Physicists Observe The First Natural Biomolecule Behaving Like A Quantum Wave

  • For the first time, physicists observe the wave-particle duality in gramicidin molecules. 
  • Gramicidin is a natural antibiotic with 15 amino acids. 
  • The findings pave the way for a new era of quantum biology. 

In quantum mechanics, objects behave like waves and like particles. This wave-particle duality has become a crucial aspect of modern physics.

Various studies have proved that a single particle — such as a photon or an electron — can interfere with itself, like a wave. Since everything is quantum in nature, they all have a specific wavelength.

As per quantum laws, which describe nature at the smallest scale, microscopic objects should also exhibit such wave-particle duality. However, scientists haven’t yet found a way to measure the wave-like nature of large objects.

Though they have managed to analyze the wave-like nature of larger molecules in the last two decades. In 1999, for example, a team of physicists observed the wave-particle duality in carbon-60 molecules.

A few groups observed the same nature with even larger molecules. In 2019, a team illustrated the delocalization of massive molecules containing 40,000 neutrons, electrons, and protons. But the question is how big they can go. Is it possible to measure the quantum properties of natural biomolecule?

It seems that researchers at the University of Vienna have got the answer. They have observed quantum interference in gramicidin molecules for the first time. Gramicidins are linear peptides with 15 amino acids.

3D rotating image of Gramicidin A 

How Did They Do This?

To observe the wave-particle duality in gramicidin, researchers created a beam of ultracold gramicidin molecules. This beam interferes with itself, which is clear evidence of the wave-like nature of biomolecules. The team used a complex setup to analyze the interference pattern.

Reference: arXiv:1910.14538 | Wikipedia 

The experiment is not as easy as it sounds. Since gramicidin is an extremely fragile antibiotic, its molecules could easily break apart. This makes it even trickier to create the beam of individual biomolecules.

What researchers did is they coated a spinning wheel’s edge with a thin layer of gramicidin. They then fired short laser pulses (of few femtoseconds in length) at the wheel’s edge to knock the molecules of gramicidin off the surface (without damaging them). 

Courtesy of researchers 

The beam of argon atoms (traveling at 600 m/s) then sweeps up the free-floating biomolecules that have a wavelength of 350 femtometers. To analyze the pattern formed by the wave interfering with itself, researchers used a special technique called Talbot-Lau interferometry. 

The outcomes are impressive: ‘the molecular coherence is delocalized over more than twenty times the molecular size’. The pattern observed in this study wouldn’t be possible if molecules of gramicidin were pure particles. This confirms that gramicidins exhibit wave-particle duality.

Although other experiments have analyzed the wave-like nature of larger molecules, they relied on methods that destroy the molecules. The new technique, on the other hand, opens new avenues to study the quantum nature of biomolecules as well as the optoelectronic properties of neutral biomolecular systems.

Read: Quantum Tunneling | How Long It Takes For A Particle To Tunnel Through A Barrier?

The study will also allow scientists to set experiments that exploit the quantum nature of DNA and enzymes.

Written by
Varun Kumar

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