High-efficiency gate-defined quantum dot to single mode fiber interface assisted by a photonic crystal cavity

Abstract

Efficiently interfacing photonic with semiconductor qubits plays an important role in future quantum communication applications. In this paper, we model a photon to exciton interface based on an optically active gate-defined quantum dot (OAQD) embedded in a carefully designed photonic crystal cavity constraining its emission profile via the Purcell effect while maintaining a low enough quality factor to allow for electrical tuning of the emission wavelength. By matching the in-plane k-vector of a cavity mode and the reciprocal lattice constant of the photonic crystal, vertical emission is obtained. A back-reflection mirror located below the cavity and integrated as part of an already predefined process flow allows for not only the increasing of the light extraction efficiency but also the tailoring of the extracted beam profile to match that of a single mode fiber. We numerically show that a photon emitted by the OAQD can be coupled to the targeted free-space Gaussian beam with a probability above 50%, limited by electrode absorption. Further efficiency improvement up to 90% is possible by using indium tin oxide instead of gold as a gate material.

Highly efficient spin qubit to photon interface assisted by a photonic crystal cavity

“…For simplicity, the membrane is assumed to be surrounded by vacuum on both sides here, even though in a realistic fabrication scenario a polymer might be located between the membrane and the bottom reflector onto which it is mounted. While this can have some impact on the device performance in the order of a few additional percents drop in extraction efficiency [21], we expect to maintain a collection efficiency above 50% even then if a sufficiently wide NA is used. The device is described in more detail in the following.…”

“…A reflector is placed beneath the layer stack to recycle the downward propagating light. Moreover, the far-field emission pattern of the OAQD can be modified by adjusting the distance between the OAQD and the reflector, due to selective constructive interference between the upwards emitted and redirected beams for selected in-plane k-vectors [21]. A Gaussian-like far field pattern is obtained when the constructive interference condition is satisfied for in-plane k-vectors equal to 0.…”

“…A recent study reports the cavity enhanced photoluminescence of a QW embedded in a PCC with an OAQD defined by electrodes deposited on the surface of the semiconductor-air interface [20]. We have proposed PCC enhanced photon extraction from an OAQD embedded in a carefully designed photonic crystal H4 cavity [21], with a device modeled to have a photon extraction efficiency of 55.8% in an almost ideal Gaussian-shaped far field pattern (overlap > 95%). However, a complete device integrating a coupled GDQD spin qubit and an OAQD in a PCC has not yet been studied.…”

“…The cavity is designed in such a way that highly efficient vertical emission is achieved at the working wavelength of the OAQD (823 nm). A metal back-reflector is assumed to be deposited on the silicon substrate onto which the GaAs/AlGaAs stack is transferred [21] and serves to coherently recycle photons that are emitted downwards, comparable to what is commonly done in grating couplers [22,23]. Moreover, the far field emission pattern can be optimized by adjusting the position of the back-reflector by selecting in k-space which field components of the PCC mode are preferentially extracted [21].…”

“…A metal back-reflector is assumed to be deposited on the silicon substrate onto which the GaAs/AlGaAs stack is transferred [21] and serves to coherently recycle photons that are emitted downwards, comparable to what is commonly done in grating couplers [22,23]. Moreover, the far field emission pattern can be optimized by adjusting the position of the back-reflector by selecting in k-space which field components of the PCC mode are preferentially extracted [21]. According to our numerical calculations, this structure achieves a power extraction efficiency over 50% if collection optics with a numerical aperture (NA) greater than 0.6 is used.…”