Revealed: The Physics of Sticky Tape (from Cosmos Magazine)

This article that I wrote for Cosmos Magazine in 2019 was selected for the 2020 Anthology of Best Australian Science Writing, my third guernsey in three years.

Bizarrely, it’s no long on the Cosmos website – although lots of my other stories are. They can’t explain this, so – since I am sure you’ve all been looking for it incessantly – I have found a web archive of it and posted it here for your delectation.

Continue Reading Revealed: The Physics of Sticky Tape (from Cosmos Magazine)

Teleportation fidelity the big winner in the quantum lottery

Sophie Zhao

by Phil Dooley

Running your quantum system as a lottery turns out to be a way to improve the transmission of data via quantum teleportation.

Researchers at the Research School of Physics used a probabilistic twist to develop a new transmission protocol that set a new record in data transmission: 92 percent fidelity, which more than halves the loss in previous experiments.

The new protocol will enable encrypted data, for example in finance or military settings, to be sent with higher accuracy.

“Our protocol improves the capability of the quantum teleporter to protect fragile quantum states during long-distance transmission, making the system resilient to noise and loss,” said lead researcher Dr Sophie Jie Zhao, from the Department of Quantum Sciences and the CQC2T ARC Centre of Excellence, who is the lead author in the team’s publication in Nature Communications.

Quantum teleportation is already being used in encrypted networks. It allows information to be shared instantly between linked, or entangled, quantum objects. 

However, the entanglement between the objects can easily be destroyed by interactions with external entities. This at once makes quantum teleportation extremely secure – as any tampering instantly destroys the data transfer – but also very prone to degradation through noise due to environmental interactions.

With entanglement degradation limiting their existing teleportation’s fidelity and distance, the team set their mind to improving the teleportation efficacy by leveraging the paradoxes of the Heisenberg Uncertainty Principle.

In these experiments, the ends of the teleportation link are two photons from the same source, which creates entanglement in their properties. These photons are sent to two separate locations, untouched, which leaves their properties unknown, and able to appear in any possible state.

The signaller then gets the information to be teleported to interact with one of the photons, and measures the photon’s properties – in this case amplitude and phase – making the photon choose a state. This causes the other photon (the receiver) to instantly choose its state as well. Because the two photons are linked, information about the signaller’s experiment can be deduced by the receiver.

This deduction relies on the sender separately conveying to the receiver the result of the experiment. This does not reveal the teleported information, as it is the result of the mashup between that information and the original photon. However, this result acts as a key that allows the receiver to work backwards from the result at their end and disentangle the teleported information.

It is crucial that the sender can’t know what the teleported information is – that would constitute a measurement and collapse the quantum information, said University of Queensland researcher and CQC2T member Professor Tim Ralph.

“The information needs to be hidden in uncertainty so the sender doesn’t know exactly what they are sending. The more they know about the signal, the more they destroy it,” he said.

Quantum uncertainty resulting from the mixing of possible states can be cancelled out with the key, however uncertainty resulting from noise from entanglement degradation is harder to cancel out.

To filter this noise the team leveraged the fact that the mixed states have a Gaussian distribution. They realised that a lottery, a protocol in which a subset of the measurements was selected randomly in a way that actually narrowed the Gaussian distribution, while other measurements were randomly discarded, could help filter out noise.

“Adding an element of chance to our protocol has the effect of distilling the quantum information,” Dr Zhao said.

“The post-selection effectively biases the Gaussian distribution in favour of high-amplitude outcomes than outcomes close to the origin of phase space, hence acting as an amplifier. Since this amplification is noiseless and takes over from part of the amplification applied by the receiver in standard teleportation protocols, the teleported states suffer less from the noise added due to imperfect entanglement.”

An interesting quirk of the system is that the balance between the probabilistic factor and the noise reduction can be tuned. By simply reducing the probability of measurements being selected in the protocol the teleportation fidelity can be increased.

To achieve their record 92 percent fidelity the team used a success rate of less than one in a hundred thousand, sampling the system for around two hours.

In the new protocol, the success of the teleportation relies on the stability of the laser system, instead of being limited by environmental noise, Dr Zhao said.

