Experimental Multi-state Quantum Discrimination in the Frequency Domain with Quantum Dot Light

The quest for the realization of effective quantum state discrimination strategies is of great interest for quantum information technology, as well as for fundamental studies. Therefore, it is crucial to develop new and more efficient methods to implement discrimination protocols for quantum states. Among the others, single photon implementations are more advisable, because of their inherent security advantage in quantum communication scenarios. In this work, we present the experimental realization of a protocol employing a time-multiplexing strategy to optimally discriminate among eight non-orthogonal states, encoded in the four-dimensional Hilbert space spanning both the polarization degree of freedom and photon energy. The experiment, built on a custom-designed bulk optics analyser setup and single photons generated by a nearly deterministic solid-state source, represents a benchmarking example of minimum error discrimination with actual quantum states, requiring only linear optics and two photodetectors to be realized. Our work paves the way for more complex applications and delivers a novel approach towards high-dimensional quantum encoding and decoding operations

Post-fabrication tuning of circular Bragg resonators for enhanced emitter-cavity coupling

Solid-state quantum emitters embedded in circular Bragg resonators are attractive due to their ability to emit quantum states of light with high brightness and low multi-photon probability. As for any emitter-microcavity system, fabrication imperfections limit the spatial and spectral overlap of the emitter with the cavity mode, thus limiting their coupling strength. Here, we show that an initial spectral mismatch can be corrected after device fabrication by repeated wet chemical etching steps. We demonstrate ~16 nm wavelength tuning for optical modes in AlGaAs resonators on oxide, leading to a 4-fold Purcell enhancement of the emission of single embedded GaAs quantum dots. Numerical calculations reproduce the observations and suggest that the achievable performance of the resonator is only marginally affected in the explored tuning range. We expect the method to be applicable also to circular Bragg resonators based on other material platforms, thus increasing the device yield of cavity-enhanced solid-state quantum emitters

Signatures of the Optical Stark Effect on Entangled Photon Pairs from Resonantly-Pumped Quantum Dots

Two-photon resonant excitation of the biexciton-exciton cascade in a quantum dot generates highly polarization-entangled photon pairs in a near-deterministic way. However, there are still open questions on the ultimate level of achievable entanglement. Here, we observe the impact of the laser-induced AC-Stark effect on the spectral emission features and on entanglement. A shorter emission time, longer laser pulse duration, and higher pump power all result in lower values of concurrence. Nonetheless, additional contributions are still required to fully account for the observed below-unity concurrence.Comment: 7 pages, 3 figure

A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot

A quantum-light source that delivers photons with a high brightness and a high degree of entanglement is fundamental for the development of efficient entanglement-based quantum-key distribution systems. Among all possible candidates, epitaxial quantum dots are currently emerging as one of the brightest sources of highly entangled photons. However, the optimization of both brightness and entanglement currently requires different technologies that are difficult to combine in a scalable manner. In this work, we overcome this challenge by developing a novel device consisting of a quantum dot embedded in a circular Bragg resonator, in turn, integrated onto a micromachined piezoelectric actuator. The resonator engineers the light-matter interaction to empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator manipulates strain fields that tune the quantum dot for the generation of entangled photons with fidelities up to 0.96(1). This hybrid technology has the potential to overcome the limitations of the key rates that plague current approaches to entanglement-based quantum key distribution and entanglement-based quantum networks. Introductio

Lubricin on Platinum Electrodes: A Low-Impedance Protein-Resistant Surface Towards Biomedical Implantation

Biofouling on surfaces compromises the function of biomedical devices whose function involves contact with biological fluids. In the context of electrochemical devices, proteins are attracted to the surface via coaction of various forces (hydrogen bond, hydrophobic effect, and other polar interactions) and protein interaction with the surface can significantly alter the surface chemistry. In response to this issue, we have developed an efficient anti-biofouling surface that employs a glycoprotein, lubricin (LUB), and which generates low impedance layers compatible with electrochemical applications. Herein, we investigate how different LUB densities on platinum (Pt) electrodes affect the surface electrochemistry and its ability to prevent nonspecific adsorption of protein to the surface. Surfaces with higher densities of LUB were more resistant to protein adsorption. The LUB modified Pt electrodes were challenged in artificial perilymph (AP) media under passive and electrically stimulated conditions over 7-day periods throughout which the LUB layer retained its anti-biofouling and surface coating stability

Tuning drug dosing through matching optically active polymer composition and NIR stimulation parameters

