arXiv subjects

Davide Nigro

Publications and source records attributed to Davide Nigro.

14 recordsLinked to original sources

arXiv2024

A single-photon microwave switch with recoverable control photon

Scalable quantum technologies may be applied in prospective architectures employing traditional information processing elements, such as transistors, rectifiers, or switches modulated by low-power inputs. In this respect, recently developed quantum processors based, e.g., on superconducting circuits may alternatively be employed as the basic platform for ultra-low-power consumption classical processors, in addition to obvious applications in quantum information processing and quantum computing. Here we propose a single-photon microwave switch based on a circuit quantum electrodynamics setup, in which a single control photon in a transmission line is able to switch on/off the propagation of another single photon in a separate line. The performances of this single-photon switch are quantified in terms of the photon flux through the output channel, providing a direct comparison of our results with available data. Furthermore, we show how the design of this microwave switch enables the recovery of the single control photon after the switching process. This proposal may be readily realized in state-of-art superconducting circuit technology.

quant-ph↗

arXiv2024

Supersolidity of polariton condensates in photonic crystal waveguides

Condensation of exciton-polaritons has been recently observed in one-dimensional photonic crystal waveguides, exploiting the interplay of long-lived gap confined eigenmodes and negative mass polariton branches. Here we focus on the theoretical emergence of a second emission threshold, in addition to the one associated with condensation at zero-momentum, due to the nonlinear polariton scattering from the condensate into finite momentum eigenmodes. The physics of this spatially modulated condensate is related to a spontaneous breaking of both phase and translational symmetries simultaneously, bearing strong similarities with the highly sought supersolid phase in Helium and ultracold atomic gases but with a novel mechanism typical of the driven-dissipative scenario. We then propose clear-cut and unequivocal experimental signatures that would allow to identify supersolidity phenomena in polariton condensates

cond-mat.quant-gas↗

arXiv2024

Emerging supersolidity from a polariton condensate in a photonic crystal waveguide

A supersolid is a counter-intuitive phase of matter where its constituent particles are arranged into a crystalline structure, yet they are free to flow without friction. This requires the particles to share a global macroscopic phase while being able to reduce their total energy by spontaneous, spatial self-organisation. This exotic state of matter has been achieved in different systems using Bose-Einstein condensates coupled to cavities, possessing spin-orbit coupling, or dipolar interactions. Here we provide experimental evidence of a new implementation of the supersolid phase in a novel non-equilibrium context based on exciton-polaritons condensed in a topologically non-trivial, bound-in-the-continuum state with exceptionally low losses. We measure the density modulation of the polaritonic state indicating the breaking of translational symmetry with a remarkable precision of a few parts in a thousand. Direct access to the phase of the wavefunction allows us to additionally measure the local coherence of the superfluid component. We demonstrate the potential of our synthetic photonic material to host phonon dynamics and a multimode excitation spectrum.

cond-mat.mes-hall↗

arXiv2024

Exponential optimization of adiabatic quantum-state preparation

The preparation of a given quantum state on a quantum computing register is a typically demanding operation, requiring a number of elementary gates that scales exponentially with the size of the problem. Using the adiabatic theorem for state preparation, whose error decreases exponentially as a function of the preparation time, we derive an explicit analytic expression for the dependence of the characteristic time on the Hamiltonian used in the adiabatic evolution. Exploiting this knowledge, we then design a preconditioning term that modifies the adiabatic preparation, thus reducing its characteristic time and hence giving an exponential advantage in state preparation. We prove the efficiency of our method with extensive numerical experiments on prototypical spin-models, which gives a promising strategy to perform quantum simulations of manybody models via Trotter evolution on near-term quantum processors.

quant-ph↗

arXiv2023

Deterministic entangling gates with nonlinear quantum photonic interferometers

The quantum computing paradigm in photonics currently relies on the multi-port interference in linear optical devices, which is intrinsically based on probabilistic measurements outcome and thus non-deterministic. Devising a fully deterministic, universal, and practically achievable quantum computing platform based on integrated photonic circuits is still an open challenge. Here we propose to exploit weakly nonlinear photonic devices to implement deterministic entangling quantum gates, following the definition of dual rail photonic qubits. It is shown that a universal set of single- and two-qubit gates can be designed by a suitable concatenation of few optical interferometric elements, with optimal fidelities arbitrarily close to 100% theoretically demonstrated through a bound constrained optimization algorithm. The actual realization would require the concatenation of a few tens of elementary operations, as well as on-chip optical nonlinearities that are compatible with some of the existing quantum photonic platforms, as it is finally discussed.