“You can always get better fidelity if you are willing to sacrifice your success rate. But then you need a longer sampling time.

“If the system were stable enough to allow us to sample for say, 20 hours, then I believe we could go above 95 percent,” she said.

Originally published on ANU Physics website

Continue Reading Teleportation fidelity the big winner in the quantum lottery

The Physics of Beer

It’s a common pub prank to tap the top of a friend’s beer, to make it suddenly erupt in froth. Funny to some people, annoying to others; but to Spanish physicist Javier Rodríguez-Rodríguez, intriguing.

Rodríguez-Rodríguez, from the University Carlos III of Madrid, decided to investigate the strange phenomenon, and in the process has discovered a host of complex physics in a glass of beer, which could help scientists understand all kinds of processes, from volcanic eruptions to the formation of asteroids.

“There are many different physical phenomena going on in a beer glass, and every time you drink a beer, all this physics is right before your eyes,” Rodríguez-Rodríguez says.

His thirst for knowledge has even led him to convince his PhD students to drop beer off a 100-metre high tower to study bubble formation in the micro-gravity environment of free-fall.

“Carbonated beverages are portable laboratories that can be used to demonstrate in an amusing way the working of many flows also found in nature and industry,” he and co-author Robert Zenit write in a review of the beer facts they have discovered, published in the magazine Physics Today.

The key to many of the processes in beer is that it is carbonated – a colloquial term for it being a super-saturated carbon dioxide solution. As the beer brews, fermentation by yeast emits micro-farts of carbon dioxide, building up pressure in the bottle.

Some of the carbon dioxide gas dissolves into the beer: the fraction is determined by Henry’s law, which holds that the higher the pressure, the more gas is dissolved.

When the bottle is opened, the pressure is released, meaning that amount of gas the liquid can hold is lower: suddenly the solution is super-saturated. But it takes a while for the solution to catch up. Over a few hours the carbon dioxide seeps out until it reaches its new equilibrium point, termed by beer lovers as “flat”.

The rate at which the gas departs, and the dynamics it sets off, forms the basis for much of beer’s intriguing behaviour – such as in the beer-tapping prank.

Rodríguez-Rodríguez’s study of it was first published in the journal Physical Review Letters and revealed that the trigger for the beer volcano is a pressure wave sweeping upward through the liquid.

The sudden jolt leaves the beer behind momentarily. At the sides of the bottle, the effect is minimal as the glass slides past the beer.

However, the downward shift of the base of the bottle has much greater ramifications, and creates a sudden drop in pressure in the liquid at the bottom. This low-pressure region propagates upward, triggering the dissolved carbon dioxide in the beer to suddenly form bubbles.

The beer then catches up with the bottle and the pressure rebounds. This sudden high pressure fragments the bubbles that have only just formed. Rodríguez-Rodríguez found each one breaks into as many as a million smaller bubbles.

These, now in a cloud formation, begin to rise, growing as they suck in more carbon dioxide. It takes a second or two before they reach the top and froth up.

The rise of the cloud is due to the buoyancy of the bubbles, which set Rodríguez-Rodríguez and his team thinking about what would happen in zero gravity.

Rather than sending beer into space, they decided to drop some off the 100-metre high drop tower of the Centre of Applied Space Technology and Microgravity (ZARM) in Bremen, Germany.

For the actual experiment they had to find a substitute liquid. “We cannot use beer,” says Rodríguez-Rodríguez. “It’s too dirty.”

Using carbonated water, the team could observe the evolution of the bubble cloud as it hovered within the liquid, capturing high-speed video of the process.

As well as being of relevance to the formation of bodies such as asteroids and meteorites in low gravity environments, Rodríguez-Rodríguez’s research addresses the potentially important issue of astronauts drinking beer.

The buoyancy of the bubbles is what enables the gas from the carbonated drink to rise from the stomach and be expelled, but Rodríguez-Rodríguez points out that in zero gravity, they would not be buoyant.

“The bubbles would not be able to escape the liquid within the digestive system, leading to painful bloating in the stomach and intestines. So, sorry, no bubbly drinks for space people!” he and Zenit write in their review article.

