Quantum superposition reaches the microscopic world: Is a quantum computing revolution on the horizon?

Quantum physics prevails in the microscopic world, while classical physics rules in the macroscopic domain. The ‘handover’ between these two domains remains a mystery to scientists as to the scale and mechanisms. A recent experiment using an acoustic resonator made it possible to highlight quantum superposition – the simultaneous occupation of two distinct quantum states – in a group of 10¹⁶ Atoms weigh about one microgram. These findings push the boundaries of “quantum” for nearly all macroscopic objects and could revolutionize quantum computing.

Les atoms and autres objets microscopiques obéissent aux lois de la mécanique quantique, tandis que les objets plus volumineux, tels qu’un vase ou même un sable grain, suivent les règles de la mécanique classique établies by Isaac Newton in the preceding 340 years .

In simple terms, quantum mechanics suggests that an atom can behave like a wave and thus be in several places at once, whereas in classical mechanics a falling vase breaks without any other possible alternatives. A particle can also be in two quantum states at the same time (superposition).

Numerous experiments have confirmed the strange properties of quantum particles over the past 100 years. However, the underlying reason for the difference in behavior between microscopic and macroscopic organisms is still unknown.

Recently, Mathieu Fadel of the Swiss Federal Institute of Technology Zurich (ETH) and colleagues were able to place a single-microgram crystal in a state of quantum superposition to test the validity of quantum mechanics in the microscopic world. The results of their research have been published in the journal
Physical review letters. This work should make it possible to test quantum mechanics and its possible modifications using massive objects of microscopic size.

Quantum states of a vibrating crystal

To study quantum mechanics on more massive objects, Mathieu Fadell and his team used sound wave resonators. These are tiny sheets of sapphire designed to vibrate, and then their vibrations are measured.

In order to generate vibrations that are superposition states in quantum mechanics — the equivalent of an atom or molecule being in two places at once — a piezoelectric crystal (which generates an electric field when matter deforms) is coupled to a superconducting circuit that acts as a quantum bit, or qubit — that is used to Quantum computers.

A qubit can take on one of two possible quantum states or a superposition of the two. By coupling the qubit to the crystal, the superposition state of the qubit can be transferred to the collective vibrations of the atoms in the crystal. In addition, the qubit can then be used to sense the state of vibration of the crystal.

Using this procedure, the researchers were able to create quantum mechanical superposition states of a sapphire crystal made up of ten trillion atoms (a number with 16 zeros). They cooled the crystal, which vibrated about six billion times per second, to a hundredth of a degree above absolute zero to reduce thermal fluctuations.

After placing the crystal into a specific quantum state, the researchers detected its state after a variable period using a qubit. This allowed them to determine whether the crystal’s vibrational state was truly quantum mechanical or could be described by classical mechanics. During their experiment, they observed the quantum features in the crystal’s vibration for approximately 40 microseconds.

A revolution in quantum mechanics?

in communicationFadel explains:
Combined with the large mass of the crystal, this coherence time suggests a test of the quantum superposition principle at a level close to what can currently be achieved using interferometers. [instrument permettant de créer des
interférences d’ondes électromagnétiques et d’étudier la
superposition des ondes] “. Add : ” With some improvements, we should be able to study other macroscopic objects in the near future, surpassing the results obtained with particles and thus testing quantum mechanics in hitherto unexplored systems. “.

Fadel’s ultimate goal is to discover what happens with quantum effects in the intermediate mass system between atoms or molecules on the one hand and macroscopic objects on the other. Some current theories postulate that the loss of quantum coherence as objects get larger is somehow done in quantum mechanics.

Determining whether the Schrödinger equation (famously drawn by a cat alive and dead in a box) needs to be modified is not only of great importance for basic science, as Fadel points out: This will have important implications, for example, for computers and quantum sensors “.

As the number of qubits in these quantum devices grows, decoherence effects due to their size may impose unexpected limitations on their functionality.

source : Physical review letters