Probing Sensitivity near a Quantum Exceptional Point using Waveguide Quantum Electrodynamics

• URL: http://arxiv.org/abs/2510.21554v1
• Date: Fri, 24 Oct 2025 15:13:18 GMT
• Title: Probing Sensitivity near a Quantum Exceptional Point using Waveguide Quantum Electrodynamics
• Authors: Aziza Almanakly, Reouven Assouly, Harry Hanlim Kang, Michael Gingras, Bethany M. Niedzielski, Hannah Stickler, Mollie E. Schwartz, Kyle Serniak, Max Hays, Jeffrey A. Grover, William D. Oliver,
• Abstract summary: PT symmetric Hamiltonians have generated interest due to the emergence of exceptional-point degeneracies.<n>Because of the abrupt spectral response near exceptional points, such systems have been proposed as candidates for precision quantum sensing.<n>This study elucidates the limitations of exceptional-point systems as candidates for quantum-enhanced sensing.
• Score: 0.3793559415247259
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Non-Hermitian Hamiltonians with complex eigenenergies are useful tools for describing the dynamics of open quantum systems. In particular, parity and time (\PT) symmetric Hamiltonians have generated interest due to the emergence of exceptional-point degeneracies, where both eigenenergies and eigenvectors coalesce as the energy spectrum transitions from real- to complex-valued. Because of the abrupt spectral response near exceptional points, such systems have been proposed as candidates for precision quantum sensing. In this work, we emulate a passive \PT~dimer using a two-mode, non-Hermitian system of superconducting qubits comprising one high-coherence qubit coupled to an intentionally lossy qubit via a tunable coupler. The loss is introduced by strongly coupling the qubit to a continuum of photonic modes in an open waveguide environment. Using both pulsed and continuous-wave measurements, we characterize the system dynamics near the exceptional point. We observe a behavior broadly consistent with an ideal passive \PT~dimer with some corrections due to the tunable coupler element. We extract the complex eigenenergies associated with the two modes and calculate the sensitivity as a function of the coupling strength. Confirming theoretical predictions, we observe no sensitivity enhancement near the quantum exceptional point. This study elucidates the limitations of exceptional-point systems as candidates for quantum-enhanced sensing.

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