Quantum metrology is one of the most promising applications quantum technologies. The aim this research field estimation unknown parameters exploiting resources, whose application can lead to enhanced performances with respect classical strategies. Several physical systems be employed develop sensors, and photonic represent ideal probes for a large number metrological tasks. Here, authors review basic concepts behind then focus on technology task, particular attention phase estimation....

Structured light is attracting significant attention for its diverse applications in both classical and quantum optics. The so-called vector vortex beams display peculiar properties contexts due to the nontrivial correlations between optical polarization orbital angular momentum. Here we demonstrate a new, flexible experimental approach classification of beams. We first describe platform generating arbitrary complex inspired photonic walks. then exploit recent machine learning...

Phase estimation has applications from quantum imaging to gravitational-wave detection. In areas such as biological-system sampling or metrology, it is crucial optimally acquire information a very limited number of probes. To address this need, the authors describe and experimentally verify machine-learning method for optimal adaptive single-photon phase based on small trials. This approach could be used optimize metrology protocols, can extended general multiparameter scenarios.

The capability to generate and manipulate quantum states in high-dimensional Hilbert spaces is a crucial step for the development of technologies, from communication computation. One-dimensional walk dynamics represents valid tool task engineering arbitrary states. Here we affirm such potential linear-optics platform that realizes discrete-time walks orbital angular momentum degree freedom photons. Different classes relevant qudit six-dimensional space are prepared measured, confirming...

Multiparameter estimation is a general problem that aims at measuring unknown physical quantities, obtaining high precision in the process.In this context, adoption of quantum resources promises substantial boost achievable performances with respect to classical case.However, several open problems remain be addressed multiparameter scenario.A crucial requirement identification suitable platforms develop and experimentally test novel efficient methodologies can employed framework.We report...

Photon entanglement is at the basis of many protocols in photonic quantum technologies, from computing to simulation and sensing.The generation entangled photons integrated waveguides particularly advantageous due enhanced stability more efficient nonlinear interaction.Here we realize an source wavelength-degenerate based on hybrid interfacing circuits different materials, all inscribed by femtosecond laser pulses.We show that our source, spontaneous parametric down-conversion telecom...

Estimation of physical quantities is at the core most scientific research, and use quantum devices promises to enhance its performances. In real scenarios, it fundamental consider that resources are limited, Bayesian adaptive estimation represents a powerful approach efficiently allocate, during process, all available resources. However, this framework relies on precise knowledge system model, retrieved with fine calibration, results often computationally experimentally demanding. We...

Recent developments have led to the possibility of embedding machine learning tools into experimental platforms address key problems, including characterization properties quantum states. Leveraging on this, we implement a extreme in photonic platform achieve resource-efficient and accurate polarization state photon. The underlying reservoir dynamics through which such input evolves is implemented using coined walk high-dimensional orbital angular momentum performing projective measurements...

Wave-particle duality is the most fundamental description of nature a quantum object which behaves like classical particle or wave depending on measurement apparatus. On other hand, entanglement represents nonclassical correlations composite systems, being also key resource in information. Despite very recent observations wave-particle superposition and entanglement, whether these two traits mechanics can emerge simultaneously remains an open issue. Here we introduce experimentally realize...

Abstract The launch of a satellite capable distributing entanglement through long distances and the first loophole-free violation Bell inequalities are milestones indicating clear path for establishment quantum networks. However, nonlocality in networks with independent sources has only been experimentally verified simple tripartite networks, via bilocality inequalities. Here, by using scalable photonic platform, we implement star-shaped consisting up to five distant nodes four sources. We...

Calibration of sensors is a fundamental step to validate their operation. This can be demanding task, as it relies on acquiring detailed modelling the device, aggravated by its possible dependence upon multiple parameters. Machine learning provides handy solution this issue, operating mapping between parameters and device response, without needing additional specific information functioning. Here we demonstrate application Neural Network based algorithm for calibration integrated photonic...

Abstract Entanglement-based quantum key distribution can enable secure communication in trusted node-free networks and over long distances. Although implementations exist both fiber free space, the latter approach is often considered challenging due to environmental factors. Here, we implement a protocol during daytime for first time using dot source. This technology presents advantages terms of narrower spectral bandwidth—beneficial filtering out sunlight—and negligible multiphoton emission...

