Silicon color centers have emerged as promising candidates for quantum information technologies, yet their interaction with electric fields is not well understood. We will discuss electrical manipulation of G-centers in silicon -- quantum emitters that photoluminesce in the telecom O-band. We fabricated lateral electrical diodes with an integrated ensemble of G centers in a commercial silicon on insulator wafer. Under application of a reverse-biased DC electric field, the ensemble of G-centers redshifts by approximately 1.4 GHz/V above a threshold “turn-on voltage.” The fluorescence intensity is modulated by increasing electric field, ultimately achieving 100% extinction. Finally, we use G center fluorescence to directly image the electric field distribution within the devices, obtaining insight into the spatial and voltage-dependent variation of the junction depletion region and the associated mediating effects on the ensemble. The emitter-field coupling is correlated to the photocurrent generated in the device. Our device architecture uniquely enables simultaneous optical and electrical manipulation of quantum emitters, and it is readily extensible to other quantum emitters.

In this work we exploit entangled twin-beam to enhance quantitative phase retrieval of an object in a non-interferometric setting, only measuring the propagated intensity pattern after interaction with the object. The scheme achieves full field phase reconstruction with quasi-single-shot acquisition, not requiring time consuming raster-scanning of the sample. In our experiment a 40% improved precision has been achieved with respect to the corresponding classical scheme.

In quantum mechanics, the precision achieved in parameter estimation using a quantum state as a probe is determined by the measurement strategy employed. The quantum precision limit, a fundamental boundary, is defined by the intrinsic characteristics of the state and its dynamics. Theoretical results have revealed that in interference measurements with two possible outcomes, like the Hong Ou-Mandel interference, this limit can be reached under ideal conditions of perfect visibility and zero losses. However, in practice, this cannot be achieved, so precision never reaches the quantum limit. But how do experimental setups approach precision limits under realistic circumstances? In this work, we provide a general model for precision limits in two-photon Hong-Ou-Mandel interferometry for non-perfect visibility and validate it experimentally using different quantum states. A remarkable ratio of 0.97 between the experimental precision and the quantum limit is observed, establishing a new benchmark in the field.

Hybrid photonic devices, harnessing the advantages of multiple materials while mitigating their respective weaknesses, represent a promising solution to the effective on-chip integration of generation and manipulation of non-classical states of light encoding quantum information. We demonstrate a hybrid III-V/Silicon quantum photonic device combining the strong second-order nonlinearity and compliance with electrical pumping of the III-V semiconductor platform with the high maturity and CMOS compatibility of the silicon photonic platform. Our device embeds the Spontaneous Parametric Down-Conversion (SPDC) of photon pairs into an AlGaAs source and their subsequent routing to a silicon-on-insulator circuitry. This enables the on-chip generation of broadband telecom photon pairs by type zero and type two SPDC from the hybrid device, at room temperature and with strong rejection of the pump beam. Two-photon interference with 92% visibility proves the high energy-time entanglement quality characterizing the produced quantum state, thereby enabling a wide range of quantum information applications.

Entangled photon-pairs are crucial for applications like quantum key distribution, sensing and imaging. For prospective use in real world devices, the challenge for Entangled Photon-Pair Sources (EPS) is to simultaneously meet high requirements regarding state fidelity, tunability etc. while maintaining a small footprint and high robustness. In this work, we develop an EPS that meets these demands. Using a sub-micron thick Transition Metal Dichalcogenide (TMD) crystal, we show tunable generation of polarization entangled Bell states via Spontaneous Parametric Down-Conversion (SPDC). To the best of our knowledge, this is the first realization of SPDC in a TMD. In particular, we employ the TMD 3R-phase molybdenum disulfide (3R-MoS2), which due to its crystal symmetry intrinsically creates entanglement without needing external optical components. We experimentally demonstrate tuning between different maximally entangled states with constant generation efficiency and show pathways towards highly efficient and tunable TMD-based EPS using quasi-phasematching or cavity integration.

