Quantum Zeno effect and dynamics

Frequent observations to a quantum system modify its coherent evolution through the Zeno effect and Zeno dynamics. Generally, the measurement process destroys the evolution environment of the monitored system, making repeated observations remain a challenge. Here, using the quantum analogy experiments, we realize and engineer the Zeno effect and Zeno dynamics in optical waveguide arrays, where the optical modes correspond to distinct quantum states, and the temporal evolution is mapped into the spatial propagation. We propose a new, extensible experimental strategy for realizing an optical analog of stroboscopic measurements, which are performed by the build-in, on-demand segmented waveguide portions. The weak-to-strong stroboscopic measurements are realized, where the monitored system undergoes a transition from free evolution to optical Zeno freezing. Setting the measurements in the strong regime, the optical Zeno effect and optical Zeno dynamics are successfully generated, and their relationship is demonstrated in optics. We then propose a novel quantum Zeno slicing approach, which allows us to dynamically engineer the Hilbert space of the monitored system. This generic approach is verified by generating a series of Zeno subspaces with different measurement projectors, based on the quantum-optical analogy. The complexity of light dynamics is largely increased, providing full control of the propagation via steering Zeno dynamics. Our results pave the way for manipulation of quantum states by harnessing Zeno dynamics in integrated photonics.

This work shows that engineered waveguide-based systems can be designed to control photon tunneling decay, providing an experimentally accessible laboratory tool to test the universal features of dynamical control via parametric modulations, recently proposed for quantum mechanical decay. This study demonstrates the realization of quantum decay control and Zeno dynamics in photonic structures. By a proper design of the structure, acceleration or deceleration the tunneling decay rate, as well as suppression of fractional, can be achieved.

With the quantum Zeno dynamics, we present a scheme for realizing a quantum phase gate for two atoms trapped in two separate cavities connected by an optical fiber. Compared with the previous schemes, quantum Zeno dynamics shows different evolution properties in the atom–cavity–fiber system. The scheme needs only one step to perform the gate, which largely reduces the complexity of the experiment. We also numerically simulate the influence of photon leakage and atomic spontaneous emission on the fidelity of the phase gate. The result shows that our scheme is very robust against cavity decay and very promising for realization with current experimental technology.

Quantum Zeno effect can be applied to quantum information processing，and can reveal the nature of quantum measurement. In addition, it has also many potential applications. This suggests that studying the quantum Zeno effect has great theoretical and experimental significance. In this work, the system of a two-level atom interacting with a single mode field is considered and the dynamics of the system subjected to successive projection measurements is studied, and the quantum Zeno effect is presented. Moreover, the influence of the quantum Zeno effect on atomic population inversion is discussed. Based on Schrödinger equation, the survival probability of the initial state of the two-level atom subjected to frequently repeated measurements can be obtained. The survival probability depends on the time interval between measurements. It is seen that the exponential decay of the system under slowly frequent measurements is presented instead of the naturally oscillatory process. For slowly repeated measurements the atomic population inversion and the survival probability of initial state decline rapidly at the early time and then both of them become unchanged. As the time intervals of the measurements are sufficiently short, the quantum Zeno effect occurs. These results have also shown how the measurement can inhibit the atomic population inversion.

Markov chains with doubly stochastic transition matrices and application to a sequence of non-selective quantum measurements

Reiterated or continuous measurement on a quantum system impedes the quantum object's evolution. This "quantum Zeno" effect (QZE), contemplated for decades, has been conventionally attributed to the reaction of the measuring device on the quantum object being measured, in the sense of the Heisenberg microscope. However, even reactionless "quantum non-demolition" measurements seem to qualify for that inhibition to take place and may constitute a "quantum Zeno paradox" (QZP). An experimental proof of QZE had been attempted in the past on clouds of ions confined in a Paul trap. In the meantime it has been shown, however, that the anticipated impediment of the quantum evolution by a sheer gain of information, i.e. by reactionless measurement cannot be, in principle, proven with an ensemble. Recently, experiments have been performed with the use of a single quantum system: an 172Yb+ ion, laser-driven on its E2 line S1/2 - D5/2, or an 171Yb+ ion, microwave-driven on its ground-state hyperfine resonance. The results of these experiments demonstrate that mere gain of information on the quantum system, while lacking dynamic action, modifies the system's evolution as it is predicted by quantum mechanics, based on the system's preparation. This seems plausible if we attribute reality to the results of the measurements. If, in contrast, reality is claimed for the prediction, two-fold discontinuity must be admitted: loss of coherence with potential measurements, and renormalization from the results of actual measurements.

The quantum Zeno effect (QZE) is often associated with the ironic maxim, “a watched pot never boils”, although the notion of “watching” suggests a continuous activity at odds with the usual (pulsed measurement) presentation of the QZE. We show how continuous watching can provide the same halting of decay as the usual QZE, and, for incomplete hindrance, we provide a precise connection between the interval between projections and the response time of the continuous observer. Thus, watching closely, but not so closely as to halt the “boiling”, is equivalent to—gives the same degree of partial hindrance as—pulsed measurements with a particular pulsing rate. Our demonstration is accomplished by treating the apparatus for the continuous watching as a fully quantum object. This in turn allows us a second perspective on the QZE, in which it is the modified level structure of the combined system/apparatus Hamiltonian that slows the decay. This and other considerations favor the characterization “dominated time evolution” for the QZE.

The change of dynamics in a quantum system under frequent or continuous observation, known as the quantum Zeno effect, is generally derived from the projection or reduction of the wave-packet hypothesis that is the central postulate in the theory of quantum measurements. The only experiment in which the Zeno effect has yet been clearly demonstrated, though, allows no conclusion on the necessity or validity of the projection postulate. This is shown by calculating, in detail, the outcome of the experiment on the basis of the standard three-level Bloch equations. These equations follow from the quantum theory of irreversible processes with no additional assumptions necessary, such as which part of the system serves as measuring apparatus or how efficient the measurement would be.

The evolution of a quantum system subjected to infinitely many measurements in a finite time interval is confined in a proper subspace of the Hilbert space. This phenomenon is called ‘quantum Zeno effect’: a particle under intensive observation which does not evolve. This effect is at variance with the classical evolution, which obviously is not affected by any observations. By a semiclassical analysis, we will show that the quantum Zeno effect vanishes at all orders, when the Planck constant tends to zero, and thus it is a purely quantum phenomenon without classical analog, at the same level of tunneling.

A neutron-spin experimental test of the quantum Zeno effect (QZE) is discussed from a practical point of view, where the nonideal efficiency of the magnetic mirrors, used for filtering the spin state, is taken into account. In the idealized case, the number N of (ideal) mirrors can be indefinitely increased, yielding an increasingly better QZE. In contrast, in a practical situation with imperfect mirrors, there is an optimal number of mirrors, ${N}_{\mathrm{opt}},$ at which the QZE becomes maximum: more frequent measurements would deteriorate the performance. However, a quantitative analysis shows that a good experimental test of the QZE is still feasible. These conclusions are of general validity: in a realistic experiment, the presence of losses and imperfections leads to an optimal frequency ${N}_{\mathrm{opt}},$ which is in general finite. One should not increase N beyond ${N}_{\mathrm{opt}}.$ A convenient formula for ${N}_{\mathrm{opt}},$ valid in a broad framework, is derived as a function of the parameters characterizing the experimental setup.

Generation of three-qutrit singlet states for three atoms trapped in separated cavities

A protocol to generate steady Knill–Laflamme–Milburn (KLM) states of two Rydberg atoms with dissipation and Lyapunov control is proposed. Herein, combining with the quantum Zeno dynamics and the Rydberg antiblockade, a unique and steady solution of the master equation of the system is obtained, which satisfies the definition of KLM states. Furthermore, to polish the convergence rate, well‐designed additional coherent control (ACC) fields with Lyapunov control are added into the traditional dissipation process. Numerical simulation reveals that the steady target state generation is prominently accelerated and the protocol is robust against the stochastic noise errors caused by laser fields. It is hoped that the work may provide an alternative protocol to polish the generation of entanglement.

Data and code for "Portfolio Optimization via Quantum Zeno Dynamics on a Quantum Processor"

Based on shortcuts to adiabaticity and quantum Zeno dynamics, we present a protocol to implement quantum state transfer (QST) in a quantum spin-1/2 chain. In the protocol, the complex Hamiltonian of an $N$-site system is simplified, and a simple effective Hamiltonian is present. It is shown that only the control of the coupling strengths between the boundary spins and the bulk spins are required for QST. Numerical simulations demonstrate that the protocol possesses high efficiency and is robust against the decay and the fluctuations of the control fields. The protocol might provide an alternative choice for transferring quantum states via spin chain systems.

We propose a scheme to prepare W state for three atoms in a cavity via adiabatic passage and quantum Zeno dynamics. Appropriate Rabi frequencies of the classical fields are selected to realize the present scheme. Numerical analysis is showed, which indicates that the scheme is robust against the floating of the pulse delay and laser intensity, and the atomic spontaneous radiation and the cavity decay are efficiently suppressed by engineering adiabatic passage. Moreover, the scheme is more achievable in experiment than other existing schemes. Based on the current experimental technology, this scheme for generation of high-fidelity W state for three atoms can be achieved.