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

Kavli Affiliate: Biao Huang

| First 5 Authors: Zehang Bao, Shibo Xu, Zixuan Song, Ke Wang, Liang Xiang

| Summary:

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.

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