organisms. Due to the importance of this class of compounds in medicinal chemistry and growing drug resistance, efforts to discover, characterize and isolate new or improved antibiotics are continually increasing. The assignment of the absolute configuration (AC) adopted by these compounds is a crucial aspect of the characterization step and knowledge of the stereochemistry is an important factor in deciphering the interaction of these compounds with the organism and thus, the mechanism of action. In order to assign the AC, several techniques, such as X-ray diffraction and NMR experiments as well as the standard electronic spectroscopy experiments (UV-Vis, ECD, etc.) or less widespread vibrational and rotational spectroscopy experiments (VCD, ROA, etc.) can be used, often in combination. However, sophisticated synthetic strategies or difficult isolation of the natural compound often leads to a small amount of product available, making some of the previous techniques unpractical; in addition to the potential structural complexity of the molecule, this can make the experimental assignment of the AC problematic. For this reason, a computational approach, aimed at calculating observable properties of the products, generating spectra and assigning the AC through comparison between the calculated and the experimental spectra, has proven useful in many cases. Formicamycin is a natural product, isolated from a new member of Streptomyces bacteria, which has shown great activity against pathogenic drug-resistant bacteria and fungi, without developing antimicrobial resistance. This dissertation shows that the chiral axis of Formicamycin can be assigned as R, through the calculation of electronic circular dichroism (ECD) spectra and comparison to the experimentally determined spectrum in methanol. ECD spectroscopy is very sensitive to the chiral environment of chromophores and can be used to distinguish between different isomers. The computational procedure has been broadly defined in previous studies and involves three general steps: 1) generation of an ensemble of structures, 2) optimization of the structures and calculation of the rotational strengths of each and 3) generation of the Boltzmannweighted spectrum. Here, two different force fields (OPLS3 and MMFFs) were used for generating the ensemble of conformers, followed by PBE0 DFT calculations to determine the optimal geometry and finally, TDDFT calculations to compute the rotational strengths of each conformer. Furthermore, the spectra were calculated in four different solvents, using the implicit SMD method, in order to inform future studies about “variable solvent circular dichroism”. Different conformations of a molecule can be controlled by the choice of solvent and it is hypothesised that a change in solvent will result in a “fingerprint” shift in the ECD spectra that could permit assignment of the stereochemistry. The entire process was automated using a module written in Python