Rodríguez-Rodríguez admits to enjoying drinking his experimental apparatus sometimes, but is careful to point out he is not doing so with government research funds. He says the guidelines for research preclude expenditure on alcohol, so he buys all beer for experiments from his own money.

“I consider it the Rodríguez-Rodríguez Foundation for the Advancement of Science,” he adds.

Results from the microgravity experiments are in preparation, and will be submitted to a journal soon.

Original published 29/5/19 https://cosmosmagazine.com/physics/in-lager-veritas-the-physics-of-beer

Continue Reading The Physics of Beer

The hard questions

The hard questions

The easy part’s the answer

The resolution to the cadence, the final pose of the dancer

The hard work’s dynamic tension

build the elegant clash, the clarity in a question

 

World shaking shift of continental drift

Earthquaking violence from a pace so placid

The twist in dioxy-ribonucleic acid

 

Einstein astride a soaring light beam

Nothing’s as absolute as it seemed

The revelation comes at the speed of light

A universe of relative wrongs and rights

No more can you trust the rules you revere

Time stops, space shrinks as it all becomes clear.

 

by Phil Dooley, written for The Poet’s Guide to Science play.

First performed at Smiths Alternative in Canberra, August 24, 2018, as part of National Science Week.

Continue Reading The hard questions

Bubbles! The Physics of Champagne

Phil plus bubbles
Bubbles – the physics is surprisingly complex.

Original published in Cosmos Magazine, 6 November 2018. This has attracted media attention – check my Phil Up On Science Live page for radio interview times.

Opening a bottle of champagne not only signifies the start of a celebration, but also uncorks a swathe of sophisticated physics phenomena that contribute to the special appeal of bubbly.

Just as the pop of a cork marks a change in mood, it also marks a sudden change for the champagne. Pressure that has been building for months during the fermentation process is quickly released and suddenly things are out of equilibrium. What makes champagne fun are the dynamic processes that bring the system back into balance – pops, bubbles and fizz.

But where did the pressure come from in the first place? The answer is micro-farts. The yeast introduced by the winemaker feeds on sugar in the wine, using its energy to power its life, and then ejects its waste: carbon dioxide.

In each bottle of sparkling wine, yeast microbes produce more than 10 grams of this gas. That equates, in the confines of the sealed bottle, to a pressure about three times that found inside a car tyre. Under these conditions most of the carbon dioxide dissolves in the wine.

As the cork is loosened the pressure of the gas in the bottle pushes it out. Cork speeds can reach more than 50 kilometres per hour, says Gérard Liger-Belair from University of Reims Champagne-Ardenne in France.

Liger-Belair has made a career of studying the physics of bubbly; for him a glass of champagne is “a fantastic playground”, although he insists he does not drink his experimental samples.

Instead, he enjoys a glass of champagne with laser tomography, infrared imaging, high-speed cameras and mathematical models.

His measurements show the speed of the cork depends on the temperature of the wine. The carbon dioxide is much less soluble at higher temperatures, which leads to a higher pressure inside the bottle and thus a faster launch speed.

At the perfect drinking temperature of eight to 10 degrees Celsius the corks pops out at around 40 kilometres per hour. His experiments extend only to 20 degrees Celsius, at which the speed is in the low fifties. Presumably, champagne warmer than that is inconceivable in France.

In the moments after the it pops, fleeting wisps of fog appear – another dynamic phenomenon. The sudden five-fold drop in the pressure of the gas in the neck of the bottle causes a temperature decrease of around 80 degrees Celsius. As it momentarily dips below minus-70, traces of water and alcohol in the gas condense into an evanescent mist that quickly evaporates as the gas approaches room temperature.

Next the fizz begins, as the carbon dioxide dissolved in the wine starts to escape. If one were to let the contents of the bottle go absolutely flat, it would take more than 10 hours and involve the release of more than six litres of gas.

A bad pour can let the fizz out too quickly, says Liger-Belair. He recommends a gentle stream into a tilted glass to preserve bubbles. Pouring into the middle of a vertical flute will stir up the wine and release too much carbon dioxide immediately.

