arXiv subjects

David J. Bishop

Publications and source records attributed to David J. Bishop.

17 recordsLinked to original sources

arXiv2026

Reconfigurable Superconducting Quantum Circuits Enabled by Micro-Scale Liquid-Metal Interconnects

Modular architectures are a promising route toward scalable superconducting quantum processors, but finite fabrication yield and the lack of high quality temporary interconnects impose fundamental limitations on system size. Here, we demonstrate chip-scale liquid-metal interconnects that show promise for plug-and-play superconducting quantum circuits by enabling non-destructive module replacement while maintaining high microwave performance. Using gallium-based liquid metals, we realize high-quality inter-module signal and ground interconnects, comparable in performance to conventional coplanar waveguide resonators. We illustrate consistent device characteristics across three thermal cycles between room temperature and 15 mK, as well as the ability to reform superconducting connections following module replacement. A width-dependent resonance frequency shift reveals a significant kinetic inductance fraction, which we attribute to the presence of $β$-phase tantalum as confirmed by X-ray characterization. Finally, we investigate power-dependent loss mechanisms and observe high-power dissipative nonlinearities qualitatively consistent with a readout-power heating model. These results establish liquid metals as viable chip-scale interconnects for reconfigurable, modular superconducting quantum systems.

quant-ph↗

arXiv2024

Seeking the Casimir Energy

Since its first description in 1948, the Casimir effect has been studied extensively. Standard arguments for its existence hinge on the elimination of certain modes of the electromagnetic field because of the boundary conditions in the Casimir cavity. As such, it has been suggested that the ground state energy of the vacuum within the cavity may be reduced compared to the value outside. Could this have an effect on physical phenomena within the cavity? We study this Casimir energy and probe whether the critical temperature $T_c$ of a superconductor is altered when it is placed in the cavity. We do not detect any change in $T_c$ larger than 12 microKelvin, but theoretically expect a change on the order of 0.025 microKelvin, roughly 1000 times lower than our achieved sensitivity.

quant-ph↗

arXiv2024

Low-loss liquid metal interconnects for superconducting quantum circuits

Building a modular architecture with superconducting quantum computing chips is one of the means to achieve qubit scalability, allowing the screening, selection, replacement, and integration of individual qubit modules into large quantum systems. However, the nondestructive replacement of modules within a compact architecture remains a challenge. Liquid metals, specifically gallium alloys, can be alternatives to solid-state galvanic interconnects. This is motivated by their self-healing, self-aligning, and other desirable fluidic properties, potentially enabling the nondestructive replacement of modules at room temperatures, even after operating the entire system at millikelvin regimes. In this study, we present coplanar waveguide resonators (CPWRs) interconnected by gallium alloy droplets, achieving high internal quality factors up to nearly one million and demonstrating performance on par with the continuous solid-state CPWRs. Leveraging the desirable fluidic properties of gallium alloys at room temperature and their compact design, we envision a modular quantum system enabled by liquid metals.

physics.app-ph↗

arXiv2024

Zeptonewton and Attotesla per Centimeter Metrology With Coupled Oscillators

We present the coupled oscillator: a new mechanism for signal amplification with widespread application in metrology. We introduce the mechanical theory of this framework, and support it by way of simulations. We present a particular implementation of coupled oscillators: a microelectromechanical system (MEMS) that uses one large (~100mm) N52 magnet coupled magnetically to a small (~0.25mm), oscillating N52 magnet, providing a force resolution of 200zN measured over 1s in a noiseless environment. We show that the same system is able to resolve magnetic gradients of 130aT/cm at a single point (within 500um). This technology therefore has the potential to revolutionize force and magnetic gradient sensing, including high-impact areas such cardiac and brain imaging.

physics.app-ph↗

arXiv2022

Tuning the pH Response of Monolayer Hexagonal Boron Nitride/Graphene Field-Effect Transistors

