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Optical and Quantum Sensing and Precision Metrology II

Quantum noise sensing via quantum Zeno and anti-Zeno effects

Fabrizio Piacentini, Salvatore Virzì, Laura T. Knoll, Alessio Avella, Stefano Gherardini, Tomáš Opatrný, Abraham G. Kofman, Gershon Kurizki, Marco Gramegna, Filippo Caruso, Ivo Pietro Degiovanni, Marco Genovese

Published Mar 19, 2025• 0 citations

Abstract

Quantum control is a fundamental tool for quantum technologies, and quantum Zeno (QZE) and anti-Zeno (AZE) effects, respectively denoting the slowdown and speedup of quantum system evolution by frequent interruptions/operations, represent quantum control paradigms. Indeed, they allow either protecting (QZE) or steering (AZE) the state of a quantum system via the interplay between frequent operations (system control) and the coupling of the system to its environment. Here we present two experiments demonstrating the possibility to exploit QZE and AZE to extract information on noise processes occurring in a quantum channel. In the first experiment, we realize the first noise diagnostics scheme based on repeated quantum measurements, showing how a single photon undergoing a noise process (in our case, random polarization fluctuations) can quantify non-Markovian temporal correlations within such a noise. In the second experiment, we show how a QZE-protection mechanism applied to a quantum state can become a noise sensing technique, allowing to estimate the statistical distribution of decoherence effects occurring on a photonic qubit during its propagation in a noisy quantum channel.

DOI: 10.1117/12.3053453

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Quantum control is a fundamental tool for quantum technologies, and quantum Zeno (QZE) and anti-Zeno (AZE) effects, respectively denoting the slowdown and speedup of quantum system evolution by frequent interruptions/operations, represent quantum control paradigms. Indeed, they allow either protecting (QZE) or steering (AZE) the state of a quantum system via the interplay between frequent operations (system control) and the coupling of the system to its environment. Here we present two experiments demonstrating the possibility to exploit QZE and AZE to extract information on noise processes occurring in a quantum channel. In the first experiment, we realize the first noise diagnostics scheme based on repeated quantum measurements, showing how a single photon undergoing a noise process (in our case, random polarization fluctuations) can quantify non-Markovian temporal correlations within such a noise. In the second experiment, we show how a QZE-protection mechanism applied to a quantum state can become a noise sensing technique, allowing to estimate the statistical distribution of decoherence effects occurring on a photonic qubit during its propagation in a noisy quantum channel.

We experimentally demonstrate, for the first time, noise diagnostics by repeated quantum measurements, establishing the ability of a single photon subjected to random polarization noise to diagnose non-Markovian temporal correlations of such a noise process. Both the noise spectrum and temporal correlations are diagnosed by probing the photon with frequent (partially) selective polarization measurements. We show that noise with positive temporal correlations corresponds to our single photon undergoing a dynamical regime enabled by the quantum Zeno effect (QZE), whereas noise characterized by negative (anti) correlations corresponds to regimes associated with the anti-Zeno effect (AZE). This is the first step toward a novel noise spectroscopy based on QZE and AZE in single-photon state probing able to extract information on the noise while protecting the probe state, a conceptual paradigm shift with respect to traditional interferometric measurements.

We investigate the application of the quantum Zeno effect (QZE) for the preparation of non-Gaussian states in optomechanical systems. By frequently monitoring the system, the QZE can suppress transitions away from desired subspaces of states. We show that this enables the preparation of states in qubit subspaces even in the presence of noise and decoherence. Through analytical and numerical analysis, we demonstrate that QZE-based protocols can achieve robust state preparation of qubit states in continuous variable architectures. Our results extend the utility of the QZE beyond discrete systems, highlighting its potential for enhancing quantum control in more complex quantum information processing environments. These findings offer a promising approach for achieving reliable non-Gaussian states in optomechanical systems, with implications for the development of photonic quantum computing and quantum sensing.

The quantum-Zeno and anti-Zeno effects (QZE/AZE) are known for a long time, in a quantum system with coupled levels, the measurement of a particular level population can lead to either acceleration (i.e. AZE) or retardation (i.e. QZE) of its population transfer to other levels. Here we consider how one can control the population flow from a coupled quantum state by measurement at a particular time, and what system parameters are responsible for that. We propose a framework for analysis of quantum Zeno dynamics based on time-dependent density matrix perturbation theory. This framework allows us to clearly separate state populations from their coherences and to predict appearance of either QZE or AZE. We illustrate our analysis on two model systems: 1) two coupled levels and 2) a level coupled to a continuum. In both cases dynamics of quantum coherences play a crucial role, and perturbative considerations allow us to predict the effect of projective measurements. In addition, we have extended our consideration to a closely related coherent control scenario, a unitary transformation flipping a sign of a state in a coherent superposition describing the system wavefunction.

We propose and experimentally demonstrate a general method allowing us to unravel microscopic noise events that affect a continuous quantum variable. Such unraveling is achieved by frequent measurements of a discrete variable coupled to the continuous one. The experimental realization involves photons traversing a noisy channel. There, their polarization, whose coupling to the photons' spatial wave packet is subjected to stochastic noise, is frequently measured in the quantum Zeno regime. The measurements not only preserve the polarization state, but also enable the recording of the full noise statistics from the spatially resolved detection of the photons emerging from the channel. This method proves the possibility of employing photons as quantum noise sensors and robust carriers of information.

The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here, we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though the quantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions.