Quantum Zeno Effects from Measurement Controlled Qubit-Bath Interactions

Abstract

The Zeno and anti-Zeno effects are features of measurement-driven quantum evolution where frequent measurement inhibits or accelerates the decay of a quantum state. Either type of evolution can emerge depending on the system-environment interaction and measurement method. In this experiment, we use a superconducting qubit to map out both types of Zeno effect in the presence of structured noise baths and variable measurement rates. We observe both the suppression and acceleration of qubit decay as repeated measurements are used to modulate the qubit spectrum causing the qubit to sample different portions of the bath. We compare the Zeno effects arising from dispersive energy measurements and purely-dephasing 'quasi'-measurements, showing energy measurements are not necessary to accelerate or suppress the decay process.A projective measurement should reset the clock of a decay process, reinitializing the system to its excited state and therefore inhibiting decay in a variety of situations ranging from nuclear physics [1] to optical lattices [2]. The suppression of a decay process-and more broadly quantum evolution-by frequent measurement is referred to as the "Zeno effect" [3]. The fact that the Zeno effect in decay processes is almost universally negligible is evident by considering Fermi's golden rule for determining a decay rate: the decay rate depends on the density of states only at the transition frequency and repeated measurement effectively samples a larger range of frequencies in the calculation. If the bath is white on the probed band, then the decay rate is unchanged. Therefore, the Zeno effect will only occur under the special circumstance where the noise spectral density varies quickly over the probed band. Moreover, the opposite "anti-Zeno effect," where frequent measurements accelerate decay, is predicted to be a more ubiquitous phenomenon [4][5][6]. Here we perform a detailed study of both Zeno effects using a superconducting qubit as an emitter coupled to a transmission line with a tunable structured bath. Frequent measurements alter the qubit-bath interaction leading to both accelerated and suppressed decay. Our study expands on the role of measurement in the Zeno effects and highlights new ways to control quantum evolution with tunable bath interactions [7].The original development of the Zeno effect predicted the inhibition of particle decay and non-exponential dynamics due to time-evolution interruption from frequent observations [3]. The general case for any quantum system under continuous measurement, dubbed the 'watchdog-effect ' [8], was explained in terms of cancelation of wavefunction coherence caused from measurement induced perturbations, thus slowing evolution from an initial state [9]. The first experimental measurements of the Zeno effect, conducted with trapped ions [10], incited much discourse on the nature of measurement, the essential features of the Zeno effect, and how the effect compares to simple perturbation dynamics due to exter-nal coupling [11,12]. In recent years, the ef...

Criterion for quantum Zeno and anti-Zeno effects

“…The second-order effective Hamiltonian with no rotating-wave approximation (19) can be derived by using the following unitary transformation:…”

Quantum Brownian motion under generalized position measurements: a converse Zeno scenario

“…In figure 4 this quantity is plotted by using the exact expression(21) for different measurement rates and dissipation strengths. The time evolution and stationary values of the curves at the higher monitoring rates μ are qualitatively accounted for by the small-τ limit (23). In particular, figure 4 depicts the linear increase of Σ τ 2 (t) with increasing time at γ=0 (see equation (24)).…”

“…, defined in equation (19), is displayed as a function of the elapsed time t t t F 0 =for different values of the friction parameter γ (in units of ω 0 ) and of the measurement rate μ=τ −1 (in units of ω 0 /2π). The symmetrized correlation function S(t) was numerically determined by truncating the sum in equation (16) to the first 2000 terms The behavior at large μ is accounted for by the analytical small-τ expression (23). In particular, at γ=0, the width Σ τ 2 (t) increases linearly with time, with a coefficient proportional to μ=τ −1 (see equation (24)).…”

“…The QZE was first experimentally observed in trapped ions [11] and later, along with the anti-Zeno effect, in a cold atomic gas [12]. Further realizations are found in a variety of experimental setups [13][14][15][16][17][18][19][20][21][22][23].…”

Engineering Photon Delocalization in a Rabi Dimer with a Dissipative Bath

“…Conventionally, the quantum Zeno effect refers to the suppression of quantum evolution by frequent measurements . A recent scheme treats the system–environment interactions as “quasi‐measurements” which also can lead to quantum Zeno effect . In our model, the qubit–bath coupling works as the quasi‐measurements of the state of the qubits, hindering qubit flipping.…”