Quantum simulation with light: Frustrations between photon pairs

Already the behavior of relatively small quantum systems cannot be calculated because quantum states contain much more information than their classical counter-parts. However, if another quantum system is used to simulate the quantum system of interest, then answers about the properties of the complex quantum system can be obtained.

When is a quantum system frustrated?
Currently, many international groups are focusing their research on frustrated quantum systems, which have been conjectured to explain high-temperature superconductivity. A quantum system is frustrated if competing requirements cannot be satisfied simultaneously. The Viennese research group realized for the first time an experimental quantum simulation, where the frustration regarding the "pairing" of correlations was closely investigated.

Using two pairs of entangled photons, a frustrated quantum system could be simulated that consists of four particles. “Just the recent development of our quantum technology allows us to not only rebuild other quantum systems, but also to simulate its dynamics” says Philip Walther (University of Vienna). “Now we can prepare quantum states of individual photons to gain insights into other quantum systems”, explains Xiao-song Ma (Austrian Academy of Sciences).Therefore, two in polarization entangled photons exhibit in many ways the same quantum physical properties as for example electrons in matter.

Conflict over partnerships
The research team of international scientists from China, Serbia, New Zeeland and Austria prepared single photons that were facing the conflict over partnerships between each other. Each photon can establish a single bond to only one partner exclusively, but wants to get correlated with several partners – obviously this leads to frustration. As a result, the quantum system uses “tricks” that allow quantum fluctuations that different pairings can coexist as superposition.

The work of the Viennese group underlines that quantum simulations are a very good tool for calculating quantum states of matter and are thus opening the path for the investigation of more complex systems.

Publication
Xiao-song Ma, Borivoje Dakic, William Naylor, Anton Zeilinger & Philip Walther: Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems. In: Nature Physics 7, 399–405 (2011) doi:10.1038/nphys1919
Full Text: http://www.nature.com/nphys/journal/v7/n5/full/nphys1919.html

Scientific Contact
Univ.-Ass. Dr. Philip Walther
Quantum Optics, Quantum Nanophysics, Quantum Information
Faculty of Physics
University of Vienna
1090 Vienna, Boltzmanngasse 5
T +43-1-4277-295 75
philip.walther(at)univie.ac.at

Queries
Mag. Ursula Gerber
Quantum Optics, Quantum Nanophysics, Quantum Information
Faculty of Physics
University of Vienna
1090 Vienna, Boltzmanngasse 5
T +43-1-4277-512 66
ursula.gerber(at)univie.ac.at