Tag Archives: absolute zero

Scientists chill LEGO bricks to nearly absolute zero

Credit: University of Lancaster.

LEGOs have always found their use in cool scientific experiments, but new developments from Lancaster University in the UK took things to a whole new level. Using a sophisticated setup, the researchers chilled LEGO bricks extremely close to absolute zero (the coldest temperature possible) and, in the process, gained useful insights that might one-day help us build better quantum computers.

Brick by brick

Quantum computers are machines that operate on qubits or quantum bits, rather than classical bits (1s or 0s). By exploiting the quirky nature of quantum mechanics, such machines are able to encode information in 1s, 0s, or both states at the same time. This allows quantum computers to perform computations orders of magnitude more complex than a classic computer is capable of doing.

Two-qubits can perform operations on four values, three on eight values and so on in powers of two. Today’s computers have millions of transistors. Now imagine a quantum logic gate that works with millions of qubits. The computing force would be unheard of.

In October, Google made a controversial announcement, claiming its machines have reached “quantum supremacy” — a term that describes crossing the threshold where quantum computers can do things that conventional computers cannot.

The main challenge that quantum computers face is qubits failing due to decoherence caused by vibrations, temperature fluctuations, electromagnetic waves and other interactions with the outside environment, which ultimately destroys the exotic quantum properties of the computer.

This is why quantum computers are such cumbersome machines — they require a huge setup that involves pumps, compressors, and liquid nitrogen in order to chill things close to absolute zero.

But, where do LEGOs fit into all this? As it so happens, LEGOs have thermal properties that make them highly appealing for insulating a quantum computer’s components.

In an experiment, physicists at the University of Lancaster stacked four LEGOs and introduced them in a special refrigerating device that mixes two helium isotopes to generate ultra-cold temperatures.

The bottom of the stack was placed right where the isotopes mix while the top brick was fitted with a small heater and thermometer.

The bottom LEGOs were exposed to frigid temperatures ranging from 70 milliKelvin to 1.8 Kelvin — up to thousands of times colder than outer space.

Despite the ultra-cold temperature, heating the top LEGO brick barely changed the temperature of the bottom brick, making LEGOs extremely good thermal insulators. In fact, they performed better than some of the most expensive plastics on the market used for this purpose, the researchers reported.

All of this doesn’t mean that we’ll see LEGO bricks in quantum computers any time soon (or who knows, really?). Instead, the insights gained by the study could be used to design insulators that are custom made for perfect integration with the demands of quantum computing.

“This work suggests that custom-built modular materials with even better thermal performance could be readily and cheaply produced by 3D printing,” the authors wrote.

The findings were reported in the journal Scientific Reports.

This microscopic vibrating drum was, at one point, colder than anything found in nature. Credit: Teufel/NIST

Tiny aluminium drum cooled beyond quantum limit proves we can make things even colder. Possibly down to absolute zero

This microscopic vibrating drum was, at one point, colder than anything found in nature. Credit: Teufel/NIST

This microscopic vibrating drum was, at one point, colder than anything found in nature. Credit: Teufel/NIST

Nothing can be chilled below absolute zero ( −273.15°C) because at this temperature all molecular motion stops completely. Per Heisenberg’s uncertainty principle the forces of real particle velocities will always be above zero. It’s a fundamental limit that can’t seem to be broken. That’s fine just fine — what bothers scientists, however, are other limits that keep them from cooling things near absolute zero.

For decades, researchers have used lasers to cool down atoms very close to absolute zero. However, when you try to cool close to zero something macroscopically, like a power cable or even a coin, you get hit by a brick wall — a ‘quantum limit’ that keeps mechanical objects from getting too cold.

Physicists from the National Institute of Standards and Technology (NIST) weren’t sure that this is a fundamental limit and good thing they experimented because their findings suggest macroscopic objects can be cooled more than previously thought possible.

[ALSO SEE] The minimum and maximum temperatures 

Using lasers, the NIST team cooled an aluminum drum to 360 microKelvin or 10,000 times colder than the vacuum of space. The tiny vibrating membrane is 20 micrometers in diameter and 100 nanometers thick. It’s the coldest thing we’ve ever seen that’s larger than a few atoms across.

