Simple Experimental Implementation Research Articles

Simultaneous single-qubit driving of semiconductor spin qubits at the fault-tolerant threshold

Practical Quantum computing hinges on the ability to control large numbers of qubits with high fidelity. Quantum dots define a promising platform due to their compatibility with semiconductor manufacturing. Moreover, high-fidelity operations above 99.9% have been realized with individual qubits, though their performance has been limited to 98.67% when driving two qubits simultaneously. Here we present single-qubit randomized benchmarking in a two-dimensional array of spin qubits, finding native gate fidelities as high as 99.992(1)%. Furthermore, we benchmark single qubit gate performance while simultaneously driving two and four qubits, utilizing a novel benchmarking technique called N-copy randomized benchmarking, designed for simple experimental implementation and accurate simultaneous gate fidelity estimation. We find two- and four-copy randomized benchmarking fidelities of 99.905(8)% and 99.34(4)% respectively, and that next-nearest neighbor pairs are highly robust to cross-talk errors. These characterizations of single-qubit gate quality are crucial for scaling up quantum information technology.

Temporal and spectral multiplexing for EUV multibeam ptychography with a high harmonic light source.

We demonstrate temporally multiplexed multibeam ptychography implemented for the first time in the EUV, by using a high harmonic based light source. This allows for simultaneous imaging of different sample areas, or of the same area at different times or incidence angles. Furthermore, we show that this technique is compatible with wavelength multiplexing for multibeam spectroscopic imaging, taking full advantage of the temporal and spectral characteristics of high harmonic light sources. This technique enables increased data throughput using a simple experimental implementation and with high photon efficiency.

Bandwidth control of the biphoton wavefunction exploiting spatio-temporal correlations

In this work we study the spatio-temporal correlations of photons produced by spontaneous parametric down conversion. In particular, we study how the waists of the detection and pump beams impact on the spectral bandwidth of the photons. Our results indicate that this parameter is greatly affected by the spatial properties of the detection beam, while not as much by the pump beam. This allows for a simple experimental implementation to control the bandwidth of the biphoton spectra, which only entails modifying the optical configuration to collect the photons. Moreover, we have performed Hong–Ou–Mandel interferometry measurements that also provide the phase of the biphoton wavefunction, and thereby its temporal shape. We explain all these results with a toy model derived under certain approximations, which accurately recovers most of the interesting experimental details.

Tunable exciton-polaritons emerging from WS2 monolayer excitons in a photonic lattice at room temperature

Engineering non-linear hybrid light-matter states in tailored lattices is a central research strategy for the simulation of complex Hamiltonians. Excitons in atomically thin crystals are an ideal active medium for such purposes, since they couple strongly with light and bear the potential to harness giant non-linearities and interactions while presenting a simple sample-processing and room temperature operability. We demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer. We experimentally observe the emergence of the canonical band-structure of particles in a one-dimensional lattice at room temperature, and demonstrate frequency reconfigurability over a spectral window exceeding 85 meV, as well as the systematic variation of the nearest-neighbour coupling, reflected by a tunability in the bandwidth of the p-band polaritons by 7 meV. The technology presented in this work is a critical demonstration towards reconfigurable photonic emulators operated with non-linear photonic fluids, offering a simple experimental implementation and working at ambient conditions.

Quantum Key Distribution with Nonbinary Phase–Time Encoding That Admits an Exact Proof of Secrecy

A quantum key distribution (QKD) protocol with nonbinary encoding is proposed that admits an exact proof of secrecy. The protocol provides higher rate of key generation compared with the BB84 protocol and, moreover, has a simple experimental implementation without active elements on the receiver side, that does not require polarization matching at the output of the communication line.

The dynamics of the magnetic linear accelerator examined by video motion analysis

Amagnetic linear accelerator (or Gauss accelerator) is a device that uses the conversion of magnetic energy into kinetic energy to launch an object with high velocity. A simple experimental implementation consists of a line of steel spheres in which the first one is a permanent magnetic sphere. If another steel ball collides with the magnetic sphere from the left, the rightmost steel sphere is ejected at a much larger velocity than the impacting steel sphere. Several approaches have been published to determine the velocity of the ejected sphere, for example by using photogates or by measuring the impact position of the ejected sphere after falling from a table. All of these approaches have in common that the measurement of the velocity is a static process. This article describes an approach in which video motion analysis on tablet computers is used to measure simultaneously the time course of the velocity of the impacting steel sphere as well as the ejected steel sphere, thus giving students insight into the dynamics of the processes that lead to a higher kinetic energy of the ejected sphere.

