Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a major challenge is the efficient generation of entanglement between stationary (spin) and flying (photon) qubits. Here we report the observation of quantum entanglement between a semiconductor quantum dot spin and the color of a propagating optical photon. As an extension experiment, we report the generation of a single-photon frequency qubit, interference of resonance fluorescence from two distant quantum dots and the teleportation from a flying photon to a quantum dot spin.
Defects in photonic crystals (PCs) can support localized light modes with extremely small mode volumes. Depending on the symmetry of the PC, and the means of fabrication of the PC, extremely high quality factors (Q) are also possible. The combination of high Q and small mode volume should allow us to observe strong coupling between the cavity and quantum dot (QD) emitters that are strategically embedded within the cavity. This, in turn, has important implications for a variety of optical phenomena, such as single-photon sources. We describe the fabrication of PCs formed within membranes (180 nm thick) of GaAs, of either triangular or square lattice symmetry. The structures incorporate InAs QDs, grown monolithically with the PC material by Molecular Beam Epitaxy (MBE). We have observed emission from the smallest volume cavities (i.e. single-hole defects) in both the triangular and square lattice structures. The cavities have lattice constants ranging from 0.25 - 0.40 μm, and Q factors as high as 8500. To improve the probability of coupling a single QD to a cavity mode, we have developed a lithographic positioning technique capable of aligning a cavity to a feature on the surface within 50 nm, adequate to overlap a QD with a cavity mode. We will report on the progress achieved thus far with these structures and the challenges remaining to achieve strong coupling with specific QDs.
We propose a technique that allows to laser cool a nanomechanical resonator mode to its motional ground state. The method is based on resonant laser excitation of a phonon sideband of an embedded self-assembled quantum dot. The strength of this sideband coupling is determined directly by the difference between the electron-phonon couplings of the initial and final states of the quantum dot (QD) optical transition. When compared with the analogous sideband-cooling of a trapped-ion (TI), we find novel quantum interference effects in the cooling cycle and that the finite Q-value can lead to regimes where the final occupancy is proportional to the initial one -- with their ratio determined by the product of the "effective Lamb-Dicke" parameter and the Q-value. The interactions underlying this cooling scheme also provide a tool-box for quantum state engineering in these systems.
We have measured quality factors as high as 4000 for cavity resonances at 1.3 eV in photonic crystal microcavities formed by removing seven holes. In this paper, we discuss the prospect of coupling a single optical mode of a photonic crystal microcavity to the single-exciton (1X) level of a semiconductor quantum dot.
We propose a new class of intersubband lasers and amplifiers that achieve net gain without population inversion. The laser scheme is based on a unipolar semiconductor double quantum- well structure where gain occurs at a transition between conduction band subbands. In order to achieve net gain without inversion, we utilize Fano-type interferences. The semiconductor laser scheme that we are considering is analogous to the atomic lambda system that has been extensively analyzed in the context of electromagnetically induced transparency and lasing without inversion. A coherent coupling field however, is not required in the present scheme. The electronic coherence necessary for Fano-type interferences is established by resonant tunneling. For nonlinear optics applications, the asymmetry of the structure allows for (chi) (2) processes and therefore higher conversion efficiency or parametric gain.
KEYWORDS: Heterojunctions, Gallium arsenide, Semiconductors, Quantum wells, Single photon detectors, Monte Carlo methods, Semiconductor lasers, Electron holes, Optoelectronics, Photon transport
We describe a single-photon turnstile device that is based on a double-barrier mesoscopic p-i-n heterojunction driven by an alternating voltage source. In such a semiconductor device, Coulomb blockade and quantum confinement effects together can suppress the quantum fluctuations usually associated with electron and hole injection processes. It is therefore possible to generate heralded single-photon states without the need for high-impedance current source. The present scheme promises high- precision photon-flux state and current standards, as the repetition rate of the single-photon states and the magnitude of the junction current are determined by the frequency of the alternating voltage source.
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