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New Journal of Physics

Control of atomic state decay in cavities and microspheres

Gershon Kurizki, Abraham G. Kofman, Alexander E. Kozhekin, G. Harel

Published Dec 1, 2000• 14 citations
Publisher

Abstract

Novel methods are discussed for the state control of atoms coupled to single-mode and multi-mode cavities and microspheres. (1)Excitation decay control: The quantum Zeno effect, i.e. inhibition of spontaneous decay by frequent measurements, is observable in high-Qcavities and microspheres using a sequence of evolution-interrupting pulses or randomly-modulated CW fields. By contrast, in 'bad' cavities or open space, frequent measurements can onlyacceleratethe decay, causing the anti-Zeno effect. (2)Location-dependent interference of decay channels: Control of two metastable states is feasible viaresonantsingle-photon absorption to an intermediate state, by engineering spontaneous emission in a multimode cavity. (3)Decoherence control by conditionally interfering parallel evolutions: Anarbitraryinternal state of an atomic wavepacket can be protected from decoherence by interference of its interactions with the cavity over many different time intervalsin parallel, followed by the detection of appropriate atomic-momentum observables. The arsenal of control methods described above can advance the state-of-the-art of quantum information storage and manipulation in cavities.

DOI
10.1088/1367-2630/2/1/328

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Novel methods are discussed for the state control of atoms coupled to single-mode and multi-mode cavities and microspheres. (1)Excitation decay control: The quantum Zeno effect, i.e. inhibition of spontaneous decay by frequent measurements, is observable in high-Qcavities and microspheres using a sequence of evolution-interrupting pulses or randomly-modulated CW fields. By contrast, in 'bad' cavities or open space, frequent measurements can onlyacceleratethe decay, causing the anti-Zeno effect. (2)Location-dependent interference of decay channels: Control of two metastable states is feasible viaresonantsingle-photon absorption to an intermediate state, by engineering spontaneous emission in a multimode cavity. (3)Decoherence control by conditionally interfering parallel evolutions: Anarbitraryinternal state of an atomic wavepacket can be protected from decoherence by interference of its interactions with the cavity over many different time intervalsin parallel, followed by the detection of appropriate atomic-momentum observables. The arsenal of control methods described above can advance the state-of-the-art of quantum information storage and manipulation in cavities.
Novel methods are discussed for the state control of atoms coupled to multi-mode reservoirs with non-Markovian spectra: 1) Excitation decay control : we point out that the quantum Zeno effect, i.e., inhibition of spontaneous decay by frequent measurements, is observable in open cavities and waveguides using a sequence of evolution- interrupting pulses or randomly-modulated CW fields. 2) Location-dependent interference of decay channels - nonadiabatic (resonant) control : We show that the control of populations and coherences of two metastable states is feasible via resonant single-photon absorption to an intermediate state, by controlled spontaneous emission in a cavity. 3) Decoherence control by conditionally interfering parallel evolutions: We demonstrate that an arbitrary internal atomic state can be completely protected from decoherence by interference of its interactions with the reservoir over many different time interals in parallel . Such interference is conditional upon the detection of appropriate atomic-momentum observables. Realization in cavities is suggested. The rich arsenal of control methods described above can improve the performance of single-atom devices. It can also advance the state-of-the-art of quantum information encoding and processing.
Summary form only given. The quantum Zeno effect (QZE) is the striking possibility of inhibiting the decay of an unstable quantum state by sufficiently frequent measurements. This effect is currently believed to be universal, even though it has only been observed for oscillations between discrete states. Recently we showed that both the QZE and the inverse (anti-) Zeno effect (AZE) can be observed on spontaneous decay in cavities. We develop a general theory of evolution of quantum systems in the presence of frequent measurements. We consider both the ideal case of instantaneous projections of the wave function to the initial state and some possible measurement schemes. The considerations imply the impossibility of the continuous-observation limit necessary to stop quantum evolution (the quantum Zeno paradox). Indeed, this limit leads to an unbounded increase of the energy fluctuations of the system, which would cause the system to disintegrate. The present theory describes different measurement effects, including the QZE and AZE, and allows us to obtain the general criteria of their validity. In particular, we show that the AZE, rather than the QZE, is achievable for spontaneous decay of atoms in free space.
A unified theory is given of dynamically modified decay and decoherence in driven quantum systems that are coupled to arbitrary finite-temperature reservoirs and undergo random phase fluctuations. Criteria for the optimization of the suppression and the limitations of this approach are obtained. Decay acceleration by frequent measurements (interruptions of the coupling), known as the anti-Zeno effect (AZE) is argued to be much more ubiquitous than its inhibition in one- or two-level systems coupled to reservoirs (continua). In multilevel systems, frequent measurements cause accelerated decay by destroying the multilevel interference, which tends to inhibit decay in the absence of measurements.