Schrödinger’s cat can be dead and alive in two places at the same time

Designed to illustrate how an object can exist as a combination of multiple states in a quantum system, the Schrödinger cat state paradox presents a scenario in which a feline subject can both alive and dead at the same time, but a new study examines the issue from a new angle.

Writing in the May 27 edition of the journal Science, Physicist Chen Wang from Yale University and a group of researchers from INRIA Paris-Rocquencourt, a division of the French National Institute for computer science and applied mathematics, described experiments which showed how the cat could be both alive and dead, as well as in two places at the exact same time.

The study authors constructed their “cat” from coherent microwave photons, which they induced to have matching states (or to become entangled), and showed how the state of the subject can be shared by two separated cavities. The experiments, they explained in a press release, demonstrate the ability to manipulate complex quantum states, and are believed to represent the first time that scientists have been able to achieve this kind of quantum coherence at a macroscopic scale.

The ability to manipulate these multicavity quantum states, and thus sharing quantum states that are in different locations, could be a powerful tool for quantum information processing, and may have applications in the fields of computing and long-distance communication, they noted. Their work, in short, could greatly benefit the quest for reliable quantum computing.

So how were they able to pull this off?

First devised by Austrian physicist Erwin Schrödinger in 1935, the paradox is based on the idea that a cat is placed in a sealed box with a radioactive source and a poison that will be triggered if an atom of the radioactive substance decays. Quantum physics suggests that the cat is both dead and alive (a superposition of states) until the box is opened, changing the quantum state.

The core of the experiment is an investigation into how a quantum system such as a photon or an atom, can exist as a combination of states when it is not observed. Scientists who are analyzing a box containing the cat cannot know the state of that cat unless the box is opened, meaning that it is both alive and dead when nobody is looking at it.

The new Yale-led experiment takes this idea to another level by combining the Schrödinger cat experiment the concept of entanglement by having the cat live or die in two different boxes at the same time. They built a device made up of two, three-dimensional cavities and a monitoring port connected by a superconducting artificial atom. They then placed their confined microwave light “cat” in both cavities and joined them by a supercurrent, which does not require voltage.

The photons in one cavity were then subjected to a maze of gates to give them a distinct spin so that the researchers could give the photons two states – “dead” and “alive” like the cat – and they observed the similar state in photons in the adjoining cavity. Thus far, they have been able to see “cats” as large as 80 photons in size, and plan to use specially controlled pulses to observe larger ones.


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