Acceleration of quantum decay processes by frequent observations

Kofman, A. G.; Kurizki, Gershon

doi:10.1038/35014537

Cited by 525 publications

(732 citation statements)

References 13 publications

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“…Indeed, due to the interaction with detectors, the system acquires the energy ∼ / t, according to the energy-time uncertainty relation. As such, it is natural to expect an acceleration of the particle, instead of its freezing: the anti-Zeno effect [1]. Nevertheless, as demonstrated in this paper, the Zeno effect can be entirely attributed to the energy-time uncertainty relation, without the explicit use of the projection postulate.…”

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confidence: 87%

Quantum transfer through a non-Markovian environment under frequent measurements and Zeno effect

Cao

et al. 2014

Phys. Rev. A

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We study transitions of a particle between two wells, separated by a reservoir, under the condition that the particle is not detected in the reservoir. Conventional quantum trajectory theory predicts that such no-result continuous measurement would not affect these transitions. We demonstrate that it holds only for Markovian reservoirs (infinite bandwidth ). In the case of finite , the probability of the particle's interwell transition is a function of the ratio /ν, where ν is the frequency of measurements. This scaling tells us that in the limit ν → ∞, the measurement freezes the initial state (the quantum Zeno effect), whereas for → ∞ it does not affect the particle's transition across the reservoir. The scaling is proved analytically by deriving a simple formula, which displays two regimes, with the Zeno effect and without the Zeno effect. It also supports a simple explanation of the Zeno effect entirely in terms of the energy-time uncertainty relation, with no explicit use of the projection postulate. Experimental tests of our predictions are discussed. It is well known that the unitary evolution of a quantum system is interrupted by measurement, so the subsequent evolution of a system depends on the measurement record. Frequent measurements with intervals t are of special interest. In the limit t → 0, they freeze the particle's motion (the quantum Zeno effect). This result is a consequence of the projection postulate applied to sequential measurements.The Zeno effect looks very surprising since it reveals the dynamical impact of the projection postulate on quantum motion. Instead, one can try to attribute the Zeno effect to the influence of the measurement devices. At first it seems as though this cannot be the case. Indeed, due to the interaction with detectors, the system acquires the energy ∼ / t, according to the energy-time uncertainty relation. As such, it is natural to expect an acceleration of the particle, instead of its freezing: the anti-Zeno effect [1]. Nevertheless, as demonstrated in this paper, the Zeno effect can be entirely attributed to the energy-time uncertainty relation, without the explicit use of the projection postulate. It would make the Zeno effect much less surprising and in fact quite expectable.The concept of continuous measurement is inherent in the quantum trajectory (QT) approach (informational evolution), which treats quantum motion based on the results of intermediate measurements [2]. It is therefore natural to investigate the Zeno-effect dynamics in this framework. A pronounced example of the informational evolution was proposed for a two-state system (qubit), coupled to a continuously monitored reservoir under the condition that no signal is registered there [3,4]. It was predicted that the qubit can change its state despite the null-result measurements. This was confirmed in experiment with a superconducting phase qubit measured via tunneling [5].In this paper we study a different arrangement, with two distant localized states, connected by a common reservoir under cont...

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confidence: 87%

Quantum transfer through a non-Markovian environment under frequent measurements and Zeno effect

Cao

et al. 2014

Phys. Rev. A

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“…In particular, a model proposed by Kofman and Kurizki [23] is useful for highlighting the advantages of our approach. Their model deals with energy measurements associated with the decay of an unstable state.…”

Section: Introductionmentioning

confidence: 99%

Environment-induced dephasing versus von Neumann measurements in proton tunneling

2014

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In this work we compare two theoretical approaches to modeling the action of the environment on an open quantum system. It is often assumed that as the temperature of the environment surrounding a quantum system increases, so does the speed of environment-induced dephasing, or decoherence (dynamical noise), and so the efficacy of processes such as quantum tunneling drops. An alternative way of viewing the action of the environment is to consider it as carrying out von Neumann-type measurements that, in the limit of continuous observation, lead to the so-called quantum Zeno effect, whereby the system is never allowed to evolve because its wave function is collapsed to its initial state with overwhelming likelihood. However, it has been established in recent years that under certain conditions quantum processes such as tunneling can actually be enhanced (thermally assisted) when the system couples to its environment, as this allows transitions to higher-energy eigenstates closer to the top of the potential barrier. Here we show that, over a specific temperature range, increasing the temperature of the heat bath to encourage such thermally induced tunneling is equivalent to increasing the frequency of a von Neumann-type measurement on the system by the environment (an anti-Zeno effect). However, this correspondence between these two independent pictures of quantum measurement breaks down above a certain limit: Increasing the frequency of measurement above this limit leads to a reversal from an anti-Zeno to a Zeno effect and the tunneling rate decreases again, whereas raising the temperature further leads to a leveling off in the tunneling probability.

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“…After the first click, the second click has the peak probability appearing at an integer multiple of the spin precession period, so the coincidence of the two earlier clicks serves as filtering of the spin frequency and the third click would have a peak probability appearing at n 2 τ = n 1 τ , similar to the spin echo. The third-order correlation in the absence of inhomogeneous broadening is g (3) (t 1 , t 2 ) ∝ g (2) (t 1 )g (2) (t 2 ). The ensemble average leads to (2) (t 1 ) g (2) (t 2 ) to exclude the trivial background.…”

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confidence: 99%

“…To separate spin decoherence from inhomogeneous broadening, we resort to the third-order correlation g (3) (n 1 τ, n 2 τ ), the probability of having three clicks separated by n 1 − 1 and n 2 − 1 measurements. The idea can be understood in a post-measurement selection picture.…”

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confidence: 99%

Dynamics revealed by correlations of time-distributed weak measurements of a single spin

Liu

Fung

et al. 2010

New J. Phys.

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We show that the correlations in stochastic outputs of time-distributed weak measurements can be used to study the dynamics of an individual quantum object, with a proof-of-principle setup based on small Faraday rotation caused by a single spin in a quantum dot. In particular, the third order correlation can reveal the "true" spin decoherence, which would otherwise be concealed by the inhomogeneous broadening effect in the second order correlations. The viability of such approaches lies in that (1) in weak measurement the state collapse which would disturb the system dynamics occurs at a very low probability, and (2) a shot of measurement projecting the quantum object to a known basis state serves as a starter or stopper of the evolution without pumping or coherently controlling the system as otherwise required in conventional spin echo.

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Acceleration of quantum decay processes by frequent observations

Cited by 525 publications

References 13 publications

Quantum transfer through a non-Markovian environment under frequent measurements and Zeno effect

Quantum transfer through a non-Markovian environment under frequent measurements and Zeno effect

Environment-induced dephasing versus von Neumann measurements in proton tunneling

Dynamics revealed by correlations of time-distributed weak measurements of a single spin

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