Information magazine of the Department of Industrial Engineering
Università di Trento
Information magazine of the Department of Industrial Engineering
Università di Trento
In 2015, humanity “listened” for the first time to an echo of the primordial universe: a faint signal from the collision of two black holes that occurred over a billion years ago. This extraordinary milestone, made possible by the LIGO interferometers, was crowned in 2017 with the Nobel Prize in Physics.
But detecting gravitational waves is anything but simple: as these ripples in spacetime pass by, they imperceptibly deform space, changing the length of one arm of the interferometer (several kilometers long) by a fraction of an atom’s diameter. It’s like trying to detect a change in the length of a football field equal to one ten-thousandth of the thickness of a human hair.
In this context, light becomes our most powerful tool. Or better: quantum light.
To measure such tiny variations, interferometers must fight against quantum noise: fluctuations intrinsic to the very nature of light. Thanks to squeezed light (i.e., “compressed” in one of its quantum components), it is now possible to reduce this noise by up to 50%, increasing the observable volume of the universe by a factor of 3.
How does it work? Squeezed light is produced through quantum optics protocols, which manipulate photons in order to reduce the uncertainty of one variable (phase or amplitude) of light. This allows detectors to increase their precision, making the most of every single photon.
The Department of Industrial Engineering is also part of this research frontier. In the Integrated Quantum Photonics Laboratory, in collaboration with colleagues from the Department of Physics and the Advanced Interferometry and Quantum Optics Laboratory, researchers are working on a new generation of squeezed light sources based on integrated photonics.
But what does this mean? Integrated photonics is a technology that guides and manipulates light within sub-micrometric structures called waveguides, very similar to electronic circuits. The difference is that instead of electric current, light propagates through photonic circuits.
At DII’s laboratory, squeezed light is generated using thin films of lithium niobate, a material that combines excellent optical properties with integration flexibility. The goal is ambitious: to create a compact, stable, and efficient source of squeezed light, suitable for implementation in future gravitational interferometers such as the Einstein Telescope.
Researchers at DII have already achieved a significant milestone: for the first time, they managed to generate and measure squeezed light states in their lab using integrated photonics. Now, work continues to optimize these sources, evaluating their efficiency and stability, and comparing them with currently used technologies based on bulk optical crystals.
The goal is clear: to simplify future detectors, reduce their size and costs, and at the same time improve their performance. Because every photon counts when it comes to listening to the universe.
In the quantum world, even light is subject to uncertainties: it is impossible to know with absolute precision both its amplitude (intensity) and its phase (time variation). This principle, similar to Heisenberg’s uncertainty principle, generates inevitable “background noise” in optical detectors.
Squeezed light is a quantum state of light in which this uncertainty is reduced for one of the two variables (for example, phase) at the expense of the other.
In practice: by compressing uncertainty where it matters, more precise measurements can be achieved. This technique is fundamental for gravitational wave detectors, where even the smallest signal must emerge from ever-present quantum noise.
Integrated photonics is the field that develops circuits capable of manipulating light on tiny chips, using waveguides that work similarly to wires in electronic circuits.
In photonic circuits, photons—particles of light—are routed, modulated, and combined to perform complex functions, from communication to quantum computing.
Compared to traditional optics (based on mirrors and lenses), integrated photonics offers:
It is a key technology for frontier applications such as quantum optics, advanced sensors, and the gravitational wave detectors of the future.
