The peculiar properties of quantum optical states represent a new resource for innovative imaging schemes, as sub shot noise imaging or quantum illumination. Here we present in detail two works realized in INRIM. The first involves exploiting entanglement to enhance the imaging of a pure phase object in a non-interferometric setting. This wide-field method, based on the "transport of intensity equation", provides the absolute value of the phase without prior knowledge of the object. It does not require spatial and temporal coherence of the incident light. Besides improving image quality at a fixed number of photons, we demonstrate a clear reduction of the uncertainty in the quantitative phase estimation. This research also paves the way for applications at different wavelengths, e.g., x-ray imaging, where reducing the photon dose is of utmost importance. Then, we demonstrate a novel imaging technique, named Light Field Ghost Imaging, which exploits light correlations and light field imaging principles to enable overcome the limitations of ghost imaging in a wide range of applications. Notably, our technique removes the requirement to have prior knowledge of the object distance allowing us to refocus in post-processing and to perform 3D imaging while retaining all the benefits of GI protocols.

Quantum-secured optical channels based on Quantum Key Distribution technology have generated a significant global interest. Although the maturity level of the short distance (less than 100km) quantum-secured channels is at a deployment level, instituting such channels over long distance faces technological challenges, which is the subject of a world-wide research. In this article an industry perspective on the future deployment of long-distance quantum-secured optical channels in operational environments will be discussed, including the vision, requirements, and R&D activities in both terrestrial and satellite-based methodologies.

In theory, quantum key distribution (QKD) provides unconditionally secure keys due to the laws of quantum mechanics. However, real-world QKD systems often use strongly attenuated lasers which enables the photon number splitting (PNS) attack. Decoy state protocols weaken an eavesdropper’s chance to perform the compromising PNS attack undetected. In small multi-user QKD networks the photons can be distributed to the users via passive beam splitters. This approach lowers the sender-to-receiver QKD channel efficiency (relative to a standard point-to-point QKD system) and reduces the mean photon number in the sender-to-receiver channel. For this contribution, we investigated the performance of decoy state protocols in a passive multi-user system. We compared this point-to-multipoint setup to a standard point-to-point system by checking the photon number dependent yields, hereby showing that with some restrictions such a system would be safe against the PNS attack.

In this paper, we focus on quantum communication systems that facilitate either secure data transfer or quantum key distribution via free-space links. Unlike classical channels where the effects of turbulent media on the optical wave front is well known and can be predicted with existing theoretical models, the mechanism described in the latter cannot be directly applied to quantum states. In our approach that relies on emitting correlated photon pairs with polarization entanglement, another realm of problems is encountered, which is not related to wave front distortions, but rather to integrity of the quantum states. Proper response of the detection system to non-classical features of light requires that photon pairs with proper polarization arrive to the receiver and their correlation characteristics are still preserved. Therefore, it is necessary to research a wide array of operating conditions corresponding to different levels of turbulence and finding proper mechanisms to replicate those on our laboratory testbed. In this paper, we present a system that integrates an atmospheric chamber developed by the AFRL, a link emulating quantum communication and analysis instrumentation. A system is developed that allows scaling the experiments over different ranges and quantitative analysis of entanglement characteristics of the received signals. Integrity of the quantum states is evaluated under practical operating conditions.

This work proposes a circuit implementation of the encoding circuit for an N × N grayscale-based Flexible Representation of Quantum Images (FRQI). The implementation is tested on the Qiskit simulator before being executed on real IBM Quantum hardware. The encoded FRQI, with a searched pixel encoded by a single qubit, is considered an unsorted database with a single table, where the key of the table represents the pixel’s position (x, y). The other columns represent the grayscale level at this position and the searched grayscale level, which are encoded by rotation angles and implemented using several multi-controlled rotation gates along the y-axis. Subsequently, Grover ’s algorithm is used to retrieve the position from the FRQI after performing a comparison with the given grayscale level of an individual pixel. The physical constraints associated with the IBM quantum device used are discussed, and the limitations of Grover ’s algorithm for searching the pixel are addressed.

Optical system is an appealing system for quantum computation as it has tremendous scalability over typical matter-based qubit. This is thanks to its rich degree of freedom that allows multiplexing. A particularly promising approach is the time-domain multiplexing approach where large-scale entangled resources and their usages have been demonstrated. To achieve quantum computation, these resources have to be combined with a type of states called non-Gaussian states. Non-Gaussian state generation requires strong nonlinearity which is challenging in optical system, compared to the matter-based system. In this work, we explain our recent work in the generation of the non-Gaussian states for optical quantum computer. In the first half, we discuss the demonstration of cat-breeding protocol for the generation of Gottesman-Kitaev-Preskill (GKP) qubit. In the second half, we show the demonstration of generation of cat states from broadband light source. In the future, by combining these two techniques, we can achieve high-rate high-quality GKP states crucial for optical quantum computer.

Quantum Key Distribution (QKD) enables the secure distribution of secret keys for cryptographic purposes between two trusted parties over a quantum channel. For reaching global-scale quantum key distribution, satellite-based approaches are most promising as already demonstrated by the Chinese MICIUS mission. Here, we summarize our efforts in building a very compact QKD sender unit featuring polarization-encoded BB84 with weak coherent pulses. The unit is suitable for deployment in cube satellites such as our missions QUBE and QUBE-II which aim to demonstrate that affordable and scalable key distribution is possible in the near future.