Relevant metrological scenarios involve the simultaneous estimation of multiple parameters. The fundamental ingredient to achieve quantum-enhanced performance is based on use appropriately tailored quantum probes. However, reaching ultimate resolution allowed by physical laws requires nontrivial strategies from both a theoretical and practical point view. A crucial tool for this purpose application adaptive learning techniques. Indeed, provide flexible approach obtain optimal...

Entanglement distribution between distant parties is one of the most important and challenging tasks in quantum communication. Distribution photonic entangled states using optical fiber links a fundamental building block towards networks. Among different degrees freedom, orbital angular momentum (OAM) promising due to its natural capability encode high dimensional states. In this article, we experimentally demonstrate hybrid polarization-vector vortex photon pairs. To end, exploit recently...

Abstract Achieving ultimate bounds in estimation processes is the main objective of quantum metrology. In this context, several problems require measurement multiple parameters by employing only a limited amount resources. To end, adaptive protocols, exploiting additional control parameters, provide tool to optimize performance sensor work such data regime. Finding optimal strategies tune during process non-trivial problem, and machine learning techniques are natural solution address task....

The orbital angular momentum (OAM) of light is an infinite-dimensional degree freedom with several applications in both classical and quantum optics. However, to fully take advantage the potential OAM states, reliable detection platforms characterize generated states experimental conditions are needed. Here, we present approach reconstruct input from measurements spatial intensity distributions they produce. To obviate issues arising intrinsic symmetry Laguerre-Gauss modes, employ a pair...

Abstract Adopting quantum resources for parameter estimation discloses the possibility to realize sensors operating at a sensitivity beyond standard limit. Such an approach promises reach fundamental Heisenberg scaling as function of employed N in process. Although previous experiments demonstrated precision approaching Heisenberg-limited performances, reaching such regime wide range remains hard accomplish. Here, we show method that suitably allocates available permitting them same power...

Bell's theorem is typically understood as the proof that quantum theory incompatible with local-hidden-variable models. More generally, we can see violation of a Bell inequality witnessing impossibility explaining correlations classical causal The inequality, however, does not exclude models where some level measurement dependence allowed, is, choice made by observers be correlated source generating systems to measured. Here, show quantitatively upper bounded if arrange test within network....

Randomness certification is a foundational and practical aspect of quantum information science, essential for securing communication protocols. Traditionally, these protocols have been implemented validated with single entanglement source, as in the paradigmatic Bell scenario. However, advancing to support more complex configurations involving multiple sources key building robust architectures realizing large-scale networks. In this work, we show how certify randomness an...

The violation of a Bell inequality is the paradigmatic example device-independent quantum information: nonclassicality data certified without knowledge functioning devices. In practice, however, all experiments rely on precise understanding underlying physical mechanisms. Given that, it natural to ask: Can one witness nonclassical behavior in truly black-box scenario? Here, we propose and implement, computationally experimentally, solution this ab initio task. It exploits robust automated...

Since Bell's theorem, it is known that local realism fails to explain quantum phenomena. Bell inequality violations manifestly show the incompatibility of theory with classical notions cause and effect. As recently found, however, instrumental scenario-a pivotal tool in causal inference-allows for nonclassicality signatures going beyond this paradigm. If we are not limited observational data can intervene our setup, then witness bounds on influence among involved variables even when no...

Using a quantum triangle network, in which each of the three parties can perform number separable and independent measurements, genuine tripartite nonlocality is achieved without employment source.

Abstract In a Bell experiment, it is natural to seek causal account of correlations wherein only common cause acts on the outcomes. For this structure, inequality violations can be explained if dependencies are modeled as intrinsically quantum. There also exists vast landscape structures beyond that witness nonclassicality, in some cases without even requiring free external inputs. Here, we undertake photonic experiment realizing one such example: triangle network, consisting three...

Abstract Bell nonlocality refers to correlations between two distant, entangled particles that challenge classical notions of local causality. Beyond its foundational significance, is crucial for device-independent technologies like quantum key distribution and randomness generation. Nonlocality quickly deteriorates in the presence noise, restoring nonlocal requires additional resources. These often come form many instances input state joint measurements, incurring a significant resource...

The quest for precision in parameter estimation is a fundamental task different scientific areas. relevance of this problem thus provided the motivation to develop methods application quantum resources protocols. Within context, Bayesian offers complete framework optimal metrology techniques, such as adaptive However, use approach requires extensive computational resources, especially multiparameter estimations that represent typical operational scenario sensors. Hence, requirement...