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Probing Sensitivity Near a Quantum Exceptional Point Using Waveguide Quantum Electrodynamics
Aziza Almanakly1,2, Réouven Assouly1, Harry Hanlim Kang1,2
1Massachusetts Institute of Technology, Research Laboratory of Electronics, Cambridge, Massachusetts 02139, USA.
Physical Review Letters
|May 22, 2026
Summary
Researchers explored parity-time (PT) symmetric systems for quantum sensing. They found that exceptional points in these systems do not enhance sensitivity, limiting their use in precision quantum sensing applications.
Area of Science:
- Quantum physics
- Open quantum systems
- Superconducting circuits
Background:
- Non-Hermitian Hamiltonians describe open quantum systems with complex eigenenergies.
- Parity-time (PT) symmetric systems exhibit exceptional points where eigenvalues and eigenvectors merge.
- Exceptional points are theoretically proposed for precision quantum sensing due to abrupt spectral responses.
Purpose of the Study:
- To emulate a passive parity-time (PT) dimer using superconducting qubits.
- To investigate the quantum dynamics and sensitivity of PT-symmetric systems near exceptional points.
- To explore the potential of waveguide quantum electrodynamics for studying non-Hermitian dynamics.
Main Methods:
- Emulation of a passive PT dimer using a two-mode non-Hermitian superconducting qubit system.
- Introduction of loss by coupling a qubit to a continuum of photonic modes in an open waveguide.
- Characterization of system dynamics and eigenenergies using pulsed and continuous-wave measurements.
Main Results:
- Observed behavior consistent with an ideal passive PT dimer, with minor corrections from the tunable coupler.
- Extracted complex eigenenergies and calculated sensitivity as a function of coupling strength.
- Confirmed theoretical predictions of no sensitivity enhancement near the quantum exceptional point.
Conclusions:
- Exceptional-point systems do not offer enhanced sensitivity for quantum sensing.
- The study elucidates limitations of exceptional points in quantum sensing applications.
- Waveguide quantum electrodynamics provides a versatile platform for exploring non-Hermitian quantum dynamics in superconducting circuits.
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