In a joint research project, French, Austrians, and American researchers have achieved a state described in Lewis Carroll’s well loved story, Alice in Wonderland. (Three of the four institutions involved have issued news releases, as this is the only one to feature a quote from Alice in Wonderland describing the state, it gets mentioned first.) From a July 29, 2014 Chapman University news release on EurekAlert,
… “Well! I’ve often seen a cat without a grin,” thought Alice in Wonderland, “but a grin without a cat! It’s the most curious thing I ever saw in my life!” Alice’s surprise stems from her experience that an object and its property cannot exist independently. It seems to be impossible to find a grin without a cat. However, the strange laws of quantum mechanics (the theory which governs the microscopic world of atoms; and the most successful theory in history) tell us that it is indeed possible to separate a particle from its properties—a phenomenon which is strikingly analogous to the Cheshire Cat story. The quantum Cheshire Cat is the latest example of how strange quantum mechanics becomes when viewed through the lens of one of Aharonov’s fundamental discoveries called the “weak measurement.”
Modesty does not favour contemporary research and educational institutions and, as is common in situations where there’s significant scientific excitement with a number of collaborators, the cooperating institutions are angling to establish the importance of their institutions and/or researchers’ contributions.
Here’s more from the Chapman University news release where it establishes its claim to the theory,
The idea of the Quantum Cheshire Cat was first discovered by Chapman’s Prof. Yakir Aharonov and first published by Aharonov’s collaborator, Prof. Jeff Tollaksen (also at Chapman University), in 2001. Aharonov’s team, including Sandu Popescu (University of Bristol and Chapman’s Institute for Quantum Studies) and Daniel Rorhlich (Ben Gurion University), continued to develop the Cheshire Cat theory in more recent publications.
A July 29, 2014 Vienna University of Technology news release on EurekAlert provides this description and its claim to inventing the technique used in the latest experimental work,
According to the law of quantum physics, particles can be in different physical states at the same time. If, for example, a beam of neutrons is divided into two beams using a silicon crystal, it can be shown that the individual neutrons do not have to decide which of the two possible paths they choose. Instead, they can travel along both paths at the same time in a quantum superposition.
“This experimental technique is called neutron interferometry”, says Professor Yuji Hasegawa from the Vienna University of Technology. “It was invented here at our institute in the 1970s, and it has turned out to be the perfect tool to investigate fundamental quantum mechanics.”
A July 29, 2014 Institut Laue-Langevin (international research institute located in Grenoble, France) news release on EurekAlert establishes its claim as the location for the experimental work,
Researchers from the Vienna University of Technology have performed the first separation of a particle from one of its properties. The study, carried out at the Institute Laue-Langevin (ILL) and published in Nature Communications, showed that in an interferometer a neutron’s magnetic moment could be measured independently of the neutron itself, thereby marking the first experimental observation of a new quantum paradox known as the ‘Cheshire Cat’. The new technique, which can be applied to any property of any quantum object, could be used to remove disturbance and improve the resolution of high precision measurements.
The fourth collaborating institution (l’Université de Cergy-Pontoise) does not seem to have issued a news release in either French or English as per my August 8, 2014 searches.
The research itself is quite fascinating and it’s worth reading all three news releases for additional nuggets information hidden amongst the repetitive bits. Here’s a description you’ll find in both the Vienna University of Technology and Chapman University news releases,
Neutrons are not electrically charged, but they carry a magnetic moment. They have a magnetic direction, the neutron spin, which can be influenced by external magnetic fields.
First, a neutron beam is split into two parts in a neutron interferometer. Then the spins of the two beams are shifted into different directions: The upper neutron beam has a spin parallel to the neutrons’ trajectory, the spin of the lower beam points into the opposite direction. After the two beams have been recombined, only those neutrons are chosen, which have a spin parallel to their direction of motion. All the others are just ignored. “This is called postselection”, says Hermann Geppert. “The beam contains neutrons of both spin directions, but we only analyse part of the neutrons.”
These neutrons, which are found to have a spin parallel to its direction of motion, must clearly have travelled along the upper path – only there, the neutrons have this spin state. This can be shown in the experiment. If the lower beam is sent through a filter which absorbs some of the neutrons, then the number of the neutrons with spin parallel to their trajectory stays the same. If the upper beam is sent through a filter, than the number of these neutrons is reduced.
Things get tricky, when the system is used to measure where the neutron spin is located: the spin can be slightly changed using a magnetic field. When the two beams are recombined appropriately, they can amplify or cancel each other. This is exactly what can be seen in the measurement, if the magnetic field is applied at the lower beam – but that is the path which the neutrons considered in the experiment are actually never supposed to take. A magnetic field applied to the upper beam, on the other hand, does not have any effect.
“By preparing the neurons in a special initial state and then postselecting another state, we can achieve a situation in which both the possible paths in the interferometer are important for the experiment, but in very different ways”, says Tobias Denkmayr. “Along one of the paths, the particles themselves couple to our measurement device, but only the other path is sensitive to magnetic spin coupling. The system behaves as if the particles were spatially separated from their properties.”
Here’s an illustration the researchers have provided,
Caption: The basic idea of the Quantum Cheshire Cat: In an interferometer, an object is separated from one if its properties — like a cat, moving on a different path than its own grin.
Credit: TU Vienna / Leon Filter
Here’s a link to and a citation for the paper,
Observation of a quantum Cheshire Cat in a matter-wave interferometer experiment by Tobias Denkmayr, Hermann Geppert, Stephan Sponar, Hartmut Lemmel, Alexandre Matzkin, Jeff Tollaksen, & Yuji Hasegawa. Nature Communications 5 Article number: 4492 doi:10.1038/ncomms5492 Published 29 July 2014
This is an open access paper.
Perhaps in response to concerns about the importance of theoretical physics, Chapman University’s Jeff Tollaksen offers this about possible applications (from the Chapman University news release),
Co-Director of the Institute for Quantum Studies, Prof. Jeff Tollaksen has said: “Theoretical physics has yielded the most significant benefits for our society at the lowest costs. Discoveries in fundamental physics often lead to new industries: from electricity to smartphones to satellites. Quantum physics resulted in technological advances that drive our economy, such as the entire computer revolution, electronics, and the nuclear power industry. In addition, it impacts many other disciplines such as genetics, medicine and mathematics. Experts therefore estimate that nearly half the wealth created in the 20th century arose from quantum physics. At the Institute, we’re committed to producing the next generation of breakthroughs which will lead to the technology of the 21st century. Similarly, I’m sure this breakthrough will lead to many new applications including revised intuitions which can then serve as a guide to finding novel quantum effects.” This “Quantum Cheshire Cat” could be used for practical applications. For example, it could be used to make high precision measurements less sensitive to external perturbations. The measurements which now have been published in Nature Communications are the first experimental proof of this phenomenon.
By contrast the Europeans offer this,
With their landmark observation suitably vindicated, questions turn to the potential impact of their fundamental discovery. One application might high precision measurements of quantum systems which are often affected by disturbance. [from the Institut Laue-Langevin news release]
Or, there’s this,
This counter intuitive effect is very interesting for high precision measurements, which are very often based on the principle of quantum interference. “When the quantum system has a property you want to measure and another property which makes the system prone to perturbations, the two can be separated using a Quantum Cheshire Cat, and possibly the perturbation can be minimized”, says Stephan Sponar. [from the Vienna University of Technology news release]
The contrast is certainly interesting.