T. B. Hoang

Enhanced spontaneous emission from quantum dots in short photonic crystal waveguides

We report a study of the quantum dot (QD) emission in short photonic crystal waveguides. We observe that the quantum dot photoluminescence intensity and decay rate are strongly enhanced when the emission energy is in resonance with Fabry-Perot (FP) cavity modes in the slow-light regime of the dispersion curve. The experimental results are in agreement with previous theoretical predictions and are further supported by three-dimensional finite element simulations. Our results show that the combination of slow group velocity and Fabry-Perot cavity resonance provide an avenue to efficiently channel photons from quantum dots into waveguides for integrated quantum photonic applications.

Widely tunable, efficient on-chip single photon sources at telecommunication wavelengths

We demonstrate tunable on-chip single photon sources using the Stark tuning of single quantum dot (QD) excitonic transitions in short photonic crystal waveguides (PhC WGs). The emission of single QDs can be tuned in real-time by 9 nm with an applied bias voltage less than 2V. Due to a reshaped density of optical modes in the PhC WG, a large coupling efficiency β ≥ 65%to the waveguide mode is maintained across a wavelength range of 5 nm. When the QD is resonant with the Fabry-Perot mode of the PhC WG, a strong enhancement of spontaneous emission is observed leading to a maximum coupling efficiency β = 88%. These results represent an important step towards the scalable integration of single photon sources in quantum photonic integrated circuits.

Ultrafast non-local control of spontaneous emission

The radiative interaction of solid-state emitters with cavity fields is the basis of semiconductor microcavity lasers and cavity quantum electrodynamics (CQED) systems. Its control in real time would open new avenues for the generation of non-classical light states, the control of entanglement and the modulation of lasers. However, unlike atomic CQED or circuit quantum electrodynamics, the real-time control of radiative processes has not yet been achieved in semiconductors because of the ultrafast timescales involved. Here we propose an ultrafast non-local moulding of the vacuum field in a coupled-cavity system as an approach to the control of radiative processes and demonstrate the dynamic control of the spontaneous emission (SE) of quantum dots (QDs) in a photonic crystal (PhC) cavity on a ∼ 200 ps timescale, much faster than their natural SE lifetimes.

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

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 13u2009nm 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%.

Integrated autocorrelator based on superconducting nanowires

We demonstrate an integrated autocorrelator based on two superconducting single-photon detectors patterned on top of a GaAs ridge waveguide. This device enables the on-chip measurement of the second-order intensity correlation function g(2)(τ). A polarization-independent device quantum efficiency in the 1% range is reported, with a timing jitter of 88 ps at 1300 nm. g(2)(τ) measurements of continuous-wave and pulsed laser excitations are demonstrated with no measurable crosstalk within our measurement accuracy.

Efficient coupling of single photons to ridge-waveguide photonic integrated circuits

We demonstrate the efficient coupling of single photons emitted by single quantum dots (QDs) in a photonic crystal cavity (PhCC) to a ridge waveguide (RWG). Using a single-step lithographic process with an optimized tapering, up to 70% coupling efficiency between the photonic crystal waveguide and the RWG was achieved. The emission enhancement of single QDs inside an in-line PhCC coupled via the RWG to a single-mode fiber was observed. Single-photon funneling rates around 3.5u2009MHz from a single QD into the RWG were obtained. This result is a step toward the realization of a fully functional quantum photonic integrated circuit.

Single photons emitted by single quantum dots into waveguides: Photon guns on a chip

We report a study on single photons emitted by single quantum dots into ridge and photonic crystal waveguides using an extended micro-photoluminescence setup. Our results show promise for future applications in quantum photonic integrated circuits.

Controlling the emission from single quantum dots with electro-opto-mechanical photonic crystal cavities

We present a device for the spectral reconfiguration of a two-dimensional photonic crystal cavity (PCC) based on parallel semiconductor membranes. The mechanical motion of the slabs introduces a variation in the effective refractive index of the coupled waveguides where the photonic crystal is etched resulting in a shift of the free-space wavelength. Using an integrated electrostatic actuator we demonstrated independent tuning up to 15 nm with less than 6 V bias. We present the electromechanical control of a PCC mode in resonance to single quantum dot (QD) emission lines for the real-time compensation of the spectral mismatch due to the dots inhomogeneity. We discuss the operation of the device at low temperatures (<; 10 K) and we measured the Purcell effect via the electro-mechanical control. A reversible tuning range of 13 nm and a spontaneous emission rate control by a factor of ten has been achieved.

Spontaneous emission control of single quantum dots by electrostatic tuning of a double-slab photonic crystal cavity

We report the electromechanical control of spontaneous emission of single InAs quantum dots (QDs) embedded in wavelength-tunable double-membrane photonic crystal cavities (PCC). The tuning is achieved by modulating the distance between two parallel GaAs membranes by applying electrostatic forces across a p-i-n diode under reverse bias. The spontaneous emission rate of single dots has been modified by over a factor of ten, tuning the cavity reversibly between on- and off-resonant conditions without altering the emission energy of the dots. We also discuss a possible approach to integrate the double membrane structure with ridge waveguides, for the transmission of light within a photonic chip.

Funneling single photons into ridge-waveguide photonic integrated circuits

The generation, manipulation and detection of single photons enable quantum communication, simulation and potentially computing protocols. However scaling to several qubits requires the integration of these functionalities in a single chip. A promising approach to the integration of single-photon sources in a chip is the use of single quantum dots embedded in photonic crystal waveguides or cavities. To this aim, efficient coupling of the emission from single quantum dots in photonic crystal cavities to low-loss ridge-waveguide (RWG) circuits is needed. This is usually hampered by the large mode mismatch between the two systems. In this work the emission of a photonic crystal (PhC) cavity realized on a GaAs/AlGaAs membrane and pumped by quantum dots has been effectively coupled and transferred through a long RWG (~1mm). By continuous tapering in both horizontal and vertical direction, transmission values (fiber-in, fiber-out) around 0.16 and 0.08% for RWG and coupled PhC waveguide-RWG have been achieved, respectively. This corresponds to about 2.8% coupling efficiency between the center of the PhC waveguide and the single-mode output fiber, a value much higher than what is achieved by top collection. It further shows that around 70% of the light in the PhC waveguide is coupled to the RWG. The emission from quantum dots in the cavity has been clearly identified by exciting from the top and collecting the photoluminescence from the cleaved facet of the device 1mm away from the cavity which enables the efficient coupling of single photons to RWG and detector circuits.