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Manu jumping: the physics of making a bigger splash

From the Global Physics Summit in Anaheim, California

The greatest pleasure of being at a huge physics conference is learning about the science of something that’s familiar, but also a little bit quirky. That’s why I always try to go to sessions given by undergraduate students, because for some reason they seem to do research projects that are the most fun.

I was not disappointed by the talk given this morning by Atharva Lele, who is at the Georgia Institute of Technology here in the US. He spoke about the physics of manu jumping, a competitive sport that originates from the Māori and Pasifika peoples of New Zealand.

The general idea will be familiar to anyone who messed around at swimming pools as a child: who can make the highest splash when they jump into the water.

Cavity creation

According to Lele, the best manu jumpers enter the water back first, creating a V-shape with their legs and upper body. The highest splashes are made when a jumper creates a deep and wide air cavity that quickly closes, driving water upwards in a jet – often to astonishing heights.

Lele and colleagues discovered that a 45° angle between the legs and torso afforded the highest splashes. This is probably because this angle results in a cavity that is both deep and wide. An analysis of videos of manu jumpers revealed that the best ones entered the water at an angle of about 46°, corroborating the teams findings. This is good news for jumpers, because there is risk of injury at higher angles (think belly flop).

Another important aspect of the study looked at what jumpers did when they entered the water – which is to roll and kick. To study the effect of this motion, the team created a “manu bot”, which unfolded as it entered the water. They found that there was an optimal opening time for making the highest splashes – it is a mere 0.26 s.

I was immediately taken back to my childhood in Canada and realized that we were doing our own version of manu from the high diving board at the local pool. The most successful technique that we discovered was to keep our bodies straight, but entering the water at an angle. This would consistently produce a narrow jet of water. I realize now that by entering the water at an angle, we must have been creating a relatively deep and wide cavity – although probably not as efficiently and manu jumpers. Maybe Lele and colleagues could do a follow-up study looking at alternative versions of manu around the world.

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Innovative Dutch Technology Captures Historic Image of Mars and Deimos During ESA’s Hera Mission flyby

cosine logo

The worldwide tech leading Dutch firm, cosine, is making a big impact in space exploration. The company is playing a key role in the European Space Agency’s (ESA) Hera mission […]

The post Innovative Dutch Technology Captures Historic Image of Mars and Deimos During ESA’s Hera Mission flyby appeared first on SpaceNews.

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Quantum behaviour in brain neurons looks theoretically possible

A new study probing quantum phenomena in neurons as they transmit messages in the brain could provide fresh insight into how our brains function.

In this project, described in the Computational and Structural Biotechnology Journal, theoretical physicist Partha Ghose from the Tagore Centre for Natural Sciences and Philosophy in India, together with theoretical neuroscientist Dimitris Pinotsis from City St George’s, University of London and the MillerLab of MIT, proved that established equations describing the classical physics of brain responses are mathematically equivalent to equations describing quantum mechanics. Ghose and Pinotsis then derived a Schrödinger-like equation specifically for neurons.

Our brains process information via a vast network containing many millions of neurons, which can each send and receive chemical and electrical signals. Information is transmitted by nerve impulses that pass from one neuron to the next, thanks to a flow of ions across the neuron’s cell membrane. This results in an experimentally detectable change in electrical potential difference across the membrane known as the “action potential” or “spike”.

When this potential passes a threshold value, the impulse is passed on. But below the threshold for a spike, a neuron’s action potential randomly fluctuates in a similar way to classical Brownian motion – the continuous random motion of tiny particles suspended in a fluid – due to interactions with its surroundings. This creates the so-called “neuronal noise” that the researchers investigated in this study.

Previously, “both physicists and neuroscientists have largely dismissed the relevance of standard quantum mechanics to neuronal processes, as quantum effects are thought to disappear at the large scale of neurons,” says Pinotsis. But some researchers studying quantum cognition hold an alternative to this prevailing view, explains Ghose.

“They have argued that quantum probability theory better explains certain cognitive effects observed in the social sciences than classical probability theory,” Ghose tells Physics World. “[But] most researchers in this field treat quantum formalism [the mathematical framework describing quantum behaviour] as a purely mathematical tool, without assuming any physical basis in quantum mechanics. I found this perspective rather perplexing and unsatisfactory, prompting me to explore a more rigorous foundation for quantum cognition – one that might be physically grounded.”

