Résultats de recherche pour « Decoherence »

In this work, we study quantum decoherence as reflected by the dynamics of a system that accounts for the interaction between matter and a given field. The process is described by an important information geometry tool: Fisher’s information measure (FIM). We find that it appropriately describes this concept, detecting salient details of the quantum–classical changeover (qcc). A good description of the qcc report can thus be obtained; in particular, a clear insight into the role that the uncertainty principle (UP) plays in the pertinent proceedings is presented. Plotting FIM versus a system’s motion invariant related to the UP, one can also visualize how anti-decoherence takes place, as opposed to the decoherence process studied in dozens of papers. In Fisher terms, the qcc can be seen as an order (quantum)–disorder (classical, including chaos) transition.

Abstract We propose a general approach of protecting a two-level system against decoherence via quantum engineering of non-classical multiple superpositions of coherent states in a non-Markovian reservoir. The scheme surprisingly only uses the system-environment interaction responsible for the decoherence and projective measurements of the two-level system. We demonstrate the method on the example of an excitonic qubit in self-assembled semiconductor quantum dots coupled to the super-Ohmic reservoir of acoustic phonons.

We investigate the validity of exponential models in the analysis of Ramsey coherence measurements and show that finite environmental memory is consistent with a systematic bias in the extracted decoherence rate. Starting from a system–bath Hamiltonian, we derive a finite-memory decoherence function using a second-order cumulant expansion under the assumption of Gaussian noise with finite correlation time. The resulting dynamics exhibit a time-dependent effective decay rate, reducing to exponential behavior only in the long-time limit. We derive an explicit closed-form expression for the decoherence rate extracted by least-squares exponential fitting over a finite time window [0, T], as an explicit function of both T and the environmental correlation time τ_c. We show that the extracted rate γ_fit(T) strictly underestimates the intrinsic decoherence rate γ for all finite T > 0, with the deficit decaying as T⁻¹ in the long-window limit, while in the short-window limit the fitted rate scales linearly with T , a regime not directly accessible experimentally due to limited signal contrast at early times. The central implication is that decoherence rates extracted from exponential fits are not intrinsic observables in non-Markovian environments: they encode a protocol-dependent effective average that depends systematically on the chosen fitting window. The conventionally reported coherence time T₂* = 1/γ_fit is therefore protocol-dependent in non-Markovian environments. Finally, we connect this behavior to experimentally observed non-exponential decay profiles and noise spectra, providing a unified framework for interpreting deviations from exponential coherence decay. These results identify a structural limitation in standard Ramsey analysis and motivate the use of physically grounded models in extracting decoherence parameters.

Quantum decoherence is crucial to understanding the emergence of the classical world from the underlying quantum reality. Decoherence dynamics are unitary, although they superselect a preferred eigenbasis. Decoherence dynamics result in stable macroscopic, localized, classical-like states. We show that the above-mentioned facts imply the possibility of the existence of decoherence-like dynamics that result in stable macroscopic non-localized non-classical-like states. Being rooted in the fabric of the decoherence theory itself, this property implies environments that steer the decoherence towards, for example, spatial superpositions of macroscopic objects. To demonstrate this, we provide thought-experimental, mathematical and philosophical arguments.