Coexistence of weak and strong coupling in a photonic molecule through dissipative coupling to a quantum dot

We study the emission from a molecular photonic cavity formed by two proximal photonic crystal defect cavities containing a small number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo> <mml:mrow><mml:mo><</mml:mo> <mml:mn>3</mml:mn></mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:math> of In(Ga)As quantum dots. Under strong excitation, we observe photoluminescence from the bonding and antibonding modes in agreement with ab initio numerical simulations. Power dependent measurements, however, reveal an unexpected peak, emerging at an energy between the bonding and antibonding modes of the molecule. Temperature-dependent measurements indicate that this unexpected feature is photonic in origin. Time-resolved measurements show the emergent peak exhibits a lifetime <i>τ</i> _M = 0.75(10) ns, similar to both bonding and antibonding coupled modes. Comparisons of experimental results with quantum optical modeling suggest that this new feature arises from a coexistence of weak and strong coupling, due to the molecule emitting in an environment whose configuration permits or, on the contrary, impedes its strong coupling. This scenario is reproduced theoretically with a master equation reduced to the key ingredients of its dynamics and that roots the mechanism to a dissipative coupling between bare modes of the system. Excellent qualitative agreement is obtained between experiment and theory, showing how solid-state cavity QED can reveal intriguing new regimes of light-matter interaction.