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

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