A phase resonance approach for modal testing of structures with nonlinear dissipation

The concept of nonlinear modes is useful for the dynamical characterization of nonlinear mechanical systems. While efficient and broadly applicable methods are now available for the computation of nonlinear modes, nonlinear modal testing is still in its infancy. The purpose of this work is to overcome its present limitation to conservative nonlinearities. Our approach relies on the recently extended periodic motion concept, according to which nonlinear modes of damped systems are defined as family of periodic motions induced by an appropriate artificial excitation that compensates the natural dissipation. The particularly simple experimental implementation with only a single-point, single-frequency, phase resonant forcing is analyzed in detail. The method permits the experimental extraction of natural frequencies, modal damping ratios and deflection shapes (including harmonics), for each mode of interest, as function of the vibration level. The accuracy, robustness and current limitations of the method are first demonstrated numerically. The method is then verified experimentally for a friction-damped system. Moreover, a self-contained measure for estimating the quality of the extracted modal properties is investigated. The primary advantages over alternative vibration testing methods are noise robustness, broad applicability and short measurement duration. The central limitation of the identified modal quantities is that they only characterize the system in the regime near isolated resonances.

Deterministic Approaches for Simulation of Nitroxide-Mediated Radical Polymerization

Since its development in the last decades, controlled radical polymerization (CRP) has become a very promising option for the synthesis of polymers with controlled structure. The design and production of tailor-made materials can be significantly improved by developing models capable of predicting the polymer properties from the operating conditions. Nitroxide-mediated polymerization (NMP) was the first of the three main variants of CRP to be discovered. Although it has lost preference over the years against other CRP alternatives, NMP is still an attractive synthesis method because of its simple experimental implementation and environmental friendliness. This review focuses on deterministic methods employed in mathematical models of NMP. It presents an overview of the different techniques that have been reported for modelling NMP processes in homogeneous and heterogeneous media, covering from the prediction of average properties to the latest techniques for modelling univariate and multivariate distributions of polymer properties. Finally, an outlook of model-based design studies of NMP processes is given.

Detector Imperfections of Schrödinger Cat Generation with Ancillary Coherent States

Measurement-induced nonlinear operation in linear optics is a promising technique to realize quantum computation and communications. Such an operation has been demonstrated via the generation of photon-subtracted squeezed states, namely, Schrodinger-cat states. Nielsen and Molmer have proposed an efficient scheme to generate the cat states with larger amplitudes relative to previous experimental results. We present a simple experimental implementation of their scheme and analyze it while considering experimental imperfections. Our study indicates that the current photon detection technology meets the conditions necessary for their operation.

Bessel beam coherent anti-Stokes Raman scattering microscopy

We report about laser scanning coherent anti-Stokes Raman scattering (CARS) microscopy using a Bessel beam to enhance the lateral resolution. This study covers a numerical investigation that predicts an improvement in the lateral resolution by a factor of up to 1.33, while the axial depth of view increases up to a factor of 2 for an ideal Bessel beam serving as both a pump and a probe. Further, we present a simple experimental implementation of a Bessel-like beam by adding only two axicons and a telescope to a conventional CARS laser scanning microscopy setup. The predicted resolution improvement is demonstrated for well-scattering, structured polymer samples.

Hyperspectral imaging with in-line interferometric femtosecond stimulated Raman scattering spectroscopy

We present the hyperspectral imaging capabilities of in-line interferometric femtosecond stimulated Raman scattering. The beneficial features of this method, namely, the improved signal-to-background ratio compared to other applicable broadband stimulated Raman scattering methods and the simple experimental implementation, allow for a rather fast acquisition of three-dimensional raster-scanned hyperspectral data-sets, which is shown for PMMA beads and a lipid droplet in water as a demonstration. A subsequent application of a principle component analysis displays the chemical selectivity of the method.

Reflection of a polarized light cone

We introduce a visually appealing experimental demonstration of Fresnel reflection. In this simple optical experiment, a polarized light beam travels through a high numerical-aperture microscope objective, reflects off a glass slide, and travels back through the same objective lens. The return beam is sampled with a polarizing beam splitter and produces a surprising geometric pattern on an observation screen. Understanding the origin of this pattern requires careful attention to geometry and an understanding of the Fresnel coefficients for S and P polarized light. We demonstrate that in addition to a relatively simple experimental implementation, the shape of the observed pattern can be computed both analytically and by using optical modeling software. The experience of working through complex mathematical computations and demonstrating their agreement with a surprising experimental observation makes this a highly educational experiment for undergraduate optics or advanced-lab courses. It also provides a straightforward yet non-trivial system for teaching students how to use optical modeling software.

