Continuous and Pulsed Quantum Zeno Effect

Abstract

Continuous and pulsed quantum Zeno effects were observed using a 87 Rb Bose-Einstein condensate (BEC). Oscillations between two ground hyperfine states of a magnetically trapped condensate, externally driven at a transition rate ωR, were suppressed by destructively measuring the population in one of the states with resonant light. The suppression of the transition rate in the two level system was quantified for pulsed measurements with a time interval δt between pulses and continuous measurements with a scattering rate γ. We observe that the continuous measurements exhibit the same suppression in the transition rate as the pulsed measurements when γδt = 3.60(0.43), in agreement with the predicted value of 4. Increasing the measurement rate suppressed the transition rate down to 0.005ωR.PACS numbers: 03.65. Xp,03.75.Mn,42.50.Xa The quantum Zeno effect (QZE) is the suppression of transitions between quantum states by frequent measurements. It was first considered as a theoretical problem where the continuous observation of an unstable particle would prevent its decay [1]. Experimental demonstrations of the QZE [2,3,4,5,6,7,8] have been driven by interest in both fundamental physics and practical applications. Practical applications of the QZE include reducing decoherence in quantum computing [8,9,10], efficient preservation of spin polarized gases [3,4,6], and dosage reduction in neutron tomography [11].The QZE is a paradigm and test bed for quantum measurement theory [12,13]. In one interpretation, it involves many sequential collapses of the wavefunctions of the system. Quantum Zeno experiments provide constraints for speculative extensions of quantum mechanics where the collapse of the wavefunction is created by extra terms in a modified Schrödinger equation [14]. It is still an open question how close one can approach the limit of an infinite number of interrogations due to the Heisenberg uncertainty involved in shorter measurement times. These conceptional questions provide the motivation to extend experimental tests of the quantum Zeno phenonmenon. A major improvement to a quatum Zeno experiment with ultracold neutrons [15] is in preparation.In this letter we compare the suppression of the transition rate in an oscillating two level system by continuous and pulsed measurements. Our QZE experiments were carried out with Bose-Einstein condensed atoms [16,17,18]. The long coherence time and the high degree of control of the position and momentum of the atoms created a very clean system and allowed us to observe much stronger quantum Zeno suppression than before [2,5,7]. In the experiment with pulsed measurements up to 500 measurements could be carried out and survival probabilities exceeded 98%. Furthermore, we have performed the first quantitative comparison between the pulsed and continuous measurement QZE. This is important since any real pulsed measurement is only an approximation based on a series of weak continuous measurements [19,20].Let us consider a two-level system which is externally driven at a ...

Control of a Bose-Einstein condensate by dissipation: Nonlinear Zeno effect

“…The prevention of losses of atoms by a strong dissipation resembles the Zeno effect observed experimentally in a different setup [18]. Specifically, expressing our Γ QT through the tunneling frequency ω R = 2J/ we recover the decay rate Γ QT = ω 2 R /Γ which appears in the continuous Zeno effect of Ref.…”

“…Specifically, expressing our Γ QT through the tunneling frequency ω R = 2J/ we recover the decay rate Γ QT = ω 2 R /Γ which appears in the continuous Zeno effect of Ref. [18].…”

“…The macroscopic manifestation of Zeno and anti-Zeno effects in the Josephson junctions subjected to time-dependent perturbations was also studied [17]. Also, our statement of the problem, can be further developed to describe the experimental setup used in [18] for the observation of pulsed and continuous Zeno effects in an externally driven mixture of two hyperfine states of a 87 Rb BEC, using the destructive measurement of the population of the states. However, this happens in a binary mixture with nonlinear interactions between the components, while separation of the two subsystems by a potential barrier in our setting induces only a linear coupling between them (i.e.…”

Zeno physics in ultrastrong-coupling circuit QED

“…This phenomenon, known as the quantum Zeno effect [1,2], implies in particular that an atom that is being periodically or continuously monitored cannot decay, or will do it at a slower rate. This suppression of spontaneous emission was first observed in trapped ion experiments [3], followed by observations in the suppression of Rabi oscillations in cavity QED [4], the decay of ultracold atoms [5], and has been studied associated to photodetection in circuit QED [6].…”

State engineering for a Bose-Einstein condensate in an optical lattice by means of a periodic sublattice of dissipative sites

“…The long-term state of BEC in the dissipative lattice is a lowest energy subset of the effective dark states, i.e. the states almost unaffected by the dissipation as the result of the quantum Zeno effect [19,20] (see also the reviews [21,22]). Finally, in contrast to the previous works, a weak nonlinearity in our case plays only an auxiliary role (see the honeycomb lattice example below), which is to break the energy degeneracy of the effective dark states and select one particular state.…”