In quantum communication protocols, the use of photon-number-resolving detectors could open new perspectives by broadening the way to encode and decode information and merging the properties of discrete and continuous variables. In this work, we consider a quantum channel exploiting a silicon-photomultiplier-based receiver and evaluate its performance for quantum communication protocols under three possible configurations, defined by different post-processing of the detection outcomes. We investigate two scenarios: information transmission over the channel, quantified by the mutual information, and continuous-variable quantum key distribution, quantified by the key generation rate. The preliminary results encourage further use of this detection scheme in extended networks.
In quantum communication protocols, the use of photon-number-resolving detectors could open new perspectives by broadening the way to encode and decode information and merging the properties of discrete and continuous variables. In this work, we consider a quantum channel exploiting a silicon-photomultiplier-based receiver and evaluate its performance for quantum communication protocols under three possible configurations, defined by different post-processing of the detection outcomes. We investigate two scenarios: information transmission over the channel, quantified by the mutual information, and continuous-variable quantum key distribution, quantified by the key generation rate. The preliminary results encourage further use of this detection scheme in extended networks.
In quantum communication protocols, the use of hybrid devices, giving access to both particle- and wave-like properties of light, could open new perspectives for novel encoding procedures that merge the properties of discrete and continuous variables. In our work, we explore the context of continuous-variable quantum key distribution with binary modulated coherent states over a pure-loss channel with a Silicon-photomultiplier-based hybrid receiver. In particular, we investigate how the key generation rate behaves as a function of the losses affecting the coherent states and the number of data used to send them both in the case of individual and collective attacks. The obtained outcomes encourage the further exploitation of this hybrid receiver in extended networks.
Nowadays, quantum communications provide a vast field of research in rapid expansion, with a huge potential impact on the future developments of quantum technologies. In particular, continuous variable systems, employing coherent-state encoding and quadrature measurements, represent a suitable platform, due to their compatibility with both the modulation and detection systems currently employed in standard fiber-optical communications. In this work, we address some relevant aspects of the field, and provide innovative results being also experimentally oriented. In particular, we focus on two relevant paradigms: quantum decision theory and continuous variable quantum key distribution (CVQKD). In the former case, we address the problem of coherent-state discrimination and design new hybrid receivers for binary phase-shift keying discrimination, obtaining a quantum advantage over conventional detection schemes, being also robust against typical experimental imperfections. In the latter scenario, we proceed in two different directions. On the one hand, we design new CVQKD protocols employing discrete modulation of coherent states, being a feasible solution compatible with the state of the art in optical communications technologies. On the other hand, we address the more fundamental problem of performing channel losses mitigation to enhance existing protocols, and investigate the role of optical amplifiers for the task. Finally, we make a first step towards a fully non-Gaussian CVQKD scheme by proposing, for the first time, the adoption of an optimized state-discrimination receiver, commonly adopted for quantum decision theory, within the context of CVQKD, obtaining a genuine quantum enhancement over conventional protocols.
Over the past decade, binary phase-shift-keying encoding has been used as a benchmark to test the performance of different detection strategies to address the problem of state discrimination. In this context, hybrid devices, giving access to both particle- and wave-like properties of light, could offer the possibility to better discriminate the sent signals. In this work, we consider a quantum channel exploiting a hybrid receiver embedding Silicon photomultipliers as photon-number-resolving detectors. We retrieve the discrimination error probability and the mutual information between sender and receiver as functions of some relevant experimental parameters in the case of binary phase-shifted coherent states. Our promising results, supported also with numerical simulations and theoretical analysis, foster further using this kind of hybrid receiver in more complex detection schemes. • We address state discrimination by a Silicon photomultiplier-based hybrid receiver. • The hybrid receiver gives access to particle- and wave-like properties of light. • We consider error probability and mutual information in a BPSK scenario.
Twin-beam (TWB) states generated by parametric down-conversion exhibit strong photon-number correlations that can be exploited for quantum communication. In the mesoscopic regime, these correlations can be directly investigated using photon-number-resolving detectors, such as silicon photomultipliers (SiPMs). Their nonclassical nature is quantified by the noise reduction factor (NRF), which provides a witness of quantum correlations and a means of monitoring channel security. In this work, a quantum communication protocol based on TWB states, originally proposed for binary encoding, is extended to a four-state scheme capable of transmitting two bits per use. Information is encoded by combining two mean photon-number values and two mode numbers of thermal noise superimposed on one arm of the twin beam, defining four distinguishable states in the (m,R) plane. While the mean detected photon number enables the retrieval of one bit, the NRF provides discrimination of the second bit and a security check against intercept-and-resend attacks, which introduce additional noise and degrade the quantum correlations. The protocol is investigated through two experimental measurement campaigns. First, the twin-beam source is characterized in terms of photon-number statistics, NRF, and detection efficiency to establish the operating conditions of the communication channel. Subsequently, the four-state protocol is implemented and evaluated through the analysis of state distributions and their 95% confidence regions, error probability as a function of sample size, and a comparative assessment of machine learning classifiers for state discrimination. Finally, the response of the NRF to an intercept-and-resend attack is investigated to assess the protocol's ability to detect eavesdropping.
We put forward a hybrid quantum key distribution protocol based on coherent states, Gaussian modulation, and photon-number-resolving (PNR) detectors, and show that it may enhance the secret key generation rate (KGR) compared to homodyne-based schemes. Improvement in the KGR may be traced back to the dependence of the two-dimensional discrete output variable on both the input quadratures, thus overcoming the limitations of the original protocol. When reverse reconciliation is considered, the scheme based on PNR detectors outperforms the homodyne one both for individual and collective attacks. In the presence of direct reconciliation, the PNR strategy is still the best one against individual attacks, but for the collective ones the homodyne-based scheme is still to be preferred as the channel transmissivity decreases.
Quantum key distribution (QKD) enables secret-key establishment through measurements of quantum states, but practical performance depends strongly on the optical receiver, modulation format, decision process, and reconciliation strategy. This thesis develops three receiver-oriented approaches for improving the information advantage of legitimate users under explicitly stated security models. First, a dual-branch photon-number-resolving (DB-PNR) receiver is developed for coherent-state hybrid QKD. Complementary displacement branches and four photon-count outputs reduce the sign ambiguity of single-branch reception and recover information associated with both optical quadratures. Under the adopted pure-loss models, DB-PNR reception improves mutual information and secret-key-generation rate relative to homodyne, heterodyne, and single-branch PNR references. Second, a four-level multi-threshold intensity-modulation and direct-detection (MT-IM–DD) protocol is formulated. Optical intensity levels, five decision thresholds, and two erasure regions are jointly optimized under Gaussian classical, quantum, and thermal receiver-noise terms. The analysis separates conditional key rate from acceptance-weighted secret throughput and evaluates forward and reverse reconciliation under beam-splitting and intercept–resend attacks. Third, binary IM–DD is operated directly in the low-photon-number quantum regime using photon-number-resolving direct detection. Integer Poisson observations are processed with a likelihood-symmetric dual-threshold rule. The closed-form coupling between the two boundaries reduces the threshold optimization from two independent variables to one while preserving most of the benefit of free two-threshold optimization. Across all three studies, improved receiver measurements and deliberate post-selection increase performance under the stated assumptions. The results are comparative asymptotic bounds, not universal composable-security proofs. Finite-key effects, detector nonidealities, soft-information eavesdropping, general quantum attacks, and experimental validation remain necessary extensions.