The figure on the right shows what this pulse sequence does. When the state is | 00 ⟩ ⟩ , both levels are uncoupled from the Rydberg states and so the pulses do nothing. When either of the atoms is in | 0 ⟩ ⟩ state, the other one picks up a − − 1 phase due to the 2 π π pulse. When the state is | 11 ⟩ ⟩ , the second atom is off-resonant to its Rydberg state and thus does not pick up any phase, however the first one does. The truth table of this gate is given below. This is equivalent to a controlled-z gate up-to a local rotation to the hyperfine levels.