Scientists Bemused to Find Liquid Light at Room Temperature
What if your computer processor could only work at less than -200°C? Well, such is the case with almost all quantum computers, as heat tends to create errors in the qubits used in quantum computing. However, recent research reveals that liquified electric power has the potential to allow quantum computers to work at room temperature, just like your laptop, and this is not the only seemingly impossible problem liquid light can solve.
Until now, light has always been thought of as a wave or a stream of photons, and new discoveries are still taking place which unearths new properties in addition to the known wave and particle nature of light. Nevertheless, the possibility of light energy existing in liquid form at room temperature could turn out to be a ground-breaking discovery, perhaps one day transforming the energy sector, or even changing the way future technology is conceived.
Liquid light and the origin of superfluids
Liquid light can be categorized as a superfluid, derived from the ability of particles to condense in a state known as a Bose-Einstein condensate (BEC). Superfluid Bose-Einstein condensates follow the rules of quantum physics, rather than classical physics. They can carry and conduct electric power, but generally only exist for mere fractions of a second and in near absolute zero temperatures. However, a 2017 publication in the journal Nature Physics has demonstrated that this is not always necessary.
In the early 1920s, Indian scientist Satyendra Nath Bose sent Albert Einstein a paper in which he derived the Planck law for black-body radiation by treating the photons as a gas of identical particles.
Einstein generalized Bose’s theory to an ideal gas of identical atoms or molecules for which the number of particles is conserved. He also predicted that at sufficiently low temperatures, the particles would become locked together in the lowest quantum state of the system. This is the phenomenon that we now call Bose-Einstein condensation.
Bose and Einstein also worked together to develop Bose-Einstein statistics, a process for evaluating the possible states of quantum systems that contain identical particles with integer spin.
In the years that followed, many theories and experiments tried to produce BEC in the lab. However, it was not until June 5, 1995, that scientists Eric Cornell and Carl Wieman made the first condensate in 1995 at the Joint Institute for Laboratory Astrophysics (JILA) lab at the University of Colorado by cooling a cloud of 2000 rubidium atoms to near absolute zero.
This was followed by the creation of a larger condensate of sodium atoms just a few months later by a group led by Wolfgang Ketterle, a professor of physics at MIT. These early experiments by Cornell, Weiman, and Ketterle further encouraged the development of other BECs and for this exceptional contribution, all three of them were awarded 2001’s Nobel Prize in Physics.
How liquid light can exist at room temperature?
In 2017, a group of researchers from Polytechnique Montréal, Canada, and Italy’s CNR Institute of Nanotechnology teamed up to conduct an experiment that demonstrated that light can achieve a superfluid state at room temperature. Previous studies had already confirmed the possibility of light existing as a superfluid, but all previous experiments needed to use ultra-low temperatures near absolute zero to bind photons together strongly enough to for them to behave as molecules and turn into a superfluid.
During the 2017 experiment, an ultra-thin film made of organic molecules was sandwiched between two highly reflective mirrors, and this setup was further subjected to a 35 femtosecond (10⁻¹⁵ seconds) laser blast. This intense light-matter interaction led to the formation of a superfluid.
"The extraordinary observation in our work is that we have demonstrated that superfluidity can also occur at room temperature, under ambient conditions, using light-matter particles called polaritons."
Daniele Sanvitto, Researcher, CNR Nanotec
According to the researchers, "the photons interact with electron-hole pairs, called excitons, in a semiconductor. These excitons impose a dipole moment, which is combined with the dipole of the electromagnetic field, and couples strongly the excitons and the photons. The final result is a polariton, considered a quasiparticle, composed of half-light and half matter, which behaves as a Bose-Einstein condensate or superfluid, even at room temperature."
This BEC is also referred to as Liquid light.
They further add that "In this way, we can combine the properties of photons such as their light effective mass and fast velocity, with strong interactions due to the electrons within the molecules. Under normal conditions, a fluid ripples and whirls around anything that interferes with its flow. In a superfluid, this turbulence is suppressed around obstacles, causing the flow to continue on its way unaltered".
Possible applications of liquid light
The production of liquid light at room temperature promises interesting developments in the field of electronics, healthcare, data science, and many other domains:
- The number of transistors installed on a semiconductor chip is widely described as increasing by a factor of two every two years (also known as Moore’s law). This growth is necessary to meet the growing demands in increased speed needed for fast data transfer. In 2016, researchers at the University of Cambridge created a polariton switch capable of conducting electro-optical signals at high speed. This liquid light-based device has the potential to overcome the physical and technical limitations faced with current transistor chips.
- A research paper titled Phenomenological consequences of superfluid dark matter with baryon-phonon coupling, published in September 2018, theorizes that dark matter (85% matter in the universe is dark matter) is also superfluid. If this theory is proven correct, then there is a possibility that further research on liquid light (which is also a superfluid) may increase our understanding of dark matter and dark energy.
- There is a possibility that liquid light could be stored and saved for later use, this would have huge applications because, at present, electric current can not be easily stored in large amounts. Electricity needs to be continuously produced and used, which is a limiting factor in developing more sustainable energy system. Therefore, the ability to store electric power at room temperature could prove invaluable in the development of more sustainable energy sources.
- Researchers from CNR Institute and Polytechnique Montréal also suggest that liquid light technology could lead to the development of more advanced and efficient versions of laser-based equipment, computers, solar panels, and LED-based electronic appliances.
From quantum statistics to quantum computers, our knowledge of BECs and liquid light has come a long way, but will this charged superfluid ever be able to become an effective and mainstream solution for our energy needs? The answer lies in the future.
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