In this work, we introduce a new kind of nonlocal interferometer based on the delocalized addition of a single photon onto distinct field modes. Since the quantum state produced by this conditional operation strongly depends on the phase set in a physically-separated heralding station, we propose and experimentally demonstrate a remote phase estimation technique, characterized by a sensitivity...
Quantum information from spacetime dynamics
Optical non-Gaussian quantum states can be generated in a heralded manner by applying a photon subtraction operation to a Gaussian input state. In our work, we develop a theoretical framework to describe this operation in the case where the input state is spectrally multimode. This framework allows the optimal design of photon subtraction experiments. We give the exact expression of the...
Within artificial intelligence, of particular interest is reinforcement learning (RL), where autonomous agents learn to accomplish tasks via feedback exchange with their environment (the world they interact with). Thanks to rapid advances in quantum technologies, the idea of using quantum physics to boost the performance of RL agents was developed. I will focus on the bridge between RL and...
All-optical quantum teleportation relies on properties of entangled states that, in the prospect of operation in quantum networks, should be encoded on photon pairs on demand. Quantum dots are a promising solution, as shown in recent multi-photon experiments [1].
Here, we demonstrate quantum teleportation with quantum dot photons achieving improved protocol fidelity [2]. The experimental...
The tensor product postulate of quantum mechanics states that the Hilbert space of a composite system is the tensor product of the components' Hilbert spaces. All current formalizations of quantum mechanics that do not contain this postulate contain some equivalent postulate or assumption (sometimes hidden). Here we give a natural definition of composite system as a set containing the...
We draw a picture of physical systems allowing us to recognize what is the thing we call ”time”. Elements of the picture are two non-interacting, entangled quantum systems: one acting as a clock, and the other one as the evolving system. The setting is based on the ”Page and Wootters mechanism”, with tools from Lie-Group and large-N quantum approaches. The theoretical framework, based on a...
We discuss a decoherence process due to quantum gravity effects. We assume a foamy quantum spacetime with a fluctuating minimal length coinciding on average with the Planck scale. Considering deformed canonical commutation relations with a fluctuating deformation parameter, we derive a Lindblad master equation that yields localization in energy space and decoherence times consistent with the...
We address the question whether a reversible transformation produces a causal influence from one of its input systems to one of its outputs. In quantum theory causal influence is typically identified with signalling. A second notion is borrowed from the theory of quantum cellular automata. We adopt an extension of the latter, in the context of general probabilistic theories. We show that in...
Non-abelian gauge fields emerge naturally in the description of adiabatically evolving quantum systems. In this talk we show that they also play a role in Thouless pumping in the presence of degenerate bands. Specifically, we consider a photonic Lieb lattice and show that when the lattice parameters are slowly modulated, the propagation of the photons bear the fingerprints of the underlying...
In a quantum network, entanglement between qubits located in remote nodes is a fundamental resource for different applications including distributed quantum computing and quantum repeaters. Once can generate entanglement between distant ions by creating an ion-photon entangled pair at each of the two network nodes, steering the photons to opposite ports of a beamsplitter, and subsequently...
A key question for the development of quantum thermos-machines and more generally of quantum technologies is what are the ultimate bounds to the performance of heat engines. We have shown [1] that in the antiadiabatic limit a periodically driven isothermal heat engine can approach the ideal (unit) energy conversion efficiency with finite output power and vanishingly small relative power...
We study the possibility of conveying useful energy (work) along a transmission line that allows for a partial preservation of quantum coherence. As a figure of merit we adopt the maximum values that ergotropy, total ergotropy, and non-equilibrium free-energy attain at the output of the line for an assigned input energy threshold. When the system can be modelled in terms of Phase-Invariant...
A classical-quantum hybrid approach to computation is presented, allogwing for a (quadratic) performance improvement in the learning stage of a neural network. In particular, a quantum computing routine is described, which helps to prepare/update the probability distributions that drive the agent operations. This algorithm can be used not only in a reinforcement learning scenario, but also in...
Quantum Cascade Laser (QCL) frequency combs could emit nonclassical light and multimode entanglement thanks to a third order nonlinearity that allows for Four Wave Mixing in the device (Faist 2016), which makes them ideal candidates for free-space communication applications.
However, in the mid-infrared, the lack of efficient and low-noise detectors compromises enormously the ability to...
