The core principle behind this technology involves three separately controllable LC-SLMs, each consisting of pixelated cells filled with liquid crystals whose refractive indices change under an applied electrical field. By programming phase modulation patterns across these pixels, researchers imprint discrete phase shifts onto propagating optical modes. The system’s relay imaging configuration mitigates free-space propagation effects by optically aligning the modulators, enabling precise and loss-minimized manipulation of light’s spatial degree of freedom. The elegant design compresses traditionally multi-layered transformation processes into only three active layers, drastically reducing complexity while maintaining near-ideal operator fidelity.

Experimentally validated using both classical laser sources and single photons, the platform achieves the simultaneous coupling of a single input spatial mode into as many as 7,000 output modes. The liquid-crystal panels implement discrete translation-invariant unitaries in one- and two-dimensional configurations, effectively simulating quantum walks on spatial lattices. Recorded output intensity distributions closely match theoretical predictions at various time steps, confirming the platform’s remarkable accuracy. This capability presents a novel paradigm for simulating complex quantum phenomena, extending well beyond passive optical elements to actively programmable and controllable free-space photonics.

Such high-dimensional unitary transformations have remained a key challenge in photonics due to limitations in scalability, loss, and dynamic programmability. Integrated optical processors typically rely on fixed waveguide meshes, which, despite their compactness, lack flexibility in operational reconfiguration and experience fabrication inconsistencies. Recent solutions turning to multilayer free-space architectures have tended to increase depth—and thus losses—linearly with the number of spatial modes. The current platform breaks this tradeoff by leveraging a sophisticated compression scheme that condenses the requisite layers without sacrificing performance metrics.

This compression architecture arises from algorithmic insights initially developed by the research team, facilitating the synthesis of large-scale operators with minimal spatial modulation layers. Importantly, this method is realized using commercially available LC-SLM technology, demonstrating accessibility and adaptability for widespread use. Unlike static dielectric metasurfaces that provide fixed spatial transformation functions, these liquid-crystal devices offer dynamic reprogrammability, thus unlocking rapid mode transformation reconfigurations on demand. Their pixel-level electrical control through intuitive software interfaces positions them as versatile tools for a broad swath of photonic systems.

The versatility of this optical processor is further highlighted by its ability to exert full control over both spatial and vectorial modes of light, encompassing amplitude, phase, and polarization manipulation. This comprehensive mode control, effected through the simultaneous modulation of phase patterns across the three LC-SLM layers, represents a substantial extension beyond traditional scalar phase-only modulators. Consequently, the platform supports advanced quantum and classical optical experiments involving spin-orbit coupled states of light, opening frontiers for space-dependent polarization transformations and their applications in information encoding and quantum state engineering.

From a quantum optics perspective, the platform’s suitability for single-photon experiments elevates its potential impact. The authors have verified that the programmable unitary transformations operate reliably at the single-photon level, validating the processor’s quantum coherence preservation and low-loss operation critical for quantum information protocols. This combination of large-scale mode control, reconfigurability, and quantum compatibility makes the technology particularly promising for future quantum simulation and photonic quantum computing frameworks, where high-dimensional mode spaces are essential.

The system’s architecture inherently allows for real-time adaptability, whereby different unitary transformations can be uploaded via software to the LC-SLMs, enabling rapid switching between experimental configurations. This capability facilitates experimental versatility previously unattainable in free-space photonics. Researchers can now conduct extensive randomized protocols, machine-learning-assisted unitary synthesis, and dynamic quantum walk simulations without physical reconfiguration of the hardware, drastically accelerating iterative experimental cycles and data acquisition times.

Furthermore, the scalability of the processor is enabled by the modular tileability of the LC-SLMs, which each offer thousands of independently addressable pixels. This high pixel density allows for the fine spatial resolution required to implement subtle phase modulations and intricate interference patterns essential for simulating complex quantum operators. It also provides robustness against device imperfections, as phase profiles can be algorithmically optimized to compensate for non-idealities in real-world SLM responses, thus ensuring high-quality transformations.

Beyond fundamental research, the programmable optical processor holds promise for practical applications in high-capacity optical communications, classical and quantum information processing, and optical neural networks. Its ability to manipulate a broad range of spatial modes dynamically can enhance multiplexing strategies in free-space optical systems, improve error correction in quantum channels, and implement programmable photonic circuits capable of universal unitary transformations—a foundational step toward reconfigurable photonic integrated systems.

The reported advancement signifies a conceptual and technological milestone in free-space photonics, bridging the gap between static, hardwired optical components and fully programmable, large-scale photonic processors. The convergence of hardware-layer compression, pixel-precise phase modulation, and quantum compatibility positions this platform as a key enabler for next-generation light-based technologies. With further optimization and integration, this architecture could radically transform how structured light is harnessed for simulation, computation, and communication tasks in both classical and quantum domains.

This pioneering work, published in Light: Science & Applications, showcases a compact and versatile optical processor that encapsulates decades of photonic research into a portable and operational system. Capturing complex spatial transformations in just three electrically controlled layers, the platform exemplifies the fusion of algorithmic design and experimental photonics, setting a new standard for programmable, large-scale optical processing in free space.

