A highly efficient single photon-single quantum dot interface

Semiconductor quantum dots are a promising system to build a solid state quantum network. A critical step in this area is to build an efficient interface between a stationary quantum bit and a flying one. In this chapter, we show how cavity quantum electrodynamics allows us to efficiently interface a single quantum dot with a propagating electromagnetic field. Beyond the well known Purcell factor, we discuss the various parameters that need to be optimized to build such an interface. We then review our recent progresses in terms of fabrication of bright sources of indistinguishable single photons, where a record brightness of 79% is obtained as well as a high degree of indistinguishability of the emitted photons. Symmetrically, optical nonlinearities at the very few photon level are demonstrated, by sending few photon pulses at a quantum dot-cavity device operating in the strong coupling regime. Perspectives and future challenges are briefly discussed.Comment: to appear as a book chapter in a compilation "Engineering the Atom-Photon Interaction" published by Springer in 2015, edited by A. Predojevic and M. W. Mitchel

Stabilizing the Hexagonal Close Packed Structure of Hard Spheres with Polymers : Phase diagram, Structure, and Dynamics

We study the phase behaviour of a binary mixture of colloidal hard spheres and freely-jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and coworkers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures.Comment: 8 pages, 5 figure

Self-referenced continuous-variable quantum key distribution protocol

We introduce a new continuous-variable quantum key distribution (CV-QKD) protocol, self-referenced CV-QKD, that eliminates the need for transmission of a high-power local oscillator between the communicating parties. In this protocol, each signal pulse is accompanied by a reference pulse (or a pair of twin reference pulses), used to align Alice's and Bob's measurement bases. The method of phase estimation and compensation based on the reference pulse measurement can be viewed as a quantum analog of intradyne detection used in classical coherent communication, which extracts the phase information from the modulated signal. We present a proof-of-principle, fiber-based experimental demonstration of the protocol and quantify the expected secret key rates by expressing them in terms of experimental parameters. Our analysis of the secret key rate fully takes into account the inherent uncertainty associated with the quantum nature of the reference pulse(s) and quantifies the limit at which the theoretical key rate approaches that of the respective conventional protocol that requires local oscillator transmission. The self-referenced protocol greatly simplifies the hardware required for CV-QKD, especially for potential integrated photonics implementations of transmitters and receivers, with minimum sacrifice of performance. As such, it provides a pathway towards scalable integrated CV-QKD transceivers, a vital step towards large-scale QKD networks.Comment: 14 pages, 10 figures. Published versio