Even with such precautions, there is an initial rush of bubbles. University of Tokyo physicist Hiroshi Watanabe was part of a team that used supercomputers to model how quickly bubbles of different sizes form in liquids, and how the different sizes interact.

“After many bubbles appear at the moment of uncorking a champagne [bottle], the population of bubbles starts to decrease,” Watanabe said in an interview with Smithsonian.com.

“Larger bubbles become larger by eating smaller bubbles, and finally only one bubble will survive.”

Bubbles are a vital part of the taste of champagne, say researchers from the Sorbonne University in Paris, France. As they burst, they throw droplets of wine into the air above the surface and enhance the drinking experience.

The scientists identified two mechanisms that produce droplets. First, as the surface of the bubble ruptures, it throws up dollops 50 times smaller than the radius of a hair. Then as the rounded bubble shape collapses, it sends up a jet of up to 10 slightly larger droplets.

“The tiny droplets ejected during bursting are crucial for champagne tasting as their evaporation highly contribute to the diffusion of wine aroma in air,” said Elisabeth Ghabache and her colleagues in a paper in the journal Physics of Fluids.

There’s been much debate about how champagne should be served. Some insist on a narrow flute, while others prefer a wide coupe.

Liger-Belair does not recommend the coupe, despite its claim to fame as being modelled on the left breast of French queen Marie Antoinette (or Napoleon’s wife Josephine, or model Kate Moss).

His gas chromatography and infrared images showed that flutes funnelled the aroma-carrying carbon dioxide more effectively into the headspace above the glass where the drinker can inhale it. But carbon dioxide’s acidic nature is actually an irritant if the concentration is too high, so Liger-Belair recommends the middle ground, a tulip shaped wine glass.

Exactly how the flavours interact with the nose and taste buds is a very individual thing. So the scientific thing to do – even if you don’t have infrared cameras and a gas chromatography set up – is to emulate Liger-Belair at your next celebration and perform your own experiments, one glass at a time.

Continue Reading Bubbles! The Physics of Champagne

Quantum pancake reveals clues to better electronics

First published on Cosmos Magazine site, 25/9/18

An experiment with a cloud of ultracold atoms squashed into a quantum pancake has revealed never-before seen quantum effects that could lead to more efficient electronics, including high temperature superconductors.

A team at Swinburne University in Australia observed a quantum anomaly in lithium-6 gas cooled to a few billionths of a degree above absolute zero and squashed between two laser beams.

“We’re seeing quantum mechanics that’s visible on a macroscopic scale – a large collection of tens of thousands of atoms all behaving quantum mechanically,” says project leader Chris Vale, a researcher at Swinburne’s Centre of Excellence in Future Low-Energy Electronics Technologies.

The team’s work is published in the journal Physical Review Letters, concurrently with that of a team from Heidelberg in Germany which reported similar results.

The Australian team used laser beams focused into a flat plane to create a pancake of lithium-6 gas with a radius of 200 microns and the thickness of a single atom – around 500 nanometers. Then the researchers compressed the gas slightly with a magnetic field, to set it vibrating. Shining another laser from below, they measured the vibration frequency of the gas cloud by watching the shadow of the cloud on a camera.

The frequency of this radial vibration, known as a breathing mode, gave the telltale sign of a quantum anomaly: it vibrated 2.5% faster than the classical model predicted.

Symmetry in the classical model dictates that gas properties such as pressure and density should scale in a straightforward way as the size of the gas cloud oscillates. But the full quantum analysis predicts a higher frequency: the classical theory breaks down because of strong interactions between the gas particles.

To further test the model, the scientists jammed more atoms between the laser beams, and turned the pancake from a two-dimensional crepe into a fatter flapjack. Its three-dimensional nature conformed to the classical model.

Vale says the interactions between the gas particles in the quantum crepe was mid-way between two well-known states of matter: Bose-Einstein condensates, in which atoms in a gas interact strongly and exhibit uniform quantum behaviour, and low temperature superconductivity, in which electrons in a material form weakly-bound pairs known as Cooper pairs that can carry electricity through a material with no energy loss.

