Conservation of Orbital Angular Momentum in Stimulated Down-Conversion

We report on an experiment demonstrating the conservation of orbital angular momentum in stimulated down-conversion. The orbital angular momentum is not transferred to the individual beams of the spontaneous down-conversion, but it is conserved when twin photons are taken individually. We observe the conservation law for an individual beam of the down-conversion through cavity-free stimulated emission.Comment: Submitted for publication in Phys. Rev. Let

Public-Key Encryption with Quantum Keys

In the framework of Impagliazzo's five worlds, a distinction is often made between two worlds, one where public-key encryption exists (Cryptomania), and one in which only one-way functions exist (MiniCrypt). However, the boundaries between these worlds can change when quantum information is taken into account. Recent work has shown that quantum variants of oblivious transfer and multi-party computation, both primitives that are classically in Cryptomania, can be constructed from one-way functions, placing them in the realm of quantum MiniCrypt (the so-called MiniQCrypt). This naturally raises the following question: Is it possible to construct a quantum variant of public-key encryption, which is at the heart of Cryptomania, from one-way functions or potentially weaker assumptions? In this work, we initiate the formal study of the notion of quantum public-key encryption (qPKE), i.e., public-key encryption where keys are allowed to be quantum states. We propose new definitions of security and several constructions of qPKE based on the existence of one-way functions (OWF), or even weaker assumptions, such as pseudorandom function-like states (PRFS) and pseudorandom function-like states with proof of destruction (PRFSPD). Finally, to give a tight characterization of this primitive, we show that computational assumptions are necessary to build quantum public-key encryption. That is, we give a self-contained proof that no quantum public-key encryption scheme can provide information-theoretic security.Comment: This submission subsumes arXiv:2303.02080 and arXiv:2303.0536

PrivateRide: A Privacy-Enhanced Ride-Hailing Service

In the past few years, we have witnessed a rise in the popularity of ride-hailing services (RHSs), an on-line marketplace that enables accredited drivers to use their own cars to drive ride-hailing users. Unlike other transportation services, RHSs raise significant privacy concerns, as providers are able to track the precise mobility patterns of millions of riders worldwide. We present the first survey and analysis of the privacy threats in RHSs. Our analysis exposes high-risk privacy threats that do not occur in conventional taxi services. Therefore, we pro- pose PrivateRide, a privacy-enhancing and practical solu- tion that offers anonymity and location privacy for riders, and protects drivers’ information from harvesting attacks. PrivateRide lowers the high-risk privacy threats in RHSs to a level that is at least as low as that of many taxi services. Using real data-sets from Uber and taxi rides, we show that PrivateRide significantly enhances riders’ privacy, while preserving tangible accuracy in ride matching and fare calculation, with only negligible effects on convenience. Moreover, by using our Android implementation for experimental evaluations, we show that PrivateRide’s overhead during ride setup is negligible. In short, we enable privacy- conscious riders to achieve levels of privacy that are not possible in current RHSs and even in some conventional taxi services, thereby offering a potential business differentiator

The Geometry of PSR B0031-07

PSR B0031-07 is well known to exhibit three different modes of drifting sub-pulses (mode A, B and C). It has recently been shown that in a multifrequency observation, consisting of 2700 pulses, all driftmodes were visible at low frequencies, while at 4.85 GHz only mode-A drift or non-drifting emission was detected. This suggests that modes A and B are emitted in sub-beams, rotating at a fixed distance from the magnetic axis, with the mode-B sub-beams being closer to the magnetic axis than the mode-A sub-beams. Diffuse emission between the sub-beams can account for the non-drifting emission. Using the results of an analysis of simultaneous multifrequency observations of PSR B0031-07, we set out to construct a geometrical model that includes emission from both sub-beams and diffuse emission and describes the regions of the radio emission of PSR B0031-07 at each emission frequency for driftmodes A and B. Based on the vertical spacing between driftbands, we have determined the driftmode of each sequence of drift. To restrict the model, we calculated average polarisation and intensity characteristics for each driftmode and at each frequency. The model reproduces the observed polarisation and intensity characteristics, suggesting that diffuse emission plays an important role in the emission properties of PSR B0031-07. The model further suggests that the emission heights of this pulsar range from a few kilometers to a little over 10 kilometers above the pulsar surface. We also find that the relationships between height and frequency of emission that follow from curvature radiation and from plasma-frequency emission could not be used to reproduce the observed frequency dependence of the width of the average intensity profiles.Comment: 15 pages, 9 figures, 8 tables, accepted for publication in A&

Investigations of an increased incidence of non-Aspergillus invasive mould infections in an onco-haematology unit.

Invasive mould infections are life-threatening complications in patients with haematologic cancer and chemotherapy-induced neutropenia. While invasive aspergillosis represents the main cause of invasive mould infections, non-Aspergillus mould infections, such as mucormycosis, are increasingly reported. Consequently, their local epidemiology should be closely monitored. The aim of this study was to investigate the causes of an increased incidence of non-Aspergillus mould infections in the onco-haematology unit of a Swiss tertiary care hospital. All cases of proven and probable invasive mould infections were retrospectively identified via a local registry for the period 2007-2021 and their incidence was calculated per 10,000 patient-days per year. The relative proportion of invasive aspergillosis and non-Aspergillus mould infections was assessed. Factors that may affect invasive mould infections' incidence, such as antifungal drug consumption, environmental contamination and changes in diagnostic approaches, were investigated. A significant increase of the incidence of non-Aspergillus mould infections (mainly mucormycosis) was observed from 2017 onwards (Mann and Kendall test p = 0.0053), peaking in 2020 (8.62 episodes per 10,000 patient-days). The incidence of invasive aspergillosis remained stable across the period of observation. The proportion of non-Aspergillus mould infections increased significantly from 2017 (33% vs 16.8% for the periods 2017-2021 and 2007-2016, respectively, p = 0.02). Building projects on the hospital site were identified as possible contributors of this increase in non-Aspergillus mould infections. However, novel diagnostic procedures may have improved their detection. We report a significant increase in non-Aspergillus mould infections, and mainly in mucormycosis infections, since 2017. There seems to be a multifactorial origin to this increase. Epidemiological trends of invasive mould infections should be carefully monitored in onco-haematology units in order to implement potential corrective measures

On the Adsorption of CO₂ by Active Carbons

The combination of adsorption and calorimetric techniques shows that the adsorption of CO2 is a two-step process in the case of active carbons with large micropores (L > 1.2–1.5 nm). For smaller pores, on the other hand, one observes a uniform filling of the volume. These mechanisms are in agreement with earlier experiments carried out with CH2Cl2 at 293 K

Microwave Gaseous Disharges

Contains reports on seven research projects.Atomic Energy Commission under Contract AT(30-1)184