How Light Reveals the Hidden Laws of Open Systems express
Open systems exchange energy with their surroundings, like a guitar string fading into the air. Scientists built such a system out of light, twisting the beams into corkscrews and forming an artificial lattice — a maze where losses can be controlled at every step. Light in this maze always moves at the maximum possible speed, but its energy can fade or grow. By simultaneously measuring the twist and strength of the corkscrew beams, physicists reconstructed the full spectrum (color composition) depending on direction and attenuation. At certain points, two different colors of light merge into one, as if losing their individuality — something impossible in ordinary crystals. This optical technique opens access to effects that were previously only theoretical. It's already helping improve lasers and sensors, and in the future will bring us closer to ultrasensitive quantum devices.
Original abstract
as written by the authors arXiv:2511.06844
Open systems feature a variety of phenomena that arise from non-Hermitian physics. Recent theoretical studies have offered much insights into these phenomena through the non-Bloch band theory, though many of the theory's key features are experimentally elusive. For instance, the correspondence between complex momenta and non-Hermitian bands, while central to non-Bloch band theory, has so far defied direct experimental observation. Here we experimentally study the non-Hermitian spectral deformation in complex-momentum space, by implementing a non-Hermitian lattice with long-range couplings in the synthetic orbital-angular-momentum (OAM) dimension of photons inside a degenerate cavity. Encoding the complex momenta in the phase and amplitude modulations of the OAM modes, and devising a complex-momentum-resolved projective detection, we reconstruct the spectral deformation in momentum space, where the eigenspectrum on the complex plane morphs through distinct geometries. This enables us to experimentally extract key information of the system under the non-Bloch band theory, including exceptional points in the complex-momentum space, the open-boundary spectra, and the generalized Brillouin zone. Our work demonstrates a versatile platform for exploring non-Hermitian physics and non-Bloch band theory, and opens the avenue for direct experimental investigation of non-Bloch features in the complex-momentum space.
Light beams with different degrees of twist look like donuts with varying numbers of swirls, and each such donut can act as a separate data transmission channel.