Physicists discover family members of Schrödinger’s cat

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Interesting research out of the University of Queensland. I’ll just give you the press release and some details from the paper, and you can take it from there. For related conversation, check out this podcast episode.


The first new quantum state in the family of hypercubes states shown in position, momentum space.
Dateline Australia, 11 July 2019. It has been said that the internet exists chiefly to show videos of cats interacting with boxes.

An international team of researchers led by The University of Queensland has extended cats and boxes into the quantum realm, discovering that Schrödinger’s famous dead-and-alive cat is just one of an infinite family of quantum states.

ARC Centre of Excellence for Engineered Quantum Systems UQ PhD candidate Lewis Howard, said the states were all generated using multidimensional boxes called hypercubes.

“We found as the hypercubes become larger, they generated Schrödinger-cat-like states with increasingly finer features in phase space, making them more powerful for quantum applications,” Mr Howard said.

“Think striped tigers as opposed to tabbies.”

Creating these hypercube states – in this case using single particles of light and a tiny mechanical drum – is an important ingredient in quantum technologies.

“The Schrödinger Cat state, discovered in 1935, is a quantum superposition of two states, normally referred to as ‘dead’ and ‘alive’.

“In 2001, a relative of the cat was introduced – the compass state, which is made up of a superposition of four different quantum states arranged in a compass form.”

The study showed that the cat and the compass state are just the smallest two members of an infinitely large family of hypercube states.

University of Innsbruck’s Dr Martin Ringbauer, who guided the research, said that hypercube states consist of multiple quantum superpositions that map out the corners of multidimensional cubes.

“We discovered these quantum hypercube states by accident while experimenting with methods to create quantum states that could be useful in quantum sensors,” Dr Ringbaurer said.

Centre of Excellence for Engineered Quantum Systems researcher Dr Till Weinhold said that these quantum states could be used in future quantum technologies, such as super-sensitive sensors.

“When we use a ruler to measure distance, the smallest distance that can be measured depends on the grading of the ruler,” Dr Weinhold said.

“Usually quantum mechanics tells us that one cannot make the grading on the ruler finer and finer.

“Hypercube states get around this limit by using quantum interference to create features much smaller than otherwise possible.”

“The tiny features of hypercube states can act like the grading of the ruler to make hypercube states interesting candidates for next generation sensors.”

“These states allow us to exploit quantum properties to measure at scales far below what is classically possible.”

Title: Quantum Hypercube States

Authors: Weinhold, Shahandeh, Combes, Vanner, White, Ringbauer

The Abstract:

We introduce quantum hypercube states, a class of continuous-variable quantum states that are generated as orthographic projections of hypercubes onto the quadrature phase space of a bosonic mode. In addition to their interesting geometry, hypercube states display phase-space features much smaller than Planck’s constant, and a large volume of Wigner negativity. We theoretically show that these features make hypercube states sensitive to displacements at extremely small scales in a way that is surprisingly robust to initial thermal occupation and to small separation of the superposed state components. In a high-temperature proof-of-principle optomechanics experiment we observe, and match to theory, the signature outer-edge vertex structure of hypercube states.

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3 thoughts on “Physicists discover family members of Schrödinger’s cat

  1. Hi Greg,

    Thank you very much for your interest in this work. Unfortunately the paper link provided with the initial release was incorrect. For those interested the correct paper the title is Quantum hypercube states and the link is:

    https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.020402

    Here is the abstract,

    We introduce quantum hypercube states, a class of continuous-variable quantum states that are generated as orthographic projections of hypercubes onto the quadrature phase space of a bosonic mode. In addition to their interesting geometry, hypercube states display phase-space features much smaller than Planck’s constant, and a large volume of Wigner negativity. We theoretically show that these features make hypercube states sensitive to displacements at extremely small scales in a way that is surprisingly robust to initial thermal occupation and to small separation of the superposed state components. In a high-temperature proof-of-principle optomechanics experiment we observe, and match to theory, the signature outer-edge vertex structure of hypercube states.

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