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arXiv:1012.5509 · Physical Review A

From Zeno to anti-Zeno regime: Decoherence-control dependence on the quantum statistics of the bath

D. D. Bhaktavatsala Rao, Gershon Kurizki

Published Mar 8, 2011• 37 citations
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Abstract

We demonstrate through exact solutions that a spin bath leads to stronger (faster) dephasing of a qubit than a bosonic bath with an identical bath-coupling spectrum. This difference is due to the spin-bath ``dressing'' by the coupling. Consequently, the quantum statistics of the bath strongly affects the pulse sequences required to dynamically decouple the qubit from its bath.

DOI
10.1103/physreva.83.032105

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We demonstrate through exact solutions that a spin bath leads to stronger (faster) dephasing of a qubit than a bosonic bath with an identical bath-coupling spectrum. This difference is due to the spin-bath ``dressing'' by the coupling. Consequently, the quantum statistics of the bath strongly affects the pulse sequences required to dynamically decouple the qubit from its bath.
The quantum Zeno and anti-Zeno paradigms have thus far addressed the evolution control of a quantum system coupled to an immutable bath via non-selective measurements performed at appropriate intervals. We fundamentally modify these paradigms by introducing, theoretically and experimentally, the concept of controlling the bath state via selective measurements of the system (a qubit). We show that at intervals corresponding to the anti-Zeno regime of the system-bath exchange, a sequence of measurements has strongly correlated outcomes. These correlations can dramatically enhance the bath-state purity and yield a low-entropy steady state of the bath. The purified bath state persists long after the measurements are completed. Such purification enables the exploitation of spin baths as long-lived quantum memories or as quantum-enhanced sensors. The experiment involved a repeatedly probed defect center dephased by a nuclear spin bath in a diamond at low-temperature.
The quantum Zeno and anti-Zeno paradigms have thus far addressed the evolution control of a quantum system coupled to an immutable bath via non-selective measurements performed at appropriate intervals. We fundamentally modify these paradigms by introducing, theoretically and experimentally, the concept of controlling the bath state via selective measurements of the system (a qubit). We show that at intervals corresponding to the anti-Zeno regime of the system-bath exchange, a sequence of measurements has strongly correlated outcomes. These correlations can dramatically enhance the bath-state purity and yield a low-entropy steady state of the bath. The purified bath state persists long after the measurements are completed. Such purification enables the exploitation of spin baths as long-lived quantum memories or as quantum-enhanced sensors. The experiment involved a repeatedly probed defect center dephased by a nuclear spin bath in a diamond at low-temperature.
We investigate the quantum Zeno and anti-Zeno effects in spin bath models: the spin-boson model and a spin-fermion model. We show that the Zeno--anti-Zeno transition is critically controlled by the system-bath coupling parameter, the same parameter that determines spin decoherence rate. We also discuss the crossover in a biased system, at high temperatures, and for a nonequilibrium spin-fermion system, manifesting the counteracting roles of electrical bias, temperature, and magnetic field on the spin decoherence rate.
We examine the critical system parameters which affect the quantum Zeno–anti-Zeno transition in a spin–boson system by applying the notion of correlated Zeno subspaces beyond the qubit system to its decayed part represented by a collective reservoir of oscillators. We also examine the effect of coherent control via a periodic sequence of dynamical decoupling pulses prior to projective measurement. Our results show that depending on the system bias and measurement time interval of the spin–boson model, coherent control via periodic dynamical decoupling pulses eliminates the Zeno–anti-Zeno transition behavior. We extend the calculations to examine the entanglement dynamics of two initially entangled qubits coupled to independent reservoirs with varying configuration and subjected to frequent measurements. In a multipartite system, in which one or more qubit–reservoir system can undergo the Zeno–anti-Zeno transition, we show that the effects of measurements made in a one qubit–reservoir subsystem can reverberate noticeably throughout a whole array of N pairs of qubit–reservoir subsystems.