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...

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We characterize low-loss electron-beam evaporated niobium thin films deposited under ultra-high vacuum conditions. Slow deposition yields films with a high superconducting transition temperature (9.20±0.06 K) as well as a residual resistivity ratio of 4.8. We fabricate the films into coplanar waveguide resonators to extract the intrinsic loss due to the presence of two-level-system fluctuators using microwave measurements. For a coplanar waveguide resonator gap of 2 μm, the films exhibit filling-factor-adjusted two-level-system loss tangents as low as 1.5×10−7 with single-photon regime internal quality factors in excess of one million after removing native surface oxides of the niobium.

We characterize highly coherent transmon qubits fabricated with a direct-write photolithography system. Multi-layer evaporation and oxidation allow us to change the critical current density by reducing the effective tunneling area and increasing the barrier thickness. Surface treatments before resist application and again before evaporation result in high-coherence devices. With optimized surface treatments, we achieve energy relaxation T1 times in excess of 80 μs for three dimensional transmon qubits with Josephson junction lithographic areas of 2 μm2.

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