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David Vitali

Publications and source records attributed to David Vitali.

At least 73 records · Page 4Linked to original sources
arXiv2013

Reservoir engineering of a mechanical resonator: generating a macroscopic superposition state and monitoring its decoherence

A deterministic scheme for generating a macroscopic superposition state of a nanomechanical resonator is proposed. The nonclassical state is generated through a suitably engineered dissipative dynamics exploiting the optomechanical quadratic interaction with a bichromatically driven optical cavity mode. The resulting driven dissipative dynamics can be employed for monitoring and testing the decoherence processes affecting the nanomechanical resonator under controlled conditions.

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arXiv2013

Generation of two-mode entangled states by quantum reservoir engineering

A method for generating entangled cat states of two modes of a microwave cavity field is proposed. Entanglement results from the interaction of the field with a beam of atoms crossing the microwave resonator, giving rise to non-unitary dynamics of which the target entangled state is a fixed point. We analyse the robustness of the generated two-mode photonic "cat state" against dephasing and losses by means of numerical simulation. This proposal is an instance of quantum reservoir engineering of photonic systems.

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arXiv2012

Nonclassical States of Light and Mechanics

This book chapter reports on theoretical protocols for generating nonclassical states of light and mechanics. Nonclassical states are understood as squeezed states, entangled states or states with negative Wigner function, and the nonclassicality can refer either to light, to mechanics, or to both, light and mechanics. In all protocols nonclassicallity arises from a strong optomechanical coupling. Some protocols rely in addition on homodyne detection or photon counting of light.

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arXiv2012

Entanglement swapping with local certification: Application to remote micromechanical resonators

We propose a protocol for entanglement swapping which involves tripartite systems. The generation of remote entanglement induced by the Bell measurement can be easily certified by additional local measurements. We illustrate the protocol in the case of continuous variable systems where the certification is effective for an appropriate class of three-mode Gaussian states. We then apply the protocol to optomechanical systems, showing how mechanical entanglement between two remote micromechanical resonators can be generated and certified via local optical measurements.

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arXiv2012

Quantum optomechanics of a multimode system coupled via photothermal and radiation pressure force

We provide a full quantum description of the optomechanical system formed by a Fabry-Perot cavity with a movable micro-mechanical mirror whose center-of-mass and internal elastic modes are coupled to the driven cavity mode by both radiation pressure and photothermal force. Adopting a quantum Langevin description, we investigate simultaneous cooling of the micromirror elastic and center-of-mass modes, and also the entanglement properties of the optomechanical multipartite system in its steady state.

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arXiv2010

Feedback-assisted ponderomotive squeezing

We analyze how the radiation pressure interaction between a mechanical element and an intensely driven optical cavity mode can be exploited for generating squeezed light. We study in particular how the performance of the optomechanical device can be improved when a homodyne-based feedback loop is added to control the motion of the mechanical element of the system. We show that, when driving the cavity at resonance, an appropriate proportional feedback control is able to improve the generation of ponderomotive squeezing, which should be detectable with state-of-the-art apparatuses.

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arXiv2010

Implementation of a three-qubit quantum error correction code in a cavity-QED setup

The correction of errors is of fundamental importance for the development of contemporary computing devices and of robust communication protocols. In this paper we propose a scheme for the implementation of the three-qubit quantum repetition code, exploiting the interaction of Rydberg atoms with the quantized mode of a microwave cavity field. Quantum information is encoded within two circular Rydberg states of the atoms and encoding and decoding process are realized within two separate microwave cavities. We show that errors due to phase noise fluctuations could be efficiently corrected using a state-of-the-art apparatus.

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arXiv2010

Continuous-variables entanglement purification with atomic systems

We present a proposal for entanglement purification of the continuous-variable quantum state of two propagating optical fields. The scheme is based on letting each field interact with a local node, an atomic ensemble, whose internal collective excitation plays the role of an ancillary continuous variable resource. Entanglement purification is achieved by a dichotomic measurement, representing the required non-Gaussian element, and which consists in detecting the presence or absence of collective excitations in the atomic ensemble. This scheme can be extended to networks, where the nodes are single trapped atoms, and constitutes an important building block for the implementation of a continuous-variable quantum repeater.

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arXiv2010

Engineering Atomic Quantum Reservoirs for Photons

We present protocols for creating entangled states of two modes of the electromagnetic field, by using a beam of atoms crossing microwave resonators. The atoms are driven by a transverse, classical field and pump correlated photons into (i) two modes of a cavity and (ii) the modes of two distant cavities. The protocols are based on a stochastic dynamics, characterized by random arrival times of the atoms and by random interaction times between atoms and cavity modes. The resulting effective model yields a master equation, whose steady state is an entangled state of the cavity modes. In this respect, the atoms act like a quantum reservoir, pulling the cavity modes into an entangled, Einstein-Podolski-Rosen (EPR) state, whose degree of entanglement is controlled by the intensity and the frequency of the transverse field. This scheme is robust against stochastic fluctuations in the atomic beam, and it does not require atomic detection nor velocity selection.

