arXiv subjects

Ivo Pietro Degiovanni

Publications and source records attributed to Ivo Pietro Degiovanni.

At least 19 recordsLinked to original sources

arXiv2026

Table-top nanodiamond interferometer enabling quantum gravity tests

Along the path of unifying quantum theory and general relativity, it has recently been argued that the observation of gravity-induced entanglement could demonstrate the quantum nature of gravity; a few experimental proposals have been advanced, but extreme technological requirements make their implementation still far. Here we propose a table-top interferometer that, by relying on quantum superpositions of steady nanodiamonds, enables less demanding quantum gravity tests requiring short-range time-varying magnetic fields (much easier to implement) and allowing to recycle the exploited quantum probes (granting shorter acquisition times and increased precision).

quant-ph↗

arXiv2026

Spectral evolution of two-photon emission in microresonators

High-Q silicon nitride microresonators are versatile sources for generating photon pairs via four-wave mixing. We investigate the spectral coherence of this process, tracking the transition from the spontaneous quantum regime to the onset of optical parametric oscillation. By combining time-correlation measurements with phase-sensitive measurements, we continuously monitor the emission linewidth as it evolves from a cavity-lifetime-limited linewidth toward the pump-linewidth scale. This characterization is essential for optimizing integrated sources for scalable quantum networks.

quant-ph↗

arXiv2026

Universal Protection of Quantum States from Decoherence

The fragility of quantum coherence fundamentally limits the scalability of quantum technologies, as unavoidable environmental interactions induce decoherence and rapidly degrade quantum properties. The Quantum Zeno Effect offers a powerful route to suppress quantum evolution and protect coherence through frequent measurements, irrespective of the underlying dynamics. However, existing implementations require prior knowledge of the quantum state, severely restricting their applicability. Here we introduce a state- and dynamics-independent protection protocol embedding the system in a larger Hilbert space, temporarily swapping the quantum information from its original degree of freedom to a decoherence-free ancillary one. We experimentally validate the protocol on a quantum optical platform, demonstrating robust preservation of coherence and purity for arbitrary polarization qubits under decoherence, thereby enabling the universal safeguarding of unknown quantum states.

quant-ph↗

arXiv2025

Experimental Test of Nonlocality Limits from Relativistic Independence

Quantum correlations, like entanglement, represent the characteristic trait of quantum mechanics, and pose essential issues and challenges to the interpretation of this pillar of modern physics. Although quantum correlations are largely acknowledged as a major resource to achieve quantum advantage in many tasks of quantum technologies, their full quantitative description and the axiomatic basis underlying them are still under investigation. Previous works suggested that the origin of nonlocal correlations is grounded in principles capturing (from outside the quantum formalism) the essence of quantum uncertainty. In particular, the recently-introduced principle of Relativistic Independence gave rise to a new bound intertwining local and nonlocal correlations. Here we test such a bound by realizing together sequential and joint weak measurements on entangled photon pairs, allowing to simultaneously quantify both local and nonlocal correlations by measuring incompatible observables on the same quantum system without collapsing its state, a task typically forbidden in the traditional (projective) quantum measurement framework. Our results demonstrate the existence of a fundamental limit on the extent of quantum correlations, shedding light on the profound role of uncertainty in both enabling and balancing them.

quant-ph↗

arXiv2024

The Bose-Marletto-Vedral experiment with nanodiamond interferometers: an insight on entanglement detection

Recently, it has been proposed a new method [arXiv:2405.21029] to detect quantum gravity effects, based on generating gravitational entanglement between two nano-diamonds with Nitrogen-Vacancy defects, in a magnetically trapped configuration. Here we analyse in detail the proposed experimental setup, with a particular focus on implementing the detection of the gravitationally-induced entanglement using an optical readout based on measuring the position of the nano-diamonds and its complementary basis. We also summarise some of the key theoretical and experimental ideas on which this proposed scheme is based.

quant-ph↗

arXiv2024

Universal quantum theory contains twisted logic

Quantum theory is notoriously counterintuitive, and yet remains entirely self-consistent when applied universally. Here we uncover a new manifestation of its unusual consequences. We demonstrate, theoretically and experimentally (by means of polarization-encoded single-photon qubits), that Heisenberg's uncertainty principle leads to the impossibility of stringing together logical deductions about outcomes of consecutive non-compatible measurements. This phenomenon resembles the geometry of a Penrose triangle, where each corner is locally consistent while the global structure is impossible. Besides this, we show how overlooking this non-trivial logical structure leads to the erroneous possibility of distinguishing non-orthogonal states with a single measurement.

quant-ph↗

arXiv2024

Quantum super-resolution microscopy by photon statistics and structured light

We present an advanced quantum super-resolution imaging technique based on photon statistics measurement and its accurate modeling. Our reconstruction algorithm adapts to any kind of non-Poissonian emitters, outperforming the corresponding classical SOFI method. It offers sub-diffraction resolution improvement that scales with the $\sqrt{j}$, where $j$ is the highest order central moments of the photocounts. More remarkably, in combination with structured illumination a linear improvement with j can be reached. Through simulations and experiments, we prove our method's clear superiority over traditional SOFI, especially in low excitation light conditions, providing a promising avenue for non-invasive super-resolution microscopy of delicate samples.

