Global control via quantum actuators

Abstract

We introduce the concept of quantum actuators as mediators for globally controlled quantum computation. Auxiliary quantum systems act as controllable elements that transiently store and release interaction energy, enabling the selective activation of multi-qubit gates within globally driven architectures. During compilation they remain passive and require no fine-grained local control, while during operation they allow for controlled activation of interactions and directional flow of quantum information. We provide a framework for embedding quantum actuators in globally controlled processors, showing how they enhance connectivity, enable long-range entangling operations, and bridge distant regions without increasing local control overhead. We discuss physical implementations and architectural strategies illustrating how these elements extend the capabilities of global-control schemes. A complementary interpretation in terms of quantum batteries naturally emerges, connecting global-control architectures with concepts from quantum thermodynamics while highlighting the distinct operational role of quantum actuators.

Figures (5)

• Figure 1: Example of a globally driven quantum architecture with two species ($\#\mathcal{S}=2$), $A$ and $B$. Qubits are arranged on a random illustrative planar graph with always-on nearest-neighbor ZZ interactions, while species assignment satisfies constraints (P1) and (P2): no two adjacent qubits belong to the same species, and all qubits of a given species are driven by the same global control field. Different colors indicate distinct species, and edges represent static ZZ couplings.
• Figure 2: Schematic globally driven architectures supporting universal quantum computation under constraints (P1) and (P2). (a) Ladder-like architecture: logical information is encoded in an ICC separating ferromagnetic ($\ket{\rm F}$) and Néel ($\ket{\rm N}$) background phases. For simplicity, a two-species implementation is shown and double-crossed qubits are omitted. Global control sequences shift the ICC along the ladder, while crossed qubits (marked by $\times$ or $\mathbb{X}$) enable effective local single- and two-qubit gates via the blockade mechanism. (b) Conveyor-belt-like architecture: computational qubits $Q_i$ form a closed loop and are separated by auxiliary segments $S_{i,i+1}$ storing classical reference states. Alternating global pulses implement nearest-neighbor SWAP operations, allowing logical qubits to circulate around the loop. A crossed element and a parity-breaking CZZ gate complete the set of resources required for universality. Static ZZ couplings are indicated by solid links throughout.
• Figure 3: Variants of globally driven architectures inspired by Refs. menta2024globallycioni2024conveyorbeltmenta2025building, augmented with quantum actuators operating under global control—see conceptual step \ref{['conceptual1']}. (a) Ladder-like architecture, with $N-1$ quantum actuators for an $N$-qubit ICC. (b) Conveyor-belt-like architecture, in which a single quantum battery enables effective three-qubit operations for any even $N \geq 2$.
• Figure 4: Programmability via globally driven quantum actuators in a globally driven quantum processor. A layer of auxiliary quantum actuators (QAs), shown schematically above the physical qubits, is globally controlled and selectively maintained in the excited state. Actuator-assisted blockade dynamically freezes the underlying regions of the processor, preventing them from participating in the computation. By locally disabling selected QA regions, active pathways (bridges) are created that allow coherent transport of the ICC across otherwise inactive areas.
• Figure 5: Modular interconnection of globally driven conveyor-belt processors via quantum actuators. Two independent conveyor-belt architectures are linked by a bridge region containing an auxiliary quantum actuator (QA). When the QA is maintained in its excited state, blockade-type interactions dynamically isolate the two processors. Switching the QA to its ground state activates the bridge, enabling coherent two-qubit operations between boundary computational qubits. A SWAP operation allows quantum information to be transferred between modules.

Theorems & Definitions (1)

• Definition 1: Quantum actuator