Photons have a memory?

The modern quantum physics allows for many interesting applications that build on the intriguing properties of quantum mechanical systems. They may include, for example, taking advantage of the close entanglement of quantum particles to increase the efficiency of physical processes. In reality, however, quantum systems are subjected to unavoidable influences of their environment.

An open quantum system loses its ‘quantumness’ when information about the state leaks into its surroundings. Researchers now control this so-called decoherence in a single photon. By rotating an optical filter, the information flow between the photon and its environment can be tuned. This concept could be harnessed for future quantum technologies.

Source: Prof. Dr. Heinz-Peter Breuer

Realistic quantum mechanical systems are always exposed to an external environment. This often induces Markovian processes in which the system loses information to its surroundings. However, many quantum systems exhibit non-Markovian behaviour with a flow of information from the environment back to the system. The environment usually consists of large number of degrees of freedom which are difficult to control, but some sophisticated schemes for reservoir engineering have been developed. The control of open systems plays a decisive role, for example, in proposals for entanglement generation and dissipative quantum computation, for the design of quantum memories and in quantum metrology. The authors report an all-optical experiment which allows one to drive the open system from the Markovian to the non-Markovian regime, to control the information flow between the system and the environment, and to determine the degree of non-Markovianity by measurements on the open system.

According to the authors the experiment shows that photons have a memory, thus in a position to remember previous states, and regain their original quantum properties.

The paper was published in the journal Nature Physics.

Experimental control of the transition from Markovian to non-Markovian dynamics of open quantum systems.
B.-H. Liu, L. Li, Y.-F. Huang, C.-F. Li, G.-C. Guo, E.-M.
Laine, H.-P. Breuer and J. Piilo
Nature Physics, published online: 11 September 2011
DOI: 10.1038/NPHYS2085.

Source: University of Freiburg