We present an experimental study of Ogston-like sieving process of rodlike DNA in patterned periodic nanofluidic filter arrays. The electrophoretic motion of DNA through the array is described as a biased Brownian motion overcoming periodically modulated free-energy landscape. A kinetic model, constructed based on the equilibrium partitioning theory and the Kramers theory, explains the field-dependent mobility well. We further show experimental evidence of the crossover from Ogston-like sieving to entropic trapping, depending on the ratio between nanofilter constriction size and DNA size. DOI: 10.1103/PhysRevLett.97.018103 PACS numbers: 87.15.Tt, 82.75.ÿz, 87.14.Gg Perhaps the most important application of electromigration of polyelectrolytes in confining environments is the size fractionation of biomolecules with gel electrophoresis. Based on the ratio of the radius of gyration R g of the molecule to the characteristic pore size a of the gel, three different separation regimes have been identified as Ogston sieving (R g =a < 1), entropic trapping (R g =a 1), and biased reptation (R g =a > 1) [1]. In Ogston sieving, molecular sieving occurs because of steric hindrance of the molecules within the nanopore. Since R g =a < 1, the molecules move freely through the gel matrix, assuming their unperturbed coiled conformation. The standard model for interpreting mobility in the Ogston sieving regime is the so-called ''extended Ogston model '' [2], where the relative mobility , the ratio between the mobility in gel and the free solution mobility 0 , of a molecule of given size is assumed to equal the partition coefficient K of the molecule in the gel (K revolves around excluded volume in general configuration space). Even though the assumption of = 0 K has never been properly tested experimentally, largely because the mobility and the partition coefficient K of the molecule cannot be measured independently for a gel system, the extended Ogston model has been applied as the theoretical basis for the widely accepted empirical method proposed by Ferguson for determining the molecular weights of biomolecules [3]. As a near-equilibrium theory, the extended Ogston model is also known for failing to explain field-dependent mobility shifts that occur in a medium-to-high field gel electrophoresis [1,3].The theoretical study of sieving mechanisms in gel electrophoresis has been limited by the lack of wellcontrolled experimental platforms for correlating the size and shape of the sieving pores to the observed molecular dynamic behavior. Recently, various microfabricated structures have been proposed as an alternative to the gels [4]. These regular sieving structures have also proven ideal for theoretical study of molecular dynamics and stochastic motion in confining spaces [5]. More recently, patterned periodic nanofluidic filter (nanofilter) arrays were shown to provide fast separation of biomolecules such as proteins [6]. In this Letter, by using a theoretical model based on the equilibrium partitioning theory, we quantitativ...

Realizing the potential of quantum computing requires sufficiently low logical error rates1. Many applications call for error rates as low as 10−15 (refs. 2–9), but state-of-the-art quantum platforms typically have physical error rates near 10−3 (refs. 10–14). Quantum error correction15–17 promises to bridge this divide by distributing quantum logical information across many physical qubits in such a way that errors can be detected and corrected. Errors on the encoded logical qubit state can be exponentially suppressed as the number of physical qubits grows, provided that the physical error rates are below a certain threshold and stable over the course of a computation. Here we implement one-dimensional repetition codes embedded in a two-dimensional grid of superconducting qubits that demonstrate exponential suppression of bit-flip or phase-flip errors, reducing logical error per round more than 100-fold when increasing the number of qubits from 5 to 21. Crucially, this error suppression is stable over 50 rounds of error correction. We also introduce a method for analysing error correlations with high precision, allowing us to characterize error locality while performing quantum error correction. Finally, we perform error detection with a small logical qubit using the 2D surface code on the same device18,19 and show that the results from both one- and two-dimensional codes agree with numerical simulations that use a simple depolarizing error model. These experimental demonstrations provide a foundation for building a scalable fault-tolerant quantum computer with superconducting qubits.

The discovery of topological order has revolutionized the understanding of quantum matter in modern physics and provided the theoretical foundation for many quantum error correcting codes. Realizing topologically ordered states has proven to be extremely challenging in both condensed matter and synthetic quantum systems. Here, we prepare the ground state of the toric code Hamiltonian using an efficient quantum circuit on a superconducting quantum processor. We measure a topological entanglement entropy near the expected value of ln 2, and simulate anyon interferometry to extract the braiding statistics of the emergent excitations. Furthermore, we investigate key aspects of the surface code, including logical state injection and the decay of the non-local order parameter. Our results demonstrate the potential for quantum processors to provide key insights into topological quantum matter and quantum error correction.

Abstract-We present the first custom integrated circuit implementation of the compressed sensing based non-uniform sampler (NUS). By sampling signals non-uniformly, the average sample rate can be more than a magnitude lower than the Nyquist rate, provided that these signals have a relatively low information content as measured by the sparsity of their spectrum. The hardware design combines a wideband Indium-Phosphide (InP) heterojunction bipolar transistor (HBT) sample-and-hold with a commercial off-the-shelf (COTS) analog-to-digital converter (ADC) to digitize an 800 MHz to 2 GHz band (having 100 MHz of non-contiguous spectral content) at an average sample rate of 236 Msps. Signal reconstruction is performed via a non-linear compressed sensing algorithm, and an efficient GPU implementation is discussed. Measured bit-error-rate (BER) data for a GSM channel is presented, and comparisons to a conventional wideband 4.4 Gsps ADC are made.

This is a PDF file of a peer-reviewed paper that has been accepted for publication. Although unedited, the content has been subjected to preliminary formatting. Nature is providing this early version of the typeset paper as a service to our authors and readers. The text and figures will undergo copyediting and a proof review before the paper is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers apply.

Abstract-In this paper we present a complete (hardware/software) sub-Nyquist rate (×13) wideband signal acquisition chain capable of acquiring radar pulse parameters in an instantaneous bandwidth spanning 100 MHz-2.5 GHz with the equivalent of 8 ENOB digitizing performance. The approach is based on the alternative sensing-paradigm of CompressedSensing (CS). The hardware platform features a fully-integrated CS receiver architecture named the random-modulation preintegrator (RMPI) fabricated in Northrop Grumman's 450 nm InP HBT bipolar technology. The software back-end consists of a novel CS parameter recovery algorithm which extracts information about the signal without performing full timedomain signal reconstruction. This approach significantly reduces the computational overhead involved in retrieving desired information which demonstrates an avenue toward employing CS techniques in power-constrained real-time applications. The developed techniques are validated on CS samples physically measured by the fabricated RMPI and measurement results are presented. The parameter estimation algorithms are described in detail and a complete description of the physical hardware is given.

No abstract

No abstract