Quantum Key Distribution (QKD) is a technology that allows sharing secret cryptographic keys between two distant users (Alice and Bob), whose intrinsic security is guaranteed by fundamental principles of quantum mechanics. QKD is a mature technology even if one of the main remaining challenges is the integration of different solutions in already deployed telecommunication fiber networks, in particular in long-haul segments. An approach able to cover long distances is the Twin-field QKD (TF-QKD) protocol; TF-QKD exploits interference of optical pulses in a central untrusted node (Charlie), allowing to double the communication distance with respect to the conventional prepare-and-measure solutions. Here we present a solution to one of the main issues of Twin-Field QKD, the phase stabilization within the optical path, demonstrating a strong advantage in performances of real word TF- QKD and testing our solution in a segment of the Italian Quantum Backbone. Furthermore, we analyze in detail the expected gain in terms of key rate exploiting our stabilization technique in the main TF-QKD-based protocols, even when they are declared insensitive to the phase noise.

Despite its low-power and industrialization advantages, spintronics has so far not been featured among the many quantum technological platforms because embedding a quantum object with discrete electronic states within this class of solid-state device is challenging. I will present recent research into a quantum flavor of inorganic and molecular spintronics that utilizes the spin states of individual magnetic atoms to encode quantum information and autonomously harvest thermal energy within solid-state vertical pillar devices.

Quantum emitters in two-dimensional layered hexagonal boron nitride are quickly emerging as a highly promising platform for next-generation quantum technologies. However, precise identification and control of defects are key parameters to achieve the next step in their development. We conducted a comprehensive study by analyzing over 10,000 photoluminescence emission lines, revealing 11 distinct defect families within the 1.6 to 2.2 eV energy range, challenging the hypotheses of a random energy distribution. These findings provide valuable insights to decipher the microscopic origin of emitters in hBN. The spectral spacing between defect families could serve as a key parameter for theoretical investigations We also explored the influence of hBN host morphology on defect family formation, demonstrating its crucial impact. By tuning flake size and arrangement, we achieve selective control of defect types while maintaining high spatial density. This offers a scalable approach to defect emission control, diverging from costly engineering methods.

Entanglement is a central resource in quantum technologies. In this respect, high-dimensional entangled states are very promising for developing robust quantum communication schemes and enhanced imaging protocols. Being able to quantify high-dimensional entanglement quickly and accurately is therefore essential. However, to date, all experimental methods use assumptions about the detected state or imperfect measurement techniques, such as single-outcomes and accidental subtractions. Entanglement certification processes are therefore not only slow, but they also contain loopholes, which is not acceptable in adversarial scenarios such as quantum key distribution (QKD). In our work, we demonstrate the certification of high-dimensional entanglement using an event-based single-photon sensitive camera by performing measurements in two mutually unbiased bases. Our work provides an experimental method allowing for the efficient characterization of high-dimensional quantum states, paving the way for the development of high-dimensional QKD protocols and practical photon-pairs-based quantum imaging approaches.

This study falls within the field of quantum imaging. Photon-pair correlations in spontaneous parametric down conversion processes are ubiquitous in quantum photonics and its applications. In this work, researchers structure these correlations in the form of images of arbitrarily chosen objects. They show that their approach works with both amplitude and phase objects, even when the beam intensity is also spatially shaped. Furthermore, they demonstrate that - in certain cases - the transmission of quantum correlations-encoded images through scattering media is more efficient than using classical light. Their approach enables the transmission of complex, high-dimensional information using in quantum correlations of photons, which can be useful for developing quantum communication and imaging protocols.

Vectorial modes of light, a type of structured light where the polarization varies across the beam profile, are a useful tool both in classical and quantum applications. In quantum communication, for instance, these modes enable rotational invariant protocols, therefore overcoming the requirement of a shared reference frame between users. Moreover, structured light can be a resource for enhanced sensing purposes as for instance in the “photonic gears” technique. This quantum inspired scheme enables a boost of sensitivity in mechanical displacements measurement thanks to a bidirectional mapping between the polarization state and a properly tailored vectorial mode of a paraxial light beam. Finally, we will discuss how quantum interference can be controlled and tailored for structured light modes, therefore providing a key ingredient for exploiting the full potential of complex light in the quantum domain.

The continuous nature of the frequency degree of freedom in a single photon allows for a high-dimensional encoding scheme, reducing optical costs. Discretizing the frequency allows for defining qubits that are robust against temporal and spectral broadening. Errors can occur during single photon manipulation and optical fiber propagation. Crosstalk between classical and quantum signals within optical fibers also affects these encodings. To address temporal and frequency broadening issues in these encodings, two methods are explored. One relies on costly non-linear optics, while the second solely utilizes linear optics. The second method involves a teleportation-based error correction protocol, where a noisy frequency qubit carrying quantum information becomes entangled with a less noisy frequency-entangled state. This process involves Bell measurements and inherently incorporates error correction, as the remaining frequency single-photon state, following the protocol, becomes associated with a lower-noise entangled state in both time and frequency domains (Applied Sciences 13, 9462).

