37 research outputs found
Fast self-testing quantum random number generator based on homodyne detection
No full textSelf-testing and semi-device independent protocols are becoming the preferred choice for quantum technologies, being able to certify their quantum nature with few assumptions and simple experimental implementations. In particular, for quantum random number generators, the possibility of monitoring, in real time, the entropy of the source only by measuring the input/output statistics is a characteristic that no other classical system could provide. The cost of this possibility is not necessarily increased complexity and reduced performance. Indeed, here we show that with a simple optical setup consisting of commercially available components, a high bit generation rate can be achieved. We manage to certify 145.5 MHz of quantum random bit generation rate
An optical chip for self-testing quantum random number generation
No full textWe present an implementation of a semi-device-independent protocol of the generation of quantum random numbers in a fully integrated silicon chip. The system is based on a prepare-and-measure scheme, where we integrate a partially trusted source of photons and an untrusted single photon detector. The source is a silicon photomultiplier, which emits photons during the avalanche impact ionization process, while the detector is a single photon avalanche diode. The proposed protocol requires only a few and reasonable assumptions on the generated states. It is sufficient to measure the statistics of generation and detection in order to evaluate the min-entropy of the output sequence, conditioned on all possible classical side information. We demonstrate that this protocol, previously realized with a bulky laboratory setup, is totally applicable to a compact and fully integrated chip with an estimated throughput of 6 kHz of the certified quantum random bit rate
Security of quantum cryptography: from quantum random key generation to quantum key distribution
No full textQuantum technologies are today a reality, and they have been applied to different subjects, such as computing, communication, sensing and randomness generation. This thesis work will focus on two of them in particular: Quantum Key Distribution (QKD) protocols, that allow two parties to exchange a cryptographic key with unconditional security and Quantum Random Number Generators (QRNG), that allow to generate sequences which are not only uniformly distributed but also private and unforeseeable by any other observer. In my work I studied these subjects both theoretically and experimentally. This work is focused on one side on the study of the security for simplified and efficient QKD protocols and on the other side to investigate the implementation of newly developed protocols for semi-device-independent quantum random number generators, that need few assumption to prove their quantum nature, but could still be implemented with a simple set-up
Integrated photonic circuits for quantum contextuality tests
No full textLAUREA MAGISTRALEFundamental properties of quantum mechanics have been always a topic of interest in both theoretical and experimental physics. Contextuality especially, in the past few years, has been pointed out as the possible reason behind the supremacy of quantum computation. By contextuality we mean the dependence of a physical quantity on its measurement context, that is represented by the different compatible observables that are measured at the same time. It appears as a property of a system when a deterministic model is applied to explain a quantum mechanical experiment. The work of this thesis aims to show a violation of the notorious CHSH contextual inequality within the field of integrated quantum photonics. The experimental setup was divided in two different chips fabricated by femtosecond laser micromachining. The first chip had the purposes of encoding two qubits in a four level state by distributing a single photon in four distinct waveguides. The measurement stage was composed by the second chip, that contains the waveguide circuits representing the needed observables, and by four single photon detectors. By measuring the distribution probabilities of detecting a photon at the output of each measurement device, a violation of the classical inequality was successfully achieved
Integrated-optics circuits for validation of non-classicality
No full textContrarily to the classical physics picture, according to quantum mechanics the observable properties of the objects do not yield defined values, until a measurement is performed. The measurement outcome depends indeed also on the set of observables that is being measured. Such a fundamental aspect of Nature is named quantum contextuality and it has been studied in several experimental systems, including single particles. Interestingly, it was recently suggested that even the non-classical power of quantum computing originates from contextuality [4]. Therefore, it is highly relevant to find experimental evidence of this aspect in technological platforms that may be adopted in future quantum computing devices, such as integrated photonics
Detection of squeezed light with glass-integrated technology embedded into a homodyne detector setup
No full textWe design and demonstrate a homodyne detection scheme based on a glass-integrated optical device (GID) operating in the quantum regime, that is, able to detect genuine nonclassical features. Our device is entirely fabricated by femtosecond laser micromachining. The GID incorporates on the same chip a balanced waveguide beamsplitter and a thermo-optic phase shifter, allowing us to record homodyne traces at different phases and to perform reliable quantum state tomography. In particular, we show that the GID allows for the detection of nonclassical features of continuous-variable quantum states, such as squeezed states
Single-photon quantum contextuality on a chip
No full textIn classical physics, properties of the objects exist independently on the
context, i.e. whether and how measurements are performed. Quantum physics
showed this assumption to be wrong and that Nature is indeed "contextual".
