Nonadiabatic switching of a photonic band structure: Ultrastrong light-matter coupling and slow-down of light

Abstract

We map out the band structure of a one-dimensional photonic crystal while a 12-fs control pulse activates ultrastrong interaction with quantized electronic transitions in semiconductor quantum wells. Phase-locked multi-terahertz transients trace the buildup of a large vacuum Rabi splitting and an unexpected asymmetric formation of the upper and lower polariton bands. The pronounced flattening of the photonic bands causes a slow-down of the group velocity by one order of magnitude on the time scale of the oscillation period of light. In photonic crystals (PCs), periodic modulations of the refractive index have been tailored to shape photonic band structures and mold the flow of light.1 Nonresonant lightmatter interaction has been sufficient to confine optical modes with subwavelength precision 2 or to slow down the group velocity of radiation.3,4 Particularly dramatic effects on the optical eigenmodes occur when quantized emitters are resonantly coupled to the vacuum field of a microcavity. The interaction strength is quantified by the vacuum Rabi frequency R , the rate at which a virtual photon is absorbed and spontaneously reemitted. If R exceeds cavity radiative loss and emitter dephasing, the system enters the regime of strong coupling. The eigenstates are then given by light-matter mixed modes, called cavity polaritons. 5-9One of the most intriguing aspects is the limit of ultrastrong coupling (USC), where R becomes comparable with the transition frequency ω 12 of the quantum emitter itself. This extreme case has been reached by hybridizing discrete transitions between electronic subbands in semiconductor quantum wells (QWs) with the mid-infrared (MIR) photon mode of a planar waveguide.10-12 Giant splitting of the two polariton branches, by as much as 2 R = 0.5ω 12 , has been achieved in plasmonic metal structures.13-16 A theoretical description of USC has to go beyond the rotating wave approximation. 17 The resulting squeezed quantum vacuum is expected to give rise to a variety of novel quantum electrodynamical effects. [17][18][19] In particular, ultrafast modulations of R have been predicted to trigger the emission of vacuum photons in a process reminiscent of the dynamical Casimir effect.17,20 Nonadiabatic dynamics of polaritons entering the USC regime has become accessible, recently, with the aid of phase-sensitive multiterahertz optoelectronics. 21 The planar waveguide structure explored so far, however, allowed only for limited control of the spatial dispersion of the photon field.Here we merge the concept of a PC with nonadiabatic and ultrastrong light-matter coupling to approach full spatial and temporal control of a photonic band structure with subcycle and subwavelength precision. To this end, we combine a one-dimensional surface plasmon PC, operated in straightforward transmission, with optically switchable intersubband (ISB) resonances of semiconductor QWs. Phasestable multi-terahertz pulses map out ultrafast snapshots of the photonic dispersion while light-matter interaction is activated by a f...

System-environment coupling derived by Maxwell's boundary conditions from the weak to the ultrastrong light-matter-coupling regime

“…In the present paper, we supposed the simple dielectric (polariton) medium, and our results are applicable to the intersubband transition in semiconductor quantum wells [5][6][7][8][9][10] and more traditionally optical phonons, both of which show the ultrastrong light-matter coupling. On the other hand, for cavity systems with single atom (nonlinear systems) and for the Dicke model (the gauge invariance is broken) [37][38][39], it is still open to dispute whether the system-environment coupling is generally expressed by the eigen-states of the cavity system as in Eq.…”

Light-Matter Decoupling in the Deep Strong Coupling Regime: The Breakdown of the Purcell Effect

“…This phenomenon has consequences on the possibility to realise ultraefficient and ultrastrongly coupled light emitters, and it could be exploited to dynamically control the electromagnetic field distribution in optoelectronic devices, by modulating the intensity of the light matter interaction by optical or electrical means [20,29,31].…”

Effective polariton-polariton interactions of cavity-embedded two-dimensional electron gases

“…In particular, they are the normal modes due to the strong coupling between a cavity photon mode and the transition between two conduction subbands in quantum wells containing a two-dimensional electron gas. Intersubband polaritons were experimentally demonstrated for the first time in 2003 1 and their physics is the object of many interesting investigations, both fundamental [2][3][4][5][6][7][8][9][10][11][12] and applied [13][14][15][16][17][18][19][20][21] . So far, theoretical investigations have been based mostly on a bosonized Hamiltonian approach 2 .…”