The chemical activity of ionized hydrogen describes the potency of protons in solution and is used to define the pH with wide-ranging applications in biological and materials sciences. Measuring pH with graphene field-effect transistors (FETs) has been described in the past but has yet to be characterized with a monolayer hexagonal boron nitride (hBN) capping layer. hBN capping is hypothesized to lower the chemical affinity of protons to oxidized defects in the graphene crystal and lower the standard deviation of pH measurement via screening charge density. First, the electronic properties of commercial, monolayer graphene and monolayer hBN/graphene, both on four-inch 90 nm SiO2/p-type Si, were contrasted as a function of solutal pH in 10 mM phosphate buffered solution. The two-dimensional (2D) FETs were fabricated with photoresistless metallization followed by microcentrifuge tube-masking and reactive ion etching to define a quasi-pure 2D sensing mesa for pH sensing. Thereafter, the devices were exposed to phosphate buffer of varying pH and the resistance and liquid-transfer characteristics measured. The hBN/graphene/SiO2 FETs had higher linearity, and both lower standard deviation and range of Dirac voltage shifting than monolayer graphene/SiO2. Then, before microcentrifuge tube-masking, freshly metallized devices were coated with 9 nm of Al2O3 by electron beam deposition. The Al2O3/graphene/SiO2 and Al2O3/hBN/graphene/SiO2 devices showed an altered response to the pH of the phosphate buffered solutions before and after basic etching of the Al2O3 with NaOH (pH = 12). This prompted studying the pH-dependencies of the 2D devices as a function of the thickness of Al2O3 via atomic layer deposition. These results show that modifying the surface of monolayer graphene with nanoscale dielectrics enables tuning of the pH-dependent electronic properties of graphene pH sensors.

physics.app-ph↗

arXiv2022

Coronavirus RNA Sensor Using Single-Stranded DNA Bonded to Sub-Percolated Gold Films on Monolayer Graphene Field-Effect Transistors

Electrical detection of messenger ribonucleic acid (mRNA) is a promising approach to enhancing transcriptomics and disease diagnostics because of its sensitivity, rapidity, and modularity. Reported here is a fast SARS-CoV-2 mRNA biosensor (<1 minute) with a limit of detection of 1 aM, and dynamic range of 4 orders of magnitude and a linear sensitivity of 22 mV per molar decade. These figures of merit were obtained on photoresistlessly patterned monolayer graphene field-effect transistors (FETs) derived from commercial four-inch graphene on 90 nm of silicon dioxide on p-type silicon. Then, to facilitate mRNA hybridization, graphene sensing mesa were coated with an ultrathin sub-percolation threshold gold film for bonding 3'-thiolated single-stranded deoxyribonucleic acid (ssDNA) probes complementary to SARS-CoV-2 nucleocapsid phosphoprotein (N) gene. Sub-percolated gold was used to minimize the distance between the graphene material and surface hybridization events. The liquid-transfer characteristics of the graphene FETs repeatedly shows correlation between the Dirac voltage and the copy number of polynucleotide. Ultrathin percolated gold films on graphene FETs facilitate two-dimensional electron gas (2DEG) mRNA biosensors for transcriptomic profiling.

q-bio.BM↗

arXiv2021

Analysis of a Casimir-driven Parametric Amplifier with Resilience to Casimir Pull-in for MEMS Single-Point Magnetic Gradiometry

The Casimir Force, a quantum mechanical effect, has been observed in several microelectromechanical systems (MEMS) platforms. Due to its extreme sensitivity to the separation of two objects, the Casimir Force has been proposed as an excellent avenue for quantum metrology. Practical application, however, is challenging due to attractive forces leading to stiction and failure of the device, called Casimir pull-in. In this work, we design and simulate a Casimir-driven metrology platform, where a time-delay based parametric amplification technique is developed to achieve a steady state and avoid pull-in. We apply the design to the detection of weak, low frequency, gradient magnetic fields, similar to those emanating from ionic currents in the heart and brain. Simulation parameters are selected from recent experimental platforms developed for Casimir metrology and magnetic gradiometry, both on MEMS platforms. While MEMS offer many advantages to such an application, the detected signal must typically be at the resonant frequency of the device, with diminished sensitivity in the low frequency regime of biomagnetic fields. Using a Casimir-drive parametric amplifier, we report a 10,000 fold improvement in the best-case resolution of MEMS single-point gradiometers, with a maximum sensitivity of 6 Hz/(pT/cm) at 1 Hz. The development of the proposed design has the potential to revolutionize metrology, and specifically may enable unshielded monitoring of biomagnetic fields in ambient conditions.

quant-ph↗

arXiv2021

Direct laser writing for cardiac tissue engineering: a microfluidic heart on a chip with integrated transducers

We have designed and fabricated a microfluidic-based platform for sensing mechanical forces generated by cardiac microtissues in a highly-controlled microenvironment. Our fabrication approach combines Direct Laser Writing (DLW) lithography with soft lithography. At the center of our platform is a cylindrical volume, divided into two chambers by a cylindrical polydimethylsiloxane (PDMS) shell. Cells are seeded into the inner chamber from a top opening, and the microtissue assembles onto tailor-made attachment sites on the inner walls of the cylindrical shell. The outer chamber is electrically and fluidically isolated from the inner one by the cylindrical shell and is designed for actuation and sensing purposes. Externally applied pressure waves to the outer chamber deform parts of the cylindrical shell and thus allow us to exert time-dependent forces on the microtissue. Oscillatory forces generated by the microtissue similarly deform the cylindrical shell and change the volume of the outer chamber, resulting in measurable electrical conductance changes. We have used this platform to study the response of cardiac microtissues derived from human induced pluripotent stem cells (hiPSC) under prescribed mechanical loading and pacing.

