Objects that comply with the rules of quantum mechanics behave very differently from those in the familiar world around us. This difference leads to an obvious question: is it possible to get an everyday item to start behaving like a quantum object?
But to see quantum behavior requires limiting an object̵
So far, researchers have largely approached this challenge by upscaling systems that were relatively easy to work with. But in today’s edition of Science, researchers report that they have come close to putting a large object in its quantum state.-one really big object: the 40 kilogram mirrors from the gravitational wave observatory known as LIGO.
Mirrors are central to LIGO’s function. They are located at opposite ends of long tunnels so that laser light bounces back and forth along the tunnels many times. This makes the distance traveled much greater and therefore more likely to experience a measurable influence from a passing gravitational wave.
Any noise in mirrors will cause problems for the function of the detector, so they have been stabilized in different ways. To begin with, they are heavy and weigh 40 kg (88.2 lbs). They are also suspended in rigid cables, making the mirror look like a pendulum. Finally, a damping system reads the position of the mirror and exerts force to hold it in the intended place.
This damping system was the key to the current experiment. The setup contains some gold electrodes that polarize mirrors themselves. This allows control voltages to transmit a force to the mirror. Measurements of the position and movement of the mirror are processed and compensating forces are calculated and the relevant signals are generated to apply this force via the electrical system.
This system has a necessary delay as the calculations involved in the control loop are not performed immediately. And since the system acts as a pendulum, any force applied to it can either act to slow its current oscillation or accelerate it to oscillate at a different frequency.
Fortunately, the delay here turned out to dampen the system rather than change its frequency. (This technically only applies to a single state or frequency range of the pendulum swing.) Over time, as the system was constantly adjusted, the effect was to soften energy from the system and effectively cool it. At the end of an operating period, the researchers estimate that its effective temperature was only 77 nano-Kelvin or very close to absolute zero.
The researchers also put it in the form of phonons, a quantum unit of vibration. At the end of the process, there were probably 11 phones in the 40kg mirror. It is not the quantum earth condition that will involve emptying the phonon system. But it is quite dense and could potentially already be useful for studying quantum phenomena on large objects; if not, it would not require much improvement to get it there.
The most intriguing prospect that the authors see is that the motion of the pendulum is also dependent on gravitational effects, which we have not been able to reconcile with quantum mechanics. The new work, they suggest, “suggests exciting prospects for studying the decoherence of gravity on massive quantum systems.” And compared to a grain of sand, 40 kg certainly qualifies as solid.
Science, 2021. DOI: 10.1126 / science.abh2634 (On DOIs).