Fundamental phenomena like Quantum Zeno effect (QZE) and Anti-Zeno Effect (AZE) have been recognized as relevant tools for quantum control. Along this line, here we present two experiments in which we demonstrate the capability to extract information on noise events by exploiting QZE and AZE. In the first experiment, we realize noise diagnostics by frequent measurement, showing how a single photon undergoing a noise process (e.g., random polarization fluctuations) can diagnose non-Markovian temporal correlations within such a noise. In the second one, instead, we show how, by protecting via QZE a photonic qubit in a noisy quantum channel, it is possible to estimate the statistical distribution of the microscopic noise (decoherence) events by using the qubit itself as a probe. These techniques can become indispensable under extremely faint illumination, when traditional interferometric methods are usually ineffective.

We present a turn-key portable picosecond fiber laser for efficient quantum dot excitation to generate single photons. The laser combines a mode-hop-free tunability in the regions 770-980 nm and 1150-1500 nm with a high pulse-to-pulse coherence of 98%. A high single photon purity and indistinguishability were demonstrated. An excellent long-term power stability with a standard deviation of less than 0.3% and wavelength stability of better than 5 pm were achieved. The laser enables excitation of different semiconductor quantum dots and excitation schemes, essential for versatile easy-to-use single-photon sources based on quantum dots for research applications and commercial quantum computing.

Spontaneous-Parametric-Down-Conversion-produced photons, which are positively correlated in frequency, possess properties favorable in the context of Fourier-domain Quantum Optical Coherence Tomography (Q-OCT). These include the ease of generation and a high number of anti-diagonals needed for efficient artefact removal. On the other hand, a small diagonal width leads to a reduced axial resolution of the resultant images. The spectral characteristics of such light is analyzed both theoretically and experimentally and its validity for Q-OCT imaging discussed.

In this work, we focus on optimizing waveguides based on Lithium Niobate on Insulator (LNOI) for the generation of cross-polarized spectrally pure photons at telecommunication wavelength using type II spontaneous Parametric Down-Conversion (SPDC) process. Our optimization process is based on avoiding lateral leakage losses for all the modes involved in considered SPDC process by choosing waveguide parameters appropriately. In addition, we also ensure single mode operation for all the interacting wavelengths. We further engineer the waveguide such that it satisfies group index matching for generating spectrally pure single photons with high purity (⪆95 %). Such single-mode and loss-free waveguides are poised to have broad applications in both classical and quantum optical fields.

We present our first results concerning a compact dual cold atom accelerometer-gyroscope, which is incorporated within the framework of the development of a cold atom inertial measurement unit. The sensor is sensitive to rotations if the atoms enter the interferometer with an initial velocity. We therefore propose a scheme compatible with a compact multi-axis sensor in which the atoms are horizontally launched thanks to a magnetic gradient and interrogated with a single Raman laser. In this work, the quantum sensor has been hybridized with a conventional accelerometer and gyroscope, which has resulted in respectively 100-fold and 5-fold bias stability improvements compared to the conventional sensors alone. Dynamic rotation rate measurements have also been performed and demonstrated a 1% agreement between the two sensors. This work provides a pathway towards autonomous navigation using cold-atom sensors.

This study explores the versatile framework of time-frequency variables in the context of quantum information, with a specific focus on the use of single photons as a paradigmatic system. In our first analysis, we discern the contributions of intensity and spectral resources, unveiling their impacts on the precision of parameter estimation as the number of probes increases. Remarkably, we demonstrate the potential for quadratic scaling using quantum mode correlations and derive mathematical expressions for the optimal states. In a second investigation, inspired by the state achieving the Heisenberg limit, we introduce a novel method for encoding GKP (Gottesman, Kitaev, and Preskill) states in our paradigmatic system. We analyze the scalability of error detection and correction with the total photon number. We demonstrate that these codes can effectively correct displacements in time-frequency phase space and photon losses. This research highlights the unifying potential of time-frequency variables as a platform for diverse quantum applications.

