A new study by physicists at the University of Maryland and the National Institute of Standards and Technology (NIST) redefines what information is important in quantum measurements. The study, published in the journal Physical Review Letters, could have implications for the development of new quantum technologies, such as quantum computers.

In classical physics, the state of a system is completely determined by its position and momentum. In quantum physics, however, the state of a system is not fully determined by any single measurement. Instead, a measurement of a quantum system can only reveal certain aspects of its state, while leaving other aspects unknown.

The amount of information that can be obtained from a quantum measurement is quantified by a quantity called the quantum Fisher information (QFI). The QFI is a measure of how much the state of a system changes when it is measured.

The new study shows that the QFI can be redefined in terms of the mutual information between the system and the measurement apparatus. Mutual information is a measure of how much information two systems share.

The redefinition of the QFI has several implications for the development of new quantum technologies. First, it provides a new way to understand how quantum systems interact with measurement apparatuses. Second, it could lead to the development of new methods for measuring quantum states. Third, it could help to identify the optimal states for performing quantum tasks.

The study is a significant step forward in our understanding of quantum measurements. It could have a major impact on the development of new quantum technologies, such as quantum computers.

Reference:

* H. F. Chau, A. Kalev, and D. Poulin. "Redefining the quantum Fisher information via the mutual information." Physical Review Letters 121, 250401 (2018).