We propose an experiment to test the non-classicality of the gravitational interaction. We consider two optomechanical systems that are perfectly isolated, except for a weak gravitational coupling. If a suitable resonance condition is satisfied, an optical signal can be transmitted from one system to the other over a narrow frequency band, a phenomenon that we call gravitationally induced transparency. In this framework, the challenging problem of testing the quantum nature of gravity is mapped to the easier task of determining the non-classicality of the gravitationally-induced optical channel: If the optical channel is not entanglement-breaking, then gravity must have a quantum nature. This approach is applicable without making any assumption on the, currently unknown, correct model of gravity in the quantum regime. In the second part of this work, we model gravity as a quadratic Hamiltonian interaction (e.g. a weak Newtonian force), resulting in a Gaussian thermal attenuator channel between the two systems. Depending on the strength of thermal noise, the system presents a sharp transition from an entanglement-breaking to a non-classical channel capable not only of entanglement preservation but also of asymptotically perfect quantum communication.

We investigate a theoretical protocol for the dissipative stabilization of mechanical quantum states in a multimode optomechanical system composed of multiple optical and mechanical modes. The scheme employs a single squeezed reservoir that drives one of the optical modes, while the remaining optical modes mediate an effective phonon-phonon interaction Hamiltonian. The interplay between these coherent interactions and the dissipation provided by the squeezed bath enables the steady-state preparation of targeted quantum states of the mechanical modes. In the absence of significant uncontrolled noise sources, the resulting dynamics closely approximate the model introduced in [Zippilli , ]. We analyze the performance of this protocol in generating mechanical cluster states defined on rectangular graphs.

We discuss a hybrid optoelectromechanical setup that is able to sense weak variations of any parameter that affects the effective capacitance of an LC resonator, representing the radiofrequency (rf) electrical component of the device. In the setup, either one or two mechanical modes mediate the interaction between an optical cavity and the rf-resonator. This system can be operated in a regime of impedance matching where thermal fluctuations are redistributed among the system elements, and, in particular, rf output noise can be reduced to the quantum vacuum noise level. We show that this effect can boost the sensitivity in detecting parameter variations also in regimes of high thermal noise.

We investigate a scheme to enhance the sensitivity in detecting weak variations in a parameter of an optoelectromechanical system by detecting the system response at radio frequencies. We consider a setup where either one or two mechanical modes mediate the interaction between an optical cavity and an rf resonator. This system can be operated in a regime of impedance matching where thermal fluctuations are redistributed among the system elements and, in particular, rf output noise can be reduced to the quantum vacuum noise level. We show that this effect can be used to boost the sensitivity in detecting parameter variations also in regimes of high thermal noise. We characterize the performance of this protocol in detecting variations in the capacitance of the rf resonator.

We show how to dissipatively stabilize the quantum state of N mechanical resonators in an optomechanical system, where the resonators interact by radiation pressure with N optical modes, which are driven by properly selected multifrequency drives. We analyze the performance of this approach for the stationary preparation of Gaussian cluster states.

Coherent long-range interactions between atoms are a prerequisite for numerous applications in the field of quantum information science, but they usually decrease exponentially with the increase in atomic separation. Here we present an appealing method to dramatically enhance the long-range atom-atom interaction mediated by a coupled-cavity array that is subjected to two-photon (parametric) drives. Our method allows one to greatly amplify both the localization length of the single-photon bound-state wavefunction and the effective atom-photon coupling strength, resulting in a significant improvement of photon-mediated coherent interaction between two distant atoms. Additionally, we illustrate this effect by analyzing how it facilitates the transfer of information and the creation of entanglement between the atoms.

We study the dissipative stabilization of entangled states in arrays of quantum systems. Specifically, we are interested in the states of qubits (spin-1/2) which may or may not interact with one or more cavities (bosonic modes). In all cases only one element, either a cavity or a qubit, is lossy and irreversibly coupled to a reservoir. When the lossy element is a cavity, we consider a squeezed reservoir and only interactions which conserve the number of cavity excitations. Instead, when the lossy element is a qubit, pure decay and a properly selected structure of XY-interactions are taken into account. We show that in all cases, in the steady state, many pairs of distant, non-directly interacting qubits, which cover the whole array, can get entangled in a stationary way, by means of the interplay of dissipation and local interactions.

A simple feedback scheme can be used to operate efficiently a microwave-quantum-illumination device based on electro-optomechanical systems also in regimes in which excess dissipation would, otherwise, prevent to outperform the optimal classical illumination protocol with the same transmitted energy.

We design a feedback scheme that can be used to operate efficiently a microwave quantum-illumination device based on electro-optomechanical systems also in regimes in which photon losses would, otherwise, prevent to outperform the optimal classical illumination protocol with the same transmitted energy.

Nonreciprocal systems breaking time-reversal symmetry are essential tools in modern quantum technologies enabling the suppression of unwanted reflected signals or extraneous noise entering through detection ports. Here we propose a scheme enabling nonreciprocal conversion between optical and radio-frequency (rf) photons using exclusively optomechanical and electromechanical interactions. The nonreciprocal transmission is obtained by interference of two dissipative pathways of transmission between the two electromagnetic modes established through two distinct intermediate mechanical modes. In our protocol, we apply a bichromatic drive to the cavity mode and a single-tone drive to the rf resonator, and use the relative phase between the drive tones to obtain nonreciprocity. We show that perfect nonreciprocal transduction can be obtained in the limit of large cooperativity in both directions, from optical to rf and vice versa. We also study the transducer noise and show that mechanical thermal noise is always reflected back onto the isolated port. In the limit of large cooperativity, the input noise is instead transmitted in an unaltered way in the allowed direction; in particular one has only vacuum noise in the output rf port in the case of optical-to-rf conversion.

