Fundamental phenomena like Quantum Zeno effect (QZE) and Anti-Zeno Effect (AZE) have been recognized as relevant tools for quantum control. Along this line, here we present two experiments in which we demonstrate the capability to extract information on noise events by exploiting QZE and AZE. In the first experiment, we realize noise diagnostics by frequent measurement, showing how a single photon undergoing a noise process (e.g., random polarization fluctuations) can diagnose non-Markovian temporal correlations within such a noise. In the second one, instead, we show how, by protecting via QZE a photonic qubit in a noisy quantum channel, it is possible to estimate the statistical distribution of the microscopic noise (decoherence) events by using the qubit itself as a probe. These techniques can become indispensable under extremely faint illumination, when traditional interferometric methods are usually ineffective.
We report on a robust method for reconstructing multi-mode optical fields. In particular, our method correctly identifies the number and types of modes as well as each mode’s energy, which we demonstrated experimentally. Our method uses multidetector trees and both high-order autocorrelation functions of detected photons (the Glauber function) and high-order autocorrelation functions of no-photon detection. Here we show successful reconstruction for classical and nonclassical multimode fields that contain up to 4 modes whose types are not disclosed to the reconstruction algorithm. This method is significantly more successful than the previously reported one, based on high-order Glauber functions only.
Quantum teleportation relies on entanglement as the quantum resource to be able to communicate with fidelities beyond the classical limit. Nevertheless, the entangled resource may be afflicted by local noise, affecting its ability to serve as the entangled resource for quantum teleportation. We obtain experimental data on the influence of different local environments on the ability of an initially entangled pair of qubits to act as a teleportation resource, after it has been disturbed by noise. We generate selected conditions on the noise parameter space, both theoretically and experimentally, and we find that an already noisy protocol can be made practically insensitive to a further addition of noise. The experimental results are based on a photonic implementation of the quantum teleportation algorithm, with a polarization-entangled pair acting as the quantum resource. The state to be teleported is an additional qubit encoded in the path internal degree of freedom of Alice's photon. Interactions with different local environments on both sides of the system are either implemented with an extra qubit as the environment, or simulated as a weighed average of pure states. We compare our experimental results with the theoretical predictions, and by performing quantum process tomography we can calculate the fidelity of the quantum teleportation scheme and evaluate the effect of local environments.
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