As shown in previous work, quantum contextuality can be represented by interference effects in a three-path interferometer. A Hardy-like paradox is obtained when the absence of photons in two internal paths seems to contradict the presence of photons in a specific input port. Here, we consider the effects of counterfactual control on this scenario by analyzing the changes to the paths through the interferometer when the seemingly impossible input path is blocked. The effects on photons that never interact with the absorber in the blocked path reveals a characteristic signature of quantum contextuality that may help to explain why quantum interference is incompatible with measurement independent realities.

We propose using thin-film lithium niobate on insulator (LNOI) doped with Erbium (Er³⁺) as a promising solution for implementing large-scale quantum memory. However, the transition from bulk crystals to thin films poses challenges, notably reduced optical depth, which is critical for broad atomic frequency comb memory. To address this, we plan to utilize impedance-matched cavities, increasing the effective optical depth. Furthermore, the cavity would boost the rate of spontaneous emission, increasing the efficiency of spectral hole burning. Our preliminary results reveal high-Q micro-ring resonators (Q≈190k) on Er³⁺: LNOI, demonstrating a nearly 3.5-fold reduction in the optical lifetime due to cavity resonance.

A ring-laser-gyro (RLG) is a rotation sensor based on the Sagnac effect. Its ultimate sensitivity is given by the shot-noise. RLG are ring optical cavities where an in-cavity optically active laser volume emits two counter propagating beams. They, if the cavity is rotating and due to the Sagnac effect, show different frequencies. This frequency difference is proportional to the rotation rate of the ring itself. Here we present noise floor measurement for a large ring laser showing that the reached sensitivity level is not consistent with an independent beam model. The measured sensitivity is, indeed, about one order of magnitude better than expected. This is most probably due to coupling of the phases of the two beams mediated by the laser medium and mirror back-scattering. This result paves the way to the use of large RLGs in a wide range of measures in fundamental physics as well as to experimentally investigating quantum effects in non-inertial reference frames. In this contribution, starting from the experimental findings, we will discuss the necessary modifications to the theory and give some hints to understand the role of the above-mentioned mechanisms.

The typical approach to quantum optics is to quantize the electromagnetic field over a volume of space and evolve the field in time with the Hamiltonian. To do this, one should know a priori the spatial modes of the theory. However, for nonlinear optics in structured media it is often challenging to form a basis of solutions. To circumvent this issue, we derive a theory of flux quantization in which the equations of motion evolve the field operators through space. The equal space canonical commutation relations are adjusted to make the quantum theory more amenable to solving steady state solutions. We conclude by outlining the form of a transfer matrix superoperator method for obtaining steady state solutions to photon fields in stratified nonlinear dielectrics.

We present a loop-based optical processor compatible with probabilistically generated phase-sensitive non-Gaussian state. This processor enables storage of a non-Gaussian state for up to seven round trips while preserving its Wigner negativity and phase coherence. Our work integrates non-Gaussian states with time multiplexing, laying the foundation for large-scale universal quantum information processing.

Certification of genuine quantum steering is crucial for the verification of an untrusted node in quantum networks. Yadin, Fadel and Gessner (YFG) have shown how a violation of the Cram´er-Rao bound hints the presence of quantum steering in the probe state. We recently extended the YFG method to the noisy and non-asymptotic regime. However, in such a scenario, the prior distribution encoding our prior information on the target parameter plays a fundamental role; therefore a prior distribution as reliable as possible is highly recommended. In this work we investigate the role of prior information in the parameter estimation and the certification of quantum steering via a quantum optics experiment with polarization encoding.

In recent years, there have been significant advancements in various aspects of quantum computing. However, despite this substantial progress, the availability of fault-tolerant quantum computers is still out of reach and may remain so for decades. Therefore, a key challenge is to leverage current NISQ devices to achieve a quantum advantage effectively. In this context, the Quantum Approximate Optimization Algorithm (QAOA) was proposed to potentially demonstrate computational advantages in combinatorial optimization problems using NISQ computers. Meanwhile, quantum error mitigation (QEM) techniques have been developed to address errors, with their effectiveness validated in practical problems involving more than 100 qubits. Therefore, in this paper, we optimize QAOA circuits and apply various error mitigation methods, such as dynamic decoupling and Pauli-twirling, to scale problem sizes on IBM quantum processors. Additionally, we discuss optimal implementation strategies for scalable QAOA. We test our implementations on Max-Cut problems and compare our results with previous works.

To factor an integer N into a product of two other numbers N₁ and N₂, Shor’s algorithm uses the Quantum Fourier Transform on n qubits, denoted QFT_n, to determine the period r of a Modular Exponentiation Function (MEF), which is later used to compute a factor of N. In this work, we present Shor’s algorithm for factoring an integer of n qubits and illustrate an example with n=4. We implement our algorithm using Qiskit and IBM quantum computers, which also can be adapted on other quantum computing platforms with minor adjustments. We discuss the IBM quantum computer limitations for running our circuit and show the impact of device imperfections on the factored result.

Quantum distillation is the task of concentrating quantum correlations present in N imperfect copies using free operations by involving all P the parties sharing the quantum correlation. We present a threshold quantum distillation task where the same objective is achieved but using a lesser number of parties (K<P). In particular, we give exact local filtering operations by the participating parties sharing a high-dimension multipartite entangled state to distil the perfect quantum correlation. Later, we bridge a connection between threshold quantum entanglement distillation and quantum steering distillation.