Posted: February 5, 2010

A quantum physicists' stroboscope - resonator emits brief flashes of light for entangled photons

(Nanowerk News) An important step in the way towards the quantum computer is the generation and testing of systems made up of several entangled quantums.
When constructing such quantum systems, photons, light particles, are well suited. In the context of the Cluster of Excellence “Munich-Centre for Advanced Photonics” (MAP), Professor Harald Weinfurter and his team of physicists from the LMU Munich and the MPI of Quantum Optics have now come up with a new method enabling the generation of ultrafast flashes of light in very high intensity in rapid succession, as they are needed for the creation of entangled photons. Aside from the quantum computer as a long-term goal, new possibilities in different areas of application are opening up, for instance optical spectroscopy ("Ultraviolet enhancement cavity for ultrafast nonlinear optics and high-rate multiphoton entanglement experiments").
“Spooky action at distance” is what Einstein termed the mysterious interaction of entangled photons, in which the measuring of one photon’s condition influences another photon’s condition. Therefore, it is one of the researchers’ goals to entangle many photons and examine what happens. This does not only concern the development of a quantum computer, but also contributes to a better understanding of the quantum world and the question of how the entanglement spreads over large quantum systems.
However, several entangled photons can only be generated using ultra quick and high-energy light pulses. So far, the high pulse energy necessary could not be realized; especially when the single light pulses need to be generated stroboscopically fast, intense and in sufficiently quick succession in the ultraviolet spectrum of light.
For the first time, the Munich team transferred a process working well with infrared light frequencies to the high in energy spectrum of ultraviolet light. They deployed a Resonator, in order to chase the UV-light pulses lasting only few femtoseconds from one side to the other with high frequency. Thereby, the pulses continuously add up, provided each incoming pulse superimposes the already existing pulses in the resonator precisely.
This way, ultra short light pulses are formed in rapid succession. Those pulses are more than fifty times more intense than those being generated by commercial laser systems. Facilitated by the light pulses, a crystal is stimulated to send out entangled photons in the resonatorRoland Krischek, one of the resonance chamber’s constructors, sees great potential within it: “Our light resonator enables us to examine the entanglement over large systems closely”. His colleague Witlef Wieczorek adds: “By using this resonator, one can not only generate entangled photons, but also study molecular properties of charge transportation in semiconductors.”
Source: Ludwig-Maximilians-Universität München