High fidelity dispersive qubit readout with two-mode squeezed light

High fidelity qubit measurement is essential for scalable, fault-tolerant quantum computing. In superconducting circuits, qubit readout with fidelity above 99% has been achieved by using a quantum-limited parametric amplifier such as the Josephson Parametric Converter (JPC) as the first stage amplifier. However, the Signal-to-Noise Ratio (SNR) of such readout is fundamentally limited by quantum fluctuations in the coherent readout pulse. Alternatively, readout with squeezed light can be used to reduce fluctuation along certain quadratures and thus improve the SNR. In this talk, we investigate a readout scheme with two-mode squeezed light both produced and amplified by JPCs in a simple interferometer unbalanced by a transmon qubit/cavity. This configuration has been predicted to improve the SNR compared to readout with both coherent states and single-mode squeezed light [1]. This readout method, which sends two-mode squeezed light along two paths simultaneously is also of interest for remote entanglement of qubits. We will present preliminary data and discuss optimization in the presence of JPC imperfections and photon loss.

[1] Sh. Barzanjeh et al., PRB 90, 134515 (2014).