Dynamical control of two-level system's decay and long time freezing

TL;DR

This paper demonstrates how periodic phase modulation pulses can coherently control the decay of a two-level quantum system, achieving decay suppression, acceleration, and long-time freezing depending on the spectral conditions and pulse timing.

Contribution

It introduces a method for dynamical control of quantum decay using ideal phase pulses, revealing decay freezing phenomena not previously reported.

Findings

Decay can be suppressed or accelerated depending on spectral peak position.

Decay freezing occurs after many pulses with short delay, reaching half the initial decay.

Control effectiveness varies with spectrum type and pulse timing.

Abstract

We investigate with exact numerical calculation coherent control of a two-level quantum system's decay by subjecting the two-level system to many periodic ideal $2\pi$ phase modulation pulses. For three spectrum intensities (Gaussian, Lorentzian, and exponential), we find both suppression and acceleration of the decay of the two-level system, depending on difference between the spectrum peak position and the eigen frequency of the two-level system. Most interestingly, the decay of the two-level system freezes after many control pulses if the pulse delay is short. The decay freezing value is half of the decay in the first pulse delay.