Yan Zhou, Anthony Colombo, David Grimes, Robert Field Cooperative effects in a dense Rydberg gas Rydberg states Rydberg formula - A priori known energy Large dipole moment ~kiloDebye Pure electronic spectrum core-nonpenetrating Rydberg electron: | l |=1 Ion core: |N + |=0,|v + |=0 Resonance the electron and ion-core Electronic-vibration interaction Electronic-rotation interaction Experimental methods Pulsed-Field Ionization Free Induction Decay 5 cm Rydberg-Rydberg induced by CPmmW Direct transition detection: Free Induction Decay No high voltage ion detection system Stray electric field 10 GHz bandwidth, ~100 kHz resolution Reliable relative intensities: 1% accuracy Manipulation by designed pulse sequence We can now achieve >10:1 S:N in a single chirp Observing RydbergRydberg transitions directly in Calcium gas Transition: 36p 36s Chirp: 10ns, 500MHz, 300 W Acquisitions: 5000, 5min Typical Ryd-Ryd spectrum Time-domain Excitation: regular nutation envelope Max FID Min FID FID: Single exponential decay /2 pulse Maximum FID pulse Minimum FID Typical Ryd-Ryd spectrum Frequency domain Single sharp line 450kHz for He supersonic jet 250kHz for Ar supersonic jet Strange behaviors N=5x10 5 cm -3 Intense but Short FID Weak but Long FID Max FID Not /2 Strange behaviors N