arXiv subjects

Francesco Poggiali

Publications and source records attributed to Francesco Poggiali.

5 recordsLinked to original sources

arXiv2024

Energy exchange statistics and fluctuation theorem for non-thermal asymptotic states

Exchange energy statistics between two bodies at different thermal equilibrium obey the Jarzynski-Wójcik fluctuation theorem. The corresponding energy scale factor is the difference of the inverse temperatures associated to the bodies at equilibrium. In this work, we consider a dissipative quantum dynamics leading the quantum system towards a, possibly non-thermal, asymptotic state. To generalize the Jarzynski-Wójcik theorem to non-thermal states, we identify a sufficient condition ${\cal I}$ for the existence of an energy scale factor $η^{*}$ that is unique, finite and time-independent, such that the characteristic function of the exchange energy distribution becomes identically equal to $1$ for any time. This $η^*$ plays the role of the difference of inverse temperatures. We discuss the physical interpretation of the condition ${\cal I}$, showing that it amounts to an almost complete memory loss of the initial state. The robustness of our results against quantifiable deviations from the validity of ${\cal I}$ is evaluated by experimental studies on a single nitrogen-vacancy center subjected to a sequence of laser pulses and dissipation.

quant-ph↗

arXiv2023

Three-dimensional magnetic resonance tomography with sub-10 nanometer resolution

We demonstrate three-dimensional magnetic resonance tomography with a resolution down to 5.99 +- 0.07 nm. Our measurements use lithographically fabricated microwires as a source of three-dimensional magnetic field gradients, which we use to image NV centers in a densely doped diamond by Fourier-accelerated magnetic resonance tomography. We also present a compressed sensing scheme for imaging of a spatially localized ensemble from undersampled data, which allows for a direct visual interpretation without numerical optimization. The resolution achieved in our work approaches the positioning accuracy of site-directed spin labeling, paving the way to three-dimensional structure analysis by magnetic-gradient based tomography.

quant-ph↗

arXiv2020

Robust All-Optical Single-Shot Readout of NV Centers in Diamond

High-fidelity projective readout of a qubit's state in a single experimental repetition is a prerequisite for various quantum protocols of sensing and computing. Achieving single-shot readout is challenging for solid-state qubits. For Nitrogen-Vacancy (NV) centers in diamond, it has been realized using nuclear memories or resonant excitation at cryogenic temperature. All of these existing approaches have stringent experimental demands. In particular, they require a high efficiency of photon collection, such as immersion optics or all-diamond micro-optics. For some of the most relevant applications, such as shallow implanted NV centers in a cryogenic environment, these tools are unavailable. Here we demonstrate an all-optical spin readout scheme that achieves single-shot fidelity even if photon collection is poor (delivering less than 10$^3$ clicks/second). The scheme is based on spin-dependent resonant excitation at cryogenic temperature combined with spin-to-charge conversion, mapping the fragile electron spin states to the stable charge states. We prove this technique to work on shallow implanted NV centers as they are required for sensing and scalable NV-based quantum registers.

quant-ph↗

arXiv2020

Experimental test of exchange fluctuation relations in an open quantum system

Elucidating the energy transfer between a quantum system and a reservoir is a central issue in quantum non-equilibrium thermodynamics, which could provide novel tools to engineer quantum-enhanced heat engines. The lack of information on the reservoir inherently limits the practical insight that can be gained on the exchange process of open quantum systems. Here, we investigate the energy transfer for an open quantum system in the framework of quantum fluctuation relations. As a novel toolbox, we employ a nitrogen-vacancy center spin qubit in diamond, subject to repeated quantum projective measurements and a tunable dissipation channel. In the presence of energy fluctuations originated by dissipation and quantum projective measurements, the experimental results, supplemented by numerical simulations, show the validity of the energy exchange fluctuation relation, where the energy scale factor encodes missing reservoir information in the system out-of-equilibrium steady state properties. This result is complemented by a theoretical argument showing that, also for an open three-level quantum system, the existence of an out-of-equilibrium steady state dictates a unique time-independent value of the energy scale factor for which the fluctuation relation is verified. Our findings pave the way to the investigation of energy exchange mechanisms in arbitrary open quantum systems.

quant-ph↗

arXiv2018

Noise spectroscopy of a quantum-classical environment with a diamond qubit

Knowing a quantum system's environment is critical for its practical use as a quantum device. Qubit sensors can reconstruct the noise spectral density of a classical bath, provided long enough coherence time. Here we present a protocol that can unravel the characteristics of a more complex environment, comprising both unknown coherently coupled quantum systems, and a larger quantum bath that can be modeled as a classical stochastic field. We exploit the rich environment of a Nitrogen-Vacancy center in diamond, tuning the environment behavior with a bias magnetic field, to experimentally demonstrate our method. We show how to reconstruct the noise spectral density even when limited by relatively short coherence times, and identify the local spin environment. Importantly, we demonstrate that the reconstructed model can have predictive power, describing the spin qubit dynamics under control sequences not used for noise spectroscopy, a feature critical for building robust quantum devices. At lower bias fields, where the effects of the quantum nature of the bath are more pronounced, we find that more than a single classical noise model are needed to properly describe the spin coherence under different controls, due to the back action of the qubit onto the bath.

quant-ph↗