Boosting gravitational wave detectors with quantum tricks

September 03, 2018

A group of scientists from the Niels Bohr Institute (NBI) at the University of Copenhagen will soon start developing a new line of technical equipment in order to dramatically improve gravitational wave detectors.

Gravitational wave detectors are extremely sensitive and can e.g. register colliding neutron stars in space. Yet even higher sensitivity is sought for in order to expand our knowledge about the Universe, and the NBI-scientists are convinced that their equipment can improve the detectors, says Professor Eugene Polzik: "And we should be able to show proof of concept within approximately three years".

If the NBI-scientists are able to improve the gravitational wave detectors as much as they "realistically expect can be done", the detectors will be able to monitor and carry out measurements in an eight times bigger volume of space than what is currently possible, explains Eugene Polzik: "This will represent a truly significant extension".

Polzik is head of Quantum Optics (Quantop) at NBI and he will spearhead the development of the tailor made equipment for gravitational wave detectors. The research - which is supported by the EU, the Eureka Network Projects and the US-based John Templeton Foundation with grants totaling DKK 10 million - will be carried out in Eugene Polzik's lab at NBI.

A collision well noticed

News media all over the world shifted into overdrive in October of 2017 when it was confirmed that a large international team of scientists had indeed measured the collision of two neutron stars; an event which took place 140 million light years from Earth and resulted in the formation of a kilonova.

The international team of scientists - which also included experts from NBI - was able to confirm the collision by measuring gravitational waves from space - waves in the fabric of spacetime itself, moving at the speed of light. The waves were registered by three gravitational wave detectors: the two US-based LIGO-detectors and the European Virgo-detector in Italy.

"These gravitational wave detectors represent by far the most sensitive measuring equipment man has yet manufactured - still the detectors are not as accurate as they could possibly be. And this is what we intend to improve", says Professor Eugene Polzik.

How this can be done is outlined in an article which Eugene Polzik and a colleague, Farid Khalili from LIGO collaboration and Moscow State University, have recently published in the scientific journal Physical Review Letters. And this is not merely a theoretical proposal, says Eugene Polzik:

"We are convinced this will work as intended. Our calculations show that we ought to be able to improve the precision of measurements carried out by the gravitational wave detectors by a factor of two. And if we succeed, this will result in an increase by a factor of eight of the volume in space which gravitational wave detectors are able to examine at present".

A small glass cell

In July of last year Eugene Polzik and his team at Quantop published a highly noticed article in Nature - and this work is actually the very foundation of their upcoming attempt to improve the gravitational wave detectors.

The article in Nature centered on 'fooling' Heisenberg's Uncertainty Principle, which basically says that you cannot simultaneously know the exact position and the exact speed of an object.

This has to do with the fact that observations conducted by shining light on an object inevitably will lead to the object being 'kicked' in random directions by photons, particles of light. This phenomenon is known as Quantum Back Action (QBA) and these random movements put a limit to the accuracy with which measurements can be carried out at the quantum level.

The article in Nature in the summer of 2017 made headlines because Eugene Polzik and his team were able to show that it is - to a large extent - actually possible to neutralize QBA.

And QBA is the very reason why gravitational wave detectors - that also operate with light, namely laser light - "are not as accurate as they could possibly be", as professor Polzik says.

Put simply, it is possible to neutralize QBA if the light used to observe an object is initially sent through a 'filter'. This was what the article in Nature described - and the 'filter' which the NBI-scientists at Quantop had developed and described consisted of a cloud of 100 million caesium atoms locked-up in a hermetically closed glass cell just one centimeter long, 1/3 of a millimeter high and 1/3 of a millimeter wide.

The principle behind this 'filter' is exactly what Polzik and his team are aiming to incorporate in gravitational wave detectors.

In theory one can optimize measurements of gravitational waves by switching to stronger laser light than the detectors in both Europe and USA are operating with. However, according to quantum mechanics, that is not an option, says Eugene Polzik:

"Switching to stronger laser light will just make a set of mirrors in the detectors shake more because Quantum Back Action will be caused by more photons. These mirrors are absolutely crucial, and if they start shaking, it will in fact increase inaccuracy".

Instead, the NBI-scientists have come up with a plan based on the atomic 'filter' which they demonstrated in the Nature article: They will send the laser light by which the gravitational wave detectors operate through a tailor made version of the cell with the locked-up atoms, says Eugene Polzik: "And we hope that it will do the job".

Faculty of Science - University of Copenhagen

Related Gravitational Waves Articles from Brightsurf:

Weak equivalence principle violated in gravitational waves
New research published in EPJ C proves theoretically that the Weak Equivalence Principle can be violated by quantum particles in gravitational waves - the ripples in spacetime caused by colossal events such as merging black holes.

Remembrance of waves past: memory imprints motion on scattered waves
Now, it appears that between relativity and the classical (stationary) wave regime, there exists another regime of wave phenomena, where memory influences the scattering process.

New populations of black holes revealed by gravitational waves
The gravitational wave detectors LIGO and Virgo have just chalked up their biggest catch yet, a black hole 142 times the mass of the Sun, resulting from the merger of two ''lighter'' black holes.

Tabletop quantum experiment could detect gravitational waves
Tiny diamond crystals could be used as an incredibly sensitive and small gravitational detector capable of measuring gravitational waves, suggests new UCL-led research.

Gravitational waves could prove the existence of the quark-gluon plasma
According to modern particle physics, matter produced when neutron stars merge is so dense that it could exist in a state of dissolved elementary particles.

X-rays and gravitational waves will combine to illuminate massive black hole collisions
A new study by a group of researchers at the University of Birmingham has found that collisions of supermassive black holes may be simultaneously observable in both gravitational waves and X-rays at the beginning of the next decade.

Quantum expander for gravitational-wave observatories
Gravitational-wave detectors use ultra-stable laser light stored in optical cavities to achieve the high sensitivity for detecting gravitational-wave signals from merging binary black holes and neutron stars.

Gravitational lensing provides a new measurement of the expansion of the universe
Amid ongoing uncertainty around the value of the Hubble Constant, uncertainty largely created by issues around measuring distances to objects in the galaxy, scientists who used a new distance technique have derived a different Hubble value, one 'somewhat higher than the standard value,' as Tamara Davis describes it in a related Perspective.

Gravitational waves leave a detectable mark, physicists say
New research shows that gravitational waves leave behind plenty of 'memories' that could help detect them even after they've passed.

DIY gravitational waves with 'BlackHoles@Home'
Researchers hoping to better interpret data from the detection of gravitational waves generated by the collision of binary black holes are turning to the public for help.

Read More: Gravitational Waves News and Gravitational Waves Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to