Expanding the reach of quantum stochastic models

Decoherence — interactions between a quantum system and the larger macroscopic environment — has a significant impact on quantum technology applications. In particular, the theory of quantum feedback networks allows a manipulation of interconnected quantum open systems in the spirit of block design in conventional control theory.

In recent years, models that describe quantum systems and their environments have shown the importance of understanding these interactions for a large variety of areas, from quantum optics to superconducting qubits.

“In many cases, one would like to get insight about operating in a particular limit regime,” said John Gough, an author of the new paper. “It is useful to be able to replace a sequence of such models with a new one that better brings out the features that we wish to highlight.”

Gough joined Luc Bouten on a new paper that proposes ways to replace one family of limiting models with an equivalent one that better highlights certain features or characteristics.

“We may modify a system by allowing its output to be fed back into the model,” Gough said. “Two families of models are equivalent if they are related by an increasing small modification.”

The two researchers applied this approach to explore these approaches.

“We are motivated by several practical problems in quantum control and estimation theory,” said Luc Bouten, the other author of the paper. “We suspected there was a general theory behind this with a wide applicability to modeling noisy quantum systems.”

Source: “Asymptotic equivalence of quantum stochastic models,” by Luc Bouten and John E. Gough, Journal of Mathematical Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5046189 .