(麻豆淫院Org.com) -- In the development of quantum information processing, one of the key requirements is achieving quantum entanglement. But recently, physicists have been investigating other forms of quantum correlations besides entanglement, and wondering if they may be useful and if they may play a role in future quantum communication and computation. In a new study, scientists have found that other forms of quantum correlations can be used to obtain useful entanglement of macroscopic systems, providing new insight and potentially leading to novel quantum technologies.

麻豆淫院icists Laura Mazzola and Mauro Paternostro from Queen鈥檚 University Belfast have published their study on activating entanglement through non-entangled quantum correlations in a recent issue of Nature Scientific Reports. Such non-entangled quantum correlations, which are sometimes referred to as being 鈥渂eyond entanglement,鈥� can be measured using quantum discord.

In a seminal work in this area, Marco Piani of the University of Waterloos and co-workers previously demonstrated that quantum discord can produce entangled states, which is not possible when only classical correlations are available. Building on this work, Mazzola and Paternostro have shown that, by starting with a system of massive harmonic oscillators that have quantum discord, they can generate entanglement in an optomechanical setting involving light fields and mechanical oscillators.

鈥淏y running this protocol, one is able to get entanglement, which is a well-known resource for quantum technology and, allegedly, the key to the advantages of quantum information processing, from systems that shared correlations of a nonclassical nature (discord) but are not entangled at all,鈥� Paternostro told 麻豆淫院Org.com.

This new way of generating entanglement is significantly different from the way that entanglement is normally produced.

鈥淯sually, one starts from systems that do not share quantum correlations at all, in order to prove that the 鈥榤echanism鈥� that one sets up is able to produce entanglement,鈥� Paternostro explained. 鈥淚n the protocol by Piani, et al., and modified so as to adapt to the optomechanical scenario of our work, the key is that if one considers initially discorded states, entanglement is produced!鈥�

So far, this form of entanglement activation has recently been discussed for certain domains, and here Mazzola and Paternostro show that the scheme can be extended, at least in one instance, to systems that have an infinite variety of physically allowed energy configurations.

As Paternostro explained, the scheme is not only intriguing in the way in which it works, but the entanglement it produces is also intriguing in itself due to its potential availability in the macroscopic realm.

鈥淥ptomechanical entanglement is the entanglement between an optical light field and a massive, quasi-macroscopic mechanical oscillator,鈥� he said. 鈥淏y shining light onto an optical cavity endowed with a movable mirror, which embodies the mechanical oscillator, one can get entanglement between the cavity light field and the movable mirror. Therefore, optomechanical entanglement can be seen as 鈥榥ormal鈥� entanglement but, importantly, involving a massive object that verges to macroscopic dimensions (you can really see these guys with your naked eye!).鈥�

By producing optomechanical entanglement, the proposed scheme also provides indirect evidence of mechanical nonclassicality. That is, it shows that two massive mechanical objects, such as oscillators, can be in a state that cannot be described by means of classical theory alone.

鈥淭his is what we would define as mechanical nonclassicality: a quantum mechanical state involving massive mechanical systems, with no classical counterpart,鈥� Paternostro said. 鈥淪uch states are in general rather demanding to be prepared due to the fact that massive objects tend to feel the effects of the surrounding environment rather strongly. Likewise, accessing their properties is indeed difficult: any measurement performed on such systems would severely affect the nonclassical features if not destroy them altogether. The 鈥楬oly Grail鈥� in this context is to generate certified nonclassical mechanical states and be able to reveal their nonclassicality.鈥�

From a practical perspective, optomechanical entanglement could have applications in quantum communications.

鈥淏eside the fundamental implication of having entanglement between macroscopic objects, therefore pushing quantum mechanics to the realm of the observable-by-naked-eye, one could exploit optomechanical entanglement to 鈥榙istribute鈥� entanglement in a network of mechanical nodes, connected by light field,鈥� Paternostro said. 鈥淥ur goal is to show that one can use this sort of architecture to set up an efficient quantum communication 苍别迟飞辞谤办.鈥�

Since the proposed experiment uses technology similar to that used in recent optomechanics experiments, the researchers predict that demonstrating the new scheme should be feasible in the near future.

鈥淥ne of the core activities in my group at Queen's University Belfast is the demonstration that nonclassicality can be enforced in macroscopic systems,鈥� Paternostro said. 鈥淭his experiment is indeed a nice way to do it.鈥�

漏 2011 麻豆淫院Org.com