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Physical Review A

Accelerating decay by multiple 2π pulses

G. S. Agarwal, Marlan O. Scully, HERBERT WALTHER

Published Mar 6, 2001• 41 citations
Publisher

Abstract

We show how a control of the dynamics of a decay process can be achieved by the application of a series of $2\ensuremath{\pi}$ pulses on an auxiliary transition. The $2\ensuremath{\pi}$ pulse changes the phase of the ground state by $\ensuremath{\pi}$ while leaving the phase of the excited state unaltered. This produces quantum interferences between the transition amplitudes for evolution in the short interval, just before and after the $2\ensuremath{\pi}$ pulse. Such an interference under suitable tailoring of the density-of-states of the bath and the time $\ensuremath{\tau}$ leads to accelerated decay.

DOI
10.1103/physreva.63.044101

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We show how a control of the dynamics of a decay process can be achieved by the application of a series of 2\ensuremathπ2\ensuremath{\pi}2\ensuremathπ pulses on an auxiliary transition. The 2\ensuremathπ2\ensuremath{\pi}2\ensuremathπ pulse changes the phase of the ground state by \ensuremathπ\ensuremath{\pi}\ensuremathπ while leaving the phase of the excited state unaltered. This produces quantum interferences between the transition amplitudes for evolution in the short interval, just before and after the 2\ensuremathπ2\ensuremath{\pi}2\ensuremathπ pulse. Such an interference under suitable tailoring of the density-of-states of the bath and the time \ensuremathτ\ensuremath{\tau}\ensuremathτ leads to accelerated decay.
The pulse control of decoherence in a qubit interacting with a quantum environment is studied with focus on a general case where decoherence is induced by both pure dephasing and population decay. To observe how the decoherence is suppressed by periodic pi pulses, we present a simple method to calculate the time evolution of a qubit under arbitrary pulse sequences consisting of bit-flips and/or phase-flips. We examine the effectiveness of the two typical sequences: bb sequence consisting of only bit-flips, and bp sequence consisting of both bit- and phase-flips. It is shown that the effectiveness of the pulse sequences depends on a relative strength of the two decoherence processes especially when a pulse interval is slightly shorter than qubit-environment correlation times. In the short-interval limit, however, the bp sequence is always more effective than, or at least as effective as, the bb sequence.
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In this paper, I study the coherent control and suppression of the free-induction-decay emission associated with the decay from an excited multilevel atom to its ground state. It is shown here that a strong and ultrashort coupling pulse, resonant with the excited states and a lower state other than the ground state, can induce destructive quantum interferences in the decay process. The suppression is temporary and the free-induction-decay signal reappears one quantum-beat period (of the excited states) later. A sequence of equally spaced, ultrashort coupling pulses can control the moment the free-induction-decay emission occurs.