Quantum physics: Schrödinger's cat now weighs 16 micrograms
A gemstone in the footsteps of Schrödinger's cat: physicists have set a sapphire weighing 16 micrograms into a superposition of two oscillation states. A new record.
A sapphire crystal weighing 16 micrograms is the largest object ever to exist in a quantum mechanical superposition of two vibrational states. A team led by Matteo Fadel from ETH Zurich excited the crystal to vibrate in which the atoms oscillate back and forth - in what is known as superposition, they vibrate simultaneously in two opposite directions. As the research group reports in "Science", this state corresponds to the thought experiment of Schrödinger's cat, which is simultaneously alive and dead depending on the decay of an atom that destroys a vial of poison. Such macroscopic "cat states" are intended to help explain how and why the laws of the quantum world override the rules of classical physics in larger objects.
In order to make the sapphire (the cat), which consists of around one hundred quadrillion atoms, behave like a quantum mechanical object, the research group set it into oscillation and coupled it to a superconducting circuit (the atom from Schrödinger's thought experiment). This corresponds to a qubit: it is therefore simultaneously in the states "0" and "1". The superposition is then transferred to the oscillation of the crystal: the atoms in the crystal can therefore move in two directions at the same time, for example upwards and downwards - just as Schrödinger's cat is dead and alive at the same time. The important thing here is that the distance between the two states is greater than the quantum mechanical uncertainty.
With the superconducting qubit, the researchers were also able to determine the distance between the two vibrational states of the crystal. At just a billionth of a nanometre, the distance is tiny - but still large enough to distinguish the two states from each other beyond doubt.
Such superpositions of classically incompatible states are common in quantum mechanical objects. Macroscopic objects consisting of very many atoms, on the other hand, normally obey classical mechanics; they cannot assume two contradictory states at the same time. Just as a cat cannot be alive and dead at the same time, a crystal cannot swing up and down at the same time. The big puzzle, however, is why it generally cannot do this. Because no matter how big an object is, it is made up of atoms and subatomic particles that obey the rules of quantum physics.
There are a whole range of possible explanations as to why large objects do not do this. For example, because as the number of atoms increases, more and more influences cause quantum mechanical states to decay. Or that gravity could also play a role. The hope is that ever larger "cat states" can help to finally solve the puzzle of Schrödinger's cat. In addition, stable, controllable macroscopic quantum states are also of technical interest, for example for error correction processes in increasingly complex quantum computers.
Spectrum of Science
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