Ultracold Gases: Quantum Phenomena at Macroscopic Scales

By Dean Johnstone

In physics, it is common to expect the emergence of quantum effects at microscopic scales. Atoms and subatomic particles can behave both as a classical particle and quantum matter wave in accordance to Wave-particle duality. As such, all particles have a corresponding de-Brogile wavelength which depends on the mass and velocity of the particle. This wavelength can effectively be viewed as the spatial extent of the probabilistic, wavelike nature. Consequently, the small masses associated with microscopic particles means that their de-Brogile wavelength is sufficiently large compared to macroscopic objects, hence reflecting the appearance of quantum properties. For comparison, the de-Brogile wavelength of a snooker ball is about


times smaller than an electrons de-Brogile wavelength when moving at the same speed, which explains why objects above and at the macroscopic scale (visible to the eye) do not act in a quantum manner and interfere or diffract with one another.

However, as it turns out, collective quantum effects from a gas of Ultracold Atoms can in fact behave as quantum matter waves at macroscopic scales. A gas of atoms near absolute zero can effectively act as a single, giant quantum atom. This macroscopic object can then be manipulated to emulate the structure of crystals with light, fabricate an ideal quantum simulator or even generate artificial black holes in laboratories.


In this article, we shall discuss some of the important differences between classical and quantum particles before turning our attention to a gas of cold atoms. From there, we will then talk about the history and important properties of Ultracold Gases, before concluding with some of the most significant applications they hold within Physics and Technology.

Continue reading

Generating Extremes: Pressure

By Kenneth Freeman

‘Extreme’ is a relative word. At 250m below the surface of the ocean the pressure is 26 times higher than at the surface. This is about as deep as a human has ever free-dived, but is far too shallow and at too low a pressure for the blobfish that lives comfortably around 1km deep.

Pressure isn’t as intuitive to us as, say, temperature. The few times we notice it could be feeling your ears pop on takeoff as the cabin pressure quickly (and only slightly) drops, or feeling the building pressure as you dive towards the bottom of a pool.

The standard scientific unit for pressure is the Pascal (written Pa); typical atmospheric pressure  (1 atmosphere) is around 1×105  Pa (100 kPa), the pressure at the top of Everest is about a third of that and the pressure at the bottom of a 6m deep pool is around 160 kPa.

Continue reading

The coolest atoms in the universe

By Dainius Kilda

Where do we look for the coldest atoms? The official record on Earth is -89°C at the Vostok station in Antarctica. Outer space is even colder: a distinctly chilly -270°C, which is only about 3°C above the lowest possible temperature, known as absolute zero. But hidden from our eyes, an even colder spot exists in physics labs, where some adventurous physicists cool atoms down to only a few billionths of a degree (0.000000001°C) above absolute zero!

Cold matter is a big hit in physics for a reason: it is a breeding ground for quantum phenomena, including new phases of matter that only exist because of quantum mechanics. In the everyday world around us, we usually see only the familiar phases of matter: solids, liquids, gases, and plasma. But at extremely low temperatures, atoms in an ordinary gas condense into a single entity – the exotic fifth phase of matter called a Bose-Einstein condensate, in which the atoms behave like a huge quantum wave. Bose-Einstein condensates can flow without friction, cannot be rotated, and may have important applications in precision sensing, quantum computing, and several other areas.

In this article, we’ll describe what it even means for an object to get this cold, how Bose-Einstein condensates are made, and what we can do with them now we’ve got one.

Continue reading

Generating Extremes: Temperatures

By Kenneth Freeman

‘Extreme’ is a relative word: an Antarctic -30°C may seem extremely cold to you or me, but it’s fairly standard for an emperor penguin. In the laboratory, extremes can be far more dramatic: we approach the absolute limits of physical properties like temperature, reaching levels that can’t easily be comprehended. At these farthest limits we can explore exciting science which broadens our understanding of the fundamental forces in nature and provides insight that can lead to new technologies.