Implementation of Space Vector Based Hysteresis Current Control for a Three-Phase High Power Factor Converter

In this paper, an implementation of a space vector modulation (SVM) based hysteresis current controller (HCC) for the control of a three-phase high power factor rectifier is proposed. The SVM-based HCC scheme is designed, simulated and implemented. The technique combines the best features of the SVM and HCC techniques. The controller determines a set of state space vectors from a region detector and then applies a space vector selected according to HCC. A set of space vectors in a region, including the zero space vector for a reduced number of switchings, is determined from the output signals of three comparators with a hysteresis band a little larger than that of the main HCC. A simple experimental implementation is proposed and the simulation and experimental results of the SVM-based HCC are discussed in the paper.

Generation of stable concentration gradients in 2D and 3D environments using a microfluidic ladder chamber

We have developed a simple microfluidic device for generating stable concentration gradients in 2D and 3D environments. The device, termed the Ladder Chamber, uses a two-compartment diffusion system to generate steady state gradients across flow-free channels that connect the source and sink channels. To demonstrate the utility of the Ladder Chamber for cell migration, neutrophil chemotaxis was successfully observed in soluble chemoattractant (IL-8) gradient. The Ladder Chamber's simple design and experimental implementation make it an attractive approach for investigating cell migration and other biological experiments in well-defined gradients in 2D surfaces as well as in 3D gels.

Defocused imaging of second harmonic generation from a single nanocrystal

We demonstrate the direct imaging of the second harmonic generation radiation from a single nonlinear nanocrystal using defocused nonlinear microscopy. This technique allows the retrieval of complete information on the 3D orientation of a nanocrystal as well as possible deviations from its purely crystalline nature, in a simple experimental implementation. The obtained images are modeled by calculation of the radiation diagram from a nonlinear dipole that accounts for the excitation beam, the crystal symmetry and the particle size. Experimental demonstrations are performed on Potassium Titanyl Phosphase (KTP) nanocrystals. The shape and structure of the radiation images show a strong dependence on both crystal orientation and field polarization state, as expected by the specific nonlinear coherent coupling between the induced dipole and the excitation field polarization state.

Magnetic Field-Induced Spectroscopy of Forbidden Optical Transitions with Application to Lattice-Based Optical Atomic Clocks

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

Design and preliminary tests of a family of adaptive waveforms to measure blood vessel diameter and wall thickness

In this article we consider the adaptive design of waveforms to be used in vascular ultrasound. The advantage of these waveforms, when used with the proposed processing scheme, is that their application results in increased reflected energy, especially when compared with more conventional methods such as a short-gated sinusoid. This increase in reflected energy has potential to permit inferences to be made about wall thickness and vessel diameter from deeper vessels than possible with more traditional techniques. Here, the use of waveforms of the type A(t)ej(kt2), 0 < or = t < or = b, where A(t) is a specially designed envelope and k a sweep frequency, is proposed. Theorems are proved that describe how to choose an A(t) which results in either a maximum of reflected energy signal-to-noise ratio (SNR), or range resolution. The design of the waveform is adaptive in that both A(t) and k are derived in consideration of a specific blood vessel whose transfer function has been obtained experimentally. Numerical simulations illustrate the advantages of using these waveforms as well as the effects of the parameters. A simple experimental implementation of the methodology is presented on a brachial artery. The measurement of the impulse response of the artery is presented in this context. Results indicate that a processing gain in SNR over the instantaneous values obtained from the raw echo waveforms of 11 dB to 14 dB can be obtained via this methodology.

Investigation of angular and energy distributions of excited sputtered and scattered particles by using a Doppler method

The recently proposed Doppler tomography (DT) method enables the investigation of the angular and energy distributions of excited sputtered and scattered atoms and ions. A simple mathematical and experimental implementation of DT is described. It is applied to the investigation of excited particle emission due to ion bombardment of polycrystals along the normal to the surface. Data on angular and energy distributions of the sputtered excited Al atoms and scattered excited K + ions are presented.

Moire interferometric focusing system for optical microlithography

An interferometric apparatus for detecting axial and angular misalignments of the film plane in a photolithographic camera is proposed. The misalignments are observed as moire interference fringes created by the superposition of a reference interferometric fringe pattern representing the focused camera and a perturbed fringe pattern produced when the camera is misfocused. The theory and results of a simple experimental implementation are described.