Multi-Phase Hadamard receivers for classical communication on lossy bosonic channels

A scheme for transferring classical information over a lossy bosonic channel is proposed by generalizing the proposal presented in Phys. Rev. Lett. 106, 240502 (2011) by Guha. It employs codewords formed by products of coherent states of fixed mean photon number with multiple phases which, through a passive unitary transformation, reduce to a Pulse-Position Modulation code with multiple pulse phases. The maximum information rate achievable with optimal, yet difficult to implement, detection schemes is computed and shown to saturate the classical capacity of the channel in the low energy regime. An easy to implement receiver based on a conditional Dolinar detection scheme is also proposed finding that, while suboptimal, it allows for improvements in an intermediate photon-number regime with respect to previous proposals.Comment: final version: minor changes; 8+3 pages and 5 figure

The capacity of coherent-state adaptive decoders with interferometry and single-mode detectors

A class of Adaptive Decoders (AD's) for coherent-state sequences is studied, including in particular the most common technology for optical-signal processing, e.g., interferometers, coherent displacements and photon-counting detectors. More generally we consider AD's comprising adaptive procedures based on passive multi-mode Gaussian unitaries and arbitrary single-mode destructive measurements. For classical communication on quantum phase-insensitive Gaussian channels with a coherent-state encoding, we show that the AD's optimal information transmission rate is not greater than that of a single-mode decoder. Our result also implies that the ultimate classical capacity of quantum phase-insensitive Gaussian channels is unlikely to be achieved with the considered class of AD's.Comment: v3: final version; 6 pages; 2 figure

Coherent-state discrimination via non-heralded probabilistic amplification

A scheme for the detection of low-intensity optical coherent signals was studied which uses a probabilistic amplifier operated in the non-heralded version, as the underlying non-linear operation to improve the detection efficiency. This approach allows us to improve the statistics by keeping track of all possible outcomes of the amplification stage (including failures). When compared with an optimized Kennedy receiver, the resulting discrimination success probability we obtain presents a gain up to ~1.85% and it approaches the Helstrom bound appreciably faster than the Dolinar receiver, when employed in an adaptive strategy. We also notice that the advantages obtained can be ultimately associated with the fact that, in the high gain limit, the non-heralded version of the probabilistic amplifier induces a partial dephasing which preserves quantum coherence among low energy eigenvectors while removing it elsewhere. A proposal to realize such transformation based on an optical cavity implementation is presented.Comment: Final version: 6 pages and 4 figure

Decoding Protocols for Classical Communication on Quantum Channels

We study the problem of decoding classical information encoded on quantum states at the output of a quantum channel, with particular focus on increasing the communication rates towards the maximum allowed by Quantum Mechanics. After a brief introduction to the main theoretical formalism employed in the rest of the thesis, i.e., continuous-variable Quantum Information Theory and Quantum Communication Theory, we consider several decoding schemes. First, we treat the problem from an abstract perspective, presenting a method to decompose any quantum measurement into a sequence of easier nested measurements through a binary-tree search. Furthermore we show that this decomposition can be used to build a capacity-achieving decoding protocol for classical communication on quantum channels and to solve the optimal discrimination of some sets of quantum states. These results clarify the structure of optimal quantum measurements, showing that it can be recast in a more operational and experimentally-oriented fashion. Second, we consider a more practical approach and describe three receiver structures for coherent states of the electromagnetic field with applications to single-mode state discrimination and multi-mode decoding at the output of a quantum channel. We treat the problem bearing in mind the technological limitations faced nowadays in the field of optical communications: we evaluate the performance of general decoding schemes based on such technology and report increased performance of two schemes, the first one employing a non-Gaussian transformation and the second one employing a code tailored to be read out easily by the most common detectors. Eventually we characterize a large class of multi-mode adaptive receivers based on common technological resources, obtaining a no-go theorem for their capacity.Comment: PhD thesis. 171 pages, 16 figure

The role of women in the juxtaposition between Islam and political Islam: unveiling Arabian nights

