Superconducting Qubits Show Time-Crystalline Order for 120 Cycles

Researchers at Zhejiang University, Lanzhou University, University of Houston, and Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, have demonstrated a remarkably stable form of time-crystalline order in a 72-qubit superconducting processor, maintaining the exotic quantum state for 120 cycles. This mechanism divides the Fock-space network into linearly many sparse sub-networks, thereby prolonging the thermalization timescale even for initial states at high energy densities. The work reveals that approximately conserved domain wall numbers underpin this stability, offering a pathway to harness highly entangled states for quantum applications and breaking ergodicity in these systems.

Fock Space Prethermalization Suppresses Quantum System Heating A quantum processor at Zhejiang University, Lanzhou University, University of Houston, and Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, has sustained a time-crystalline order for over 120 cycles, defying typical system heating and opening new avenues for stable quantum information processing. Researchers demonstrated a mechanism called Fock space prethermalization (FSP) that dramatically slows energy absorption in a 72-qubit superconducting processor, effectively prolonging the lifespan of fragile quantum states. This finding challenges conventional understanding of how driven quantum systems behave and offers a potential pathway toward practical quantum technologies. The core of this advancement lies in how the quantum processor organizes its computational space. FSP operates by dividing the complex network of possible quantum states, known as Fock space, into a multitude of sparse, loosely connected sub-networks. Unlike previous methods relying on disorder or specific driving frequencies, FSP is a disorder-free mechanism, making it more robust and adaptable. Finite-size scaling analysis revealed size-independent regimes for FSP-thermalization crossover and linked the dynamical behaviors to the eigenstructure of the Floquet unitary. The implications extend beyond simply extending coherence times, as the work establishes FSP as a robust mechanism for breaking ergodicity, meaning the system doesn’t randomly explore all possible states, but instead remains confined within specific, predictable regions of its Fock space. This controlled behavior, the researchers believe, allows for exploring novel nonequilibrium quantum matter and its applications.

The team’s investigation revealed that domain wall numbers are approximately conserved, and that hopping between these sub-networks is suppressed, while movement within them is permitted as long as domain wall numbers are locally conserved. The paper details how the system’s structure decouples into these sparse networks, driven by large Ising interaction energy gaps.

Domain Wall Conservation Underpins Fock Space Dynamics Researchers at Zhejiang University, Lanzhou University, University of Houston, and Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, are meticulously charting the behavior of 72 superconducting qubits, revealing a surprising stability rooted in the conservation of domain walls within the quantum system.

The team’s investigation doesn’t simply extend coherence times; it identifies a fundamental mechanism driving this stability: Fock space prethermalization, or FSP. This decoupling isn’t random; it’s driven by large Ising interaction energy gaps. Domain walls, representing boundaries between opposing qubit states, act as kinetic constraints, limiting how the system evolves. By measuring site-resolved correlators, the team pinpointed the approximate domain wall conservation as the key to suppressing unwanted heating, a major obstacle in harnessing quantum systems. The implications extend beyond merely prolonging the lifespan of quantum states, suggesting the stability isn’t simply a byproduct of the specific system size, but a fundamental property of the FSP mechanism itself. Unlike methods relying on quenched disorders, FSP is a disorder-free mechanism, offering a potentially more robust pathway to stable quantum computation. The pursuit of stable quantum states has taken a step forward with the demonstration of a mechanism suppressing system heating, potentially unlocking more robust quantum technologies. Researchers from Zhejiang University, Lanzhou University, University of Houston, and Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, have identified Fock space prethermalization (FSP) as a disorder-free pathway to prolong the lifespan of highly entangled quantum states, a critical hurdle in building practical quantum devices. Further analysis, employing finite-size scaling, revealed size-independent regimes for FSP-thermalization crossover and linked the dynamical behaviors to the eigenstructure of the Floquet unitary, suggesting that the underlying mechanism is a fundamental property of the quantum system itself, rather than a byproduct of its specific dimensions. This is a significant finding, as it implies the potential for scaling up these systems without losing the benefits of FSP. The observed order persisted for over 120 cycles, highlighting the effectiveness of FSP in preserving coherence and opening new avenues for quantum research.

Ising Interactions Decouple Fock Space Networks Their work, detailed in recent findings using 72 superconducting qubits, reveals a phenomenon called Fock space prethermalization (FSP) that divides the “Fock space”, a mathematical representation of all possible quantum states, into “linearly many sparse sub-networks.” This decoupling isn’t random; it’s driven by large Ising interaction energy gaps between the qubits. As the researchers explain, this creates a kinetic constraint where the number of domain walls remains approximately conserved. This conservation isn’t absolute, but it’s strong enough to dramatically prolong the time it takes for the system to reach equilibrium. This decoupling is visually apparent when examining the Fock space network, as simulations reveal that in a standard thermal scenario, qubits flip freely, creating a densely connected network. However, under FSP conditions, the network becomes sparse and organized, with distinct sub-networks emerging. The researchers illustrate this with a schematic showing how strong Ising interactions enforce domain wall conservation, effectively isolating sections of the Fock space. “In Fock space, the time evolution unitary U of an L-qubit many-body system can be expressed as a complex network spanned by Fock bases,” they write, emphasizing the intricate structure they’ve uncovered.

The team’s investigation revealed that hopping between these sub-networks is suppressed, while movement within them is permitted as long as domain wall numbers are locally conserved. Finite-size scaling analysis reveals size-independent regimes for FSP-thermalization crossover and links these dynamical behaviors to the eigenstructure of the Floquet unitary. Source: http://link.aps.org/doi/10.1103/bq3c-c3d8 Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: