Conditional dynamics and quantum feedback, an experiment in cavity QED Luis A. Orozco

1. Conditional dynamics and quantum feedback, an experiment in cavity QED Luis A. Orozco UMD College Park

2. Students: Matthew Terraciano Basudev Roy Michael Scholten Rebecca Olson Post Doctoral Associates: Dan Freimund Daniela Manoel Former Students: Joseph Reiner Wade Smith Stephan Kuhr (Bonn) Collaborators: Howard Wiseman, Griffith University, Brisbane, Australia. Perry Rice, Miami University, Oxford, Ohio. Julio Gea-Banacloche, University of Arkansas, Fayetteville, Arkansas Supported by NSF and NIST

3. Open Quantum Systems in Quantum Optics The answer depends on how we probe the system Quantum Trajectories

6. Strong coupling: The fluctuation is larger than the mean. (The smallest fluctuation is a photon). The signal is going to be noisy. For noisy signals: Make measurements in coincidence. Example: Handbury Brown and Twiss Calibration of a high energy detector. (Geiger in 1910 )

7. Hanbury-Brown and Twiss, (1956) Measure the size of a star by looking at coincidences of the intensity fluctuations. Michelson HBT Detector Source Field interference Intensity Coincidences

8. Source A B A Electron pulses B time 4 coincidences out of 5 A detections; efficiency of B=4/5 It is not necessary to know the efficiency of A!

9. Hanbury-Brown and Twiss Intensity-Intensity Correlations The correlation is largest at equal time Schwarz

10. Intensity correlation function measurements: Gives the probability of detecting a photon at time t +tgiven that one was detected at time t. This is a conditional measurement:

11. Cavity QED Quantum Electrodynamics for pedestrians. No renormalization needed. A single mode of the electromagnetic field of a cavity. ATOMS + CAVITY MODE Non perturbative regime: Coupling > dissipation Dipole coupling between the atom and the cavity. The field of one photon in a cavity with Volume Veff is:

12. Cavity QED System Cavity length»850mm 10-4 photons in the cavity in steady state.

13. Steady State: Exchange of Excitation:

14. Regression of the field to steady state after the detection of a photon.

15. Each escape of a photon creates a very large disturbance. We want to monitor that disturbance or fluctuation. But we can only get one photon at best every time there is a disturbance. We have to average the conditional intensity. How does the data look in the lab?

38. 7 663 536 starts 1 838 544 stops Non-classical, antibunched

39. Conditioned measurements in the language of correlation functions allow the study of the dynamics of the system. Quantum conditioning, with photodetections, provides the most ideal times for controlling the evolution of the system. Feedback on a single photodetection.

40. Measurement Device Quantum System Amplifier ENVIRONMENT

42. We have to satisfy three conditions: Amplitude Sign of the step (parity) Time of the step We only have one bit of information, a click. We have good knowledge of the dynamics.

43. FieldAtomic Polarization Same coefficients when

50. Theoretical prediction.