quant-ph↗

arXiv2023

Theory of exciton-polariton condensation in gap-confined eigenmodes

Exciton-polaritons are bosonic-like elementary excitations in semiconductors, which have been recently shown to display large occupancy of topologically protected polariton bound states in the continuum in suitably engineered photonic lattices [Nature {\bf 605}, 447 (2022)], compatible with the definition of polariton condensation. However, a full theoretical description of such condensation mechanism that is based on a non equilibrium Gross-Pitaevskii formulation is still missing. Given that the latter is well known to account for polariton condensation in conventional semiconductor microcavities, here we report on its multi-mode generalization, showing that it allows to fully interpret the recent experimental findings in patterned photonic lattices, including emission characteristics and condensation thresholds. Beyond that, it is shown that the polariton condensation in these systems is actually the result of an interplay between negative mass confinement of polariton eigenstates (e.g., due to the photonic gap originated from the periodic pattern in plane) and polariton losses. We are then able to show that polariton condensation can also occur in gap-confined bright modes, i.e., coupling of QW excitons to a dark photonic mode is not necessarily required to achieve a macroscopic occupation with low population threshold.

cond-mat.other↗

arXiv2022

Single-photon nonlinearities and blockade from a strongly driven photonic molecule

Achieving the regime of single-photon nonlinearities in photonic devices just exploiting the intrinsic high-order susceptibilities of conventional materials would open the door to practical semiconductor-based quantum photonic technologies. Here we show that this regime can be achieved in a triply resonant integrated photonic device made of two coupled ring resonators, without necessarily requiring low volume confinement, in a material platform displaying an intrinsic third-order nonlinearity. By strongly driving one of the three resonances of the system, a weak coherent probe at one of the others results in a strongly suppressed two-photon probability at the output, evidenced by antibunched second-order correlation function at zero-time delay under continuous wave driving.

quant-ph↗

arXiv2021

Integrated quantum polariton interferometry

Exciton-polaritons are hybrid elementary excitations of light and matter that, thanks to their nonlinear properties, enable a plethora of physical phenomena ranging from room temperature condensation to superfluidity. While polaritons are usually exploited in high density regime, evidence of quantum correlations at the level of few excitations has been recently reported, thus suggesting the possibility of using these systems for quantum information purposes. Here we show that integrated circuits of propagating single polaritons can be arranged to build deterministic quantum logic gates in which the two-particle interaction energy plays a crucial role. Besides showing their prospective potential for photonic quantum computation, we also show that these systems can be exploited for metrology purposes, as for instance to precisely measure the magnitude of the polariton-polariton interaction at the two-body level. In general, our results introduce a novel paradigm for the development of practical quantum polaritonic devices, in which the effective interaction between single polaritonic qubits may provide a unique tool for future quantum technologies.

cond-mat.mes-hall↗

arXiv2021

Invariant Neural Network Ansatz for weakly symmetric Open Quantum Lattices

We consider $d$-dimensional open quantum lattices whose time evolution is governed by a master equation which is weakly symmetric under the action of a finite group $G$ that is a subgroup of all the possible permutations of the lattice sites. We show that, whenever the steady state is unique, one can introduce a neural network representation for the system density operator that explicitly accounts for the system symmetries and can be efficiently optimized by exploring only a relevant subspace of the parameter space. In particular, as a proof of principle, we demonstrate the validity of our approach by determining the steady state structure of the one dimensional dissipative XYZ model in the presence of a uniform magnetic field.

quant-ph↗

arXiv2019

Competing coherent and dissipative dynamics close to quantum criticality

We investigate the competition of coherent and dissipative dynamics in many-body systems at continuous quantum transitions. We consider dissipative mechanisms that can be effectively described by Lindblad equations for the density matrix of the system. The interplay between the critical coherent dynamics and dissipation is addressed within a dynamic finite-size scaling framework, which allows us to identify the regime where they develop a nontrivial competition. We analyze protocols that start from critical many-body ground states and put forward general dynamic scaling behaviors involving the Hamiltonian parameters and the coupling associated with the dissipation. This scaling scenario is supported by a numerical study of the dynamic behavior of a one-dimensional lattice fermion gas undergoing a quantum Ising transition in the presence of dissipative mechanisms such as local pumping, decaying, and dephasing.

