Pointer States via Engineered Dissipation

Abstract

Pointer states are long-lasting high-fidelity states in open quantum systems. We show how any pure state in a non-Markovian open quantum system can be made to behave as a pointer state by suitably engineering the coupling to the environment via open-loop periodic control. Engineered pointer states are constructed as approximate fixed points of the controlled open-system dynamics, in such a way that they are guaranteed to survive over a long time with a fidelity determined by the relative precision with which the dynamics is engineered. We provide quantitative minimum-fidelity bounds by identifying symmetry and ergodicity conditions that the decoherence-inducing perturbation must obey in the presence of control, and develop explicit pulse sequences for engineering any desired set of orthogonal states as pointer states. These general control protocols are validated through exact numerical simulations as well as semi-classical approximations in realistic single and two qubit dissipative systems. We also examine the role of control imperfections, and show that while pointer-state engineering protocols are highly robust in the presence of systematic pulse errors, the latter can also lead to unintended pointer-state generation in dynamical decoupling implementations, explaining the initial-state selectivity observed in recent experiments.

22 pages, 12 figures

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• Experimental bath engineering for quantitative studies of quantum control
• On the optimal feedback control of linear quantum systems in the presence of thermal noise
• GRAPE optimization for open quantum systems with time-dependent decoherence rates driven by coherent and incoherent controls
• Preferred States of Decoherence under Intermediate System-Environment Coupling
• Improving the estimation of environment parameters via initial probe-environment correlations
• Finite-temperature decoherence of spin states in a $\text{{}{\text{Cu}}_3\text{}}$ single molecular magnet
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• Pointer States in the Born-Markov approximation
• The pointer basis and the feedback stabilization of quantum systems
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• Unique determination and generation of rank two single-qubit quantum channels
• Testing the weak equivalence principle for nonclassical matter with torsion balances