Photonic Circuits Enable Scalable High-Dimensional Quantum State Manipulation.

Researchers demonstrate a reconfigurable free-space photonic system utilising structured light to implement high-dimensional unitary transformations. The platform, employing spatial light modulators and half-wave plates, simulates quantum walks across lattices, distributing input modes across over 7,000 outputs and supporting complex dynamics. Compatibility with single-photon protocols is confirmed via coincidence measurements.

The manipulation of light offers a compelling avenue for advancing computation and simulation, particularly through the development of photonic circuits capable of processing information encoded in the properties of light itself. Researchers are increasingly focused on high-dimensional systems, where information is distributed across many independent channels, to enhance processing capacity and complexity. A collaborative team, comprising Maria Gorizia Ammendola from the Scuola Superiore Meridionale and Nazanin Dehghan, Lukas Scarfe, Alessio D’Errico, Francesco Di Colandrea, and Ebrahim Karimi from the Nexus for Quantum Technologies at the University of Ottawa, alongside Filippo Cardano from the Dipartimento di Fisica at the Universitá degli Studi di Napoli Federico II, details a programmable photonic architecture in their article, “High-dimensional programmable photonic circuits with structured media”. Their work presents a reconfigurable, free-space system utilising structured light – light beams with tailored spatial properties – to implement complex transformations and simulate quantum phenomena across extended lattices, demonstrating scalability through the distribution of a single input mode across over 7,000 output modes.

Researchers present a reconfigurable free-space photonic platform capable of simulating high-dimensional quantum walks, a computational model leveraging the principles of quantum mechanics to explore complex systems. The system successfully reproduces theoretical predictions for both one- and two-dimensional lattices, achieving simulations extending to 30 time steps and distributing a single input mode across over 7,000 output modes. This demonstrates a significant capacity for simulating complex quantum phenomena.

The research validates the accurate simulation of quantum walk dynamics, alongside the implementation of diverse walk dynamics including time-dependent disorder, which introduces randomness into the system over time, and synthetic gauge fields, artificially created forces influencing particle behaviour. Notably, the team observes electric-field-induced refocusing in two-dimensional walks, a phenomenon where the probability distribution of the quantum walker concentrates due to the applied field. Strong agreement between experimental data and theoretical models confirms the validity of the platform’s configuration and associated calculations.

Further investigations explore the impact of a constant electric field on the quantum walk, inducing a predictable drift in the probability distribution, effectively steering the quantum walker. Quantum walks in one dimension, subject to temporal disorder, exhibit both diffusive behaviour, where the spread of the walker increases proportionally to time, and superdiffusive regimes, where the spread increases at a faster rate. Researchers also probe geometrical and topological features of the simulated environment using bulk observables, measurable quantities that characterise the overall system behaviour, offering insights into the underlying structure.