“The colder you can get the drum, the better it is for any application,” said NIST physicist John Teufel, who led the experiment. “Sensors would become more sensitive. You can store information longer. If you were using it in a quantum computer, then you would compute without distortion, and you would actually get the answer you want.”

“The results were a complete surprise to experts in the field,” Teufel’s group leader and co-author José Aumentado said. “It’s a very elegant experiment that will certainly have a lot of impact.”

Everyone’s familiar with lasers but firing lasers to cool stuff? It sounds counter-intuitive because we all know lasers warm targets — but that’s if you fire all of the light. The kind of lasers used for cooling fire at a specific angle and frequency. Typically multiple lasers are used. As a result of this clever tweaking photons actually end up snatching energy from its target instead of releasing it, and it’s all done by literally pushing the atoms.

Confused? It gets elementary once you understand or remember what temperature actually is — the motion of atoms. That’s it. When we feel warm, atoms are whizzing past us faster. When it’s cold outside, the molecules in the air are moving slower. So, what scientists do when they fire lasers is they push these atoms in the opposite direction of their motion. As the photon gets absorbed by the target atom(s), the photon’s momentum is transferred.

Laser pulses, however, like any light,  fires in discrete packets of energy called quanta. This means there’s a gap between packets which gives atoms the time to resume motion. That’s how light works and quantum mechanics seems to suggest there’s an upper limit. Previously, NIST researchers used sideband-cooling to limit the thermal motion of a microscopic aluminum membrane that vibrates like a drumhead to one-third the amount of its quantum motion.

The NIST researchers took laser cooling a step further by using ‘squeezed light’ — light that’s more organized in one direction than any other. By squeezing light, the noise, or unwanted fluctuations, is moved from a useful property of the light to another aspect that doesn’t affect the experiment. The NIST team used a special circuit to generate microwave photons that were purified or stripped of intensity fluctuations, which reduced inadvertent heating of the drum.

“Noise gives random kicks or heating to the thing you’re trying to cool,” Teufel said. “We are squeezing the light at a ‘magic’ level—in a very specific direction and amount—to make perfectly correlated photons with more stable intensity. These photons are both fragile and powerful.”

The NIST paper published in Nature seems to suggest squeezed light removes the generally accepted cooling limit. Teufel says their proven technique can be refined to make things even cooler — possible even to exactly absolute zero. And that, ladies and gentlemen, is the coolest thing you’ll hear today.

“In principle if you had perfect squeezed light you could do perfect cooling,” he told the Washington Post. “No matter what we’re doing next with this research, this is now something we can keep in our bag of tricks to let us always start with a colder and quieter and better device that will help with whatever science we’re trying to do.”

Researchers create coldest molecules – colder than interstellar space

MIT researchers have managed to create incredibly cold molecules, much colder than even interstellar space. In this new experiment, sodium potassium (NaK) molecules were brought down to 500 nanokelvins, just a touch more than 0 Kelvin – the absolute lowest possible temperature.

Martin Zwierlein

Absolute zero is the lower limit of the thermodynamic temperature scale –  −273.15° on the Celsius scale, which equates to −459.67° on the Fahrenheit scale. The laws of thermodynamics dictate that absolute zero cannot be reached using only thermodynamic means, but researchers have been able to cool things close to absolute zero. This MIT experiment was led by physicist Martin Zwierlein, and showed that contrary to common behavior of energy, these molecules are still very energetic when cooled down to extreme temperatures. It also broke the record for the coldest molecules ever created. The currently attained temperature knocks the previous record by a factor of 10!

“We are very close to the temperature at which quantum mechanics play a big role in the motion of molecules,” said Martin Zwierlein, one of the researchers, in a news release. “So these molecules would no longer run around like billiard balls, but move as quantum mechanical matter waves. And with ultracold molecules, you can get a huge variety of different states of matter, like superfluid crystals, which are crystalline, yet feel no friction, which is totally bizarre. This has not been observed so far, but predicted. We might not be far from seeing these effects, so we’re all excited.”

