New protocol to detect entanglement of many-particle quantum states

March 21, 2016
Quantum systems consisting of many particles can enter highly intricate states with strong so-called multiparticle entanglement. A new-found theoretical relation now allows extracting it with standard tools available in scattering experiments. Credit: IQOQI/Ritsch

Physicists have developed a new protocol to detect entanglement of many-particle quantum states using a much easier approach. The new protocol, now published in Nature Physics, is particularly interesting for characterizing entanglement in systems involving many particles. These systems could help us not only to improve our understanding of matter but to develop measurement techniques beyond current existing technologies.

In quantum theory, interactions among particles create fascinating correlations known as that cannot be explained by any means known to the classical world. Entanglement is a consequence of the probabilistic rules of quantum mechanics and seems to permit a peculiar instantaneous connection between particles over long distances that defies the laws of our macroscopic world - a phenomenon that Einstein referred to as "spooky action at a distance."

Developing protocols to detect and quantify entanglement of many-particle quantum states is a key challenge for current experiments because entanglement becomes very difficult to study when many particles are involved. "We are able to control smaller particle ensembles well, where we can measure entanglement in a relatively straight forward way," says quantum physicist Philipp Hauke. However, "when we are dealing with a large system of entangled particles, this measurement is extremely complex or rather impossible because the resources required scale exponentially with the system size."

Philipp Hauke and Peter Zoller from the Department of Theoretical Physics at the University of Innsbruck and the Institute for Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences in collaboration with Markus Heyl from the Technical University of Munich, and Luca Tagliacozzo from ICFO - The Institute of Photonic Sciences have found a new way to detect certain properties of many-particle entanglement independent of the size of the system and by using standard measurement tools.

Entanglement measurable via susceptibility

"When dealing with more complex systems, scientists had to carry out a large number of measurements to detect and quantify entanglement between many particles," says Philipp Hauke. "Our protocol avoids this problem and can also be used for determining entanglement in macroscopic objects, which was nearly impossible until now."

With this new method theoretical physicists are able to use tools already well established experimentally. In their study, published in Nature Physics, the team of researchers give explicit examples to demonstrate their framework: The entanglement of many-particle systems trapped in optical lattices can be determined by laser spectroscopy, and the well-established technique of neutron scattering may be used for measuring it in solid-state systems. As the physicists have been able to show, the quantum Fisher information, which represents a reliable witness for genuinely multipartite entanglement, is in fact measurable. The researchers have highlighted that entanglement can be detected by measuring the dynamic response of a system caused by a perturbation, which can be determined by comparing individual measurements. "For example, when we move a sample through a time-dependent magnetic field, we can determine the system's susceptibility towards the magnetic field through the measurement data and thereby detect and quantify internal entanglement," explains Hauke.

Manifold applications

Quantum metrology, i.e. measurement techniques with increased precision exploiting , is not the only important field of application of this protocol. It will also provide new perspectives for quantum simulations, where is used as a resource for studying properties of quantum systems. In solid-state physics, the protocol may be used to investigate the role of entanglement in many-body systems, thereby providing a deeper understanding of quantum matter.

Explore further: Physicists discover easy way to measure entanglement—on a sphere

More information: Measuring multipartite entanglement through dynamic susceptibilities, Nature Physics, DOI: 10.1038/nphys3700

Related Stories

New paths into the world of quasiparticles

July 9, 2014

Quasiparticles can be used to explain physical phenomena in solid bodies even though they are not actual physical particles. Physicists in Innsbruck have now realized quasiparticles in a quantum system and observed quantum ...

Three 'twisted' photons in 3 dimensions

February 29, 2016

Researchers at the Institute of Quantum Optics and Quantum Information, the University of Vienna, and the Universitat Autonoma de Barcelona have achieved a new milestone in quantum physics: they were able to entangle three ...

Recommended for you

Flexible ferroelectrics bring two material worlds together

January 17, 2017

Until recently, "flexible ferroelectrics" could have been thought of as the same type of oxymoronic phrase. However, thanks to a new discovery by the U.S. Department of Energy's (DOE) Argonne National Laboratory in collaboration ...

First-ever X-ray image capture of material defect process

January 17, 2017

From blacksmiths forging iron to artisans blowing glass, humans have for centuries been changing the properties of materials to build better tools – from iron horseshoes and swords to glass jars and medicine vials.

Theory lends transparency to how glass breaks

January 16, 2017

Over time, when a metallic glass is put under stress, its atoms will shift, slide and ultimately form bands that leave the material more prone to breaking. Rice University scientists have developed new computational methods ...

A novel way to put flame retardant in a lithium ion battery

January 16, 2017

(—A team of researchers at Stanford University has found a novel way to introduce flame retardant into a lithium ion battery to prevent fires from occurring. In their paper published in the journal Science Advances, ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Mar 23, 2016
We do understand matter. It's made of protons and electrons and the fields they produce. First, what is the boundary conditions on an electron or a proton? What is mass other than a mass of these? Why are we using a magical prediction for actuality and a clear description? Does anyone have a simulation using the Bohr model to simulate all the elements and compounds and response to a varying E field? You do know what quanta is? You do understand what a continuous space is? You do understand QM is not a sampling theorem? So what are you trying to detect again? Really?
Mar 23, 2016
This comment has been removed by a moderator.
Mar 23, 2016
This comment has been removed by a moderator.

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.