In this theoretical work, we study a double quantum dot interacting strongly with a microcavity, while undergoing resonant tunneling. Effects of interdot tunneling on the light-matter hybridized states are determined, and tunability of their brightness degrees, associated dipole moments, and lifetimes is demonstrated. These results predict dipolariton generation in artificial molecules coupled to optical resonators and provide a promising scenario for the control of emission efficiency and coherence times of exciton polaritons.

In recent years, interest for light generation from low-dimensional structures coupled to electrodynamics cavities has increased noticeably [

Those high-quality nanostructured semiconductors that can be obtained by molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) [

Considering the implementation of electronic devices, the use of artificial atoms instead of natural ones would be advantageous, given the obvious convenience of working with stable solid structures rather than with tiny and elusive atoms, for constructing on-chip light-matter hybrid structures [

In turn, microcavities confine light in a small volume and increase radiation-matter coupling as described by the Purcell effect [

On the other hand, coupling by resonant tunneling between adjacent QDs (artificial molecules) has been proposed as an efficient mechanism to improve tunability in zero-dimensional systems [

For instance, recent experiments have taken advantage of interdot coupling in artificial molecules within QED cavities, for the enhancement of hybrid qubits [

Regarding two-dimensional systems, several theoretical and experimental efforts have been carried out toward controllable condensation of multiexciton states in double-quantum wells inside cavities [

As for the direct measurement of coherent superpositions of light-matter states in QD-cavity systems, it has been achieved by a few recent experiments [

In this work, we study the properties at the small photon number scale of EP modes for a DQD embedded in a microcavity, in such a way that interdot coupling and strong radiation-matter interaction are simultaneously considered and formation of polaritons with adjustable dipole moment (dipolaritons) and reduced brightness (dark polaritons) is explored [

We consider an asymmetric double quantum dot with a slight difference in the intrinsic energy of the direct and indirect excitonic levels, coupled to a microcavity. Figure

(a) Schematics of the studied system. (b) Configuration basis.

In the absence of a bias field, the direct exciton (DX) coupled to a photonic mode would form a conventional polariton with a coupling energy given by the Rabi frequency Ω (which in turn depends on the radiation-matter constant

Application of an external bias

The tunneling rate

The Hamiltonian for the

The control parameter is the electric field

Whether the cavity is a photonic crystal, a micropillar, or an arrangement of Bragg mirrors is irrelevant for the model. What becomes important is the existence of a well-defined electromagnetic mode, whose energy difference with the ground direct and indirect excitons can be much smaller than the difference between cavity eigenfrequencies. This allows neglecting not just other modes in the cavity but also the excited levels in each dot constituting the artificial molecule (supposing dots at the order of the few nanometers in height and radius as the ones used in the current quantum optical experiments).

To obtain the bias-dependent radiative lifetimes of the EP eigenstates and their corresponding decay rates, which determine the dynamics of the system at a very-low temperature, where phonon dissipation effects can be ignored, we use the imaginary part of the effective Hamiltonian yielded by equation (

Thus, the real and imaginary parts of the eigenvalues of the matrix in equation (

By diagonalizing the Hamiltonian in equation (

(a) Lower, middle, and upper polariton modes as functions of the bias field

From the obtained coefficients shown in Figure

BPD indicates how strong is the mixing between the DX and the cavity mode, and EDM accounts for the dipole moment associated to the corresponding EP mode.

Figure

Exciton dipole moments for the (a) upper, (b) middle, and (c) lower polariton modes. Bright polariton degree for the (d) upper, (e) middle, and (f) lower polariton modes. Both quantities as functions of

Regimes (II) and (III) are particularly interesting: the former because this type of polariton states are expected to be long-living bosons, promising for exciton condensates and derived applications [

The effective tunability by electrical means of the polariton dipole moment (across one order of magnitude), shown in Figures

To evidence how polariton lifetimes can be tuned along a wide range, we calculate the system dynamics by diagonalizing the complex matrix of equation (

(a) Polariton decay rate and (b) polariton lifetime for each EP mode, as functions of

Those curves reveal how the lower and upper branches allow tuning the polariton lifetimes between tens and hundreds of picoseconds, by the application of modest bias (below

In this work, we presented a theoretical model for a quantum dot molecule strongly coupled to a microcavity, which allows the calculation of the composed system eigenenergies, as well as of the corresponding eigenstates (dressed states) and radiative decay rates. From the simulated fractional components and polariton lifetimes, as functions of a feasible tuning parameter (electric field), the possibility of generating polaritons with enhanced exciton dipole moment and adjustable emission efficiency and duration is demonstrated.

These results suggest that the proposed combination of artificial molecules with optical resonators could foster improved control of coherence times and on-demand emission of nonclassical light from strongly coupled light-matter arrangements. Thus, further motivation for the experimental realization of exciton polaritons from double-quantum dot-cavity settings is provided.

Supporting data would be available on reasonable request.

The authors declare they have no conflict of interest.

Financial support from the research division of the Universidad Pedagógica y Tecnológica de Colombia (UPTC), under grant SGI-2527, is acknowledged.