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Quantum-Enhanced Catalysis via Rydberg States Quantum-Enhanced Catalysis for Ammonia Synthesis via Rydberg States and Quantum Many-Body Dynamics A Theoretical Framework for Breaking Scaling Relations Through Coherent Quantum Control

Zeiner-Gundersen, Sindre, D H Zeiner-Gundersen

Published Jan 1, 2025• 0 citations
Publisher
DOI
10.13140/rg.2.2.15954.21441

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As quantum devices scale to larger and larger sizes, a significant challenge emerges in scaling their coherent controls accordingly. Quantum cellular automata (QCAs) constitute a promising framework that bypasses this control problem: universal dynamics can be achieved using only a static qubit array and global control operations. Despite an extensive history of theoretical explorations and proposals, QCAs have not been experimentally explored in the context of highly-scalable globally-controlled systems. Here we realize QCAs on a dual-species Rydberg array of rubidium and cesium atoms, leveraging independent global control of each species to perform multiple quantum protocols. Seeding an automaton with different initial states, we explore many-body dynamics of quasiparticles and grow GHZ states across both species, highlighting the flexibility of our approach. We further develop a second automaton using a novel mediated entangling gate, enabling generation of 96.7(1.7)%-fidelity Bell states, 17-qubit cluster states, and high-connectivity graph states. Our results demonstrate that simple global controls enable access to a rich variety of applications through the QCA framework. The versatility and scalability of QCAs present compelling opportunities for the development of quantum information systems, as well as new perspectives on quantum many-body dynamics.

quant-pharXiv:2601.16257•Jan 26, 2026•0 citations
We develop the research achievement of recent work [G\"arttner et al., Phys. Rev. Lett. 113, 233002 (2014)], in which an anomalous excitation enhancement is observed in a three-level Rydberg-atom ensemble with many-body coherence. In our theoretical analysis, this effect is ascribed to the existence of a quasidark state as well as its avoided crossings to nearby Rydberg-dressed states. Moreover, we show that with an appropriate control of the optical detuning to the intermediate state, the enhancement can evoke a direct facilitation to atom-light coupling that even breaks through the conventional N\sqrt{N}N​ limit of strong-blockaded ensembles. As a consequence, the intensity of the probe laser for intermediate transition can be reduced considerably, increasing the feasibility of experiments with Rydberg-dressed atoms.
This thesis explores the implementation of a spin-1/2 system to realise quantum simulation of Heisenberg XX and XXZ models. The spins are mapped onto two high-lying atomic levels, so-called Rydberg states, in an ultracold sample of 87Rb and coupled by a microwave field. Efficient synthesis and control of the driving field has been introduced in the setup in order to probe the spin dynamics with NMR sequences. Two- and three-photon excitation schemes are implemented to prepare the Rydberg spins. In order to spatially resolve the Rydberg excitation dynamics, a new imaging technique is employed, which uses the depletion of absorption in presence of Rydberg atoms to detect their distribution in the atomic cloud, revealing the emergence of spatial order of the Rydberg excitations due to strong van der Waals interactions. To benchmark the validity of this platform, the coherence of the spin ensemble is measured by Ramsey techniques in the low-density regime, where the single-spin dynamics accurately describes the observations. Despite the black-body redistribution of Rydberg spins setting a limit for the T2* time of the spin system, the coherence is measured to persist over long timescales on the order of 130 μs. Thus, scaling up the density of spins, first signatures of dipolar many-body effects for |nS⟩ − |nP⟩ (XX) and |nS⟩ − |(n + 1)S⟩ (XXZ) spin combinations have been observed.
We theoretically introduce a new kind of non-Gaussian state-----Laguerre polynomial excited coherent states by using the multiphoton catalysis which actually can be considered as a block comprising photon number operator. It is found that the normalized factor is related to the two-variable Hermite polynomials. We then investigate the nonclassical properties in terms of Mandel's Q parameter, quadrature squeezing, second correlation, and the negativity of Wigner function (WF). It is shown that all these properties are related to the amplitude of coherent state, catalysis number and unbalanced beam splitter (BS). In particular, the maximum degree of squeezing can be enhanced as catalysis number and keeps a constant for single-photon catalysis. In addition, we examine the effect of decoherence by Wigner function, which show that the negative region, characteristic time of decoherence and structure of WF are affected by catalysis number and unbalanced BS. Our work provides a general analysis about how to prepare theoretically polynomials quantum states.
As quantum devices scale to larger and larger sizes, a significant challenge emerges in scaling their coherent controls accordingly. Quantum cellular automata (QCAs) constitute a promising framework that bypasses this control problem: universal dynamics can be achieved using only a static qubit array and global control operations. Despite an extensive history of theoretical explorations and proposals, QCAs have not been experimentally explored in the context of highly-scalable globally-controlled systems. Here we realize QCAs on a dual-species Rydberg array of rubidium and cesium atoms, leveraging independent global control of each species to perform multiple quantum protocols. Seeding an automaton with different initial states, we explore many-body dynamics of quasiparticles and grow GHZ states across both species, highlighting the flexibility of our approach. We further develop a second automaton using a novel mediated entangling gate, enabling generation of 96.7(1.7)%-fidelity Bell states, 17-qubit cluster states, and high-connectivity graph states. Our results demonstrate that simple global controls enable access to a rich variety of applications through the QCA framework. The versatility and scalability of QCAs present compelling opportunities for the development of quantum information systems, as well as new perspectives on quantum many-body dynamics.