Speaker
Description
Propagating microwave photons in waveguides couple well to superconducting qubits and mediate long-range interactions between distant qubits causing the emergence of collective states. Of particular interest are dark or subradiant states, which are protected from decoherence as they decouple from the waveguide environment.
However, the protection from decoherence comes with a caveat that the control of such states is challenging. Recently, we probed a collective dark state formed by two transmon pairs, each pair also exhibiting a local dark state, exploiting local control.
Here, I will present the experimental characterisation of such a four qubit system with an optimised set of parameters for the implementation of a two-qubit gate operation between two local dark states in the waveguide separated by several centimetres. I will show results where we extend the system to larger arrays of transmon qubits in a planar implementation to explore higher excitation states.
Furthermore, I will show how we can use collective states of two qubits in the waveguide to build a primary thermometer which can distinguish the influence of a local bath from the temperature of the mode it
should measure.