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Advanced Quantum Technologies

Periodic Driving Enhances Quantum Zeno Protection of a Superconducting Qubit

Prince N, Lalitha Nallamothula

Published Sep 1, 2026• 0 citations
Publisher

Abstract

ABSTRACT The quantum Zeno effect, in which frequent measurements suppress the evolution of a quantum system, is well characterized for static Hamiltonians. We investigate how periodic driving modifies Zeno protection for a single qubit on the superconducting processor ibm_marrakesh . In our gate‐based protocol, an interrupted Rabi oscillation is combined with a digitized longitudinal drive of frequency and amplitude , and the number of projective measurements, , is varied. Strong driving (, , dimensionless circuit units) enhances peak survival at the optimal measurement number by approximately relative to the undriven case, and reduces the effective per‐interval decay rate by up to . The relative enhancement was reproduced across two sessions separated by a recalibration cycle ( and , consistent within the statistical uncertainty), while absolute survival shifted by about 18 percentage points, identifying the relative enhancement as the robust quantity. Exact noiseless predictions computed from the Trotterized circuit unitaries track the hardware data with a consistent decoherence offset. A Trotter‐step control experiment shows that an apparent single‐measurement survival anomaly under fast driving () is a discretization artifact, illustrating the need for convergence verification when digitizing periodic drives.

DOI
10.1002/qute.70477

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ABSTRACT The quantum Zeno effect, in which frequent measurements suppress the evolution of a quantum system, is well characterized for static Hamiltonians. We investigate how periodic driving modifies Zeno protection for a single qubit on the superconducting processor ibm_marrakesh . In our gate‐based protocol, an interrupted Rabi oscillation is combined with a digitized longitudinal drive of frequency and amplitude , and the number of projective measurements, , is varied. Strong driving (, , dimensionless circuit units) enhances peak survival at the optimal measurement number by approximately relative to the undriven case, and reduces the effective per‐interval decay rate by up to . The relative enhancement was reproduced across two sessions separated by a recalibration cycle ( and , consistent within the statistical uncertainty), while absolute survival shifted by about 18 percentage points, identifying the relative enhancement as the robust quantity. Exact noiseless predictions computed from the Trotterized circuit unitaries track the hardware data with a consistent decoherence offset. A Trotter‐step control experiment shows that an apparent single‐measurement survival anomaly under fast driving () is a discretization artifact, illustrating the need for convergence verification when digitizing periodic drives.
Decoherence remains the principal obstacle to practical quantum computation in superconducting architectures, where environmental noise and measurement backaction conspire to collapse fragile quantum states on timescales far shorter than those required for fault-tolerant operation. While the Quantum Zeno Effect offers a measurement-based mechanism for coherence stabilization, and discrete Floquet time crystals provide a framework for sustained periodic oscillation under driven dynamics, the question of whether these two phenomena can be synchronized to actively lock a qubit state against decoherence has remained unaddressed experimentally. Here we report hardware-validated observations of a reproducible coherence anomaly on IBM Quantum processors ibm_marrakesh and ibm_kingston. We identify a consistent coherence dip at Zeno period 3, reproduced across two distinct backends, interpreted as a destructive subharmonic resonance — designated the O’Reilly Effect. We further identify the Harmonic Juncture as a candidate mechanism for coherence extension, suggesting a pathway toward time-crystal-assisted quantum memory.
When a quantum state is subjected to frequent measurements, the time evolution of the quantum state is frozen. This is called the quantum Zeno effect. Here, we observe such an effect by performing frequent discrete measurements in a macroscopic quantum system, a superconducting quantum bit. The quantum Zeno effect induced by discrete measurements is similar to the original idea of the quantum Zeno effect. By using a Josephson bifurcation amplifier pulse readout, we have experimentally suppressed the time evolution of Rabi oscillation using projective measurements, and also observed the enhancement of the quantum state holding time by shortening the measurement period time. This is a crucial step to realize quantum information processing using the quantum Zeno effect.
We present a theoretical study of the quantum Zeno effect in a driven superconducting charge qubit strongly and ultrastrongly coupled to a transmission line resonator. Using the dressed-state approach, we predict the different dynamics behaviors of the dressed qubit subjected to two opposite projection measurements. We show that, for very frequent measurements, the survival probability of the initial state is of exponential form and the Zeno time of the dressed qubit can be several orders of magnitude longer than that of the bare qubit. For slowly repeated measurements, the detuning of the driving field has significant impact on the measurement dynamics, and by choosing appropriate parameters for the dressed qubit, the Zeno effect can occur in the nonresonant coupling case. Such a Zeno effect is excluded from a usual two-level system.
The quantum Zeno effect is a distinctive phenomenon in quantum mechanics, describing the nontrivial effect of frequent projective measurements on hindering the evolution of a quantum system. However, when subjected to environmental noise, the quantum system may dissipate, and the quantum Zeno effect no longer works. This research starts from the physical mechanism for the decay of the quantum Zeno effect in the presence of noise and investigates the effect of coherent quantum controls on mitigating the decrease of the survival probability that the system stays in the initial state induced by the noise. We derive the decay rate of the survival probability with and without coherent quantum controls in general, and show that when the frequency of the projective measurements is large but finite, proper coherent controls by sufficiently strong Hamiltonians can be designed to decrease the decay rate of the survival probability. A two-level quantum system suffering from typical unitary and nonunitary noise is then considered to demonstrate the effect of the proposed coherent quantum control scheme in protecting the quantum Zeno effect against the noise. The decay rate of the survival probability is obtained in the presence of noise, and the control Hamiltonian is further optimized analytically to minimize the decay rate by a variational approach. The evolution paths of the quantum system with the optimal coherent controls are illustrated numerically for different scenarios to explicitly show how the coherent control scheme works in lowering the decay of survival probability.
Abstract Achieving fast gates and long coherence times for superconducting qubits presents challenges, typically requiring either a stronger coupling of the drive line or an excessively strong microwave signal to the qubit. To address this, we introduce on-chip filters of the qubit drive exhibiting a stopband at the qubit frequency, thus enabling long coherence times and strong coupling at the subharmonic frequency, facilitating fast single-qubit gates, and reduced thermal load. The filters exhibit an extrinsic relaxation time of a few seconds while enabling sub-10-ns gates with subharmonic control. Here we show up to 200-fold improvement in the measured relaxation time at the stopband. Furthermore, we implement subharmonic driving of Rabi oscillations with a π pulse duration of 12 ns. Our demonstration of on-chip filters and efficient subharmonic driving in a two-dimensional quantum processor paves the way for a scalable qubit architecture with reduced thermal load and noise from the control line.
Repeated measurements in quantum mechanics can freeze (the quantum Zeno effect) or enhance (the quantum anti-Zeno effect) the time-evolution of a quantum system. In this paper, we present a general treatment of the quantum Zeno and anti-Zeno effects for arbitrary driven open quantum systems, assuming only that the system-environment coupling is weak. In particular, we obtain a general expression for the effective decay rate of a two-level system subjected to arbitrary driving fields as well as periodic measurements. We demonstrate that the driving fields change the decay rate, and hence the quantum Zeno and anti-Zeno behavior, both qualitatively and quantitatively. We also extend our results to systems consisting of more than one two-level system, as well as a two-level system strongly coupled to an environment of harmonic oscillators, to further illustrate the non-trivial effect of the driving fields on the quantum Zeno and anti-Zeno effects.