Review Article appeared in Nature Physics

02.04.2012

Review Article on Photonic Quantum Simulations appeared in Nature Physics

Alan Aspuru-Guzik (Harvard University) and Philip Walther (University of Vienna) review the recent progress in the field of photonic quantum simulation: their Insight Article will be published in “Nature Physics” this week.

Quantum simulators are controllable quantum systems that mimic quantum systems which are, if at all, difficult to study directly. They will enable researchers to tackle problems that are intractable using conventional computers. The main reason why quantum simulation has become one of the most active areas in quantum science is due to the vast technological developments which pave the way for realistic quantum simulation experiments. The low threshold for useful simulations of other quantum systems, as pointed out by the famous physicist Richard Feynman, makes quantum simulation one of the first potential applications of quantum computers. In fact, only a few dozen qubits are required to outperform a conventional computation. Alan Aspuru-Guzik (Harvard University) and Philip Walther (University of Vienna) review the recent progress in the field of photonic quantum simulation: their Insight Article will be published in “Nature Physics” this week.

Photonic quantum simulation experiments

This is a realistic goal for current experimental research and a particular focus of the research of Philip Walther’s group at the University of Vienna. Current photonic quantum technology has reached a stage where the simulation of interesting problems in quantum chemistry, quantum biology and solid-state physics becomes feasible. Last year a research team around Philip Walther used the precise quantum control of four entangled photons to simulate complex quantum phenomena in solid-state systems. The work which was published in Nature Physics underlined that quantum simulations are a very good tool for calculating quantum states of matter and are thus opening the possibility for researchers to investigate more complex systems.

Schematic of the photonic quantum simulation of delocalized chemical bonds. a, Two entangled photon pairs are generated through the process of parametric down-conversion. Superimposing one single photon from each pair at a tunable beam splitter results in quantum interference, such that the measured four-photon coincidences correspond to the ground state, for example of a Heisenberg-interacting spin tetramer. Dependent on the reflectivity of the beam splitter, frustration in valence-bond states or so-called spin-liquid states can be investigated. b, Future experiments using more entangled photon pairs may allow the study of the ground-state properties of molecular ground states, such as the delocalized bonds in benzene.