The created molecules did not interact with others at all and exhibited robust dipole moments which acts as the distributions of electric charges in a molecule that directs the way they attract or repel other molecules. Even with simple molecules, you can get some extremely strange properties when you get them ultracooled. Zwierlein said:

“With ultracold molecules, you can get a huge variety of different states of matter, like superfluid crystals, which are crystalline, yet feel no friction, which is totally bizarre. This has not been observed so far, but predicted. We might not be far from seeing these effects, so we’re all excited.”

Sodium potassium was chosen for the experiment because it is representative for a large class of simple molecules. The structure is made of just two atoms, bound together like in a dumbbell-like fashion.

Journal Reference: Jee Woo Park, Sebastian A. Will, and Martin W. Zwierlein. Ultracold Dipolar Gas of Fermionic Na23K40 Molecules in Their Absolute Ground State. Phys. Rev. Lett. 114, 205302

In this artist's illustration, the NaK molecule is represented with frozen spheres of ice merged together: the smaller sphere on the left represents a sodium atom, and the larger sphere on the right is a potassium atom. Illustration: Jose-Luis Olivares/MIT

Scientists cool molecules just a hair over absolute zero (1,000,000 times colder than space)

In a breakthrough moment, researchers at MIT successfully cooled sodium potassium gas molecules (NaK) near absolute zero. At this temperature, matter behaves significantly different and starts exhibiting quantum effects. This is the coldest any molecule has been measured so far.

In this artist's illustration, the NaK molecule is represented with frozen spheres of ice merged together: the smaller sphere on the left represents a sodium atom, and the larger sphere on the right is a potassium atom.  Illustration: Jose-Luis Olivares/MIT

In this artist’s illustration, the NaK molecule is represented with frozen spheres of ice merged together: the smaller sphere on the left represents a sodium atom, and the larger sphere on the right is a potassium atom.
Illustration: Jose-Luis Olivares/MIT

Normally, at ambient temperature, molecules zip by at colossal speeds, colliding and reacting with each other. There probably are millions of such collisions happening every moment in the air you breath. When matter gets really cold though, its movements near to a halt as it’s chilled closer and closer to absolute zero (0 Kelvin or -273.15 degrees Celsius). Other strange things start happening as well. For instance, when Helium is cooled down to near zero the substance (a gas at room temperature) turns into a liquid with no viscosity – a superfluid. But it’s a lot easier to cool single atoms, like He, than molecules, which comprise two or more atoms linked by electromagnetic forces.

Molecules are a lot more complicated since they exhibit more complex degrees of freedom:  translation, vibration, and rotation. So, cooling the molecules directly is challenging, if not impossible with current means. To cool the sodium potassium gas, the researchers had to employ multiple steps. First, the MIT team used lasers and evaporative cooling to cool clouds of individual sodium and potassium atoms to near absolute zero. Typically, sodium and potassium don’t form compounds because they repel each other. However, the researchers “glued” them together by prompting the atoms to bond with an electromagnetic field. This mechanism is known as “Feshbach resonance.”

The resulting bond, however, is very weak – a “fluffy molecule”, as the researchers call it. To bring the atoms closer together, and strengthen the bond as a consequence, the researchers employed a novel technique used previously  in 2008 by groups from the University of Colorado, for potassium rubidium (KRb) molecules, and the University of Innsbruck, for non-polar cesium­ (Ce) molecules. Yet again, the weak molecules were exposed to a pair of laser pulses, the large frequency difference of which exactly matched the energy difference between the molecule’s initial, highly vibrating state, and its lowest possible vibrational state. The sodium potassium molecule absorbed the lower energy from one laser and emitted energy to the higher-frequency laser. So, what the MIT researchers got at the end were very low energy state, ultra-cold molecules sitting as low as 500 nanoKelvins or just billionths of a degree above absolute zero.

The resulting ultra-cool molecules were quite stable, with a relatively long lifetime, lasting about 2.5 seconds. The molecules also exhibited very strong dipole moments — strong imbalances in electric charge within molecules that mediate magnet-like forces between molecules over large distances. Concerning their speed, at such a cool temperature, the molecules average speeds of centimeters per second and are almost at their absolute lowest vibrational and rotational states.