As such, Ghose and Pinotsis began their work by taking ideas from American mathematician Edward Nelson, who in 1966 derived the Schrödinger equation – which predicts the position and motion of particles in terms of a probability wave known as a wavefunction – using classical Brownian motion.

Firstly they proved that the variables in the classical equations for Brownian motion that describe the random neuronal noise seen in brain activity also obey quantum mechanical equations, deriving a Schrödinger-like equation for a single neuron. This equation describes neuronal noise by revealing the probability of a neuron having a particular value of membrane potential at a specific instant. Next, the researchers showed how the FitzHugh-Nagumo equations, which are widely used for modelling neuronal dynamics, could be re-written as a Schrödinger equation. Finally, they introduced a neuronal constant in these Schrödinger-like equations that is analogous to Planck’s constant (which defines the amount of energy in a quantum).

“I got excited when the mathematical proof showed that the FitzHugh-Nagumo equations are connected to quantum mechanics and the Schrödinger equation,” enthuses Pinotsis. “This suggested that quantum phenomena, including quantum entanglement, might survive at larger scales.”

Penrose and Hameroff have suggested that quantum entanglement might be related to lack of consciousness, so this study could shed light on how anaesthetics work,” he explains, adding that their work might also connect oscillations seen in recordings of brain activity to quantum phenomena. “This is important because oscillations are considered to be markers of diseases: the brain oscillates differently in patients and controls and by measuring these oscillations we can tell whether a person is sick or not.”

Going forward, Ghose hopes that “neuroscientists will get interested in our work and help us design critical neuroscience experiments to test our theory”. Measuring the energy levels for neurons predicted in this study, and ultimately confirming the existence of a neuronal constant along with quantum effects including entanglement would, he says, “represent a big step forward in our understanding of brain function”.

The post Quantum behaviour in brain neurons looks theoretically possible appeared first on Physics World.

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Global Physics Summit: this week, Anaheim is the hub of world physics

From the Global Physics Summit in Anaheim, California

I spent most of Saturday travelling between the UK and Anaheim in Southern California, so I was up very early on Sunday with jetlag. So just as the sun was rising over the Santa Ana Mountains on a crisp morning, I went for a run in the suburban neighbourhood just south of the Anaheim Convention Center. As I made my way back to my hotel, the sidewalks were already thronging with physicists on their way to register for the Global Physics Summit (GPS) – which is being held in Anaheim by the American Physical Society (APS).

The GPS combines the APS’s traditional March and April meetings, which focus on condensed-matter and particle and nuclear physics, respectively – and much more. This year, about 14,000 physicists are expected to attend. I popped out at lunchtime and spotted a “physics family” walking along Harbor Boulevard, with parents and kids all wearing vintage APS T-shirts with clever slogans. They certainly stood out from most families, many of which were wearing Mickey Mouse ears (Disneyland is just across the road from the convention centre).

Uniting physicists

The GPS starts in earnest bright and early Monday morning, and I am looking forward to spending a week surrounded by thousands of fellow physicists. While many physicists in the US  are facing some pretty dire political and funding issues, I am hoping that the global community can unite in the face of the anti-science forces that have emerged in some countries.

This year is the International Year of Quantum Science and Technology, so it’s not surprising that quantum mechanics will be front and centre here in Anaheim. I am looking forward to the “Quantum Playground”, which will be on much of this week. It promises, “themed areas; hands-on interactive experiences; demonstrations and games; art and science installations; mini-performances; and ask the experts”. I’ll report back once I have paid a visit.

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Magnetically launched atoms sense motion

Researchers in France have devised a new technique in quantum sensing that uses trapped ultracold atoms to detect acceleration and rotation. They then combined their quantum sensor with a conventional, classical inertial sensor to create a hybrid system that was used to measure acceleration due to Earth’s gravity and the rotational frequency of the Earth. With further development, the hybrid sensor could be deployed in the field for applications such as inertial navigation and geophysical mapping.

Measuring inertial quantities such as acceleration and rotation is at the heart of inertial navigation systems, which operate without information from satellites or other external sources. This relies on the precise knowledge of the position and orientation of the navigation device. Inertial sensors based on classical physics have been available for some time, but quantum devices are showing great promise. On one hand, classical sensors using quartz in micro-electro-mechanical (MEM) devices have gained widespread use due to their robustness and speed. However, they suffer from drifts – a gradual loss of accuracy over time, due to several factors such as temperature sensitivity and material aging. On the other hand, quantum sensors using ultracold atoms achieve better stability over long operation times. While such sensors are already commercially available, the technology is still being developed to achieve the robustness and speed of classical sensors.

