Breakthrough in quantum noise reduction

When scientists measure extremely small objects, such as nanoparticles, they face a difficult challenge: simply observing these particles disturbs them. This happens because photons, particles of light, used for measurement 'kick' the tiny particles they hit, an effect known as 'backaction'.

In a new study published in Physical Review Research, a team from the University's Physics Department has revealed a remarkable connection, that this relationship works both ways.

Swansea University PhD student Rafal Gajewski, first author of the study, said: "Our work has shown that if you can create conditions where measurement becomes impossible, the disturbance disappears too."

"Using a hemispherical mirror with the particle at its centre, we found that under specific conditions, the particle becomes identical to its mirror image. When this happens, you can't extract position information from the scattered light, and at the same time, the quantum backaction vanishes."

This breakthrough holds potential for a number of exciting applications, including:

• Creating quantum states with objects much larger than atoms
• Testing fundamental quantum physics at unprecedented scales
• Conducting experiments which explore the boundary between quantum mechanics and gravity
• Developing ultra-sensitive sensors for detecting tiny forces

These findings could be particularly valuable for ambitious projects like MAQRO (Macroscopic Quantum Resonators), a proposed space mission that aims to test quantum physics with larger objects than ever before.

Dr James Bateman, who supervised the research, said: "This work reveals something fundamental about the relationship between information and disturbance in quantum mechanics. What's particularly surprising is that the backaction disappears precisely when light scattering is maximised -- the opposite of what intuition might suggest.

"By engineering the environment around a quantum object, we can control what information is available about it and therefore control the quantum noise it experiences. This opens up new possibilities for quantum experiments and potentially more sensitive measurements."

The team is working on experimental demonstrations and exploring practical applications that could lead to a new generation of quantum sensors.

This research is part of a growing field of 'levitated optomechanics', which uses lasers to suspend and control tiny particles in a vacuum; recent experiments have already cooled particles to their lowest possible energy level -- quantum ground state -- showing how much control scientists can have over these systems.