Microwave Phase Sensing: Classical and Quantum Approaches with a JTWPA Source

Phase sensing in the microwave domain play a central role in quantum metrology, as the precision of phase estimation directly determines the overall sensitivity of measurements. In superconducting qubits, for example, information is often encoded in the phase of a resonator signal. However, the sensitivity of such measurements is ultimately limited by the Standard Quantum Limit (SQL), imposed by vacuum fluctuations.

One way to surpass this limit is to employ squeezed states, where the quantum noise is redistributed between the two field quadratures. By reducing the uncertainty in one quadrature while increasing it in the other, we can improve the resolution on the quantity of interest, in our case the phase. In the microwave regime, these nonclassical states can be efficiently generated through Josephson-based nonlinear devices, with the Josephson Traveling-Wave Parametric Amplifier (JTWPA) emerging as a powerful platform for broadband squeezed-state generation.



In this work, we present a comparative analysis of two phase discrimination protocols: a classical one, based on a coherent input state, and a quantum one, where the input is a squeezed coherent state produced by a JTWPA. The aim is to assess how effectively each protocol can detect a phase shift Δφ introduced by a Device Under Test (DUT). By quantifying and comparing their phase-discrimination capabilities, we seek to determine whether the quantum protocol can outperform the SQL and to identify the operating regimes that offer the greatest advantage for microwave phase measurements employing superconducting parametric devices.