Robust parallel laser driving of quantum dots for multiplexing of quantum light sources

Deterministic sources of quantum light (i.e. single photons or pairs of entangled photons) are required for a whole host of applications in quantum technology, including quantum imaging, quantum cryptography and the long-distance transfer of quantum information in future quantum networks. Semiconductor quantum dots are ideal candidates for solid-state quantum emitters as these artificial atoms have large dipole moments and a quantum confined energy level structure, enabling the realization of single photon sources with high repetition rates and high single photon purity. Quantum dots may also be triggered using a laser pulse for on-demand operation. The naturally-occurring size variations in ensembles of quantum dots offers the potential to increase the bandwidth of quantum communication systems through wavelength-division multiplexing, but conventional laser triggering schemes based on Rabi rotations are ineffective when applied to inequivalent emitters. Here we report the demonstration of the simultaneous triggering of >10 quantum dots using adiabatic rapid passage. We show that high-fidelity quantum state inversion is possible in a system of quantum dots with a 15 meV range of optical transition energies using a single broadband, chirped laser pulse, laying the foundation for high-bandwidth, multiplexed quantum networks.

Suppression of decoherence tied to electron-phonon coupling in telecom-compatible quantum dots: low-threshold reappearance regime for quantum state inversion

We demonstrate suppression of dephasing tied to deformation potential coupling of confined electrons to longitudinal acoustic (LA) phonons in optical control experiments on large semiconductor quantum dots (QDs) with emission compatible with the low-dispersion telecommunications band at 1.3 µm. By exploiting the sensitivity of the electron-phonon spectral density to the size and shape of the QD, we demonstrate a fourfold reduction in the threshold pulse area required to enter the decoupled regime for exciton inversion using adiabatic rapid passage (ARP). Our calculations of the quantum state dynamics indicate that the symmetry of the QD wave function provides an additional means to engineer the electron-phonon interaction. Our findings will support the development of solid-state quantum emitters in future distributed quantum networks using semiconductor QDs.

Simultaneous deterministic control of distant qubits in two semiconductor quantum dots

In optimal quantum control (OQC), a target quantum state of matter is achieved by tailoring the phase and amplitude of the control Hamiltonian through femtosecond pulse-shaping techniques and powerful adaptive feedback algorithms. Motivated by recent applications of OQC in quantum information science as an approach to optimizing quantum gates in atomic and molecular systems, here we report the experimental implementation of OQC in a solid-state system consisting of distinguishable semiconductor quantum dots. We demonstrate simultaneous high-fidelity π and 2π single qubit gates in two different quantum dots using a single engineered infrared femtosecond pulse. These experiments enhance the scalability of semiconductor-based quantum hardware and lay the foundation for applications of pulse shaping to optimize quantum gates in other solid-state systems.

Resonance fluorescence from a coherently driven semiconductor quantum dot in a cavity

We show that resonance fluorescence, i.e., the resonant emission of a coherently driven two-level system, can be realized with a semiconductor quantum dot. The dot is embedded in a planar optical microcavity and excited in a waveguide mode so as to discriminate its emission from residual laser scattering. The transition from the weak to the strong excitation regime is characterized by the emergence of oscillations in the first-order correlation function of the fluorescence, g(tau), as measured by interferometry. The measurements correspond to a Mollow triplet with a Rabi splitting of up to 13.3 microeV. Second-order correlation measurements further confirm nonclassical light emission.

Lasing characteristics of InAs quantum dot microcavity lasers as a function of temperature and wavelength

A Strong temperature dependence of microdisk lasers and photonic crystal nanocavity lasers with InAs quantum dot active regions is reported. These lasers operate at 1.3 microm at room temperature under optical pumping conditions. T(0, microdisk) = 31 K. T(0, photonic crystal nanocavity) = 14 K. The lasing threshold dependence on the lasing wavelength is also reported. We observe a minimum absorbed threshold pump power of 9 microW. This temperature and wavelength dependent lasing behavior is explained qualitatively by a simple model which attributes the experimental observations predominantly to surface recombination at threshold and the high quality factors of these cavities.

Edge-emitting photonic crystal double-heterostructure nanocavity lasers with InAs quantum dot active material

We report what is, to the best of our knowledge, the first demonstration of an edge-emitting photonic crystal nanocavity laser that is integrated with a photonic crystal waveguide. This demonstration is achieved with a double-heterostructure photonic crystal nanocavity incorporating an InAs quantum dot active region.

Self-aligned all-epitaxial microcavity for cavity QED with quantum dots

Using time-resolved photoluminescence spectroscopy, we have studied the Purcell spontaneous emission enhancement provided by a novel type of microcavity that forms a fully buried, all-epitaxial semiconductor heterostructure. The quantum dot containing region and the cavity boundaries are simultaneously defined in a unique way and lead to spatially self-aligned emitters. We demonstrate post-growth control of the quality factor and the capability of directly imaging the spatial field distribution that critically impacts the Purcell effect.

Isolated single quantum dot emitters in all-epitaxial microcavities

Data are presented on a fabrication approach that places an isolated single quantum dot at the center of a semiconductor microcavity. The microcavity is based on an all-epitaxial mesa-confined design that is mechanically robust and provides the thermal dissipation needed for a single photon source device technology. Microphotoluminescence is used to reveal single quantum dot emission with the essential optical properties of single quantum emitters.

Vacuum Rabi splitting with a single quantum dot in a photonic crystal nanocavity

Cavity quantum electrodynamics (QED) systems allow the study of a variety of fundamental quantum-optics phenomena, such as entanglement, quantum decoherence and the quantum-classical boundary. Such systems also provide test beds for quantum information science. Nearly all strongly coupled cavity QED experiments have used a single atom in a high-quality-factor (high-Q) cavity. Here we report the experimental realization of a strongly coupled system in the solid state: a single quantum dot embedded in the spacer of a nanocavity, showing vacuum-field Rabi splitting exceeding the decoherence linewidths of both the nanocavity and the quantum dot. This requires a small-volume cavity and an atomic-like two-level system. The photonic crystal slab nanocavity--which traps photons when a defect is introduced inside the two-dimensional photonic bandgap by leaving out one or more holes--has both high Q and small modal volume V, as required for strong light-matter interactions. The quantum dot has two discrete energy levels with a transition dipole moment much larger than that of an atom, and it is fixed in the nanocavity during growth.

Quantum correlations in the nonperturbative regime of semiconductor microcavities

The nonlinear optical response of semiconductor microcavities in the nonpertubative regime is studied in resonant single-beam-transmission and pump-probe experiments. In both cases a pronounced third transmission peak lying spectrally between the two normal modes is observed. A fully quantized theory is essential for the agreement with the experimental observations, demonstrating that quantum fluctuations leading to intraband polarizations are responsible for this effect.

Radiation fields from whispering-gallery modes of oxide-confined vertical-cavity surface-emitting lasers

Near- and far-field radiation patterns are analyzed for whispering-gallery-mode lasing in native-oxide-confined vertical-cavity surface-emitting lasers. Calculations from classical antenna theory based on the higher-order Bessel functions are compared with experiment and shown to be a useful predictor of the measured radiation fields. The most interesting features of the lasing modes are the multiple and uniformly distributed intensity spots in the near and far fields.