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arXiv2010

Compensating the Noise of a Communication Channel via Asymmetric Encoding of Quantum Information

An asymmetric preparation of the quantum states sent through a noisy channel can enable a new way to monitor and actively compensate the channel noise. The paradigm of such an asymmetric treatment of quantum information is the Bennett 1992 protocol, in which the ratio between conclusive and inconclusive counts is in direct connection with the channel noise. Using this protocol as a guiding example, we show how to correct the phase drift of a communication channel without using reference pulses, interruptions of the quantum transmission or public data exchanges.

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arXiv2009

Sub-Planck scale structures in the P{ö}schl-Teller potential and their sensitivity to perturbations

We find the existence of sub-Planck scale structures in the P{ö}schl-Teller potential, which is an exactly solvable potential with both symmetric and asymmetric features. We analyze these structures in both cases by looking at the Wigner distribution of the state evolved from an initial coherent state up to various fractional revival times. We also investigate the sensitivity to perturbations of the P{ö}schl-Teller potential and we verify that, similar to the harmonic oscillator, the presence of sub-Planck structure in phase space is responsible for a high sensitivity to phase-space displacements.

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arXiv2009

Ground-state cooling of a micromechanical oscillator: generalized framework for cold damping and cavity-assisted cooling schemes

We provide a general framework to describe cooling of a micromechanical oscillator to its quantum ground state by means of radiation-pressure coupling with a driven optical cavity. We apply it to two experimentally realized schemes, back-action cooling via a detuned cavity and cold-damping quantum-feedback cooling, and we determine the ultimate quantum limits of both schemes for the full parameter range of a stable cavity. While both allow to reach the oscillator's quantum ground state, we find that back-action cooling is more efficient in the good cavity limit, i.e. when the cavity bandwidth is smaller than the mechanical frequency, while cold damping is more suitable for the bad cavity limit. The results of previous treatments are recovered as limiting cases of specific parameter regimes.

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arXiv2009

Experimental inhibition of decoherence on flying qubits via bang-bang control

Decoherence may significantly affect the polarization state of optical pulses propagating in dispersive media because of the unavoidable presence of more than a single frequency in the envelope of the pulse. Here we report on the suppression of polarization decoherence in a ring cavity obtained by properly retooling for photonic qubits the ``bang-bang'' protection technique already employed for nuclear spins and nuclear-quadrupole qubits. Our results show that bang-bang control can be profitably extended to quantum information processes involving flying polarization qubits.

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arXiv2009

Sub-Planck scale structures in a vibrating molecule in the presence of decoherence

We study the effect of decoherence on the sub-Planck scale structures of the vibrational wave packet of a molecule. The time evolution of these wave packets is investigated under the influence of a photonic or phononic environment. We determine the master equation describing the reduced dynamics of the wave-packet and analyze the sensitivity of the sub-Planck structures against decoherence in the case of a hydrogen iodide (HI) molecule.

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arXiv2009

Optimal fidelity of teleportation of coherent states and entanglement

We study the Braunstein-Kimble protocol for the continuous variable teleportation of a coherent state. We determine lower and upper bounds for the optimal fidelity of teleportation, maximized over all local Gaussian operations for a given entanglement of the two-mode Gaussian state shared by the sender (Alice) and the receiver (Bob). We also determine the optimal local transformations at Alice and Bob sites and the corresponding maximum fidelity when one restricts to local trace-preserving Gaussian completely positive maps.

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arXiv2008

Simultaneous cooling and entanglement of mechanical modes of a micromirror in an optical cavity

Laser cooling of a mechanical mode of a resonator by the radiation pressure of a detuned optical cavity mode has been recently demonstrated by various groups in different experimental configurations. Here we consider the effect of a second mechanical mode with a close, but different resonance frequency. We show that the nearby mechanical resonance is simultaneously cooled by the cavity field, provided that the difference between the two mechanical frequencies is not too small. When this frequency difference becomes smaller than the effective mechanical damping of the secondary mode, the two cooling processes interfere destructively and cavity cooling is suppressed in the limit of identical mechanical frequencies. We show that also the entanglement properties of the steady state of the tripartite system crucially depend upon on the difference between the two mechanical frequencies. If the latter is larger than the effective damping of the second mechanical mode, the state shows fully tripartite entanglement and each mechanical mode is entangled with the cavity mode. If instead the frequency difference is smaller, the steady state is a two-mode biseparable state, inseparable only when one splits the cavity mode from the two mechanical modes. In this latter case, the entanglement of each mechanical mode with the cavity mode is extremely fragile with respect to temperature.

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arXiv2008

Time-separated entangled light pulses from a single-atom emitter

The controlled interaction between a single, trapped, laser-driven atom and the mode of a high-finesse optical cavity allows for the generation of temporally separated, entangled light pulses. Entanglement between the photon-number fluctuations of the pulses is created and mediated via the atomic center-of-mass motion, which is interfaced with light through the mechanical effect of atom-photon interaction. By means of a quantum noise analysis we determine the correlation matrix which characterizes the entanglement, as a function of the system parameters. The scheme is feasible in experimentally accessible parameter regimes. It may be easily extended to the generation of entangled pulses at different frequencies, even at vastly different wavelengths.

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