We present quantum reading [3] realisation, describing theoretically and experimentally, as that quantum advantage is obtained by practical photon-counting measurements combined with a simple maximum-likelihood decision [4], demonstrating that quantum entanglement and simple optics are able to enhance the readout of digital data.
Then we consider [5] a protocol on conformance test. We...
We first show that any Gaussian cluster state of N bosonic modes can be generated by a multi-mode squeezing transformation. and provide the explicit recipe. We then use this result to show that a large class of pure entangled CV Gaussian states, including 2D-cluster states, can be robustly generated as a unique steady state of a dissipative dynamics employing minimal resources. In fact, this...
We will report on special properties of smart superconducting circuits and of hybrid tunnel-ferromagnetic Josephson junctions (JJs) on how to engineer the macroscopic phase in quantum circuits.
The possibility to control and drive tunnel-ferromagnetic JJs through different physical means allows for novel tuning mechanisms that are not susceptible to specific noise sources in a transmon...
We review some recent results on the development of tensor network algorithms and their application to
high-dimensional many-body quantum systems and machine learning problems in High Energy Physics. In particular, we present results on
topological two-dimensional systems, two dimensional Rydberg atom systems, and two and three-dimensional lattice gauge theories in presence of fermonic...
We present a systematic study of thermal rectification, R, in a nonlinear resonator. In the strongly anharmonic regime and weak system-bath coupling we derive general upper bounds on R. Beyond the weak-coupling regime we employ different methods: (i) including cotunneling processes, using (ii) nonequilibrium Green’s function formalism and (iii) Feynman-Vernon path integral approach. We find...
We discuss two experimental results on the problem of quantum estimation applied to functions. We illustrate quantum function estimation of the phase response of a liquid crystal employing both quantum and classical resources, providing evidence of the superiority of the former strategy. Including function estimation in the toolkit of quantum metrology opens up opportunities for quantum...
In semiconductor quantum dots, the spin of a confined charge carrier, whether electron or hole, attracted a lot of interest since spin-polarized optical transitions enable the efficient generation of spin-photon and photon-photon entanglement. This could be extended to generate multi-photon entangled states, which are building blocks for quantum technologies such as measurement-based quantum...
Molecular spins hold potential for quantum information when integrated into planar superconducting microwave resonators [[AdvPhysX3,1435305(2018)]][1]. Along this line, we present our recent results on developing protocols (i.e. microwave sequences) for initializing, manipulating and reading out molecular spin ensembles. We first apply a storage/retrieval protocol on an Oxovanadyl (VO(TPP))...
We discuss the problem of entanglement protection against surrounding noise by a procedure suitably exploiting spatial indistinguishability of identical subsystems. To this purpose, we take two initially separated and entangled identical qubits interacting with two independent noisy environments. Three typical models of environments are considered: the amplitude damping channel, the phase...
For distinguishable particles, there exists an agreed upon notion of entanglement based on the possibility of addressing individually each particle. Instead, the indistinguishability hinders their individual addressability and has prompted diverse, discordant definitions of entanglement. I will present a formulatiom of emtamglement in terms of correlation functions, that provides a general...
The fast development of quantum technologies based on superconducting devices is particularly important for the search of light dark matter, such as Axions and Axion-like particles, where it is required the efficient detection of single microwave photons with low dark-count rates. We present SIMP, an experiment for the axion search based on the use of a current biased Josephson junction...
With the recent advent of noisy intermediate-scale quantum devices implemented in various platforms, entanglement and quantum coherence detection are in the focus of interest. We propose an ordered set of experimentally accessible conditions for detecting entanglement in mixed states. The k-th condition involves comparing moments of the partially-transposed density operator up to order k. Our...
Here, we present a compact formulation of the resolvent-based theory for calculating atom-photon dressed states built on the idea that the atom behaves as an effective impurity (i). This establishes an explicit connection with the standard impurity problem in condensed matter. When the impurity reduces to a vacancy, the resulting class of dressed states play a central role in the emerging...
We study the exotic interaction between emitters mediated by the photonic modes of a lossy photonic lattice described by a non-Hermitian Hamiltonian, where structured losses can seed exotic emission properties. Photons can mediate dissipative, fully non-reciprocal, interactions between emitters with range critically dependent on the loss rate. At the bare-lattice exceptional point, the...