The resurgence of Islamic Fundamentalism determined a new wave of interest about Muslim countries; Islam became a privileged category of analysis to investigate the commitment of these countries through a democratic path. Women's role in Islam is extremely relevant since the relationship between religion and gender issues has become a fertile ground of discussion in academia, and also in local and transnational politics, in colonial and postcolonial analysis, in the affirmation of economic and political powers, and in the definition of identities. This Master thesis unfolds some pivotal issues to highlight the Quran and the Sunnah’s gender egalitarian attitude. Thus Sharia is enforced on the base of an ahistorical and patriarchal interpretation of the sacred texts. Moreover, there is not only one Political Islam, and women’s living conditions vary notably from country to country, from region to region. This work aims at understanding the miscellany, the variety, the juxtaposition among Islamic morals and legislation in three case studies: Hezbollah, Hamas and the Muslim Brotherhood. Additionally, it tries to overcome several dualities offering an approach to a society founded on the Ethic of Care, on Progressive Islam and Islamic Feminism, on the base that each human being is different from others and that differences enrich us.O ressurgimento do Fundamentalismo Islâmico determinou um novo interesse pelos países muçulmanos. O Islão tornou-se um foco de análise para estudar o compromisso desses países para o caminho da democracia. O papel das mulheres no Islão é de suprema importância, até porque a interrelação entre religião e questões de género é matéria fértil não só na discussão acadêmica, mas também nas políticas nacionais/transnacionais, análises colonialistas e pós-colonialistas, na afirmação de poderes políticos e económicos, e na definição de identidades. Esta tese de Mestrado foca-se em temáticas essenciais que realçam a igualdade de género no Alcorão e na Sunnah, a pesar de que a Sharia é cumprida com base numa interpretação histórica e patriarcal dos textos sagrados. Não há um único Islã político e a condição das mulheres varia de país para país, de região para região. Este trabalho visa uma melhor compreensão da miscelânea, da variedade, da sobreposição da moral e da legislação no mundo Islâmico a partir do estudo do Hezbollah, do Hamas e da Irmandade Muçulmana. Também realça as dualidades duma sociedade baseada na ética do care, num Islão Progressista e num Feminismo Islâmico, assumindo de que cada ser humano é único e é o que nos enriquece

Optimal quantum state discrimination via nested binary measurements

A method to compute the optimal success probability of discrimination of N arbitrary quantum states is presented, based on the decomposition of any N-outcome measurement into sequences of nested two-outcome ones. In this way the optimization of the measurement operators can be carried out in successive steps, optimizing first the binary measurements at the deepest nesting level and then moving on to those at higher levels. We obtain an analytical expression for the maximum success probability after the first optimization step and examine its form for the specific case of N=3,4 states of a qubit. In this case, at variance with previous proposals, we are able to provide a compact expression for the success probability of any set of states, whose numerical optimization is straightforward; the results thus obtained highlight some lesser-known features of the discrimination problem.Comment: v2: added references to previous works closely related to Sec. II; 8+3 pages; 3 figure

Narrow Bounds for the Quantum Capacity of Thermal Attenuators

Thermal attenuator channels model the decoherence of quantum systems interacting with a thermal bath, e.g., a two-level system subject to thermal noise and an electromagnetic signal travelling through a fiber or in free-space. Hence determining the quantum capacity of these channels is an outstanding open problem for quantum computation and communication. Here we derive several upper bounds on the quantum capacity of qubit and bosonic thermal attenuators. We introduce an extended version of such channels which is degradable and hence has a single-letter quantum capacity, bounding that of the original thermal attenuators. Another bound for bosonic attenuators is given by the bottleneck inequality applied to a particular channel decomposition. With respect to previously known bounds we report better results in a broad range of attenuation and noise: we can now approximate the quantum capacity up to a negligible uncertainty for most practical applications, e.g., for low thermal noise.Comment: v4: corrected typo in Eq. 40; final version, minor corrections; 8+3 pages, 4 figure

Com avaluar el rendiment dels dispositius de comunicació quàntica

Matteo Rosati, del Grup d'Informació Quàntica, ha calculat els límits superiors de la informació quàntica que pot ser transmesa entre dos dispositius. La investigació, publicada recentment a Nature Communications, permet avaluar el rendiment teòric dels dispositius de comunicació quàntica, tant actuals com futurs.Matteo Rosati, del Grupo de Información Cuántica, ha calculado los límites superiores de la información cuántica que puede ser transmitida entre dos dispositivos. La investigación, publicada recientemente en Nature Communications, permite evaluar el rendimiento teórico de los dispositivos de comunicación cuántica, tanto actuales como futuros.Matteo Rosati, from the Grup d'Informació Quàntica, has computed upper bounds on the maximum quantum information that can be transmitted through space. The research, recently published in Nature Communications, allows to evaluate the performance of present and future quantum communication devices for all practical purposes

inkjet sensors produced by consumer printers with smartphone impedance readout

Abstract Inkjet printing technology is showing a disruptive potential for low-cost optical and electrochemical biosensors fabrication. This technology is becoming affordable for every laboratory, potentially allowing every research group to implement a biosensors fabrication platform with consumer inkjet printers, commercially available inks and smartphones for readout. In the present work we developed an example of such platform testing several inks, printers, and substrates. We defined and optimized the protocols assessing the printing limits and the fabricated biosensors electrochemical properties in standard solutions. Our platform has a total cost of less than 450 Euro and a single sensor fabrication cost of 0.026 Euro. Finally, we tested the sensitivity of smartphone-performed impedance measurements with printed biosensors surface coverage by Self Assembling Monolayers (SAM), validating them with standard instruments