There are lots of ways to take a physical object to the extreme: examples include extremes of temperature, extremes of size (very big or very small), and extremes of pressure. These three properties – temperature, size, and pressure – are quite familiar from our everyday lives. Hot and cold, big and small are simple enough; pressure may be less intuitive initially, but doesn’t require much thought to understand its effects.

In the sciences, we can consider lots of other extremes too: for example concentration, magnetic field and time (e.g. looking at incredibly fast processes). We can also combine these different extremes to create a multitude of extreme environments. Here we’ll look at the methods used to produce these conditions in the lab, and how they compare to the extremes we see in nature.

Continue reading

Extremophiles: Life at Extreme Conditions

By Katherine Brown

Extremophiles are defined as organisms that may survive comfortably in environments that would be impossible for a human to survive in – whether this be extremes of temperature, pressure, pH, salinity or radiation. The word “extremophile” is a very loose definition, and is better treated as an umbrella term, from where you must specify in which extreme environment the organism survives. To best understand life at extreme conditions, it is perhaps best to discuss the limiting factors on life.

It’s a commonly known fact that the human body operates at 37°C, and in fact all mammals have a body temperature of between 36 and 40°C. Reptiles and fish, being cold blooded, have lower body temperatures than mammals, whereas for birds it is slightly higher. All told, most animals are found to have body temperatures in the range of 8 to 48°C. So what is it that sets this limit?

The Grand Prismatic Spring in Yellowstone National Park. Waters in the middle of the spring can reach almost 90°C. The bands of colour are a result of different thermophilic bacteria that live in the spring, sticking to rings where the temperature is best for them. These thermophiles produce different levels of carotenoids, which are similar to the chlorophyll that gives plants their green colour.

Continue reading

From White Dwarfs to Black Holes: Lively Quantum Matter in Dead Stars

By Dainius Kilda

Throughout their cosmic lives, stars ‘feed’ on the energy produced by nuclear reactions that fuse lighter elements into heavier ones. Nucleosynthesis in the cores of stars calls for infernal temperatures – the inferno starting at around 10 million K. In this heat, matter exists in the state of plasma: a mess of fully ionized atoms, all their electrons unbound from the nuclei. Thermal energy that fusion produces is also what a star needs to sustain the outward pressure in its core to remain stable against the gravitational force. Just like in a normal gas, the pressure in a stellar plasma comes from ions and electrons whizzing and bouncing around at high speeds, and becomes more intense as they are heated.

After about ten billion years of shining glory, a star like our Sun will exhaust its nuclear fuel and become unable to support itself against its own gravity. It will end its life by shedding the outer layers, and the dead core will succumb to a rapid gravitational collapse, as if being crushed under its own weight. Fortunately, the quantum nature of its tiny constituents – electrons – saves the star from impending catastrophe. On quantum scales, electrons behave as particles and waves (known as de Broglie waves) at the same time. When packed closely together, de Broglie waves of electrons begin to overlap and start interacting in a quantum way. Electrons belong to a class of particles called fermions, so their way of interaction needs to comply with the rules of a fermionic society. To see how this works, imagine fermions inside a box where they can only occupy specific quantized energy states – which is exactly what electrons experience in real matter. But fermions are socially awkward beings who avoid each other: two fermions cannot occupy the same quantum state in the same volume simultaneously. This is the Pauli exclusion principle, one of the fundamental principles of quantum mechanics. The very same exclusion principle guides electrons in atoms to form well-organized orbitals, leading to the chemical elements and the periodic table.

Continue reading

Mega Magnets

By Maja Bachmann

When discussing extremes in physics, this magazine edition would not be complete without taking a look at the most extreme and powerful magnets that exist. They enable physicists to study the properties of complex materials under extreme conditions and sometimes even new phases of matter are discovered!

The most intense magnets can reach up to 3’500’000 times the strength of the Earth’s natural magnetic field. This would easily bend a bar of steel and so one of the challenges in building these magnet systems is to find materials strong enough to withstand the enormous forces that are generated while using the magnet.

Continue reading