# Lasers

Image from: D. Pierangeli, G. Marcucci, and C. Conti Phys. Rev. Lett. 122, 213902 https://doi.org/10.1103/PhysRevLett.122.213902

## Laser network as optimisation platform

Coupled laser networks are a potential candidate as the physical platform to realise the analogue computing algorithms that we study. In a typical Ising or XY optimisation problem, a suitable physical system needs to be able to represent the time evolution of the phases of spins, and the time-invariant coupling strength between spins that encode the problem, and it has been found that suitably arranged spatial light modulators can be used in experiments to represent these quantities. Hence, analogue algorithms that are implementable by laser networks can potentially be realised in experiment, pushing the research frontier beyond just computer simulations.

In addition, coupled laser networks follow well-known dynamics, which can be shown to be equivalent to the well studied Stuart-Landau dynamics under suitable conditions. Under this dynamics, it has been established that the annealing of some parameters can lead the system to the global minimum of the XY Hamiltonian. It is currently under active research how the controls of some parameters of the system can improve the probability of the system finding the global minimum.

## Advantages of laser network for computing

Computations can be performed optically with power consumption per operation orders of magnitude lower than that of electronic circuits. Matrix-vector multiplication, which is an extensively used operation in computing workload, can be efficiently realised optically. This means laser systems can perform computational tasks with much higher efficiency than digital computers. Furthermore, by utilising the dynamics of coupled laser network, it may become possible to tackle moderately-sized NP-hard optimisation problems such as the XY problem that have previously been intractable to classical computers.