Observation of Exceptional Point in Non-Dissipative Anti-Parity-Time-Symmetry with Hot Atoms

Parity-time (PT) symmetric systems are extremely sensitive to non-Hermitian parametric perturbations near the exceptional point (EP), which has led to the widespread use of EP-based precision sensing in a wide variety of systems. However, conventional PT symmetric systems require the introduction of gains and losses, which can cause quantum noise problems. The anti-PT-symmetric system can be used without introducing gains and losses and also possesses an extremely high sensitivity in the vicinity of the EP. However, the experimental verification of EP in non-dissipative anti-PT-symmetric systems with hot atoms has not yet been demonstrated. Here, we demonstrate non-dissipative anti-PT-symmetry through far-detuned four wave mixing (FWM) in hot atoms and successfully observe the EP, which will provide a practicable means for applications such as quantum sensing and quantum information processing at ambient conditions.