- Researchers test the quantum superposition principle at a massive scale like never before.
- They illustrated the delocalization of the massive molecules containing 40,000 neutrons, electrons, and protons.
- Up to 2,000 atoms remained in two places at once for 7 milliseconds – a new record of quantum superposition.
Physicists have been working for decades to reconcile the classical and quantum world. A fundamental principle of quantum mechanics, quantum superposition, states that quantum states can be added together (superposed) to output another valid quantum state.
A quantum particle can exist in two places at once: they can shift between wave-like states and particle-like states. However, the same phenomenon has not been seen in large objects: it has only been observed in tiny particles such as electrons, photons, and atoms.
Now things have begun to change. Researchers at the University of Vienna and the University of Basel have tested the quantum superposition principle at a massive scale like never before.
This type of complex experiments shows that the smallest things can be arranged in states that are not possible with normal-sized objects. Does it mean quantum physics isn’t valid at the macroscopic scale?
In 1801, a British physician Thomas Young performed an experiment with light, called double-slit experiment, demonstrating that matter and light can display properties of both classically defined particles and waves.
This is true for neutrons, electrons, protons, atoms, and molecules. However, we still don’t know how such unusual quantum effects transition into the classical world.
Quantum Superposition of Heavier Molecules
In this study, researchers tried to answer this question by showing quantum interference with heavier molecules (> 25,000 atomic mass units). They passed large molecules (containing over 40,000 neutrons, electrons, and protons) through the interferometer.
These molecules were synthesized in such a way that they remain stable while forming a molecular beam in an ultrahigh vacuum.
To make sure the experiment works correctly, researchers developed a special interferometer named Long-Baseline Universal Matter-Wave Interferometer. It is the longest interferometer to date with a baseline length of 200 centimeters. It can compensate for several technical challenges, including the Coriolis effect that interferes with sensitive instruments.
The delocalization of the large molecules used in this experiment | Courtesy of researchers
The results showed interference of large molecules containing 2,000 atoms, meaning 2,000 atoms were in two places at once. This is by far the heaviest objects shown to exhibit matter-interference.
This study puts bounds on alternative theories to quantum mechanics, for instance, how long a superposition can be maintained in a heavy particle. In this case, researchers were able to put massive molecules in a superposition for more than 7 milliseconds.
So far, we haven’t discovered any state where an object can be in two positions at once. Future studies can reveal how massive an object should be in order to exhibit quantum superposition and what the limits are.
To find any connection between the classical and quantum world, the research team plans to push the limits even further. They will increase the macroscopicity of the superposition and the mass of the interfering particles in the next experiments.