Subject of Research: Programmable free-space photonic processors for large-scale unitary transformations

Article Title: Compact and programmable large-scale optical processor in free space

News Publication Date: 2026 (exact date not specified)

Web References: http://dx.doi.org/10.1038/s41377-026-02236-2

Image Credits: Francesco Di Colandrea et al.

The intrigue of simulating complex quantum phenomena is not new. In fact, the quest for efficient calculations regarding quantum processes has occupied scientists for decades. One classic example is the challenge of understanding how cold milk disperses within hot coffee. Conventional supercomputers often fall short in tackling such complex problems that require a precise understanding of quantum behavior. A revolutionary concept was introduced by Nobel Laureate Richard Feynman in 1982, which proposed that quantum computers could be the solution for simulating complex quantum phenomena more effectively than their classical counterparts.

Fast forward to today, and advances in quantum computing have brought Feynman’s vision closer to reality. The collaboration between PSI’s Läuchli and Elben and researchers from Google and various universities across five nations led to the development and successful testing of this new quantum simulator. Their innovative approach has not only allowed for enhanced precision in simulating quantum processes but also offers a remarkable level of flexibility that can be applied across a multitude of fields, ranging from solid-state physics to astrophysics. The publication of their findings in the esteemed scientific journal Nature underscores the significance of their achievement.

At the core of this innovative quantum simulator is the combination of digital and analogue techniques facilitated by a quantum chip developed by Google that houses 69 superconducting quantum bits, or qubits. This unique architecture enables operations to be performed in both digital and analogue modes. Whereas digital quantum computers operate using universal quantum gates like classical logic gates, they can leverage the unique properties of qubits to assume more than binary states — a fundamental advantage in quantum computing. However, purely digital quantum approaches have limitations in their applications as quantum simulators.

Analogue quantum simulators offer a different advantage, allowing for the direct simulation of physical processes. They accurately model interactions among particles, providing insights into phenomena such as magnetic properties in solids. The amalgamation of these two methodologies—digital and analogue—marks the breakthrough achieved by the physicists, effectively harnessing the strengths of each approach.

The research team’s method involves establishing precise and discrete initial conditions in the digital mode, such as simulating heat introduction into a solid. This controlled setup allows for the study of subsequent physical processes in the analogue mode, akin to how milk spreads when introduced into coffee. Through this analogy, the quantum simulator is capable of tracking dynamic physical processes such as heat diffusion and the emergence of magnetic domains in solids—capabilities that are vital for exploring complex quantum behaviors.

Andreas Elben, who contributes his expertise as a tenure-track scientist at PSI, remarked on the innovative nature of the quantum simulator, highlighting its capability to observe processes that reach thermal equilibrium. In this context, the milk analogy reflects how the simulator can demonstrate the distribution of energy among particles until a state of equilibrium is achieved. Läuchli echoed these sentiments, emphasizing that this advancement showcases the potential of superconducting analogue-digital quantum processors to serve as powerful quantum simulators.

The implications of this research extend far beyond mere theoretical inquiry. With the successful demonstration of a dual-mode quantum simulator, the groundwork has been laid for creating universal quantum simulators that are not restricted to specific physical problems. The versatility of this new technology opens up pathways to investigate a wide array of topics, most notably in magnetism—a field closely associated with Läuchli’s research.

The arrangement of qubits in the Google quantum chip is rectangular in shape, and the initial magnetic orientations of these qubits exhibit orderly patterns. However, the investigators are intrigued by the challenges posed by alternative chip geometries, such as triangular configurations. The interactions of qubits in these non-standard arrangements can lead to phenomena like frustrated magnetism, where traditional alignments break down, presenting opportunities for novel computing technologies that utilize magnetic spins instead of conventional electron charges.

Further explorations promise to unlock new applications in diverse areas, including materials science where researchers aim to develop novel high-temperature superconductors, and pharmaceuticals that are designed to operate with increased precision and decreased side effects. Notably, astrophysics stands to benefit from quantum simulations as well, particularly in addressing complex issues like the information paradox associated with black holes.

In conclusion, this pioneering work serves as a significant contribution to the field of quantum research, with capabilities that could fundamentally transform our approach to understanding intricate physical processes. As the collaboration with Google concludes, Andreas Läuchli and his team at PSI look forward to continuing their efforts to solve perplexing questions within quantum physics. By leveraging advancements made in quantum computing and simulation, researchers aim to answer fundamental inquiries that impact our comprehension of the universe.

Through their work, Läuchli and Elben, alongside their team, are poised to play a crucial role in advancing the frontiers of quantum research, which will have implications that resonate far beyond scientific circles.

Subject of Research: Not applicable
Article Title: Thermalization and criticality on an analogue–digital quantum simulator
News Publication Date: 6-Feb-2025
Web References: http://dx.doi.org/10.1038/s41586-024-08460-3
References: Not applicable
Image Credits: © Paul Scherrer Institute PSI/Mahir Dzambegovic
Keywords: Quantum computing, Analogue-digital simulation, Quantum mechanics, Superconducting qubits.