“In the case where molecules are chemically reactive, one simply doesn’t have time to study them in bulk samples: They decay away before they can be cooled further to observe interesting states,” says Martin Zwierlein, professor of physics at MIT and a principal investigator in MIT’s Research Laboratory of Electronics. “In our case, we hope our lifetime is long enough to see these novel states of matter.”

The next step is cooling the molecule even further to maybe catch a glimpse of the quantum mechanical effects that are predicted should happen.  Findings appeared in the journal Physical Review Letters.

“We are very close to the temperature at which quantum mechanics plays a big role in the motion of molecules,” Zwierlein says. “So these molecules would no longer run around like billiard balls, but move as quantum mechanical matter waves. And with ultracold molecules, you can get a huge variety of different states of matter, like superfluid crystals, which are crystalline, yet feel no friction, which is totally bizarre. This has not been observed so far, but predicted. We might not be far from seeing these effects, so we’re all excited.”

edit: missed a very important “minus” sign for the absolute zero temperature value in Celsius (-273.15 degrees Celsius)

Harvard and MIT scientists create photon molecules

Photons and molecules

Mikhail Lukin - image via Harvard.

Mikhail Lukin – image via Harvard.

Scientists managed to ‘trick’ photons (the elementary particles of light and all other forms of electromagnetic radiation) into forming molecules for the first time – a state of matter that until recently had been purely theoretical.

Scientists from Harvard University and the Massachusetts Institute of Technology (MIT) are challenging the current paradigm – they want physicists to rethink what they know about light, and they didn’t have to go in another galaxy to do this.

What happened is that a group led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic managed to coax photons into binding together to form molecules. The discovery goes against decades of accepted theories and ideas on light. Photons have constantly been described as massless particles that don’t interact with each other (they are only considered to have a mass when they are moving). Shine two photon lasers at each other, and the rays will simply pass through each other – photonic molecules seems a nonsensical term.“Most of the properties of light we know about originate from the fact that photons are massless, and that they do not interact with each other,” Lukin said. “What we have done is create a special type of medium in which photons interact with each other so strongly that they begin to act as though they have mass, and they bind together to form molecules. This type of photonic bound state has been discussed theoretically for quite a while, but until now it hadn’t been observed.

What they did isn’t really a photon laser, but rather a… light saber.

Using the Force

"Photonic molecules" behave less like traditional lasers and more like something you might find in science fiction -- the light saber. (Credit: © Yana / Fotolia)

“Photonic molecules” behave less like traditional lasers and more like something you might find in science fiction — the light saber. (Credit: © Yana / Fotolia)

“It’s not an inapt analogy to compare this to light sabers,” Lukin said. “When these photons interact with each other, they’re pushing against and deflecting each other. The physics of what’s happening in these molecules is similar to what we see in the movies.”

But Harvard researchers can’t really rely on “The Force”, so instead, they began by pumping rubidium atoms into a vacuum chamber. After a while, they used lasers to cool the cloud of atoms to just a few degrees above absolute zero (the lowest thermodynamic temperature – −273.15° on the Celsius scale, −459.67° on the Fahrenheit scale). Then, using very weak lasers, they fired single photons into the cloud of atoms. As the photons enter the cloud, they give energy to atoms along their path, which causes them to slow dramatically. As the photons move through the cloud, that energy is handed off from atom to atom, and eventually exits the cloud with the photon.

“When the photon exits the medium, its identity is preserved,” Lukin said. “It’s the same effect we see with refraction of light in a water glass. The light enters the water, it hands off part of its energy to the medium, and inside it exists as light and matter coupled together. But when it exits, it’s still light. The process that takes place is the same. It’s just a bit more extreme. The light is slowed considerably, and a lot more energy is given away than during refraction.”

But when Lukin and his colleagues fired two photons into the cloud, they were really surprised to see the results – the two photons came out of the cloud together, as a single molecule. This is the effect of a rather strange and unintuitive effect, called the Rydberg blockade, which means that when an atom is excited, nearby atoms cannot be excited to the same degree. What this means for this case in particular, is that as the first photon excites an atom, it must move forward before the second one can excited nearby atoms. What’s interesting is that they tend to retain this molecule-like behavior even after exiting the cloud.

 

Photons with strong mutual attraction in a quantum nonlinear medium. Credit: Nature.
Photons with strong mutual attraction in a quantum nonlinear medium. Credit: Nature.

