Researchers have created Greenberger-Horne-Zeilinger (GHZ) states with up to 14 qubits, demonstrating the creation of large-scale multi-particle entangled quantum states. By investigating the coherence of up to 8 ions over time, they observed a decay proportional to the square of the number of qubits. This decay aligns with a theoretical model assuming correlated Gaussian phase noise, which is relevant for current quantum computing and metrology systems. Quantum states can exhibit non-classical properties, such as superposition and entanglement. Entanglement allows for the state of one subsystem to be affected by a measurement on another without direct interaction. These phenomena challenge classical intuition and raise questions about the transition from quantum to classical regimes. Decoherence mechanisms, such as spontaneous decay of atomic excited states, are typically used to describe the transition to the classical regime. However, collective decoherence can lead to "superradiance," where the decay rate is proportional to the square of the number of excited atoms. This collective decoherence also occurs in multi-qubit registers, known as "superdecoherence," which is particularly relevant for systems with non-degenerate qubits. The study introduces a model for a quantum register affected by correlated phase noise. The GHZ states, which are the archetype of multi-particle entanglement, were shown to exhibit superdecoherence, with the error probability scaling quadratically with the number of qubits. This was verified experimentally using a 14-qubit GHZ state, where the coherence decay was observed to be faster than for a single qubit. The experiment involved an ion-trap quantum processor with 40Ca+ ions, where GHZ states were created using a high-fidelity Mølmer-Sørensen entangling interaction. The coherence and fidelity of these states were measured, showing that the 14-qubit state supports genuine N-particle entanglement with a confidence level of 76%. The results highlight the importance of correlated phase noise in limiting the performance of large-scale quantum registers. The study also demonstrates the potential of these systems for quantum simulation, quantum metrology, and fundamental quantum physics research. The findings provide insights into the transition from quantum to classical regimes and the challenges of maintaining coherence in multi-qubit systems.Researchers have created Greenberger-Horne-Zeilinger (GHZ) states with up to 14 qubits, demonstrating the creation of large-scale multi-particle entangled quantum states. By investigating the coherence of up to 8 ions over time, they observed a decay proportional to the square of the number of qubits. This decay aligns with a theoretical model assuming correlated Gaussian phase noise, which is relevant for current quantum computing and metrology systems. Quantum states can exhibit non-classical properties, such as superposition and entanglement. Entanglement allows for the state of one subsystem to be affected by a measurement on another without direct interaction. These phenomena challenge classical intuition and raise questions about the transition from quantum to classical regimes. Decoherence mechanisms, such as spontaneous decay of atomic excited states, are typically used to describe the transition to the classical regime. However, collective decoherence can lead to "superradiance," where the decay rate is proportional to the square of the number of excited atoms. This collective decoherence also occurs in multi-qubit registers, known as "superdecoherence," which is particularly relevant for systems with non-degenerate qubits. The study introduces a model for a quantum register affected by correlated phase noise. The GHZ states, which are the archetype of multi-particle entanglement, were shown to exhibit superdecoherence, with the error probability scaling quadratically with the number of qubits. This was verified experimentally using a 14-qubit GHZ state, where the coherence decay was observed to be faster than for a single qubit. The experiment involved an ion-trap quantum processor with 40Ca+ ions, where GHZ states were created using a high-fidelity Mølmer-Sørensen entangling interaction. The coherence and fidelity of these states were measured, showing that the 14-qubit state supports genuine N-particle entanglement with a confidence level of 76%. The results highlight the importance of correlated phase noise in limiting the performance of large-scale quantum registers. The study also demonstrates the potential of these systems for quantum simulation, quantum metrology, and fundamental quantum physics research. The findings provide insights into the transition from quantum to classical regimes and the challenges of maintaining coherence in multi-qubit systems.