Spontaneous emission control of single quantum dots by electromechanical tuning of a photonic crystal cavity

Abstract

We demonstrate the control of the spontaneous emission rate of single InAs quantum dots embedded in a double-membrane photonic crystal cavity by the electromechanical tuning of the cavity resonance. Controlling the separation between the two membranes with an electrostatic field we obtain the real-time spectral alignment of the cavity mode to the excitonic line and we observe an enhancement of the spontaneous emission rate at resonance. The cavity has been tuned over 13 nm without shifting the exciton energies. A spontaneous emission enhancement of ≈ 4.5 has been achieved with a coupling efficiency of the dot to the mode β ≈ 92%.The coupling of a quantum emitter such as a quantum dot (QD) to a semiconductor photonic crystal cavity (PCC) has shown to be a promising method to realize single photon sources on a chip, 1 enabling applications in quantum key distribution and quantum photonic integrated circuits (QPIC). Two-dimensional PCCs are commonly used for this purpose due to the high achievable Q factors and small mode volumes. 2,3 The spontaneous emission rate of a two-level system is strongly affected by the local density of optical states provided by the surrounding electromagnetic resonator 4 and can be enhanced or suppressed depending on the spectral alignment between emitter and cavity. The spectral control of QDs has been already achieved using different methods such as temperature tuning, 5,6 Stark effect 7 and strain tuning, 8 while the control of the cavity resonance is more challenging. Cavity tuning has been obtained by controlled gas adsorption and local heating, 9,10 however this technique produces a permanent change in the QD emission energy preventing the separate control of QD and cavity. For QPIC applications, where many devices have to operate at the same wavelength, it is essential to tune each cavity independently over a wide wavelength range (> 10 nm), without affecting the QD emission wavelength and the Q factor. An attractive solution which fulfills all these requirements is provided by nano-opto-electro-mechanical structures (NOEMS). Previous works have demonstrated reconfigurable PCCs based on the electrostatic actuation of laterally coupled nanobeams, 11,12 slotted cavities 13 and twodimensional PCCs on double membranes. 14,15 The use of a vertically-coupled double-membrane is particularly convenient since it allows us to separate the QD layer from the actuation region in the vertical direction, removing any possible interaction between the electrostatic a) l.midolo@tue.nl field and the QDs. When two PCCs are brought at small distances (see inset Figure 1(a)) they couple evanescently, producing a splitting in a symmetric and an antisymmetric mode which shift in wavelength depending on the distance between the membranes. This technique has been demonstrated on InGaAsP/InP, 15 and has been shown not to affect the cavity Q. 14 However the operation at cryogenic temperatures (which is fundamental for QPIC applications) and the tuning to a single quantum dot have not yet been shown. In this ...

Design and Optical Properties of Electromechanical Double-Membrane Photonic Crystal Cavities

“…The results have been reported in previous publications [44] and [45]. Here we summarize some of the main features of the devices and discuss some open issues related to both material systems.…”

Anti-stiction coating for mechanically tunable photonic crystal devices

“…Their combination with photonic crystals (PhC) allows the control of the frequencies of optical modes without introducing additional losses [2]. For this reason, their use has attracted attention in quantum photonic integrated circuits [3], for instance to control the relative detuning between cavities and emitters [4,5] or to enhance the light-matter interaction [6].…”

Integration of Single-Photon Sources and Detectors on GaAs

“…As compared to integrated single-photon sources based on parametric processes in LiNbO 3 [9] or Si waveguides [10], QDs offer the advantage of much higher efficiency and easier filtering of the pump beam. Moreover, approaches to reproducibly control the exciton and cavity energy on chip, as needed to realize a scalable circuit, have been developed [11][12][13][14]. On the other side, superconducting single photon detectors (SSPDs) [15] based on niobium nitride (NbN) nanowires combine high detection efficiency, low dark count rates, and ultra-fast response, making them promising candidates for QIP [16].…”