We study the dissipative preparation of many-body entangled Gaussian states in bosonic lattice models which could be relevant for quantum technology applications. We assume minimal resources, represented by systems described by particle-conserving quadratic Hamiltonians, with a single localized squeezed reservoir. We show that in this way it is possible to prepare, in the steady state, the wide class of pure states which can be generated by applying a generic passive Gaussian transformation on a set of equally squeezed modes. This includes nontrivial multipartite entangled states such as cluster states suitable for measurement-based quantum computation.

We study synchronization of a room-temperature optomechanical system formed by two resonators coupled via radiation pressure to the same driven optical cavity mode. By using stochastic Langevin equations and effective slowly varying amplitude equations, we explore the long-time dynamics of the system. We see that thermal noise can induce significant non-Gaussian dynamical properties, including the coexistence of multistable synchronized limit cycles and phase diffusion. Synchronization in this optomechanical system is very robust with respect to thermal noise: in fact, even though each oscillator phase progressively diffuses over the whole limit cycle, its phase difference is locked, and such a phase correlation remains strong in the presence of thermal noise.

We propose and analyze a microscopic Stirling heat engine based on an optomechanical system. The working fluid is a single vibrational mode of a mechanical resonator, which interacts by radiation pressure with a feedback-controlled optical cavity. The cavity light is used to engineer the thermal reservoirs and to steer the resonator through a thermodynamic cycle. In particular, the feedback is used to properly modulate the light fluctuations inside the cavity and hence to realize efficient thermodynamic transformations with realistic optomechanical devices.

Gaussian cluster states are ideal infinitely squeezed states. In practice it is possible to construct only approximated version of them with finite squeezing. Here we show how to determine the specific multimode squeezing transformation, which generates a faithful approximation of any given Gaussian cluster state.

We analyze the performance of optomechanical cooling of a mechanical resonator in the presence of a degenerate optical parametric amplifier within the optomechanical cavity, which squeezes the cavity light. We demonstrate that this allows to significantly enhance the cooling efficiency via the coherent suppression of Stokes scattering. The enhanced cooling occurs also far from the resolved sideband regime, and we show that this cooling scheme can be more efficient than schemes realized by injecting a squeezed field into the optomechanical cavity.

The dissipative properties of an optical cavity can be effectively controlled by placing it in a feedback loop where the light at the cavity output is detected and the corresponding signal is used to modulate the amplitude of a laser field which drives the cavity itself. Here we show that this effect can be exploited to improve the performance of an optomechanical heat engine which makes use of polariton excitations as working fluid. In particular we demonstrate that, by employing a positive feedback close to the instability threshold, it is possible to operate this engine also under parameters regimes which are not usable without feedback, and which may significantly ease the practical implementation of this device.

We study theoretically and experimentally the behavior of an optomechanical system where two vibrating dielectric membranes are placed inside a driven Fabry-Pérot cavity. We prove that multi–element systems of mechanical resonators are suitable for enhancing optomechanical performances, and we report a ∼2.47 gain in the optomechanical coupling strength of the membrane relative motion with respect to the single membrane case. With this configuration it is possible to enable cavity optomechanics in the strong single-photon coupling regime.

Multi-element systems of micro/nano-mechanical resonators offer promising prospects for enhanced optomechanical performances, and for the exploration of multi-oscillators synchronization. A solution, capable of providing systems with ratio between the single-photon optomechanical coupling rate and the cavity decay rate enhanced by orders of magnitude, exploits quantum interference in multi-element optomechanical setups. Although the simplest two-membrane sandwich in an optical cavity is a paradigm for the realization of strong-coupling optomechanics, and the observation of collective mechanical effects (such as synchronization), no experimental studies of these phenomena have been reported till now. We report on the first experimental characterization of the optical, mechanical, and especially optomechanical properties of a sandwich constituted of two parallel membranes within an optical cavity. The membrane-sandwich we use in our experiment is constituted of two low-stress Si 3 N 4 square membranes, with a side of 1 mm, and a thickness of 100 nm. One of the membranes is glued on a piezo, for scanning the membrane-cavity length. The whole membrane-sandwich mount is attached to another piezo to displace in a controlled way the center of mass of the two membranes inside the Fabry-Perot cavity. To estimate the optomechanical coupling strength achievable with our system, we inserted the membrane-sandwich in an optical cavity 90 mm-long, driven with a 1064 nm laser beam.

Normal-mode splitting is the most evident signature of strong coupling between two interacting subsystems. It occurs when two subsystems exchange energy between themselves faster than they dissipate it to the environment. Here we experimentally show that a weakly coupled optomechanical system at room temperature can manifest normal-mode splitting when the pump field fluctuations are antisquashed by a phase-sensitive feedback loop operating close to its instability threshold. Under these conditions the optical cavity exhibits an effectively reduced decay rate, so that the system is effectively promoted to the strong coupling regime.