The emergence of multi-photon bound states is an intriguing phenomenon that can occur in quite different quantum nonlinear media, such as arrays of quantum emitters coupled to photonic waveguides and Rydberg atomic ensembles.
To theoretical study these bound states within an unified framework
we propose a spin-model formulation of quantum atom-light interactions. We solve the few- and...
We study light-matter interaction in two dimensional photonic systems in the presence of a spa- tially homogeneous synthetic magnetic field for light. Specifically, we consider one or more two-level emitters located in the bulk region of the lattice, where for increasing magnetic field the photonic modes change from extended plane waves to circulating Landau levels. This change has a drastic...
The talk will begin with a very quick pedagogical overview of cavity QED, circuit QED, and the ultra-strong coupling limit of these. Afterwards, present some more recent results, in the context of quantum nonlinear optics of qubits and resonators, coupled in various different configurations, and these qubits and resonators exchanging energy in various ways.
Recent cyber-attacks to national networks have highlighted the importance of developing an Italian cybersecurity infrastructure where QKD could play an important role by enabling the generation of secure cryptographic keys. The QuantumFuture group is involved in various research projects (eg., OPENQKD) aimed at developing fully-functioning and innovative QKD systems able to operate in the...
In multiparameter quantum metrology, asymptotic incompatibility (AI) is a recently introduced measure quantifying the quantumness of statistical models. Starting from its definition, we found that it is possible to set an upper bound on the maximum number of asymptotic compatible parameters in the statistical model. We numerically investigate the AI for the full tomography of $d$-dimensional...
Quantum states of light represent a useful tool for encoding and transmitting information.
The main obstacle to the successful implementation of communication protocols, especially over long distances, is given by the losses and noise sources affecting the transmission channels, which can irreversibly change the statistical properties of the employed nonclassical states of light.
At variance...
QFold: A Quantum Metropolis Optimization Algorithm
Quantum Machine Learning (QML) is where nowadays machine learning is going to meet quantum information science in order to realize more powerful quantum technologies. In particular, several QML schemes can arise according to the fact that the data to be processed and the algorithm processing them can be either classical or quantum. Moreover, the learning algorithms can be unsupervised,...
Quantum measurements have been recently exploited as a tool to induce e phase transition between volume- and area-law scaling of entanglement entropy. For free fermions, the transition occurs between sub-volume (logarithmic) and area-law scaling.
Here we present a free fermion model where two sets of non-commuting measurements induce a transition between area-law entanglement scaling phases of...
Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light-matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. We report on the implementation of a novel microwave architecture consisting of an array of high-impedance superconducting resonators forming a 1 GHz-wide pass...
Detecting the faint emission of a secondary source in the proximity of the much brighter one has been the most severe obstacle for using direct imaging in searching for exoplanets. Using quantum state discrimination and quantum imaging techniques, we show that one can significantly reduce the probability of error for detecting the presence of a weak secondary source, especially they are...
In the certification of (genuine multipartite) nonlocality, measured data are often postselected to purify the nonlocal features of the data. However, if this postselection requires communication between the measurement parties, it can potentially create fake correlations that mimic nonlocal features via the postselection bias. Here, we show that certain postselection strategies that require...
I will present a dynamic scaling theory aimed at addressing the out-of-equilibrium behavior of many-body systems in proximity of quantum phase transitions of any order. This can be obtained by extending the equilibrium scaling laws ruled either by the critical exponents at continuous transitions, or by the energy gap of the lowest levels at first-order transitions. I will also discuss some...
Multiterminal Josephson junctions (MJJs) constitute engineered topological systems. In [1] we studied the properties of Andreev states in a circuit with a quantum dot (QD) coupled to superconducting leads (SCs) and demonstrated that the quantum geometric tensor can be extracted by synthetically polarized microwaves. In [2] we investigated a linear chain of QDs connected to SCs and showed that...
With the development of quantum technologies, it is pivotal to discern devices exploiting quantum phenomena from faulty ones. This essential task is elusive, since eventual imperfections may go unnoticed to a direct verification. A solution to this deadlock exploits the discrepancies between classical and quantum causal predictions, which can detect nonclassical correlations, with no...
