Measuring Qubit Parity in Circuit QED
Multi-qubit parity measurements are essential to quantum error correction. Current realizations of these measurements often rely on ancilla qubits, an approach that is sensitive to faulty two-qubit gates and which requires significant experimental overhead. In this talk, I’ll introduce a method for hardware-efficient multi-qubit parity measurement exploiting the bifurcation dynamics of a parametrically driven nonlinear oscillator. This approach takes advantage of the resonator’s parametric oscillation threshold which is a function of the joint parity of dispersively coupled qubits, leading to high-amplitude oscillations for one parity subspace and no oscillation for the other. I’ll present analytical and numerical results for two- and four-qubit parity measurements with high-fidelity readout preserving the parity eigenspaces. Moreover, I’ll discuss a possible realization which can be readily implemented with the current circuit QED experimental toolbox. These results could lead to significant simplifications in the experimental implementation of quantum error correction, and notably of the surface code.