Researchers from Hiroshima University and the University of Bristol have debunked the Quantum Cheshire cat effect, which suggested that quantum particles could separate from their properties. The team, led by Jonte Hance and Holger Hofmann, found that the particles do not split from their properties, but instead display a feature of quantum mechanics known as contextuality. This means that quantum systems change depending on the measurements taken. The team aims to further understand this phenomenon and its practical applications, particularly in quantum computing. The research was published in the New Journal of Physics.
Quantum Cheshire Cat Effect: A Misunderstanding of Quantum Mechanics
The Quantum Cheshire Cat effect, named after the disappearing cat from Alice in Wonderland, was proposed in a 2013 paper. The researchers suggested that quantum particles could separate from their properties, with the properties traveling along paths the particle cannot. This concept has been extended by other researchers, who claimed to swap disembodied properties between particles, disembody multiple properties simultaneously, and even “separate the wave-particle duality” of a particle.
However, a recent study published in the New Journal of Physics on November 17, 2023 interestingly titled: “Contextuality, coherences, and Quantum Cheshire cats”, disputes these claims. The research team, led by Jonte Hance, a research fellow at Hiroshima University and the University of Bristol, argues that these experiments do not show particles splitting from their properties. Instead, they reveal another counterintuitive feature of quantum mechanics — contextuality.
Contextuality: The True Nature of Quantum Mechanics
Quantum mechanics is the study of the behavior of light and matter at the atomic and subatomic scale. It is inherently counterintuitive, and the research team aimed to understand this aspect while exploring its practical benefits.
Contextuality in quantum mechanics means that quantum systems change depending on what measurements are made on them. The order of measurements on a quantum system can produce different results. For example, measuring a particle’s location and then its speed will yield different results than measuring its speed first and then its location. This contextuality allows quantum systems to be measured as having properties that would typically be mutually incompatible.
The Quantum Cheshire Cat Paradox: A Misleading Representation
The research team argues that the original claim of the Quantum Cheshire Cat effect, that a particle and its property, such as spin or polarization, separate and travel along different paths, is a misleading representation of the actual physics.
The team analyzed the Cheshire Cat protocol by examining the relation between three different measurements regarding the path and polarization of a photon within the protocol. They found that what seemed to be a logical contradiction was actually a demonstration of the system’s contextuality.
The Quantum Cheshire Cat: A Demonstration of Coherences
The team’s analysis showed that the Quantum Cheshire Cat effect does not involve a property of the particle being disembodied. Instead, it demonstrates the effects of coherences, typically found in pre- and post-selected systems.
Future Research: Unifying Paradoxical Quantum Effects
The team plans to expand this research to unify paradoxical quantum effects as manifestations of contextuality. They aim to explain how and why measurements change quantum systems. Understanding contextuality could help realize the full potential of quantum computing, as it is inherently linked to scenarios where there is a quantum advantage over classical solutions to a given problem.
The research was funded by Hiroshima University’s Phoenix Postdoctoral Fellowship for Research, the University of York’s EPSRC DTP grant, the Quantum Communications Hub that is funded by EPSRC grants, and a JST SPRING grant.
“Most people know that quantum mechanics is weird, but identifying what causes this weirdness is still an active area of research. It has been slowly formalized into a notion called contextuality — that quantum systems change depending on what measurements you do on them,” said Jonte Hance, a research fellow at Hiroshima University and the University of Bristol.
“A sequence of measurements on a quantum system will produce different results depending on the order in which the measurements are done. For instance, if we measure where a particle is, then how fast it is travelling, this will give different results to first measuring how fast it travels, then where it is. Because of this contextuality, quantum systems can be measured as having properties which we would expect to be mutually incompatible. However, we still don’t really understand what causes this, so this is what we wanted to investigate, using the paradoxical quantum Cheshire cat scenario as a testbed,” said Hance.
“We want to correct this by showing that different results are obtained if a quantum system is measured in different ways, and that the original interpretation of the quantum Cheshire cat only comes about if you combine the results of these different measurements in a very specific way, and ignore this measurement-related change,” said Holger Hofmann, a professor at Hiroshima University.
“This will not only help us finally explain why quantum mechanics is so counterintuitive, but will also help us develop ways to use this weirdness for practical purposes. Given contextuality is inherently linked to scenarios where there is a quantum advantage over classical solutions to a given problem, only by understanding contextuality will we be able to realize the full potential of, for instance, quantum computing,” said Hance.
Quick Summary of the Research
Recent research has debunked the quantum Cheshire cat effect, which suggested that quantum particles could separate from their properties, demonstrating instead another feature of quantum mechanics known as contextuality. The study, conducted by a team at Hiroshima University and the University of Bristol, revealed that the results of quantum measurements change depending on their sequence, and the perceived separation of a particle from its properties only occurs when these measurements are combined in a specific way.
- The quantum Cheshire cat effect, named after the disappearing cat from Alice in Wonderland, was thought to show quantum particles separating from their properties. This concept was first proposed in a 2013 paper.
- However, recent research published in the New Journal of Physics on November 17, 2023, suggests that these experiments do not show particles splitting from their properties. Instead, they display another feature of quantum mechanics known as contextuality.
- Quantum mechanics, the study of light and matter at the atomic and subatomic scale, is inherently counterintuitive. Contextuality refers to the idea that quantum systems change depending on the measurements taken.
- Jonte Hance, a research fellow at Hiroshima University and the University of Bristol, and his team have been investigating this phenomenon. They argue that the original interpretation of the quantum Cheshire cat effect is misleading and that different results are obtained if a quantum system is measured in different ways.
- The team’s research shows that instead of a property of the particle being disembodied, the quantum Cheshire cat effect demonstrates the effects of coherences, typically found in pre- and post-selected systems.
- The researchers aim to expand this research to unify paradoxical quantum effects as manifestations of contextuality and to explain how and why measurements change quantum systems. This could help realise the full potential of quantum computing.
- The research team includes Jonte R. Hance, Ming Ji, and Holger F. Hofmann from Hiroshima University. Hance is also a research associate at the University of Bristol. The research was funded by Hiroshima University, the University of York, the Quantum Communications Hub, and a JST SPRING grant.
