Experimentally testing nonlocality in many-body systems

June 20, 2014, The Institute of Photonic Sciences
This image depicts an artistic impression of the experiment. Credit: ICFO

In a recent study published in Science, researchers at ICFO construct multipartite Bell inequalities built from the easiest-to-measure quantities, the two-body correlators, which are capable of revealing nonlocality in many-body systems. As these are considered a fundamental resource for quantum information theory, this study will pave a new path towards experimental detection of nonlocality in large composite quantum systems.

Science has recently published a study carried out by researchers at ICFO in collaboration with the Institute for Nuclear Research, Hungarian Academy of Sciences, which demonstrates the capability of detecting non-locality in many-body by constructing multipartite Bell inequalities involving only two-body .

In Quantum Theory, interactions among particles create fascinating correlations that cannot be explained by any means known to the Classical World. These correlations, usually known to be nonlocal, prove that the Quantum and Classical Worlds differ at the level of elementary particles. They have also become a powerful resource over the years for such real-world applications as the generation of cryptographic keys, which are perfectly secure against any malicious adversary, or perfect random number generators, which are crucial for cryptography, the numerical simulations of complex systems or fair gambling. Last but not least, these nonlocal correlations, aside from entanglement, are expected to shed a completely new light on our understanding of the physics of many-body quantum states.

An important goal for researchers in this field has been to confirm that such nonlocal correlations really exist in Nature. To date, experiments have focussed on the observation of nonlocality in only small quantum systems consisting of few particles, leaving more complex quantum systems completely unstudied. This is simply because the known tools that may reveal nonlocality, the so-called Bell inequalities, involve correlations among many parties that are still out of reach of the current experimental technology dealing with many-body quantum systems.

In this study, the research team at ICFO, comprised by Jordi Tura, Remigiusz Augusiak, Belen Sainz and ICREA Professors at ICFO Antonio Acín and Maciej Lewenstein, in collaboration with T. Vértesi from Hungary, designed classes of multipartite Bell inequalities constructed from the easiest-to-measure quantities, the two-body correlators. They showed that these inequalities are capable of revealing the nonlocality properties of several interesting many-body quantum states, in particular those relevant for nuclear and atomic physics.

They were even able to show that the inequalities proposed by this study could be verified experimentally by measuring the total spin components of the particles, thus opening a wide range of new possibilities for experimental detection of many-body nonlocality in physical systems in which individual particles cannot be addressed. Possible experimental setups in which these inequalities can be studied include cold atomic clouds and the so-called atomic ensembles, ultracold atoms (Bose condensates or spinor Bose condensates) as well as systems of atoms trapped in nanostructures, or systems of trapped ions.

In summary, the authors comment that "Our study has shown that the possibility of experimentally confirming the existence of nonlocal correlations in many-body quantum states is becoming accessible to physicists, something unimaginable before. At the fundamental level, any experiment regarding this matter would certainly provide a new proof that quantum theory correctly describes nature, even when considering complex many-body systems. In practice, a better characterization of these correlations in many-body quantum systems could not only help to create new understanding, it could lead to new applications, for instance in quantum metrology, and in particular in quantum magnetometry.

Explore further: Researchers find nondestructive method to study quantum wave systems

More information: "Detecting nonlocality in many-body quantum states", J. Tura, R. Augusiak, A. B. Sainz, T. Vértesi, M. Lewenstein, A. Acín, 2014, Science, DOI: 10.1126/science.1247715

Related Stories

Long-range tunneling of quantum particles

June 12, 2014

The quantum tunnel effect manifests itself in a multitude of well-known phenomena. Experimental physicists in Innsbruck, Austria, have now directly observed quantum particles transmitting through a whole series of up to five ...

Recommended for you

Walking crystals may lead to new field of crystal robotics

February 23, 2018

Researchers have demonstrated that tiny micrometer-sized crystals—just barely visible to the human eye—can "walk" inchworm-style across the slide of a microscope. Other crystals are capable of different modes of locomotion ...

Researchers turn light upside down

February 23, 2018

Researchers from CIC nanoGUNE (San Sebastian, Spain) and collaborators have reported in Science the development of a so-called hyperbolic metasurface on which light propagates with completely reshaped wafefronts. This scientific ...

Recurrences in an isolated quantum many-body system

February 23, 2018

It is one of the most astonishing results of physics—when a complex system is left alone, it will return to its initial state with almost perfect precision. Gas particles, for example, chaotically swirling around in a container, ...

Seeing nanoscale details in mammalian cells

February 23, 2018

In 2014, W. E. Moerner, the Harry S. Mosher Professor of Chemistry at Stanford University, won the Nobel Prize in chemistry for co-developing a way of imaging shapes inside cells at very high resolution, called super-resolution ...

Hauling antiprotons around in a van

February 22, 2018

A team of researchers working on the antiProton Unstable Matter Annihilation (PUMA) project near CERN's particle laboratory, according to a report in Nature, plans to capture a billion antiprotons, put them in a shipping ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.