Simple, smooth 50ns QND circuit-QED measurement pulses

We demonstrate a technique for greatly reducing the duration and error in circuit QED measurement tasks. We show how to suppress different errors including state discrimination, cavity reset, non-linear cavity effects, bandwidth, filtering, all while retaining QND-ness and staying within a single quadrature. The technique works for a variety of different circuit configurations, including Purcell filters, where two different cavities need to be simultaneously emptied. Moreover, the speed and quantum non-demolition nature is retained as one scales up to more qubits or quantum states, providing a blueprint for scaling up to simultaneously measure leakage state populations, multiple qubits, or multiple network modes. We show for realistic circuit parameters that not only speed can be improved by an order of magnitude but errors as well with 99.9% fidelity well within reach. The technique can be understood in terms of control-theoretic transfer function formalism or shortcuts to adiabaticity, where we can also leverage the adiabatic methodology to cancel unwanted nonlinear effects such as Kerr nonlinearity.