What question did this study set out to answer?

The aim is to compare the coherence decay of GHZ states and product states under idle noise in quantum processors.

January 18, 2026Open Access

Comparative Coherence Decay of GHZ and Product States Under Idle Noise in IBM Heron Quantum Processors

Key Points

The aim is to compare the coherence decay of GHZ states and product states under idle noise in quantum processors.
Conducted experiments on IBM Heron quantum processors across three generations.
Compared coherence decay of three-qubit GHZ states and product states over various idle delays.
Performed control experiments to analyze decay mechanisms.
GHZ states showed consistently higher fidelity compared to product states as idle delay increased.
Product states decayed 2.4–13.8 times faster than GHZ states depending on processor generation.
Dephasing noise primarily contributed to coherence decay, over energy relaxation and readout errors.

Abstract

We report experimental measurements comparing the coherence decay of three-qubit Greenberger-Horne-Zeilinger (GHZ) entangled states versus locally coherent product states (|+++⟩) under idle time evolution on IBM Heron quantum processors. Across three different processor generations (Heron r1, r2, r3), we consistently observe that the GHZ state maintains higher fidelity than the product state as idle delay increases. Decay rate analysis reveals that |+++⟩ decays 2. 4–13. 8× faster than GHZ depending on the backend. A control experiment with |000⟩ confirms the decay mechanism is dominated by dephasing (T₂-type noise) rather than energy relaxation (T₁) or readout errors. These results demonstrate a structural dependence of coherence stability on the topology of the quantum state. Backends: ibmfez (Heron r2), ibmₜorino (Heron r1), ibmboston (Heron r3) Configuration: 3 qubits, 4000 shots, 20 repetitions per delay pointDelays: 0, 500, 1000, 2000, 4000 dt

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