Creating and controlling global Greenberger-Horne-Zeilinger entanglement on quantum processors

Abstract: Greenberger-Horne-Zeilinger (GHZ) states, also known as two-component Schr\"{o}dinger cats, play vital roles in the foundation of quantum physics and, more attractively, in future quantum technologies such as fault-tolerant quantum computation. Enlargement in size and coherent control of GHZ states are both crucial for harnessing entanglement in advanced computational tasks with practical advantages, which unfortunately pose tremendous challenges as GHZ states are vulnerable to noise. Here we propose a general strategy for creating, preserving, and manipulating large-scale GHZ entanglement, and demonstrate a series of experiments underlined by high-fidelity digital quantum circuits. For initialization, we employ a scalable protocol to create genuinely entangled GHZ states with up to 60 qubits, almost doubling the previous size record. For protection, we take a new perspective on discrete time crystals (DTCs), originally for exploring exotic nonequilibrium quantum matters, and embed a GHZ state into the eigenstates of a tailor-made cat scar DTC to extend its lifetime. For manipulation, we switch the DTC eigenstates with in-situ quantum gates to modify the effectiveness of the GHZ protection. Our findings establish a viable path towards coherent operations on large-scale entanglement, and further highlight superconducting processors as a promising platform to explore nonequilibrium quantum matters and emerging applications.

• The paper introduces a novel protocol for generating GHZ entanglement with up to 60 qubits using a scalable radial expansion method.
• The study embeds GHZ states within a discrete time crystal framework to preserve coherence over 30 experimental cycles.
• The findings offer a promising approach for robust quantum operations on superconducting processors and advancements in error correction.

Essay on "Creating and controlling global Greenberger-Horne-Zeilinger entanglement on quantum processors"

This paper presents a significant contribution to quantum computing, focusing on the generation and manipulation of large-scale Greenberger-Horne-Zeilinger (GHZ) states using superconducting quantum processors. The study is notable for its method in creating, preserving, and controlling GHZ entanglement and presents detailed empirical results using two separate quantum processors.

Overview of Methodology and Findings

The authors describe an innovative strategy to generate GHZ entangled states with up to 60 qubits, which marks a notable advance over previously reported GHZ sizes. The GHZ states were generated using a novel entangling protocol, which leverages a radial expansion of entanglement in two-dimensional quantum processor layouts. This technique appears efficient and scalable for large qubit numbers.

Significant efforts were focused on addressing the notoriously short-lived nature of GHZ states. The paper reports embedding GHZ states within a discrete time crystal (DTC) framework, specifically a "cat scar" DTC. This approach aims to use the inherent stability of DTCs to protect the fragile GHZ states from decoherence. The cat scar DTC preserves the coherence of the GHZ states over multiple evolution cycles, establishing novel connections between time crystals and quantum information science.

Empirical findings suggest a protective advantage when DTCs are employed compared to isolated Rabi oscillations or free decay, demonstrated by the observed lifecycle extension of the entanglement. The authors report achieving a substantial degree of coherence preservation over 30 cycles under experimental conditions.

Implications and Future Directions

The work offers a well-elucidated framework for manipulating GHZ states, including dynamic protocol adjustments to preserve entanglement during operations. This provides a new paradigm in which quantum processors are used to explore and manipulate nonequilibrium quantum matters. There is a clear demonstration of the potential of superconducting quantum circuits as a versatile platform for studying quantum state evolution dynamics.

Practically, this work lends itself to future research on robust quantum operations in highly entangled systems, potentially informing approaches to error correction and fault-tolerant quantum computation. The intersection with nonequilibrium quantum physics may further open pathways for emerging quantum technologies and innovative applications, such as quantum sensing and enhanced quantum communication protocols.

The theoretical development of embedding GHZ states within DTCs provides a structural basis for exploring more complex quantum systems, potentially extending to exotic many-body phenomena. The study suggests future investigations could be directed towards leveraging these dynamics in larger and more complex quantum systems, along with exploring other forms of entanglement and their protection mechanisms.

Conclusion

This paper presents critical advancements in quantum computing and entanglement physics by demonstrating effective techniques for generating and preserving large-scale GHZ entangled states. The use of a DTC framework extends the applicability of GHZ states, underpinning theoretical trends towards integrating quantum computational goals with time crystal dynamics. Overall, the research provides a meaningful foundation for future experimental and theoretical work in the quantum sciences.