© 2019 Elsevier B.V. Controlled release is at the forefront of modern bioscience as it aims to address challenges associated with the dosing of drugs within required levels for therapeutic effect. Many materials and approaches can be used to control the release from different reservoirs including nanoparticles, liposomes and hydrogels. Using thermoresponsive hydrogels, near infrared illumination of plasmonic nanoparticles can be used to control the hydrogel through localised surface plasmon resonance heating. This work extends beyond a material level and pursues detailed examination of the drug release characteristics of a variable acrylic acid poly(N-isopropylacrylamide) coated gold nanorod system using dexamethasone as a model drug. Release was examined under different irradiation power densities and exposure times. Bulk heating effects in all stimulation protocols did not exceed the lower critical solution temperature of the system, but a marked increase in release was seen following stimulation. This was likely due to more intense heating occurring around the nanorods. A release model was established to describe the amount of drug eluted relative to input energy, suggesting that shorter irradiation periods release the drug more efficiently. The data reported establishes plasmonically modulated thermosensitive hydrogels as a candidate material that can be tailored to specific clinical applications of stimulated release

Quantum dot optomechanics in suspended nanophononic strings

The optomechanical coupling of quantum dots and flexural mechanical modes is studied in suspended nanophononic strings. The investigated devices are designed and monolithically fabricated on an (Al)GaAs heterostructure. Radio frequency elastic waves with frequencies ranging between $f$=250 MHz to 400 MHz are generated as Rayleigh surface acoustic waves on the unpatterned substrate and injected as Lamb waves in the nanophononic string. Quantum dots inside the nanophononic string exhibit a 15-fold enhanced optomechanical modulation compared to those dynamically strained by the Rayleigh surface acoustic wave. Detailed finite element simulations of the phononic mode spectrum of the nanophononic string confirm, that the observed modulation arises from valence band deformation potential coupling via shear strain. The corresponding optomechanical coupling parameter is quantified to $0.15 \mathrm{meV nm^{-1}}$. This value exceeds that reported for vibrating nanorods by approximately one order of magnitude at 100 times higher frequencies. Using this value, a derive vertical displacements in the range of 10 nm is deduced from the experimentally observed modulation. The results represent an important step towards the creation of large scale optomechanical circuits interfacing single optically active quantum dots with optical and mechanical waves.Comment: Submitted manuscrip

Adhesion and self-assembly of lubricin (PRG4) brush layers on different substrate surfaces

Lubricin (LUB, aka PRG4), a mucin-like glycoprotein, is best known for the significant role it plays in the boundary lubrication, wear protection, and adhesion control systems in human joints. However, LUB exhibits a number of diverse and useful properties, including a remarkable ability to self-assemble into a telechelic brush structure onto virtually any substrate. This self-assembly behavior has spawned the emergence of numerous nontraditional applications of LUB coatings in numerous areas such as microfluidics, electrochemical sensors, contact lenses, antifouling surfaces, and bionic neural interfaces. Although LUB will readily self-assemble on most substrates, it has become apparent that the substrate has a significant influence on the LUB layer\u27s demonstrated lubrication, antiadhesion, electrokinetic, and size-selective transport properties; however, investigations into LUB-substrate interactions and how they influence the self-assembled LUB layer structure remain a neglected aspect of LUB research. This study utilizes AFM force spectroscopy to directly assess the adhesion energy of LUB molecules adsorbed to a wide variety of different substrates which include inorganic, polymeric, and metallic materials. An analysis of the steric repulsive forces measured on approach provides a qualitative assessment of the LUB layer\u27s mechanical modulus, related to the chain packing density, across substrates. These modulus measurements, combined with characteristic features and the dwell time dependence of the LUB adhesion forces provide insight into the organization and uniformity of the LUB brush structure. The results of these measurements indicate that LUB interactions with different substrates are highly variable and substrate-specific, resulting in a surprisingly broad spectrum of adhesion energies and layer properties (i.e., chain density, uniformity, etc.) which are not, themselves, correlated or easily predicted by substrate properties. In addition, this study finds exceptionally poor LUB adhesion to both mica and poly(methyl methacrylate) surfaces that remain widely used substrates for constructing model surfaces in fundamental tribology studies which may have significant implications for the findings of a number of foundational studies into LUB tribology and molecular synergies

Lubricin (PRG4) reduces fouling susceptibility and improves sensitivity of carbon-based electrodes

2019 Elsevier Ltd In order to overcome the problems of reliability and accuracy often associated with electrochemical sensing in bioassays due to electrode surface fouling, we present an innovative antifouling surface coating based on lubricin (LUB). LUB is a large glycoprotein found in the articular joints of mammals with the ability to self-assemble on surfaces of different nature, creating an antiadhesive brush layer. This work demonstrates the size selective and antiadhesive properties of LUB coatings which prevent large biomolecules from adhering onto the electrode surface while simultaneously allowing smaller electroactive species to pass through the layer unimpeded. Electrochemical and surface characterisation experiments were performed using glassy carbon (GC), carbon black SPEs (CB), and reduced graphene oxide SPEs (rGO) in order to evaluate the antifouling capabilities of LUB coatings in solutions containing bovine serum albumin (BSA) and human saliva. The LUB coatings have been shown to exhibit outstanding antiadhesive properties, size selectivity, self-assembly as well as providing excellent electrochemistry in these highly fouling solutions