quant-ph↗

arXiv2024

Detection Efficiency Characterization for Free-Space Single-Photon Detectors: Measurement Facility and Wavelength-Dependence Investigation

In this paper, we present a new experimental apparatus for the measurement of the detection efficiency of free-space single-photon detectors based on the substitution method. For the first time, we extend the analysis to account for the wavelength dependence introduced by the transmissivity of the optical window in front of the detector's active area. Our method involves measuring the detector's response at different wavelengths and comparing it to a calibrated reference detector. This allows us to accurately quantify the efficiency variations due to the optical window's transmissivity. The results provide a comprehensive understanding of the wavelength-dependent efficiency, which is crucial for optimizing the performance of single-photon detectors in various applications, including quantum communication and photonics research. This characterization technique offers a significant advancement in the precision and reliability of single-photon detection efficiency measurements.

quant-ph↗

arXiv2024

Phase Noise in Real-World Twin-Field Quantum Key Distribution

The impact of noise sources in real-world implementations of Twin-Field Quantum Key Distribution (TF-QKD) protocols is investigated, focusing on phase noise from photon sources and connecting fibers. This work emphasizes the role of laser quality, network topology, fiber length, arm balance, and detector performance in determining key rates. Remarkably, it reveals that the leading TF-QKD protocols are similarly affected by phase noise despite different mechanisms. This study demonstrates duty cycle improvements of over a factor of two through narrow-linewidth lasers and phase-control techniques, highlighting the potential synergy with high-precision time/frequency distribution services. Ultrastable lasers, evolving toward integration and miniaturization, offer promise for agile TF-QKD implementations on existing networks. Properly addressing phase noise and practical constraints allows for consistent key rate predictions, protocol selection, and layout design, crucial for establishing secure long-haul links for the Quantum Communication Infrastructures under development in several countries.

quant-ph↗

arXiv2023

Single-pair measurement of the Bell parameter

Bell inequalities are one of the cornerstones of quantum foundations, and fundamental tools for quantum technologies. Recently, the scientific community worldwide has put a lot of effort towards them, which culminated with loophole-free experiments. Nonetheless, none of the experimental tests so far was able to extract information on the full inequality from each entangled pair, since the wave function collapse forbids performing, on the same quantum state, all the measurements needed for evaluating the entire Bell parameter. We present here the first single-pair Bell inequality test, able to obtain a Bell parameter value for every entangled pair detected. This is made possible by exploiting sequential weak measurements, allowing to measure non-commuting observables in sequence on the same state, on each entangled particle. Such an approach not only grants unprecedented measurement capability, but also removes the need to choose between different measurement bases, intrinsically eliminating the freedom-of-choice loophole and stretching the concept of counterfactual-definiteness (since it allows measuring in the otherwise not-chosen bases). We also demonstrate how, after the Bell parameter measurement, the pair under test still presents a noteworthy amount of entanglement, providing evidence of the absence of (complete) wave function collapse and allowing to exploit this quantum resource for further protocols.

quant-ph↗

arXiv2022

Mode structure reconstruction by detected and undetected light

We introduce a novel technique for the reconstruction of multimode optical fields, based on simultaneously exploiting both the generalized Glauber's $K^{th}$-order correlation function $g^{(K)}$ and a recently proposed anti-correlation function (dubbed $θ^{(K)}$) which is resilient to Poissonian noise. We experimentally demonstrate that this method yields mode reconstructions with higher fidelity with respect to those obtained with reconstruction methods based only on $g^{(K)}$'s, even requiring less "a priori" information. The reliability and versatility of our technique make it suitable for a widespread use in real applications of optical quantum measurement, from quantum information to quantum metrology, especially when one needs to characterize ensembles of single-photon emitters in the presence of background noise (due, for example, to residual excitation laser, stray light, or unwanted fluorescence).

quant-ph↗

arXiv2022

Sensing microscopic noise events by frequent quantum measurements

We propose and experimentally demonstrate a general method allowing us to unravel microscopic noise events that affect a continuous quantum variable. Such unraveling is achieved by frequent measurements of a discrete variable coupled to the continuous one. The experimental realization involves photons traversing a noisy channel. There, their polarization, whose coupling to the photons spatial wavepacket is subjected to stochastic noise, is frequently measured in the quantum Zeno regime. The measurements not only preserve the polarization state, but also enable the recording of the full noise statistics from the spatially-resolved detection of the photons emerging from the channel. This method proves the possibility of employing photons as quantum noise sensors and robust carriers of information.