 This could prove to be valuable for developing quantum computers; quantum logic requires interactions between individual quanta so that quantum systems can be switched to perform information processing.

“What we demonstrate with this process allows us to do that,” Lukin said. “Before we make a useful, practical quantum switch or photonic logic gate, we have to improve the performance. So it’s still at the proof-of-concept level, but this is an important step. The physical principles we’ve established here are important.”

The process could be used in the future to create 3D structures, such as crystals, solely out of light.

“What it will be useful for we don’t know yet. But it’s a new state of matter, so we are hopeful that new applications may emerge as we continue to investigate these photonic molecules’ properties,” he said.

Scientists reproduce conditions from early universe

Physicists have successfully reproduced a pattern resembling the cosmic microwave background radiation in an experiment which used ultracold cesium atoms in a vacuum chamber. This is the first experiment which recreates at least some of the conditions from the Big Bang.

“This is the first time an experiment like this has simulated the evolution of structure in the early universe,” said Cheng Chin, professor in physics. Chin and his associates reported their feat in the Aug. 1 edition of Science Express, and it will appear soon in the print edition of Science.

universe big bang

The cosmic microwave background radiation (CMB or CMBR) is basically the thermal radiation left over from the Big Bang. It is very interesting for astrophyicists because it apparently exhibits a large degree of uniformity throughout the entire universe (it has more or less the same values everywhere you look for it). If you analyze the “void” between stars and even galaxies with a sufficiently sensitive radio telescope, you’ll see a faint background glow, almost exactly the same in all directions, that is not associated with … anything. The glow has the most energy in the microwave spectrum. Its rather serendipitous discovery took place in 1964, and it earned its finders a Nobel prize in 1978.

You can think of this radiation as the echo of the Big Bang – by studying it, we get a somewhat clear idea how the Universe looked some 380,000 years following its ‘birth’ – incredibly early; it doesn’t go much before or after, it’s basically a snapshot of the past. But as it turns out, under certain conditions, a cloud of atoms chilled to a billionth of a degree above absolute zero in a vacuum chamber displays phenomena similar to those which followed the big bang.

“At this ultracold temperature, atoms get excited collectively. They act as if they are sound waves in air,” he said.

This neatly correlates with what cosmologists speculated:

“Inflation set out the initial conditions for the early universe to create similar sound waves in the cosmic fluid formed by matter and radiation,” Hung said.

big bang

The tiny universe which was simulated in Chin’s laboratory measured no more than 70 microns across (about as big as a human hair) – but the physics is the same regardless of the size of your universe.

“It turns out the same kind of physics can happen on vastly different length scales,” Chin explained. “That’s the power of physics.”

But there is an important difference – and one that works greatly to our advantage:

“It took the whole universe about 380,000 years to evolve into the CMB spectrum we’re looking at now,” Chin said. But the physicists were able to reproduce much the same pattern in approximately 10 milliseconds in their experiment. “That suggests why the simulation based on cold atoms can be a powerful tool,” Chin said.

If you want, you can think of the Big Bang in oversimplified terms as an explosion which made a big BOOM! These sound waves began interfering with each other creating complicated patterns – the so-called Sakharov acoustic oscillations.

“That’s the origin of complexity we see in the universe,” he said.

This is indeed a powerful tool to find out more about our infant universe, but this is just the first step. Chin and his team plan to move on to use these Sakharov oscillations to study the property of this two-dimensional superfluid at different initial conditions, then cross check their results with what is observed by cosmologists. They will use the same type of experiment but branch out to other fields of cosmology, including the formation of galaxies and even black hole dynamics.

“We can potentially use atoms to simulate and better understand many interesting phenomena in nature,” Chin said. “Atoms to us can be anything you want them to be.”

Interestingly enough, nobody on this team was a cosmologist.

Journal Reference: C.-L. Hung, V. Gurarie, C. Chin. From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in a Quenched Atomic Superfluid. DOI: 10.1126/science.1237557

Physicists create negative temperature state – thermodynamic laws still stand

Well, the year really kicked off in style. This research is really next level physics, and in order to understand it (even slightly), we’re going to delve into some serious physics.