Now, the Cold Atom Group of the French Aerospace Lab (ONERA) has devised a new method in atom interferometry that uses ultracold atoms to measure inertial quantities. By launching the atoms using a magnetic field gradient, the researchers demonstrated stabilities below 1 µm/s2 and 1 µrad/s for acceleration and rotation measurements over 24 hours respectively. This was done by continuously performing a 4 s interferometer sequence on the atoms for around 20 min to extract the inertial quantities. That is equivalent to driving a car for 20 min straight and knowing the acceleration and rotation to the µm/s2 and µrad/s level.

Cold-atom accelerometer–gyroscope

They built their cold-atom accelerometer–gyroscope using rubidium-87 atoms. By holding the atoms in a magneto-optical trap, the researchers cool them down to 2 µK, enabling good control over the atoms for further manipulation. By releasing the atoms from the trap, the atoms freely fall along the gravity direction. This allows the researchers to measure their free falling acceleration using atom interferometry. In their protocol, a series of three light pulses that coherently splits an atomic cloud into two paths, redirects and then recombines it allowing the cloud to interfere with itself. From the phase shift of the interference pattern, the inertial quantities can be deduced.

Measuring their rotation rates however, requires that the atoms have an initial velocity in the horizontal direction. This is done by applying a horizontal magnetic field gradient, which results in a horizontal force on atoms with magnetic moments. The rubidium atoms are prepared in one of the magnetic states known as the Zeeman sublevels. The researchers then use a pair of coils that they called the “launching coils” in the horizontal plane to create the necessary magnetic field gradient to give the atoms a horizontal velocity. The atoms are then transferred back to the ground non-magnetic state using a microwave pulse before performing atom interferometry. This avoids any additional magnetic forces that can affect interferometer’s outcome.

Analysing the launch velocity using laser pulses with tuned frequencies, the researchers are able to discriminate the velocity of the atoms whether it being from the magnetic launching scheme or other effects. The researchers observe two dominant and symmetric peaks associated to the velocity of the atoms due to the magnetic launching. However, they also observe a third smaller peak in between. This peak is due to an unwanted effect from the laser beams that transfers additional velocity to the atoms. Further improvement in the stability of the laser beams’ polarization – the orientation of its oscillating electric field with respect to its propagation axis, as well the current noise in the launching coils will allow for more atoms to be launched.

Using their new launch technique, the researchers operated their cold-atom dual accelerometer–gyroscope for two days straight, averaging down their results to obtain an acceleration measurement of 7×10−7 m/s2 and a rotation rate of 4×10−7 rad/s, limited by residual ground vibration noise.

Best of both worlds

While classical sensors suffer from long term drifts, they operate continuously in comparison to a quantum sensor that requires preparation of the atomic sample and the interferometry process which takes around half a second. For this reason, a classical–quantum hybrid sensor benefits from the long-term stability of the quantum sensor and the fast repetition rate of the classical one. By attaching a commercial classical accelerometer and a commercial classical gyroscope to the atom interferometer, they implemented a feedback loop on the classical sensor’s outputs. The researchers demonstrated a respective 100-fold and three-fold improvement on the acceleration and rotation rates stabilities, respectively, of the classical sensors compared to when they are operated alone.

Operating this hybrid sensor continuously and utilizing their magnetic launch technique, the researchers report a measure of the local acceleration due gravity in their laboratory of 980,881.397 mGal (the milligal is a standard unit of gravimetry). They measured Earth’s rotation rate to be 4.82 × 10−5 rad/s. Cross checking with another atomic gravimeter, they find their acceleration value deviating by 2.3 mGal, which they regard to be due to misalignment of the vertical interferometer beams. Their rotation measurement has a significant error of about 25%, which the team attributes to wave-front distortions for the Raman beams used in their interferometer.

Yannick Bidel, a researcher working on this project, explains how such an inertial quantum sensor has room for improvement. Large-momentum-transfer, a technique to increase the arm separation of the interferometer, is one way to go. He further adds that once they reach bias stabilities of 10−9 to 10−10 rad/s within a compact size atom interferometer, such a sensor could become transportable and ready for in-field measurement campaigns.

The research is described in Science Advances.

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