Stephan Smolka

Cavity quantum electrodynamics with Anderson-localized modes

Scattered and Coupled Cavity electrodynamics explores the coupling of light with matter—ideally, that of a single photon with a single atom. Typically, this requires that the photon and the atom be confined to increase the likelihood of interaction, but scattering of light is an unavoidable product of an engineered device and is usually considered to be detrimental because it leads to loss of the photons from the cavity. Sapienza et al. (p. 1352; see the Perspective by Wiersma) saw extreme light scattering as an opportunity for the spontaneous generation of localized modes of light that can be exploited to induce light-matter coupling. Thus, working with a process where scattering is considered a resource rather than a nuisance, as in this case, may prove useful for realizing robust quantum information devices. Optical scattering is used to induce quantum coupling between light and an artificial atom. A major challenge in quantum optics and quantum information technology is to enhance the interaction between single photons and single quantum emitters. This requires highly engineered optical cavities that are inherently sensitive to fabrication imperfections. We have demonstrated a fundamentally different approach in which disorder is used as a resource rather than a nuisance. We generated strongly confined Anderson-localized cavity modes by deliberately adding disorder to photonic crystal waveguides. The emission rate of a semiconductor quantum dot embedded in the waveguide was enhanced by a factor of 15 on resonance with the Anderson-localized mode, and 94% of the emitted single photons coupled to the mode. Disordered photonic media thus provide an efficient platform for quantum electrodynamics, offering an approach to inherently disorder-robust quantum information devices.

Demonstration of quadrature squeezed surface-plasmons in a gold waveguide

The first experiment demonstrating the quantum optical properties of SPPs was the preservation of entanglement under plasmon assisted transmission through sub-wavelength holes in a conductor [1,2].

Density of states controls Anderson localization in disordered photonic crystal waveguides

We prove Anderson localization in the slow-light regime of a photonic crystal waveguide by measuring the ensemble-averaged localization length which is controlled by the dispersion of the disordered photonic crystal waveguide.

Observation of spatial quantum correlations induced by multiple scattering of nonclassical light.

We present the experimental realization of spatial quantum correlations of photons that are induced by multiple scattering of squeezed light. The quantum correlation relates photons propagating along two different light paths through the random medium and is infinite in range. Both positive and negative spatial quantum correlations are observed when varying the quantum state incident to the multiple scattering medium, and the strength of the correlations is controlled by the number of photons. The experimental results are in excellent agreement with recent theoretical proposals by implementing the full quantum model of multiple scattering.

Continuous-wave spatial quantum correlations of light induced by multiple scattering

We present theoretical and experimental results on spatial quantum correlations induced by multiple scattering of nonclassical light. A continuous-mode quantum theory is derived that enables determining the spatial quantum correlation function from the fluctuations of the total transmittance and reflectance. Utilizing frequency-resolved quantum noise measurements, we observe that the strength of the spatial quantum correlation function can be controlled by changing the quantum state of an incident bright squeezed-light source. Our results are found to be in excellent agreement with the developed theory and form a basis for future research on, e.g., quantum interference of multiple quantum states in a multiple scattering medium.

Angle-resolved photon-coincidence measurements in a multiple-scattering medium

We present angle-resolved correlation measurements between photons after propagation through a three-dimensional disordered medium. The multiple-scattering process induces photon correlations that are directly measured for light sources with different photon statistics. We find that multiple-scattered photons between different angular directions with angles much larger than the average speckle width are strongly correlated. The time dependence of the angular photon correlation function is investigated, and the coherence time of the light source is determined. Our results are found to be in excellent agreement with the continuous mode quantum theory of multiple scattering of light. The presented experimental technique is essential in order to study quantum phenomena in multiple-scattering random media, such as quantum interference and quantum entanglement of photons.

Quantum Electrodynamics with Semiconductor Quantum Dots Coupled to Anderson‐localized Random Cavities

We demonstrate that the spontaneous emission decay rate of semiconductor quantum dots can be strongly modified by the coupling to disorder‐induced Anderson‐localized photonic modes. We experimentally measure, by means of time‐resolved photoluminescence spectroscopy, the enhancement of the spontaneous emission decay rate by up to a factor 15 and an efficiency of channeling single photons into Anderson‐localized modes reaching values as high as 94%. These results prove that disordered photonic media provide an efficient platform for quantum electrodynamics, offering a novel route to quantum information devices exploiting disorder as a resource rather than a nuisance.

Controlling Anderson localization in disordered photonic crystal waveguides

We prove Anderson localization in the slow-light regime of a photonic crystal waveguide by measuring the ensemble-averaged localization length which is controlled by the dispersion of the disordered photonic crystal waveguide.

Spatial photon correlations in multiple scattering media

We present the first angle-resolved measurements of spatial photon correlations that are induced by multiple scattering of light. The correlation relates multiple scattered photons at different spatial positions and depends on incident photon fluctuations.

Cavity quantum electrodynamics in the Anderson-localized regime

We experimentally measure, by means of time-resolved photoluminescence spectroscopy, a 15-fold enhancement of the spontaneous emission decay rate of single semiconductor quantum dots coupled to disorder-induced Anderson-localized modes with efficiencies reaching 94%.