First attempt at quantum drumming

A simple experiment in which a tiny drum is beaten with a drumstick made of light could make quantum mechanics visible to the naked eye, elevating it from its usual mysterious atomic-scale behaviour.

Using a mechanism from a mobile phone and an off-the-shelf silicon nitride membrane designed for electron microscopes, a team of researchers at University of Queensland in Australia deployed a 20 year-old laser to study the interaction between light and vibrations.  

The quantum effect the team was looking to demonstrate involved the membrane – the drum head – vibrating and being still at the same time – a quantum condition known as a superposition of states.

Superpositions have been observed with single atoms and photons, but the team’s new technique potentially allows them to extend that capability enormously. The 1.7 millimetre square membrane comprises a million billion atoms.

The ability to understand and control the quantum behaviour of objects made of so many atoms could enable the development of incredibly sensitive detectors, said team member Till Weinhold.

“This could assist in the detection of gravitational waves with higher sensitivity, or for stabilisation in space flight,” he says.

Weinhold hopes the new method will help unlock more secrets of quantum physics.

“I think it should give us a new understanding of how our world is quantum mechanical, yet we don’t observe it,” he explains. 

“We should be able to understand that line between the classical world that we live in and the quantum world that underlies it much better by pushing macroscopic objects into the quantum regime.

“We should get a much better understanding of why nature behaves the way it does.”

While the team’s method, reported in the New Journal of Physics, does not achieve enough sensitivity to observe quantum behaviour, they are confident the method will inspire other research groups to use the approach to study the quantum nature of light interacting with vibrating objects.

The team’s method was adapted from previous experiments that used elaborate set-ups including high vacuums, and dropping the temperature to close to absolute zero (minus-273 degrees Celsius) to create hybrid quantum states.

In this work, the team simply observed many reflections from the drum, and selected the rare events which became superpositions.

They identified photons that bounced back in a superposition state by splitting the laser beam in two, directing one onto a static reflector and the other instead onto the vibrator – a set-up known as an interferometer. 

By recombining the halves of the beam as they returned they could tell how it had interacted with the vibration.

If the beam came back from the drum in a hybrid state it reflected into a detector, which told them they’d found what they were looking for.

The team’s initial prototype had too much noise to fully confirm they had created quantum behavior, because the energy imparted to the drum by the phone vibrator was equivalent to heating it to millions of degrees, a similar temperature to the centre of the sun.

To reduce the noise enough to see accurate results, the researchers will need to perform the experiment in a cooled environment and in a vacuum, but not at the level of previous experiments.

“Depending on the system, it might be a factor of 20 warmer – a million times easier to achieve,” Weinhold says. 

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