Continuous and Pulsed Quantum Zeno Effect*

The quantum Zeno effect is the suppression of transitions between quantum states by frequent measurement. Oscillation between two ground hyperfine states of a magnetically trapped $^{87}$Rb Bose-Einstein condensate, externally driven at a transition rate $\omega_R$, was substantially suppressed by destructively measuring one of the levels with resonant optical scattering. While an ideal continuous measurement will stop the transition, any real measurement method will occur at a finite rate. The suppression of the transition rate in the two level system was quantified for pulsed measurements with a time between pulses $\delta t$ and weak continuous measurements with a scattering rate $\gamma$. We observe that the weak continuous measurements exhibit the same suppression in the transition rate as the pulsed measurements when $\gamma\delta t=3.60(0.43)$, in agreement with the previously predicted value of 4. Increasing the measurement frequency suppressed the transition rate down to $0.005\omega_R$.