6 mins read 06 Jul 2020

Scientists Observe Quantum Mechanics Affecting Everyday Objects

Scientists at OzGrav, working as part of the LIGO collaboration, have observed for the first time the effects of quantum noise on 40 kg mirrors thanks to technology pioneered at ANU.

Measuring the effects of quantum mechanics on human-sized objects was once considered impossible. However, scientists working as part of the Laser Interferometer Gravitational-wave Observatory (LIGO) have done just that, by measuring the movement of a mirror due to quantum noise. 

Thanks to ‘light-squeezing’ technology from the Australian National University (ANU), LIGO scientists can now make more precise measurements that surpass the standard quantum limit and see the effects of quantum noise. 

Scientists from ANU, University of Western Australia (UWA), and University of Adelaide (UA) contribute to the research through ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav.

Dr. Robert Ward, a physicist from ANU, emphasises the importance of this achievement. “When I first started studying Physics many years ago, I was fascinated by the weirdness of quantum mechanics, and wanted to know why quantum physics didn’t apply to everyday life in the same way as gravity.  To now be involved in research that could see quantum physics effects on human sized objects is absolutely amazing,” he said.

The Weird World of Quantum Mechanics

An artistically enhanced image produced from a bubble chamber, tracking the motions of particles. Credit: CERN.

Quantum Mechanics is a field of physics that looks at particles that are smaller than the atom. These particles, such as photons and electrons, exhibit behaviour that can be difficult to grasp as part of our everyday experiences, and that rely on the calculation of probabilities in order to understand what is going on. 

One key postulate in this field is Heisenberg’s Uncertainty Principle, which states that we cannot know both the position and momentum of one of these particles with absolute certainty due to their nature. As we observe and measure one of these parameters with more certainty, we also lose our certainty about the other. This uncertainty is called quantum noise. 

Heisenberg’s Uncertainty Principle therefore imposes a limit as to how precisely we can measure something in the subatomic realm. This limit is called the Standard Quantum Limit (SQL).

Detecting Gravitational Waves

A diagram of the LIGO interferometer. Credit: LIGO

The SQL affects many areas of quantum mechanics, including the measurement of gravitational waves. 

Gravitational waves are minute distortions in the fabric of space-time due to the movement of massive objects in the universe, such as collisions between black holes. We can measure these distortions using a gravitational wave detector, and determine the types of objects that produce these ripples that traverse the Universe. 

The LIGO collaboration hosts two of these detectors in the USA, with Virgo (also a part of the collaboration) hosts a third in Italy. These instruments measure gravitational waves using a system of mirrors and lasers in a formation known as an interferometer. The distortions from gravitational waves cause the distances between the mirrors to change ever so slightly, which causes an inference pattern to be formed by the laser. This pattern can be measured to calculate information about gravitational waves. 

Because gravitational wave distortions are extremely small, there are lots of sources of error when it comes to measuring them. Even the laser which is used to measure the disturbances and inference patterns triggered by gravitational waves can cause quantum noise, and hence the SQL imposes a limit as to how precise our measurements of gravitational waves can be. 

Breaking the Standard Quantum Limit

Astrophysicists from ANU developed a new technique last year to enable LIGO to get past the SQL. This technology, called ‘squeezed light’, allows scientists at the LIGO collaboration to tune the properties of the quantum noise within their interferometer. Therefore, measurements can become more precise scientists are now able to dampen the effects of quantum noise, and we can break the SQL. 

In going beyond the SQL, scientists at LIGO also compared the results of their interferometer with and without using squeezed light. In doing so, they found that they achieved quantum uncertainty 3 decibels below the standard quantum limit, meaning that they were able to achieve more certainty with the application of squeezed light. 

They also measured the movement of the mirrors in their interferometer, and were able to observe that quantum noise alone was enough to displace the mirrors 10-20 meters - in terms of scale this measurement is to a hydrogen atom what a hydrogen atom is to a human. This observation proves to scientists that the effects of quantum mechanics on human-sized objects can be measured. Several scientists involved in this project agreed that to see the effects of the subatomic realm on 40 kg mirrors is an impressive feat.

Nutsinee Kijbunchoo (left) and Terry McRae (right) building a light squeezer table at LIGO Hanford. Credit: Nutsinee Kijbunchoo, ANU.

Dr. Terry McRae, an OzGrav researcher from ANU commented, “This result definitively shows that Quantum mechanics applies to the large scale world of  multi kilogram objects and not just to atoms molecules and small microgram scale objects. This ability to make more precise measurements of natural phenomenon has historically been one of the driving forces for technological innovation.”  

A physicist from UWA, Dr. Carl Blair, ruminated on the implications of these results. “Will we see quantum quirkiness in the human scale world some time soon? - Like tunneling through impossible barriers or entanglement where 2 objects separated by vast distances act like one object?” 

In light of these possibilities, ANU’s development of light-queezing technology played a very strong role in this experiment. Nutsinee Kijbunchoo, a PhD student at ANU and one of the lead authors of the resulting paper, said, “This is yet another result of a strong collaborative effort. ANU made a valuable contribution to the development, installation, and commission of the squeezed light apparatus at the LIGO observatories which eventually led to this groundbreaking result”.

Now that we can see that the quantum world affecting large objects, it will be interesting to see how this will affect the technology of the future.