quant-ph↗

arXiv2022

Magnesium-vacancy optical centers in diamond

We provide the first systematic characterization of the structural and photoluminescence properties of optically active defect centers fabricated upon implantation of 30-100 keV Mg+ ions in artificial diamond. The structural configurations of Mg-related defects were studied by the emission channeling technique for 27Mg implantations performed both at room-temperature and 800 °C, which allowed the identification of a major fraction of Mg atoms (~30-42%) in sites which are compatible with the split-vacancy structure of the MgV complex. A smaller fraction of Mg atoms (~13-17%) was found on substitutional sites. The photoluminescence emission was investigated both at the ensemble and individual defect level in a temperature range comprised between 5 K and 300 K, offering a detailed picture of the MgV-related emission properties and revealing the occurrence of previously unreported spectral features. The optical excitability of the MgV center was also studied as a function of the optical excitation wavelength enabling to identify the optimal conditions for photostable and intense emission. The results are discussed in the context of the preliminary experimental data and the theoretical models available in the literature, with appealing perspectives for the utilization of the tunable properties of the MgV center for quantum information processing applications.

cond-mat.mtrl-sci↗

arXiv2021

Unexpected detection rate dependence of the intrinsic detection efficiency in single-photon detectors based on avalanche diodes

Single-photon detectors are a pivotal component in photonic quantum technologies. A precise and comprehensive calibration of the intrinsic detection efficiency is of utmost importance to ensure the proper evaluation of the performance in view of the specific technological application of interest, such as the protection against security breaches in quantum cryptographic solutions. Here we report on a systematic study on and comprehensive analysis of the estimation of the intrinsic detection efficiency of two commercial single-photon detectors based on single-photon avalanche diodes (SPADs) for various mean photon numbers and at high laser pulse repetition rates using different techniques. We observed an unexpected and signifucant drop in intrinsic detection efficiency at detection rates of 10 % and higher relative to the maximum detection rate. It is demonstrated that for data analysis a statistical model for the detection rate conveniently can be used if no timestamped data are available. We conclude that the full characterization of single-photon detectors used in critical applications should include the sensitivity of their intrinsic detection efficiency to high event rates.

quant-ph↗

arXiv2021

Quantum Conformance Test

We introduce a protocol addressing the conformance test problem, which consists in determining whether a process under test conforms to a reference one. We consider a process to be characterized by the set of end-product it produces, which is generated according to a given probability distribution. We formulate the problem in the context of hypothesis testing and consider the specific case in which the objects can be modeled as pure loss channels. We demonstrate theoretically that a simple quantum strategy, using readily available resources and measurement schemes in the form of two-mode squeezed vacuum and photon-counting, can outperform any classical strategy. We experimentally implement this protocol, exploiting optical twin beams, validating our theoretical results, and demonstrating that, in this task, there is a quantum advantage in a realistic setting.

quant-ph↗

arXiv2021

Temporal teleportation with pseudo-density operators: how dynamics emerges from temporal entanglement

We show that, by utilising temporal quantum correlations as expressed by pseudo-density operators (PDOs), it is possible to recover formally the standard quantum dynamical evolution as a sequence of teleportations in time. We demonstrate that any completely positive evolution can be formally reconstructed by teleportation with different temporally correlated states. This provides a different interpretation of maximally correlated PDOs, as resources to induce quantum time-evolution. Furthermore, we note that the possibility of this protocol stems from the strict formal correspondence between spatial and temporal entanglement in quantum theory. We proceed to demonstrate experimentally this correspondence, by showing a multipartite violation of generalised temporal and spatial Bell inequalities and verifying agreement with theoretical predictions to a high degree of accuracy, in high-quality photon qubits.

quant-ph↗

arXiv2021

Emergence of Constructor-based Irreversibility in Quantum Systems: Theory and Experiment

The issue of irreversibility in a universe with time-reversal-symmetric laws is a central problem in physics. % , and, in particular, to statistical mechanics, information theory and quantum thermodynamics. In this letter, we discuss for the first time how irreversibility can emerge within the recently proposed constructor theory framework. Here irreversibility is expressed as the requirement that a task is possible, while its inverse is not. In particular, we demonstrate that this irreversibility is compatible with quantum theory's time reversal symmetric laws, by exploiting a specific model, based on the universal quantum homogeniser, realised experimentally with high-quality single-photon qubits.

quant-ph↗

arXiv2021

Spectral emission dependence of tin-vacancy centers in diamond from thermal processing and chemical functionalization

We report a systematic photoluminescence (PL) investigation of the spectral emission properties of individual optical defects fabricated in diamond upon ion implantation and annealing. Three spectral lines at 620 nm, 631 nm, and 647 nm are identified and attributed to the SnV center due to their occurrence in the PL spectra of the very same single-photon emitting defects. We show that the relative occurrence of the three spectral features can be modified by oxidizing the sample surface following thermal annealing. We finally report the relevant emission properties of each class of individual emitters, including the excited state emission lifetime and the emission intensity saturation parameters.

quant-ph↗