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Chinese Physics Letters

Constraint Dynamics and Tracking Control to Coherence of a Thermal Dissipative Qubit

Jun‐Hong An, Shun-Jin Wang, Hong‐Gang Luo

Published Nov 28, 2005• 2 citations
Publisher

Abstract

Constraint dynamics and tracking control strategy to stabilize the coherence of a decoherent system is applied to a dissipative qubit system at a finite temperature. By using a control field dependent on the dynamical state of the qubit via the constraint equations, we show that the coherence of the qubit can be preserved within a finite time duration by the feedback effect of the qubit system. It is also shown that the temperature plays a negative role to this coherence control strategy.

DOI
10.1088/0256-307x/22/12/007

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Constraint dynamics and tracking control strategy to stabilize the coherence of a decoherent system is applied to a dissipative qubit system at a finite temperature. By using a control field dependent on the dynamical state of the qubit via the constraint equations, we show that the coherence of the qubit can be preserved within a finite time duration by the feedback effect of the qubit system. It is also shown that the temperature plays a negative role to this coherence control strategy.
When a quantum system interacts with its environment, the so-called decoherence effect will normally destroy the coherence in the quantum state and the entanglement between its subsystems. We propose a feedback control strategy based on quantum weak measurements to protect coherence and entanglement of the quantum state against environmental disturbance. For a one-qubit quantum system under amplitude damping and dephasing decoherence channels, our strategy can preserve the coherence based on the measured information about the population difference between its two levels. For a two-qubit quantum system disentangled by independent amplitude damping and dephasing decoherence channels, the designed feedback control can preserve coherence between the ground state and the highest excited states by tuning the coupling strength between the two qubits, and at the same time minimize the loss of entanglement between the two qubits. As a consequence of dynamic symmetry, the generalization of these results derives the concept of control-induced decoherence-free observable subspace, for which several criteria are provided.
Engineering dissipation has emerged as a powerful strategy for controlling quantum many-body dynamics, complementing purely coherent control for state preparation. However, finite-time driving across a quantum critical point generates nonadiabatic excitations and coherences, and existing dissipation-engineering approaches have largely characterized how a fixed environment modifies critical dynamics rather than actively steering a system toward a prescribed thermal trajectory. Here we develop a Markovian dissipative framework for finite-time thermal-state tracking based on engineered population currents with non-negative transition rates, and apply it to the transverse-field Ising model driven across its quantum critical point. Compared with unitary dynamics and a natural thermal bath, the engineered dynamics strongly suppresses thermal excitation deviations and provides additional control over coherence damping through a free common current QkQ_kQk​, while exhibiting a substantially steeper residual scaling, δnexth∼(v/vch)2δn_{\mathrm{ex}}^{\mathrm{th}}\sim(v/v_{\mathrm{ch}})^2δnexth​∼(v/vch​)2, than the Kibble--Zurek behavior recovered for unitary evolution. These results point toward engineered dissipation as a route for controlling thermal-state preparation in driven quantum critical systems.
Abstract We present a comprehensive study of quantum coherence dynamics in a qubit–qutrit system coupled to a resonator and exposed to an external noisy environment. Unlike prior works, we focus on the comparative analysis of three distinct coherence measures–l 1-norm of coherence, relative entropy of coherence, and Jensen–Shannon coherence–under dynamic modulation of the resonator frequency. Our key innovation lies in introducing time-dependent sinusoidal and standing wave modulations to the oscillator frequency, revealing nontrivial effects on coherence preservation that are highly sensitive to the modulation parameters. Remarkably, we uncover parameter regimes where coherence revivals are enhanced, even under strong decoherence, a phenomenon not observed in static systems. Additionally, our results demonstrate distinct sensitivity patterns among the coherence measures, highlighting their complementary roles in capturing system-environment interactions. This reanalysis is crucial as it reveals previously unexplored mechanisms for coherence control in hybrid quantum systems, offering novel strategies for improving the robustness of quantum technologies against environmental disturbances.