q-bio.TO↗

arXiv2021

Probing Subcellular Nanostructure of Engineered Human Cardiomyocytes in 3D Tissue

The structural and functional maturation of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is essential for application to pharmaceutical testing, disease modeling, and ultimately therapeutic use. Multicellular 3D-tissue platforms have improved functional maturation of hiPSC-CMs, but probing cardiac contractile properties remains challenging in a 3D environment, especially at depth and in live tissues. Using small angle X-ray scattering (SAXS) images, we show that hiPSC-CMs, matured and examined in a 3D environment, exhibit periodic spatial arrangement of the myofilament lattice, which has not been previously detected in hiPSC-CMs. Contractile force is found to correlate with both scattering intensity (R2=0.44) and lattice spacing (R2=0.46). Scattering intensity also correlates with lattice spacing (R2=0.81), suggestive of lower noise in our structural measurement relative to the functional measurement. Notably, we observe decreased myofilament ordering in tissues with a myofilament mutation known to lead to hypertrophic cardiomyopathy (HCM). Our results highlight the progress of human cardiac tissue engineering and enable unprecedented study of structural maturation in hiPSC-CMs.

physics.bio-ph↗

arXiv2020

Searching for the Casimir Energy

In this article, we present a nano-electromechanical system (NEMS) designed to detect changes in the Casimir Energy. The Casimir effect is a result of the appearance of quantum fluctuations in the electromagnetic vacuum. Previous experiments have used nano- or micro- scale parallel plate capacitors to detect the Casimir force by measuring the small attractive force these fluctuations exert between the two surfaces. In this new set of experiments, we aim to directly detect shifts in the Casimir $\textit{energy}$ in the vacuum due to the presence of metallic parallel plates, one of which is a superconductor. A change in the Casimir energy of this configuration is predicted to shift the superconducting transition temperature (T$_\textrm{c}$) because of an interaction between it and the superconducting condensation energy. The experiment we discuss consists of taking a superconducting film, carefully measuring its transition temperature, bringing a conducting plate close to the film, creating a Casimir cavity, and then measuring the transition temperature again. The expected shifts will be small, comparable to the normal shifts one sees in cycling superconducting films to cryogenic temperatures and so using a NEMS resonator and doing this in situ is the only practical way to obtain accurate, reproducible data. Using a thin Pb film and opposing Au surface, we observe no shift in T$_\textrm{c}$ greater than 12 $μ$K down to a minimum spacing of approximately 70 nm.

physics.app-ph↗

arXiv2019

100pTcm Sensitive MEMS Resonant Magnetometer from a Commercial Accelerometer

Magnetic sensing is present in our everyday interactions with consumer electronics, and also demonstrates potential for measurement of extremely weak biomagnetic fields, such as those of the heart and brain. In this work, we leverage the many benefits of the micro-electromechanical systems (MEMS) devices to fabricate a small, low power, inexpensive sensor whose resolution is in the range of weak biomagnetic fields. The sensor works at room temperature, and is suitable for consumer electronics integration. At present, such biomagnetic fields can only be measured by expensive mechanisms such as optical pumping and superconducting quantum interference devices (SQUIDs). Thus, our sensor suggests the opening of a large phase space for medical and consumer applications. The prototype fabrication is achieved by assembling micro-objects, including a permanent micromagnet, onto a post-release commercial MEMS accelerometer. With this system, we demonstrate a room temperature MEMS magnetometer, whose design is only sensitive to gradient magnetic fields and is generally insensitive to the Earth's uniform field. In air, the sensor's response is linear with a resolution of 1.1 nT cm-1 and spans over 3 decades of dynamic range to 4.6 μT cm-1. In 1 mTorr vacuum with 20 dB magnetic shielding, the sensor achieved 100 pT cm-1 resolution at resonance. The theoretical floor of this design is 110 fT cm-1 Hz-1/2 with a resolution of 13 fT cm-1, thus these devices hold promise for both magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

physics.app-ph↗

arXiv2018

Modeling and Thermal Metrology of Thermally Isolated MEMS Electrothermal Actuators for Strain Engineering of 2D Materials

