Physicists propose second quantization level for quantum Shannon theory

The theory of information, developed by Claude Shannon from the late 1940s, deals with issues such as the speed with which information can be transmitted through a noisy communication channel. The information carriers (for example, photons) and the channel (for example, the fiber optic cable) are supposed to be classical systems, with well defined and perfectly distinguishable states.

Over the last two decades, physicists have developed a quantum version of information theory in which the internal state of each medium of information has quantum properties, such as superposition: possibility of occupying two or several classic states at a time. But the lines of transmission are usually still considered classic, so that the path taken by the messages in space is always well defined.

In a new article, physicists Giulio Chiribella and Hlér Kristjánsson from Oxford University and the University of Hong Kong have proposed a second level of quantification, in which information carriers and channels can be quantum superimposed . In this new communication paradigm, information carriers can borrow multiple channels simultaneously.

"This work lays the foundation for a new theory of communication in which the spread of information in space and time is processed mechanically quantum way," said Chiribella. Phys.org. "This opens new avenues for quantum communication networks and for a future quantum internet, where data could be sent from one sender to one recipient via multiple quantum servers." Exploiting the interference of different paths of communication, it will be possible to communicate more effectively and more effectively, more fundamentally, the transmission of messages on multiple trajectories could give rise to fundamental tests of the quantum nature of space-time. "

This phenomenon of channel superposition can be observed in the famous double-slot experiment, in which a single photon seems to cross two slots at a time. Even if only one photon is used, the photon creates an interference pattern on the detector. The best explanation for the interference pattern is that the photon interferes with itself, like a wave, after having simultaneously traversed the two slots along two different paths.

When an information carrier is allowed to travel simultaneously on two communication channels, it may offer benefits such as noise reduction (due to noise interference on different paths) and a capability to upper channel. These benefits have been demonstrated in recent experiments with photons.

In the new article, physicists were facing some of the challenges associated with incorporating channel superposition into a quantum information theory. One of the challenges is to describe the channel overlay in a compositional way, so that the behavior of a channel can be predicted when it is used in combination with other channels. A second challenge is that the overlay of internal states of the information carriers must be clearly separated from the overlay of paths. Otherwise, the path itself becomes part of the message and the system can be described using the conventional quantum structure.

In tackling these problems, physicists have developed a quantum communication model that can be used to calculate the amount of information that can be reliably transmitted when using a number given channels in a quantum superposition. Counter-intuitively, physicists have shown that, for some types of noise, channel overlay as well as the ability to swap a channel with itself could be used to completely suppress all noise. This opens up the possibility of getting a perfect quantum communication in a noisy channel.

"Our work has defined a communication model and provided some examples of proof of principle," said Chiribella. "However, this has only touched the surface of what can be accomplished with the superposition of quantum communication channels.We now explore the power of correlations between them.If two trajectories visit the same region, the process experienced by the information carrier in the first trajectory can be correlated with the process experienced in the second trajectory.Taking advantage of these correlations in an intelligent way, it is possible to improve the communication performance at the beyond what can be done with the superposition of independent channels, will give us new insights into the particular ways in which quantum information propagates in space and time. "

© 2019 Science X Network