“Schrödinger Cat States” (SCS), which are coherent superpositions of two dephased coherent states, have been proven to be valuable resources for quantum computing, quantum communication, and quantum metrology. In this work, we present an experimental implementation of a SCS source using an iterative scheme. We use a heralded photon source based on parametric down conversion and a quantum memory cavity. The latter consists of a low losses cavity comprising a fast Pockels cell and a Polarizing Beam Splitter (PBS), allowing us to store a first single photon, waiting for a second one to be generated. We then entangle the stored photon and the incoming photon using the PBS and the Pockels cell to perform polarization manipulation. A homodyne detection then performs a quadrature measurement on one part of the entangled state. This is conditioning measurement: if the result is “X=0”, then the other part of the state is projected on a SCS. A first version of the experiment allowed us to generate SCS at a rate of 100 Hz with a fidelity of 47% after a 184ns long storage.

This study falls within the emerging field of quantum optics in scattering media. By employing wavefront shaping, researchers successfully transmitted spatially entangled photon pairs through scattering media, mitigating optical disturbances by wavefront shaping. They maintained entanglement with a dimensionality of 17 after propagation, opening avenues for applications in quantum microscopy and quantum communication. Interestingly, this work also shows that in certain cases, quantum entanglement can be transmitted through a complex medium, while classical light remains scattered.

Bell tests serve as a fundamental tool in both quantum technologies and quantum foundations investigation. The traditional Bell test framework involves the use of projective measurements, which, because of the wavefunction collapse and the Heisenberg uncertainty principle, do not allow for the full estimation of the Bell parameter from each entangled pair. In this work, we propose a novel weak-measurement-based scheme enabling the complete estimation of the entire Bell parameter from each entangled pair. Moreover, this approach prevents the collapse of the quantum state wavefunction, thereby preserving the entanglement within it. Our results, showing a 6 standard deviations violation of the Bell inequality tested, are obtained while leaving the entanglement within the photon pair almost unaltered after the weak measurement scheme (as demonstrated by our quantum tomographic reconstructions), allowing to exploit it for further foundational or practical purposes.

The quantum technology unit of the Leonardo Labs has designed an imaging system that can be employed in Non-Line-of-Sight scenarios where an obstacle is in between the target and the imager. In this scenario, laser pulses are used to scan surfaces that scatter and diffuse the light into the concealed areas, then the photons that interact with the target and are back-reflected to the imager are detected. The hidden area is finally retrieved with a sophisticated computational algorithm that tackles the inverse problem, unveiling real-time images of hidden targets. An Artificial Intelligence approach further optimizes target profile reconstruction using correlation from high-resolution acquisitions, potentially transforming defense and security applications. Leonardo's quantum imaging technology has the power to reveal and track previously imperceptible targets, as evidenced by real-time non-line-of-sight imaging experiments.

We experimentally realized a chip-based source-independent QRNG. The source-independent scheme provides a solution for the balance between the practical and device-independent QRNGs, which closes the security loopholes from the source, and can be easily realized with respect to the device-independent scheme based on loophole-free Bell test. For the measurement part, the imperfections of the detector are modeled and the practical loopholes in receiver side are thus closed. For the producibility, we use the Silicon-On-Illustrator (SOI) platform to integrate the optical path and detectors on chip. In this way, except for the local oscillator source, all the devices required by our QRNG scheme are integrated on a chip, which significantly promotes the miniaturization and scaling capabilities. The final generation rate is 15.6 Gbps, and the final random numbers well pass all the test items of NIST statistical tests, which demonstrates the practicability of a QRNG with source loophole-free, complete practical receiver modeling and chip-based devices.

In the simplest definition, a quantum battery is defined as a quantum system that can store energy. Recently, quantum battery has attracted a lot of interest due to its better performance than the classical one in terms of charging speed and stored energy. This superior performance comes from the quantum effects, such as quantum entanglement and correlations. The main problem to tackle in quantum battery is to achieve a quantum battery that stores more energy with faster charging time. In this work, we consider a model of quantum battery with nonlinearity effect: Kerr nonlinearity and quadratic driving. We show by adding nonlinearity to the system, the performance of the quantum battery in terms of stored energy and charging time becomes better. The Kerr nonlinearity induces an-harmonicity in the energy levels of the battery, from which we show that the charging time of the Kerr battery is faster than the case of harmonic oscillator battery, while the stored energy is larger than the case of qubit battery. On the other hand, quadratic driving leads to a squeezed quantum battery, which generates plentiful useful energy near to critical points.