“There’s a continuous crossover between these two limits, what happens in the middle is not well understood,” he says

“There’s a lot of interesting physics there. For example, this is where we find the highest superfluid transition temperatures, in the intermediate zone where the binding energy of the fermion pairs is similar to the natural energy scale for the system, the Fermi energy.”

By studying a two-dimensional system, Vale hopes to spark developments of new materials for the electronics industry, for example topological insulators or high-temperature superconductors.

In the current highest-temperature superconductors, ceramics based on copper oxide, the superconducting current is carried in two-dimensional layers within the material – although exactly how the electrons pair up is not fully understood.

The power of the experiments at Swinburne is their simplicity, says Vale – the microscopic properties of the lithium atoms and their interactions are precisely known, which is not always possible in more complex materials such as solids.

“In a sense, our cold atoms are acting as a quantum simulator, where we can test models of many-body physics with precisely known inputs that can be difficult to pin down in other materials,” he says.

Continue Reading Quantum pancake reveals clues to better electronics

Wave of the Century

 Originally published in ANU Reporter. 

The discovery of gravitational waves is the culmination of a search by a generation of ANU physicists, reports DR PHIL DOOLEY, BSc (Hons) ’90, PhD ’99.

An excited hush fell over the briefing room at Parliament House as Professor David McClelland stepped up to the microphone.

“I’m pretty sure you all know by now but I want to say it. We’ve done it,” he said as his voice quavered.

Spontaneous applause broke out, as McClelland allowed himself a smile. Camera flashes popped and TV cameras zoomed in.

“We detected a gravitational wave that was generated 1.3 billion years ago when two black holes crashed into each another… the most violent event ever witnessed.”

The announcement was sweet reward for McClelland, an ANU laser physicist who has spent his career working towards this moment.

Albert Einstein predicted the existence of gravitational waves but thought they were too small for humans to ever detect.

To prove Einstein wrong and right in a single stroke is rare treat for a scientist.

“This is a moment that will be remembered for a thousand years,” McClelland said.

Gravitational waves are vibrations of space and time themselves, one of the most outlandish predictions of Einstein’s 1916 General Theory of Relativity. Yet, they appeared exactly as predicted and join the long list of successes of Einstein’s theory over the last century.

The first success of Relativity came three years after Einstein’s publication, when a solar eclipse allowed astronomers to pick out the tiny deflection of distant starlight by the sun’s gravity.

In 1990, at the ANU Physics Department, McClelland and Emeritus Professor Hans Bachor AM gathered people from across the world to assess the challenges of that dream.

The microscopic effect was exactly what Einstein’s revolutionary concept of space and time that was warped by huge masses predicted. The charismatic genius became a superstar overnight.

Einstein’s vision of stretchy space was not just static, it also predicted large masses moving or colliding would make waves through space, effectively a spacequake.

To make a gravitational wave of any significance needs a cataclysmic event happening to a huge mass, a star exploding or black holes colliding.

But such events are rare and unlikely to happen close to Earth, so scientists need to extend their search beyond our galaxy.

25 years of chasing Einstein’s theory

 

It would be 75 years before physicists would dare dream of looking for gravitational waves.

In 1990, at the ANU Physics Department, McClelland and Emeritus Professor Hans Bachor AM gathered people from across the world to assess the challenges of that dream.

One-by-one, a who’s who of gravitational wave specialists laid out the seemingly impossible tasks.

The basic concept was clear: a stable laser beam bouncing between mirrors in a vacuum.

When a gravitational wave came past and warped the space between the mirrors, it would momentarily disturb the stability of the laser.

Surpassing scientific challenges

But the practicalities were not so simple.

“Everything needed to be roughly a factor of 1000 more powerful or sensitive than we had at the time,” Bachor recalls.

Laser technology was weak. Nobody knew how to build a good enough mirror, it had to be massive and perfectly smooth, and with losses less than one part in a billion.

The experiment would need to be enormous, preferably 10 or more kilometres long.

Damping out vibrations from the environment was another huge challenge. The smallest earth tremor, or a passing truck, threatened to obliterate the tiny ripples from distant spacequakes.

But they didn’t know the size and shape of the ripples they were searching for, says Professor Susan Scott, from the Research School of Physics and Engineering (RSPE).

