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Scientific Reports

Suppressing spectator-induced dephasing through optimized dynamical decoupling implementation

Hayoung Jeong, Youngdu Kim, Beomgyu Choi, M.-H. Cho, Seungwook Woo, Yonuk Chong, Yongho Lee, Hwan‐Seop Yeo

Published May 28, 2025• 2 citations
Publisher

Abstract

Dynamical decoupling (DD) is a well-established technique for protecting quantum systems from environmental noise. DD effectively mitigates decoherence in superconducting quantum computing systems, where precise implementation plays a crucial role in optimizing its performance. This study investigates how DD implementation timing and sequence design critically affect spectator-induced dephasing from adjacent qubits. We find that excited states of adjacent qubits dramatically degrade operational qubit coherence. We demonstrate that DD sequences applied to adjacent qubits effectively suppress this dephasing. This protection persists even when adjacent qubits remain in superposition states during the sequence. Through systematic characterization of Carr-Purcell-Meiboom-Gill (CPMG) sequences, we show that implementation timing strongly impacts protection effectiveness. While optimal timing achieves substantial coherence enhancement, improper sequence delays can severely degrade protection. Our results highlight the importance of precise timing control for implementing DD in optimizing multi-qubit quantum circuits.

DOI
10.1038/s41598-025-02370-8

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Dynamical decoupling (DD) is a well-established technique for protecting quantum systems from environmental noise. DD effectively mitigates decoherence in superconducting quantum computing systems, where precise implementation plays a crucial role in optimizing its performance. This study investigates how DD implementation timing and sequence design critically affect spectator-induced dephasing from adjacent qubits. We find that excited states of adjacent qubits dramatically degrade operational qubit coherence. We demonstrate that DD sequences applied to adjacent qubits effectively suppress this dephasing. This protection persists even when adjacent qubits remain in superposition states during the sequence. Through systematic characterization of Carr-Purcell-Meiboom-Gill (CPMG) sequences, we show that implementation timing strongly impacts protection effectiveness. While optimal timing achieves substantial coherence enhancement, improper sequence delays can severely degrade protection. Our results highlight the importance of precise timing control for implementing DD in optimizing multi-qubit quantum circuits.
Dynamical decoupling (DD) and Decoherence free subspace (DFS) are powerful techniques in quantum computing aimed at enhancing fidelity by mitigating the detrimental effects of noise and environmental interactions. In quantum systems, noise and decoherence can degrade the coherence of quantum states, leading to errors and reduced computational accuracy. DD employs carefully designed sequences of control pulses to periodically intervene and counteract these undesired interactions, while DFS utilizes subspace encoding techniques to protect quantum information from decoherence. To evaluate and compare the fidelity achieved by DD and DFS, this paper presents a series of experiments considering the effect of time and the number of qubits. The experiments provide valuable insights into the performance of both methods under different conditions. By systematically examining the fidelity results, the impact of time and the scaling behavior with increasing qubits can be assessed. The experimental findings showcase the effectiveness of DD in reducing the impact of noise and extending the coherence time of quantum states. By strategically manipulating the quantum system, DD minimizes error accumulation and preserves the integrity of fragile quantum information. It is observed that the decrease in fidelity with increasing t is relatively small and gradual. Despite being outperformed by DD, the DFS method exhibits robustness and maintains a high degree of fidelity even in the presence of extended time durations.
Dynamical decoupling (DD) is perhaps the simplest and least resource-intensive error-suppression strategy for improving quantum computer performance. Here we report on a large-scale survey of the performance of 60 different DD sequences from ten families, including basic as well as advanced sequences with high-order error cancelation properties and built-in robustness. The survey is performed using three different superconducting-qubit IBMQ devices, with the goal of assessing the relative performance of the different sequences in the setting of arbitrary quantum state preservation. We find that the high-order universally robust (UR) and quadratic DD (QDD) sequences generally outperform all other sequences across devices and pulse-interval settings. Surprisingly, we find that DD performance for basic sequences such as the Carr-Purcell-Meiboom-Gill and XY4 sequences can be made to nearly match that of UR and QDD sequences by optimizing the pulse interval, with the optimal interval being substantially larger than the minimum interval possible on each device.
One of the simplest and least resource-intensive methods to suppress decoherence for qubit operations, namely, dynamical decoupling (DD), is investigated for a broad range of realistic noise sources with time-retarded feedback. By way of example, the Carr-Purcell-Meiboom-Gill sequence is analyzed in a numerically rigorous manner accounting also for correlations between qubits and environments. Since experimentally noise sources are characterized through spectral densities, we adopt the spin-boson model as a suitable framework to describe the qubit dynamics under DD for a given spectral density J ( ω ) ∝ ω s . Motivated by the situation for superconducting qubits, the spectral exponent s is varied from s = 1 (Ohmic bath) to a substantially small value 0 < s ≪ 1 (deep sub-Ohmic bath), in order to investigate the impact of time-nonlocal back action on DD performances for enhanced coherence times. As reference to the DD schemes, dynamics of a single qubit subject to Ramsey sequences without any pules and Hahn echo sequences are also investigated.
Theoretically understanding and experimentally characterizing and modifying the underlying Hamiltonian of a quantum system is of utmost importance in achieving high-fidelity quantum gates for quantum computing. In this work, we explore the use of dynamical decoupling (DD) in characterizing and suppressing undesired two-qubit couplings as well as the underlying single-qubit decoherence, both significant hurdles to achieving precise quantum control and realizing quantum computing on many hardware prototypes. Through discrete search of DD sequences, we identify sequences that protect against decoherence and selectively target unwanted two-qubit interactions of general form. On a transmon-qubit-based superconducting quantum device, we identify separate white and 1/f1/f1/f noise components underlying the single-qubit decoherence and a static ZZ coupling between pairs of qubits. A family of syncopated DD sequences is found and their efficiency is demonstrated in two-qubit benchmarking experiments. The syncopated decoupling technique significantly boosts performance in a realistic algorithmic quantum circuit.
In quantum information processing, it is vital to protect the coherence of qubits in noisy environments. Dynamical decoupling (DD), which applies a sequence of flips on qubits and averages the qubit-environment coupling to zero, is a promising strategy compatible with other desired functionalities, such as quantum gates. Here, we review the recent progresses in theories of dynamical decoupling and experimental demonstrations. We give both semiclassical and quantum descriptions of the qubit decoherence due to coupling to noisy environments. Based on the quantum picture, a geometrical interpretation of DD is presented. The periodic Carr-Purcell-Meiboom-Gill DD and the concatenated DD are reviewed, followed by a detailed exploration of the recently developed Uhrig DD, which employs the least number of pulses in an unequally spaced sequence to suppress the qubit-environment coupling to a given order of the evolution time. Some new developments and perspectives are also discussed.
Active protection of quantum states is an essential prerequisite for the implementation of quantum computing. Dynamical decoupling (DD) is a promising approach that applies sequences of control pulses to the system in order to reduce the adverse effect of system-environment interactions. Since every hardware device has finite precision, the errors of the DD control pulses can themselves destroy the stored information rather than protect it. We experimentally compare the performance of different DD sequences in the presence of an environment that was chosen such that all relevant DD sequences can equally suppress its effect on the system. Under these conditions, the remaining decay of the qubits under DD allows us to compare very precisely the robustness of the different DD sequences with respect to imperfections of the control pulses.