High efficiency optical modulation at a telecom wavelength using the quantum Zeno effect in a ladder transition in Rb atoms

We demonstrate a high-efficiency optical modulator at ̃1323 nm using the quantum Zeno effect in a ladder transition in a Rb vapor cell. The lower leg of the transitions represents the control beam while the upper leg of the transitions represents the signal beam. The cross-modulation of the signal beam transmission is observed as the control beam is intensity modulated, and is explained in terms of the quantum Zeno effect. We observe a modulation depth of near 100% at frequencies up to 1MHz and demonstrate modulation at speeds up to 75 MHz, with a 3 dB bandwidth of about 5 MHz, limited by the homogeneous linewidth of the intermediate state. We also describe how much higher modulation speeds could be realized by using a buffer gas to broaden the transitions. We identify and explain the special conditions needed for optimizing the modulation efficiency. Numerical simulations of modulation at ̃1GHz are presented. The maximum modulation speed is found to scale with the pressure-broadened linewidth of the intermediate state, so that much higher speeds should be attainable.