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Illustration of open quantum systems and non-Hermitian topology. Credit: Jose Lado, Aalto University.

Scientists have discovered a method for predicting the behavior of many-body quantum systems coupled to their environment. This advancement is essential for safeguarding quantum data in quantum devices, paving the way for practical applications of quantum technology.

In a paper published in Physical Review Letters, a team of researchers from Aalto University in Finland and IAS Tsinghua University in China unveiled a novel approach for predicting the behavior of quantum systems, like particle groups, when connected to external environments. Typically, connecting a system like a quantum computer to its environment leads to decoherence and information leakage, compromising the data within the system. However, the researchers have devised a technique that transforms this issue into a beneficial solution.

The research was carried out by Aalto doctoral researcher Guangze Chen under the supervision of Professor Jose Lado and in collaboration with Fei Song from IAS Tsinghua. Their approach combines techniques from two domains, quantum many-body physics, and non-Hermitian quantum physics.

One of the most intriguing and powerful phenomena in quantum systems is many-body quantum correlations. Understanding these and predicting their behavior is vital because they underpin the exotic properties of key components of quantum computers and quantum sensors. While a lot of progress has been made in predicting quantum correlations when matter is isolated from its environment, doing so when matter is coupled to its environment has so far eluded scientists.

In the new study, the team showed that connecting a quantum device to an external system can be a strength in the right circumstances. When a quantum device is host to so-called non-Hermitian topology, it leads to robustly protected quantum excitations whose resilience stems from the very fact that they are open to the environment. These kinds of open quantum systems can potentially lead to disruptive new strategies for quantum technologies that harness external coupling to protect information from decoherence and leaks.

The study establishes a new theoretical method to calculate the correlations between quantum particles when they are coupled to their environment. The method we developed allows us to solve correlated quantum problems that present dissipation and quantum many-body interactions simultaneously. As a proof of concept, we demonstrated the methodology for systems with 24 interacting qubits featuring topological excitations, says Chen.

Professor Lado explains that their approach will help move quantum research from idealized conditions to real-world applications. Predicting the behavior of correlated quantum matter is one of the critical problems for the theoretical design of quantum materials and devices. However, the difficulty of this problem becomes much greater when considering realistic situations in which quantum systems are coupled to an external environment. Our results represent a step forward in solving this problem, providing a methodology for understanding and predicting both quantum materials and devices in realistic conditions in quantum technologies, he says.

Reference: Topological Spin Excitations in Non-Hermitian Spin Chains with a Generalized Kernel Polynomial Algorithm by Guangze Chen, Fei Song and Jose L. Lado, 7 March 2023, Physical Review Letters.DOI: 10.1103/PhysRevLett.130.100401

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Quantum Breakthrough: New Method Protects Information From Decoherence and Leaks - SciTechDaily