The cooperative Lamb shift (CLS) is hard to measure because in samples much larger than a resonant wavelength it is much smaller, for an initially prepared resonantly phased state, than the cooperative decay rate (CDR). We show, however, that if the phasing of the initial state is detuned so that the spatial wave vector is $k_1\cong k_0\pm O(\frac{1}{R})$ (where $k_0={\omega }_0/c$ is the resonant frequency), the CLS grows to “giant” magnitudes making it comparable to the CDR. Moreover, for certain controlled values of detuning, the initial CDR becomes small so that the dynamical Lamb shift (DLS) can be measured over a considerable period of time.

• Received 3 March 2010

DOI:https://doi.org/10.1103/PhysRevA.81.043845