Increasing qubit readout fidelity and efficiency with two-mode squeezed light

Implementing quantum information processing on a large scale with flawed components requires highly efficient, quantum non-demolition (QND) qubit readout. In superconducting circuits, qubit readout using coherent light 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, further improvement of such measurement is fundamentally limited by the vacuum fluctuations on the ports of the JPC. Alternatively, readout with squeezed input can entangle the vacuum fluctuations in different modes, thus allowing for the reduction of the noise by controlling their interference. In this talk, we demonstrate a dispersive qubit readout scheme which exploits the two-mode squeezed light generated by a first JPC and processed by a second JPC to form an amplified interferometer [1]. We have observed a 22% improvement in the voltage Signal-to-Noise Ratio (SNR) of the measurement compared to coherent light. We can also extend this scheme to generate remote entanglement. We will discuss how the role of losses changes in this system for coherent vs two-mode squeezed light.

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