Dancing around absolute zero

quantum gas 0Over the years, physicists have made significant progress in cooling objects closer to absolute zero (0 Kelvin, the temperature at which all molecular motion stops because there is no energy in the classical sense. Absolute zero is the absolute zero, and you can’t reach it, so ultimately, you are limited. So how can you go below 0 Kelvin?

First of all, you have to understand that thermodynamics doesn’t define temperature as a physical parameter, but rather as a statistic of the energy distribution present so basically, you can create crazy temperatures with unusual distributions. Therefore, it is theoretically possible to have a negative value – just note that for this particular case, as weird as it would seem, negative doesn’t mean lower than zero. So how did they do it?

Well, you first want to bring the gas to almost zero temperature;  two concepts appear here: laser trapping and evaporative cooling. Basically, you have a flow of atoms running around in one direction. You point a laser exactly at them, in the opposite direction. Just like you would try running against a stream or a very powerful wind, the atoms are slowed down, stopped, or even pushed backwards. Then you put another laser in their original flow direction to even it out, and they are practically stuck. Do the same thing from up and down lasers, and you’ve trapped the atoms which are now stuck in your trap. That’s when evaporative cooling kicks in. Now remember, the temperature of the atoms is dependant strictly on their energy, so if we could somehow remove the high-state energy atoms, then we would be left only with the lower energy ones – the temperature would drop, and so would the temperature. To do this, researchers loosen the trap just a tiny bit – that way, the higher energy atoms can escape. Rinse and repeat, loosening it more and more, until you are stuck with only the low energy atoms and the low temperature. The thing is, even an extremely low amount of energy is some energy, so you can’t really do it until you reach 0 K(elvin). This is what researchers typically use when they want to drop temperatures close to 0, but in order to go negative, you have to use something different.

The physics

In a negative temperature system, temperatures get lower as more atoms pile up close to its maximum energy.

In a negative temperature system, temperatures get lower as more atoms pile up close to its maximum energy.

Again, many sites and magazines, even high quality ones are dancing around the issue here, so I’d like to underline it again: having negative temperatures on the Kelvin scale and going below absolute zero are not the same thing. In fact, they are fundamentally different.

Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany reached such sub-zero temperatures; after bringing them to extremely low temperatures, they used an ultracold quantum gas made up of potassium atoms, using lasers and magnetic fields to keep the individual atoms in a lattice arrangement. At positive temperatures, the atoms repel, making the configuration stable. The team then quickly adjusted the magnetic fields, causing the atoms to attract rather than repel each other – causing a major shift in the atoms.

“This suddenly shifts the atoms from their most stable, lowest-energy state to the highest possible energy state, before they can react,” says Schneider. “It’s like walking through a valley, then instantly finding yourself on the mountain peak.”

Wait, what? Here’s a relatively layman explanatiopn that I hope will clarify things. For a typical material with positive temperature, adding energy in the form of heat makes it more disordered, incerasing its entropy. Entropy can be loosely defined as a measure of the chaos in the system, so imagine this system. Say you have a system with equally equivalent atoms, all of which are in a low energy state (pretty much all systems have most atoms in low energy states). The system is perfectly ordered. Now, say you give the system just enough energy to lift one atom to a superior energy state; the entropy has increased – you have no way of telling which atom will rise, and the system suddenly becomes more chaotic, disordered. But say you somehow manage to create a system where all atoms but one are in a high energy state; when you add the same amount of energy, your system will become more ordered, as you know exactly which atom will rise, and you’ll again have a perfectly ordered system. That’s the thing here; if you give energy to a system it will become more and more disordered, up until a point where giving it energy will actually make it more ordered.

The team’s result marks the transition from just above absolute zero to a few billionths of a Kelvin below absolute zero.

Peculiarities

The whole idea is counter intuitive and requiers a firm understanding of thermodynamic principles to grasp, so it’s a little quirky to talk about what’s peculiar here, but what is just down right strange is that sub zero gases mimic ‘dark energy‘ – the mysterious form of energy which pushes and expands our Universe faster and faster, against the Universe’s own gravity.

“It’s interesting that this weird feature pops up in the Universe and also in the lab,” Schneider says. “This may be something that cosmologists should look at more closely.”