We present electrothermal microelectromechanical (MEMS) actuators as a practical platform for straining 2D materials. The advantages of the electrothermal actuator is its high output force and displacement for low input voltage, but its drawback is that it is actuated by generating high amounts of heat. It is crucial to mitigate the high temperatures generated during actuation for reliable 2D material strain device implementation. Here, we implement a chevron actuator design that incorporates a thermal isolation stage in order to avoid heating the 2D material from the high temperatures generated during the actuation. By comparing experiment and simulation, we ensure our design does not compromise output displacement, while keeping the 2D material strain device stage cool. We also provide a simple analytical model useful for quickly evaluating different thermal isolation stage designs.

physics.app-ph↗

arXiv2018

Building a Casimir Metrology Platform with a Commercial MEMS Accelerometer

The Casimir Effect is a physical manifestation of quantum fluctuations of the electromagnetic vacuum. When two metal plates are placed closely together, typically much less than a micron, the long wavelength modes between them are frozen out, giving rise to a net attractive force between the plates, scaling as d^-4 (or d^-3 for a spherical-planar geometry) even when they are not electrically charged. In this paper we observe the Casimir Effect in ambient conditions using a modified capacitive MEMS accelerometer. Using a feedback assisted pick-and-place assembly process we are able to attach various micro-structures onto the post-release MEMS, converting it from an inertial force sensor to a direct force measurement platform with pN resolution. With this system we are able to directly measure the Casimir force between a silver-coated microsphere and gold-coated silicon plate. This device is a step towards leveraging the Casimir Effect for cheap, sensitive, room temperature quantum metrology.

physics.app-ph↗

arXiv2018

Monolayer MoS$_2$ Strained to 1.3\% with a Microelectromechanical System

We report on a modified transfer technique for atomically thin materials integrated onto microelectromechanical systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar structures and fragility of MEMS, while still providing precise positioning and crack free transfer of flakes. Further, our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time, increases the yield, and allowed us to exploit the strong mechanical coupling between 2D crystal and polymer to strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS$_2$) with MEMS devices for the first time and achieved greater than 1.3\% strain, marking a major milestone for incorporating 2D materials with MEMS We used the established strain response of MoS$_2$ Raman and Photoluminescence spectra to deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment and literature.

cond-mat.mtrl-sci↗

arXiv2018

High Performance, Continuously Tunable Microwave Filters using MEMS Devices with Very Large, Controlled, Out-of-Plane Actuation

Software defined radios (SDR) in the microwave X and K bands offer the promise of low cost, programmable operation with real-time frequency agility. However, the real world in which such radios operate requires them to be able to detect nanowatt signals in the vicinity of 100 kW transmitters. This imposes the need for selective RF filters on the front end of the receiver to block the large, out of band RF signals so that the finite dynamic range of the SDR is not overwhelmed and the desired nanowatt signals can be detected and digitally processed. This is currently typically done with a number of narrow band filters that are switched in and out under program control. What is needed is a small, fast, wide tuning range, high Q, low loss filter that can continuously tune over large regions of the microwave spectrum. In this paper we show how extreme throw MEMS actuators can be used to build such filters operating up to 15 GHz and beyond. The key enabling attribute of our MEMS actuators is that they have large, controllable, out-of-plane actuation ranges of a millimeter or more. In a capacitance-post loaded cavity filter geometry, this gives sufficient precisely controllable motion to produce widely tunable devices in the 4-15 GHz regime.

physics.ins-det↗

arXiv2016

High speed control of electro-mechanical transduction Advanced Drive Techniques for Optimized Step-and-Settle Response of MEMS Micromirrors

Micro/Nano Electro Mechanical Systems (MEMS/NEMS) provide the engineer with a powerful set of solutions to a wide variety of technical challenges. However, because they are mechanical systems, response times can be a limitation. In some situations, advanced engineered drive techniques can improve response times by as much as a thousand, significantly opening up the application space for MEMS/NEMS solutions.

physics.ins-det↗

arXiv2013

Atomic Calligraphy: The Direct Writing of Nanoscale Structures using MEMS

We present a micro-electromechanical system (MEMS) based method for the resist free patterning of nano-structures. Using a focused ion beam (FIB) to customize larger MEMS machines, we fabricate apertures as small as 50 nm on plates that can be moved with nanometer precision over an area greater than 20x20 μm^2. Depositing thermally evaporated gold atoms though the apertures while moving the plate results in the deposition of nanoscale metal patterns. Adding a shutter only microns above the aperture, enables high speed control of not only where but also when atoms are deposited. Using a shutter, different sized apertures can be selectively opened and closed for nano-structure fabrication with features ranging from nano- to micrometers in scale. The ability to evaporate materials with high precision, and thereby fabricate circuits and structures in situ, enables new kinds of experiments based on the interactions of a small number of atoms and eventually even single atoms.

cond-mat.mes-hall↗