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February 21, 2024

Harvard creates matter, light sabers

By SOPHIA GAUTHIER | September 27, 2013

Until recently, the concept of squirrels dueling with light sabers was a complete work of science fiction and loopy Internet humor. However, now, a team of Harvard and MIT scientists are claiming to have created of a new form of matter — from light. They make an analogy between the newly created “photonic molecules” and a light saber. And they aren’t joking.

The group of pioneers was led by Mikhail Lukin, a professor of physics at Harvard University and Vladan Vuletic, also a professor of physics at MIT. In creating this new form of of matter, Lukin, Vuletic and colleagues somehow managed to cajole an assemblage of light particles, or photons, into interacting and forming clusters of molecules.

The phenomenon is incredibly counterintuitive to years of accepted thought in the scientific community. For starters, photons were always believed to be massless. The fact that photons can now be made to form cohesive groups in a semi-solid state is incredibly akin to ideas once only entertained behind the scenes of movie sets like Star Wars.

It was also once commonly believed that photons did not interact with one another. A common example given involves the interface between two laser beams. When such beams are shined in opposing directions, they simply pass through one another, as if the other weren’t there. With the help of fields like quantum physics and breakthroughs such as this, we are now quickly coming to the conclusion that this is no longer the case.

Lukin and Vuletic describe their work in a paper titled, “Attractive photons in a quantum nonlinear medium,” which was published in the world-renowned Nature journal. In this paper, they detail the procedures they used to essentially create the world’s first light saber-like matter.

Scientists on the team started off their experiments by pumping rubidium atoms into a vacuum. Rubidium is a metallic alkali metal that is highly reactive, even with air. They then cooled the system down to a temperature of almost absolute zero. Absolute zero is the coldest temperature possible where all vibration of molecules cease to persist. After this, the researchers fired pulses of single photons into the group of rubidium atoms.

As each photon travels through the cloud of atoms, its energy is transferred to the surrounding rubidium atoms. This creates two observable phenomenon: the excitation of the rubidium atoms and the slowing down of the photon. However, once the photon leaves the cloud, its energy is preserved.

Lukin describes this occurrence as similar to light passing through different mediums. When light passes from the air into a glass panel, the light bends due to the difference in refractive indices between the air and the glass. However, when the light beam exits the glass panel, it returns to its original direction of travel, thus preserving its original ‘identity.’

While this is an interesting observation, the science is only beginning to get wonky. Lukin and colleagues noticed that when the team fired two protons into the cloud of rubidium atoms, the two photons exited together, as a single entity. According to Lukin, this happening can be explained by the Rydberg blockade. This blockade describes way in which photons excite the atoms that they pass between. When one atom is excited, other neighboring atoms are prevented from obtaining the same amount of energy.

Once the second photon enters the group of rubidium atoms, the first photon must be pushed along in order to allow the second photon to hand off its energy.

One could almost argue the the second photon is physically pushing the first photon through the vacuum of rubidium. In this way, both photons highly interact and are able to create such “photonic molecules.”

This new technology has immense implications for the technological world. It is commonly known that light is the most efficient means of tranferring informaton. With the ability to lock photons into an ordered state, the creation of a quantum computer may be within reach.

But let’s be real. Most of us just are just excited about light sabers.


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