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Physical Review A

Quantum nondemolition measurement of quantum beats and the enforcement of complementarity

Barry C. Sanders, Gerard J Milburn

Published Dec 1, 1989• 1 citation
Publisher

Abstract

In a three-level ssv-type atom, which has two excited levels and a ground level, the fluorescence exhibits quantum beats due to a correlation between the two excited levels. However, a measurement of the atomic level yields information about the atomic state but completely suppresses the quantum beats. Here we discuss a modification of the atomic-level measurement to allow for a continuous transition from perfect quantum beats to complete information of the atomic level. The complementary relation between the beats and knowledge of the atomic level is quantitatively shown to be a proportionality between the beat visibility and the probability of making an incorrect measurement of the atomic level. We discuss the realization of the scheme in the context of current experimental proposals involving atomic-level measurements via Fock number states in micromaser cavities. Imperfect photodetector efficiency and micromaser cavity damping are incorporated into the formalism.

DOI
10.1103/physreva.40.7087

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In a three-level ssv-type atom, which has two excited levels and a ground level, the fluorescence exhibits quantum beats due to a correlation between the two excited levels. However, a measurement of the atomic level yields information about the atomic state but completely suppresses the quantum beats. Here we discuss a modification of the atomic-level measurement to allow for a continuous transition from perfect quantum beats to complete information of the atomic level. The complementary relation between the beats and knowledge of the atomic level is quantitatively shown to be a proportionality between the beat visibility and the probability of making an incorrect measurement of the atomic level. We discuss the realization of the scheme in the context of current experimental proposals involving atomic-level measurements via Fock number states in micromaser cavities. Imperfect photodetector efficiency and micromaser cavity damping are incorporated into the formalism.
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We propose a quantum nondemolition measurement of the photon-number distribution for a two-mode cavity field. In the scheme two sequences of two-level atoms interact dispersively with the respective cavity modes and resonantly with two classical fields, and then are detected continually. The field finally reduces to a two-mode Fock state. The probability of collapsing to a given Fock state is determined by the initial photon-number distribution. The scheme can be easily generalized to a field with N modes.
The quantum electrodynamics of two atoms in free space, separated by many wavelengths and interacting with one another via the coupling of their dipole moments to the electromagnetic field, is studied using the Heisenberg-operator approach. The problem is formulated in such a way that one of the atoms, which has two levels, plays the role of a detector; the other atom, whose levels are arbitrary but do not involve cascadelike transitions, plays the role of the source. Several aspects of the interaction are considered, including: a review of photodetection theory, the theory of an alternative detection method that uses an excited-state detector, and a study of quantum beats. These dynamical studies of emission and detection provide new insights into the observation of quantum beats in the transition rate of a detector. We show that ground-state beats are not observed by a detector atom making an upward transition, but that ground-state beats are, in principle, observable if the detector atom makes a downward transition.
Abstract We theoretically investigate two-time intensity–intensity correlation spectroscopy in three-level atoms, a spectroscopic method that allows for direct detection of energy level structures and resonances in complex molecules. We show that in three-level Λ or V -systems, a richer spectroscopic signature is obtained when the applied fields are detuned from the transitions to values other than the typical zero-detuning or two-photon detuning settings. This allows us to identify, in the limit in which the overall decoherence rate from an excited state is much smaller than the Rabi frequency of the driving field, areas of parameter space for a three-level V -system in which low-frequency quantum beats can be generated while still maintaining significant signal amplitude. This may prove advantageous in improving the quality and ease of measurements in quantum beat spectroscopy as this type of experimental technique requires a high degree of time resolution.