“We really had no idea of the enormity of the task which lay ahead of us. We were searching for a needle in a cosmic haystack, extremely faint signals in very noisy data.

“We had early meetings with submarine intelligence experts but we quickly realised we were facing a much more daunting task than theirs,” she said.

But, as in 1916, the scientists were not discouraged.

“The amazing thing was that the mood at the end of the conference was ‘Let’s go for it,’ ” Bachor says.

“We were eternal optimists. These people were pioneers who had seen the progress over the previous 20 years. We trusted that the technology would evolve.”

The start of a technological revolution

But political realities posed a big obstacle to progress.

The Russians quickly realised they could not afford to build an experiment.

The UK could not find the land and teamed up with Germany to build a smaller experiment, GEO 600, only 600 metres long. Japan set up small experiments in disused mines.

Australia had the land but lost out on funding against stiff competition from more developed astronomy projects, such as the Square Kilometre Array, which could guarantee data.

The gravitational astronomy world’s hopes lay with the two four-kilometre long experiments at the Laser Interferometer Gravitational-Wave Observatory (LIGO) at either end of the US, and the French-Italian Virgo project.

The nations apportioned the tasks, and set to work.

Over the next 20 years technological revolution after technological revolution achieved the impossible.

Joining the hunt as an honours student in 1996, Daniel Shaddock, was dismayed by the challenge.

“When I first heard about the sensitivity needed for gravitational waves, I thought that’s crazy, we’re never going to see them,” said Shaddock, now a professor in the RSPE.

“But you start working through the challenges and before you know it, you’re in a position where you have the measurement technology that you need.”

Also drawn to the quest was Dutch student Bram Slagmolen, who travelled around the globe in 1999 to work with McClelland.

“We’ve done things I wouldn’t have dreamed of back then,” says Slagmolen, now a research fellow at ANU and the leader of the Australian Consortium for Interferometric Gravitational Astronomy.

“Although the final experiment would be on a large scale and hideously complex, we ran little experiments that gave us understanding and allowed us to go the next step.”

In Italy, the Virgo experiment was dogged by technical hitches, but by mid-2015, LIGO scientists – including many Australians led by McClelland – believed their twin US experiments could start, and flicked on the many systems required to isolate Einstein’s elusive echoes of intergalactic impacts.

The Universe delivers an extraordinary result

Then the Universe delivered something truly extraordinary.

The team had estimated they might have to spend a couple of years sifting through their data to find matched sets of tiny wobbles from outer space.

But while they were still doing final tests with simulated data, still days away from the first official science run, the detector twanged with a signal so clear that the team could see it above the background without any filtering.

“The signal matched perfectly to the predicted pattern of two black holes colliding, but it was so strong we thought it must be a blind injection of a simulated signal, ” Scott says.

“We were aware very quickly that this was not the case and so this signal that had thundered into our detectors was probably real, and from surprisingly large black holes.”

A long time ago in a galaxy far, far away, there had been an invisible collision that had unleashed more energy than any other event humans had witnessed.

The peak power had been 50 times that of total output of every star in the visible universe.

There was no accompanying flash of an explosion.

After a trip of 1.3 billion years across the cosmic pond, the ripples had died down so much that they moved LIGO’s mirrors by about one thousandth of the diameter of a proton.

The signal was imperceptible to normal humans but clear as a bell in the detector in Louisiana and then, seven milliseconds later, in the Washington State detector.

Just the beginning of gravitational wave physics

McClelland’s search is not over now their tool is working.

“This is just the beginning,” he says.

“It’s like the moment when Galileo first turned a telescope towards the skies and started a new epoch of astronomy. Here we shall begin a whole new and fundamentally different way of observing the Universe.”

Bram Slagmolen was jubilant.

“I was always convinced we would see them, it was just a question of when,” he says.

“We’ll definitely see more now, by the end of the year we should have multiple detections, in the bag, it will be fabulous for the whole community.”

Aside from observing the antics of invisible black holes, gravitational waves help scientists see further back in time than conventional astronomy, says Professor Scott.

“This is a big deal. One of our holy grails is to understand the beginning of the Universe.”

And so another search begins.

Continue Reading Wave of the Century

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