Thermal cat states in a high Q niobium cavity setup

The standard paradigm for creating quantum states has been to cool the system of interest to the ground state or decouple it sufficiently from any hot thermal bath. For example, in circuit QED experiments, filters and attenuators in the drive and measurement lines are used to prevent thermal noise reaching the quantum systems.

Here, we demonstrate that starting from a classical thermal state, we can create coherent superpositions of these thermal states aka thermal cat states with visible interference fringes highlighting their non-classical nature. Using a high Q Niobium cavity coupled to a superconducting transmon qubit, we experimentally prepare thermal cat states up to a large thermal population of n_th>2.

These experiments are especially relevant for applications to opto-mechanical setups and macroscopic quantum systems. Due to the typical kHz-regime mechanical frequencies, there is a large thermal population of the mechanical modes, thus making it challenging to cool to the ground state. With our experiments we show that this is not a necessary requirement for creating non-gaussian states.