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Control protocols for manipulation of ground-state quantum beats in a cavity QED system

Andres D. Cimmarusti

Published Jan 1, 2014• 0 citations
Publisher

Abstract

Cavity quantum electrodynamics (QED) captures the essential interaction between two quantum systems, an atom (for example) and the quantized electromagnetic field. The cavity reduces the plethora of spatial modes of the field in free-space to one or two. This simplification facilitates the study and control of atom-light interactions. In this thesis we show results where we control both aspects of the interaction. Our first measurements demonstrate the implementation of a simple feedback mechanism on a two-mode cavity QED system to preserve the Zeeman coherence of a ground state superposition that generates quantum beats. Our investigation shows how to prevent a shift away from the Larmor frequency and associated decoherence caused by Rayleigh scattering. The protocol consists of turning off the drive of the system after the detection of a first photon and letting it evolve in the dark. Turning the drive back on after a pre set time reveals a phase accumulated only from Larmor precession, with the amplitude of the quantum beat more than a factor of two larger than with continuous drive. We present preliminary conditional measurements in a new cavity QED apparatus that show an environment-assisted speed-up of the evolution of our cavity photon state under weak driving. Changes in the number of atoms (N) that can couple to the field is our way of tailoring the environment. Our results indicate that as N increases, the rate of the re-population of the cavity photon state increases.

DOI
10.13016/m2cs34

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Cavity quantum electrodynamics (QED) captures the essential interaction between two quantum systems, an atom (for example) and the quantized electromagnetic field. The cavity reduces the plethora of spatial modes of the field in free-space to one or two. This simplification facilitates the study and control of atom-light interactions. In this thesis we show results where we control both aspects of the interaction. Our first measurements demonstrate the implementation of a simple feedback mechanism on a two-mode cavity QED system to preserve the Zeeman coherence of a ground state superposition that generates quantum beats. Our investigation shows how to prevent a shift away from the Larmor frequency and associated decoherence caused by Rayleigh scattering. The protocol consists of turning off the drive of the system after the detection of a first photon and letting it evolve in the dark. Turning the drive back on after a pre set time reveals a phase accumulated only from Larmor precession, with the amplitude of the quantum beat more than a factor of two larger than with continuous drive. We present preliminary conditional measurements in a new cavity QED apparatus that show an environment-assisted speed-up of the evolution of our cavity photon state under weak driving. Changes in the number of atoms (N) that can couple to the field is our way of tailoring the environment. Our results indicate that as N increases, the rate of the re-population of the cavity photon state increases.
We implement a simple feedback mechanism on a two-mode cavity QED system to preserve the Zeeman coherence of a ground state superposition that generates quantum beats on the second-order correlation function. Our investigation includes theoretical and experimental studies that show how to prevent a shift away from the Larmor frequency and associated decoherence caused by Rayleigh scattering. The protocol consists of turning off the drive of the system after the detection of a first photon and letting it evolve in the dark. Turning the drive back on after a pre-set time reveals a phase accumulated only from Larmor precession, with the amplitude of the quantum beat more than a factor of two larger than with continuous drive.
Conditional measurements on the undriven mode of a two-mode cavity QED system prepare a coherent superposition of ground states which generate quantum beats. The continuous system drive induces decoherence through the phase interruptions from Rayleigh scattering, which manifests as a decrease of the beat amplitude and an increase of the frequency of oscillation. We report recent experiments that implement a simple feedback mechanism to protect the quantum beat. We continuously drive the system until a photon is detected, heralding the presence of a coherent superposition. We then turn off the drive and let the superposition evolve in the dark, protecting it against decoherence. At a later time we reinstate the drive to measure the amplitude, phase, and frequency of the beats. The amplitude can increase by more than fifty percent, while the frequency is unchanged by the feedback.
\nConditional measurements on the undriven mode of a two-mode cavity QED system prepare a coherent superposition of ground states which generate quantum beats. The continuous system drive induces decoherence through the phase interruptions from Rayleigh scattering, which manifests as a decrease of the beat amplitude and an increase of the frequency of oscillation. We report recent experiments that implement a simple feedback mechanism to protect the quantum beat. We continuously drive the system until a photon is detected, heralding the presence of a coherent superposition. We then turn off the drive and let the superposition evolve in the dark, protecting it against decoherence. At a later time we reinstate the drive to measure the amplitude, phase, and frequency of the beats. The amplitude can increase by more than fifty percent, while the frequency is unchanged by the feedback.\n
We probe a ground-state superposition that produces a quantum beat in the intensity correlation of a two-mode cavity QED system. We mix drive with scattered light from an atomic beam traversing the cavity, and effectively measure the interference between the drive and the light from the atom. When a photon escapes the cavity, and upon detection, it triggers our feedback which modulates the drive at the same beat frequency but opposite phase for a given time window. This results in a partial interruption of the beat oscillation in the correlation function, that then returns to oscillate.
Abstract. We probe a ground-state superposition that produces a quantum beat in the intensity correlation of a two-mode cavity QED system. We mix drive with scattered light from an atomic beam traversing the cavity, and effectively measure the interference between the drive and the light from the atom. When a photon escapes the cavity, and upon detection, it triggers our feedback which modulates the drive at the same beat frequency but opposite phase for a given time window. This results in a partial interruption of the beat oscillation in the correlation function, that then returns to oscillate. 1.