Jan 15, 2025 12:00:00

Research report on the development of a quantum bit that realizes 'Schrödinger's cat' on a silicon chip

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Schrödinger's cat ,' a thought experiment in which a cat placed in a box is considered to be alive or dead, was proposed by Austrian physicist Erwin Schrödinger in the early 20th century. A research team from the University of New South Wales announced that they have realized the quantum state of Schrödinger's cat on a silicon chip.

Schrödinger cat states of a nuclear spin qudit in silicon | Nature Physics
https://www.nature.com/articles/s41567-024-02745-0

Quantum engineers create a 'Schrödinger's cat' inside a silicon chip
https://phys.org/news/2025-01-quantum-schrdinger-cat-silicon-chip.html

In 1935, Schrödinger proposed a thought experiment called 'Schrödinger's cat' to argue that quantum mechanics, which is governed by probability, is incomplete.

Imagine placing a radioactive element, a device with a Geiger counter, and a live cat in a box. The radioactive element decays and emits radiation with a 50% probability per hour, and the device with the Geiger counter emits poisonous gas when it detects radiation. Of course, the cat will die if poisonous gas is produced, so the probability that the cat will be alive in the box after one hour is 50%. In other words, until the box is opened to check, the state inside the box can be said to be a superposition of 'the cat is alive' and 'the cat is dead.'

by ADA&Neagoe

The point of 'Schrödinger's cat' is that it links quantum mechanical phenomena to macroscopic, i.e. human-scale observable states of 'living cats' and 'dead cats.' In other words, 'Schrödinger's cat' raises the question of 'how do microscopic quantum phenomena determine the state of the macroscopic world?'

This time, the research team reported that they have succeeded in creating a quantum state that is more complex than conventional qubits by using

antimony atoms embedded in silicon nanoelectronic devices. They also defined the state of Schrödinger's cat as a 'superposition of widely separated coherent states ,' and claimed that the qubit using antimony atoms realizes this.

A quantum bit, the smallest unit of a quantum computer, uses a 'superposition of different states' of the quantum spin direction to simultaneously take on the values '0' and '1.' While a normal quantum bit has only two types of spin directions, up and down, antimony atoms have eight different spin directions.

In the case of antimony atoms, there are six intermediate states between the up and down states, so the distance between '0' and '1' is greater than in a normal quantum bit. The research team refers to this 'superposition of more widely separated states' as 'realizing Schrödinger's cat.'

By Vicky Somma

In addition, this research has a practical purpose beyond simply realizing 'Schrödinger's cat,' by proposing a new quantum bit system.

In a normal quantum bit, any sudden change in the spin direction would immediately result in a logic error, turning a '0' into a '1' or vice versa, making the quantum information extremely fragile. However, the team explained that their system uses antimony atoms to create a mechanism where a single error between '0' and '1' cannot break the quantum code.

Professor Andrea Morello, leader of the research team, likened the technology to a 'cat with seven lives.' 'They say cats have nine lives, but our cat has seven lives. It takes seven consecutive errors to change from 0 to 1,' he said.

The team explains that the antimony qubits are implemented on silicon chips, allowing them to precisely control their quantum state, and that the use of silicon chips suggests that in the future this technology could be scaled up using methods similar to how computer chips are currently manufactured.