cond-mat.stat-mech↗

arXiv2019

On the complexity of the steady-state of weakly symmetric open quantum lattices

We investigate the properties of Lindblad equations on $d$-dimensional lattices supporting a unique steady-state configuration. We consider the case of a time evolution weakly symmetric under the action of a finite group $G$, which is also a symmetry group for the lattice structure. We show that in such case the steady-state belongs to a relevant subspace, and provide an explicit algorithm for constructing an orthonormal basis of such set. As explicitly shown for a spin-1/2 system, the dimension of such subspace is extremely smaller than the dimension of the set of square operators. As a consequence, by projecting the dynamics within such set, the steady-state configuration can be determined with a considerably reduced amount of resources. We demonstrate the validity of our theoretical results by determinining the \emph{exact} structure of the steady-state configuration of the two dimensional XYZ model in the presence of uniform dissipation, with and without magnetic fields, up to a number of sites equal to 12. As far as we know, this is the first time one is capable of determining the steady-state structure of such model for the 12 sites cluster exactly. Altough in this work we consider explicitly only spin-1/2 systems, our approach can be exploited in the characterisation of arbitrary spin systems, fermion and boson systems (with truncated Fock space), as well as many-particle systems with degrees of freedom having different statistical properties.

quant-ph↗

arXiv2018

Scaling properties of work fluctuations after quenches at quantum transitions

We study the scaling properties of the statistics of the work done on a generic many-body system at a quantum phase transition of any order and type, arising from quenches of a driving control parameter. For this purpose we exploit a dynamic finite-size scaling framework. Namely, we put forward the existence of a nontrivial finite-size scaling limit for the work distribution, defined as the large-size limit when appropriate scaling variables are kept fixed. The corresponding scaling behaviors are thoroughly verified by means of analytical and numerical calculations in two paradigmatic many-body systems as the quantum Ising model and the Bose-Hubbard model.

cond-mat.stat-mech↗

arXiv2018

On the uniqueness of the steady-state solution of the Lindblad-Gorini-Kossakowski-Sudarshan equation

The aims of this paper are two. The first is to give a brief review of the most relevant theoretical results concerning the uniqueness of the steady-state solution of the Lindblad-Gorini-Kossakowski-Sudarshan master equation and the criteria which guarantee relaxingness and irreducibility of dynamical semigroups. In particular, we test and discuss their physical meaning by considering their applicability to the characterisation of the simplest open quantum system \emph{i.e.} a two-level system coupled to a bath of harmonic oscillators at zero temperature. The second aim is to provide a set of sufficient conditions which guarantees the uniqueness of the steady-state solution and its attractivity. Starting from simple assumptions, we derive simple criteria that can be efficiently exploited to characterise the behavior of dissipative systems of spins and bosons (with truncated Fock space), and a wide variety of other open quantum systems recently studied.

quant-ph↗

arXiv2017

Trap effects and continuum limit of the Hubbard model in the presence of a harmonic potential

We give a prescription to perform the continuum limit of the $d$-dimensional Hubbard model in the presence of a harmonic trap at zero temperature. We perform the continuum limit at fixed number of particles. In $d\geq3$ the lattice system of spin-1/2 particles is mapped into a non-interacting two-component Fermi gas in a harmonic trap. In $d=1$ and $d=2$ the particles with opposite spin interact via a Dirac delta interaction. We show that the properties of this continuum limit can be put in correspondence with those derived applying the Trap-Size scaling (TSS) formalism to the confined Hubbard model in the so called Dilute Regime (fixed number of particles and weak confinement). The correspondence in $d=1$ and $d=2$ has been tested comparing the numerical results obtained for lattice system with those of the continuum limit in the case of two-particle and in absence of spin-polarization ($N=2$,$N_{\uparrow}=N_{\downarrow}=1$).

cond-mat.quant-gas↗