Contextuality has been observed in the simplest physical systems such as single
particles, and plays fundamental roles in quantum computation advantage. Here,
we demonstrate for the first time quantum contextuality in an integrated
photonic chip. The chip implements different combinations of measurements on a
single photon delocalized on four distinct spatial modes. We show violations of
a CHSH-like non-contextuality inequality by 14 standard deviations. This paves
the way to compact and portable devices for contextuality-based quantum-powered
protocols
Breve descrittione del monasterio di S. Ambrosio Maggiore di Milano, et sua chiesa de cisterciensi monaci : l'origine della congregatione cisterciense di Lombardia : con la descrittione del monasterio di Chiaraualle di Milano : et la vita del cardinale Ascanio Maria Sforza, commendatario dell' uno & l'altro monasterio & chiese /
No full textSignatures: A⁴(A1+chi1) B-I⁴.Woodcut printer's device on t.p. (Bona Fortunae). Cut on verso of dedicatory leaf with emblem, motto and coat of arms.A smaller sheet (19 cm.) with Rusca's dedication to Francesco Alzani is bound after A1.Mode of access: Internet.Marginal annotations throughout c. 1, now quite faint.Binding, c. 1: 19th-century morocco-grained cloth, backed in green goatskin. Author & title on spine in gilt
La censura imperfetta. La satira di Richard Aldington nell’Italia fascista
No full textThrough the epistolary dialogue between the British author Richard Aldington and his
translator Alessandra Scalero, this article sheds some light on the editorial events that led
to the publication of Women must work and All men are enemies, and to the rejection of
Death of a Hero and The colonel’s daughter. Considered by Luigi Rusca – Mondadori’s codirector – “particularly important”, these books, as well as their author, are now largely
forgotten, even if during the Thirties Italian readers were fascinated by Aldington’s biting
satire. Exponent of British Imagism, Richard Aldington was closed to the Fabian Society’s
vision of the world which pervaded all his works, built around the themes of women’s
emancipation and social consequences of the First World War. The “heterodoxy” of such
contents made the translation activity particularly complex; the author himself was not
always available to soften the tone, accepting cuts and changes
Quantum Keyless Private Communication Versus Quantum Key Distribution for Space Links
No full textWe study information-theoretical security for space links between a satellite and a ground station.Quantum key distribution (QKD) is a well-established method for information-theoretical secure communication, giving the eavesdropper unlimited access to the channel and technological resources limited by only the laws of quantum physics. But QKD for space links is extremely challenging, the achieved key rates are extremely low, and daytime operating impossible. However, eavesdropping on a channel in free space without being noticed seems complicated, given the constraints imposed by orbital mechanics. If we also exclude the eavesdropper's presence in a given area around the emitter and receiver, we can guarantee that he has access to only a fraction of the optical signal. In this setting, quantum key-less private (direct) communication based on the wiretap channel model is a valid alternative to provide information-theoretical security. Like for QKD, we assume that the legitimate users are limited by state-of-the-art technology, while the potential eavesdropper is only limited by physical laws: either by specifying her detection strategy (Helstrom detector) or by bounding her knowledge, assuming the most powerful strategy through the Holevo information. Nevertheless, we demonstrate information-theoretical secure communication rates (positive keyless private capacity) over a classical-quantum wiretap channel using on-off keying of coherent states. We present numerical results for a setting equivalent to the recent experiments with the Micius satellite and compare them to the fundamental limit for the secret key rate of QKD. We obtain much higher rates compared with QKD with an exclusion area of less than 13 m for low earth orbit satellites. Moreover, we show that the wiretap channel quantum keyless privacy is much less sensitive to noise and signal dynamics and daytime operation is possible
