Observation of Parity-Time Symmetry in Optically Induced Atomic Lattices

Abstract

We experimentally demonstrate PT-symmetric optical lattices with periodical gain and loss profiles in a coherently prepared four-level N-type atomic system. By appropriately tuning the pertinent atomic parameters, the onset of PT-symmetry breaking is observed through measuring an abrupt phase-shift jump between adjacent gain and loss waveguides. The experimental realization of such a readily reconfigurable and effectively controllable PT-symmetric waveguide array structure sets a new stage for further exploiting and better understanding the peculiar physical properties of these non-Hermitian systems in atomic settings.

Parity‐Time‐Symmetric Optical Lattice with Alternating Gain and Loss Atomic Configurations

“…Figure h theoretically predicts the evolution of the phase difference in a PT‐symmetric lattice with ten coupled gain–loss channels. The dynamical behaviors of the system is calculated based on the paraxial wave equation , where V ( x ) is the potential of the periodic gain–loss structure and E is the electric field envelope in each channel . The results from this theoretical simulation can well explain our experimentally observed phase difference jump across the threshold point.…”

“…The gain–loss profiles are generated by the active Raman gain and modified (EIT) absorption due to laser‐induced atomic coherence effects. Compared to the previous work based on discrete diffraction for the signal field, the current scheme is much easier to operate in real experiment. More importantly, the gain and loss coefficients can be adjusted more independently, which will be easier to control the gain, loss, and coupling coefficients to realize the PT‐symmetric condition and study related effects.…”

“…When the coupling beam is sent in with an extended uniform (Gaussian) profile and two signal beams are injected in the same directions as the two pump beams, the detected signal‐field profile exhibits interference pattern with the peak experiencing gain due to the four‐level Raman gain process and the valley experiencing loss due to three‐level EIT (with the weak pump field). This scheme is quite different from the one adopted in our previous work, and consequently requires a distinct laser configuration. In the current work, the refractive index along the x direction can be spatially engineered in a periodic way with the assistance of an EIT window generated by the co‐propagating standing‐wave signal field (formed by two signal beams with different intensities) and Gaussian coupling field.…”

Four-wave mixing in spin–orbit coupled Bose–Einstein condensates

“…In optics, for example, one can satisfy the matching conditions for the FWM of light propagating in homogeneous parity-time (PT )-symmetric coupled waveguides with gain and losses [12]. One can also consider the matching conditions, and thus observation of the FWM in PT -symmetric optical lattices which are available experimentally [13]. And yet another interesting application was demonstrated in multi-component vector solitons consisting of two perpendicular FWM dipole components created by electromagnetically induced gratings [14].A similar situation naturally occurs for spinor Bose-Einstein condensate, where coupling between two atomic states by means of the spin-orbit coupling (SOC) allows one to manipulate the dispersion relation in the presence of external potential.…”

Incident Direction Independent Wave Propagation and Unidirectional Lasing

“…Our findings provide insights into light control and may shed light on the explorations of desirable functionality in fundamental research and practical applications. Introduction.-Parity-time (PT ) symmetry has been theoretically and experimentally investigated in a variety of non-Hermitian systems ; non-Hermiticity controls the exact and broken PT -symmetric phases [18][19][20][21][22]. The phase transition points are exceptional points [23][24][25][26][27] utilized for sensing enhancement [28][29][30][31][32].…”