We derive fundamental bounds on the maximal achievable precision in multiparameter noisy quantum metrology, tighter than a direct use of single-parameter results. This allows us to study the effect of incompatibility of optimal probe states for simultaneous estimation of multiple parameters in generic channels, so far studied mostly in noiseless scenarios. We apply our results to several...
Entangling solid-state quantum repeater nodes
Bell's theorem shows that no hidden-variable model can explain the measurement statistics of a quantum system shared between two parties, thus ruling out a classical (local) understanding of nature. In this work we demonstrate that by relaxing the positivity restriction in the hidden-variable probability distribution it is possible to derive quasiprobabilistic Bell inequalities whose sharp...
We are experimentally investigating possible departures from the standard quantum mechanics’ predictions at the Gran Sasso underground laboratory in Italy.
In particular, we are searching signals predicted by the collapse models which were proposed to solve the “measurement problem” in quantum physics.
I shall discuss our recent results published in Nature Physics, where we ruled out the...
Standard photonic simulations of lattice quantum dynamics rely on our ability to shape optical modes and their relative couplings. In these platforms, reproducing temporally-long evolutions is challenging, as required setups are complex and lossy. Here we report the realization of long-time photonic quantum walks, based on light propagation through a limited number of birefringent optical...
Integrated photonics is a key enabler for quantum technologies, with significant improvements introduced in quantum computing, sensing and communications. Femtosecond laser writing of photonic circuits brings key advantages in terms of unprecedented 3D circuit layouts, possibility to manipulate polarization encoding, multimaterial devices and rapid prototyping. All these advantages are widely...
Mapping quantum error correcting codes to classical statistical mechanics models has proven a powerful tool to study the fundamental error thresholds of quantum error correcting codes under phenomenological noise models. In this work, we extend this mapping to realistic faulty quantum circuits by deriving the associated strongly correlated classical spin models for the example of a quantum...
Ultracold atoms and trapped ions have proven to be valuable resources for getting new insights on fundamental physical phenomena. Trapped ions can be individually addressed and coherently manipulated. Ultracold gases, instead, provide large atomic samples where trapping potentials and interactions are controlled externally, making them well suited for systematic studies of many-body quantum...
Shortcuts to adiabaticity in adiabatic quantum computation can be realized either by optimal designs of the annealing schedules or by using external control fields, such as counterdiabatic (CD) driving operators. I will discuss how genetic algorithms can help in determining optimal annealing schedules. Secondly, I will introduce the variational approach to CD driving in closed quantum systems...
We simulate the preparation of a superposition of vortex states in a Bose-Einstein condensate trapped in a ring geometry. It has been proposed that a vortex-antivortex superposition can be used as an inertial sensor, e.g. to measure rotations, or as a magnetic field sensors [1,2]. In both cases, the external influence causes a precession of the BEC standing wave, which can be measured...
Variational quantum algorithms aim at harnessing the power of noisy intermediate-scale quantum computers, by using a classical optimizer to train a parameterized quantum circuit to solve tractable quantum problems. The variational quantum eigensolver is one of the aforementioned algorithms designed to determine the ground-state of many-body Hamiltonians. Here, we apply the variational quantum...
Ensembles of Rydberg atoms, in the Electromagnetic Induced Transparency
setup, have proved to be a possible route to obtain photon-photon
nonlinear interaction. Thanks to the Rydberg blockade
mechanism, a single
photon is indeed able to saturate the atomic
response of a considerably large portion of the
ensemble, that appears opaque to a second
incoming one. While the continuous wave...
Entanglement and symmetries are two pillars of modern physics. Surprisingly, only in very recent times the interplay between these two fundamental concepts became the theme of an intense research activity merging together notions and ideas from quantum information, quantum field theory, quantum optics, holography, many-body condensed matter, and many more. In this talk, I will review some of...
The quantum state fidelity is the textbook measure of the difference between two quantum states. Yet, it is inadequate to compare the complex configurations of many-body systems. We introduce the weighted distances, a new class of information-theoretic measures that overcome these limitations. They quantify how hard it is to discriminate
between two quantum states of many particles, factoring...
A notion of coherence vector of a general quantum state is introduced on the framework of quantum coherence resource theory [1]. This generalized
coherence vector completely characterizes the notions of being incoherent, as well as being maximally coherent. Moreover, using this notion and the majorization relation, a necessary condition for the conversion of general quantum states by means of...
