arXiv subjects

Vandiver Chaplin

Publications and source records attributed to Vandiver Chaplin.

At least 19 recordsLinked to original sources

arXiv2023

Benchmarking a trapped-ion quantum computer with 30 qubits

Quantum computers are rapidly becoming more capable, with dramatic increases in both qubit count and quality. Among different hardware approaches, trapped-ion quantum processors are a leading technology for quantum computing, with established high-fidelity operations and architectures with promising scaling. Here, we demonstrate and thoroughly benchmark the IonQ Forte system: configured as a single-chain 30-qubit trapped-ion quantum computer with all-to-all operations. We assess the performance of our quantum computer operation at the component level via direct randomized benchmarking (DRB) across all 30 choose 2 = 435 gate pairs. We then show the results of application-oriented benchmarks and show that the system passes the suite of algorithmic qubit (AQ) benchmarks up to #AQ 29. Finally, we use our component-level benchmarking to build a system-level model to predict the application benchmarking data through direct simulation. While we find that the system-level model correlates with the experiment in predicting application circuit performance, we note quantitative discrepancies indicating significant out-of-model errors, leading to higher predicted performance than what is observed. This highlights that as quantum computers move toward larger and higher-quality devices, characterization becomes more challenging, suggesting future work required to push performance further.

quant-ph↗

arXiv2021

Detecting Qubit-coupling Faults in Ion-trap Quantum Computers

Ion-trap quantum computers offer a large number of possible qubit couplings, each of which requires individual calibration and can be misconfigured. To enhance the duty cycle of an ion trap, we develop a strategy that diagnoses individual miscalibrated couplings using only log-many tests. This strategy is validated on a commercial ion-trap quantum computer, where we illustrate the process of debugging faulty quantum gates. Our methodology provides a scalable pathway towards fault detections on a larger scale ion-trap quantum computers, confirmed by simulations up to 32 qubits.

quant-ph↗

arXiv2019

Efficient Arbitrary Simultaneously Entangling Gates on a trapped-ion quantum computer

Efficiently entangling pairs of qubits is essential to fully harness the power of quantum computing. Here, we devise an exact protocol that simultaneously entangles arbitrary pairs of qubits on a trapped-ion quantum computer. The protocol requires classical computational resources polynomial in the system size, and very little overhead in the quantum control compared to a single-pair case. We demonstrate an exponential improvement in both classical and quantum resources over the current state of the art. We implement the protocol on a software-defined trapped-ion quantum computer, where we reconfigure the quantum computer architecture on demand. Together with the all-to-all connectivity available in trapped-ion quantum computers, our results establish that trapped ions are a prime candidate for a scalable quantum computing platform with minimal quantum latency.

quant-ph↗

arXiv2019

Ground-state energy estimation of the water molecule on a trapped ion quantum computer

Quantum computing leverages the quantum resources of superposition and entanglement to efficiently solve computational problems considered intractable for classical computers. Examples include calculating molecular and nuclear structure, simulating strongly-interacting electron systems, and modeling aspects of material function. While substantial theoretical advances have been made in mapping these problems to quantum algorithms, there remains a large gap between the resource requirements for solving such problems and the capabilities of currently available quantum hardware. Bridging this gap will require a co-design approach, where the expression of algorithms is developed in conjunction with the hardware itself to optimize execution. Here, we describe a scalable co-design framework for solving chemistry problems on a trapped ion quantum computer, and apply it to compute the ground-state energy of the water molecule. The robust operation of the trapped ion quantum computer yields energy estimates with errors approaching the chemical accuracy, which is the target threshold necessary for predicting the rates of chemical reaction dynamics.

quant-ph↗

arXiv2017

A random phased-array for MR-guided transcranial ultrasound neuromodulation in non-human primates

Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650kHz. The array is randomized with 128 elements, radius of curvature 7.2cm, and opening diameter 10.3cm (focal ratio 0.7). Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. A novel combination of optical tracking and acoustic mapping enabled measurement of the 3D pressure distribution in the cortical region of an ex vivo skull to within ~3.5 mm of the surface, and allowed accurate modelling of the experiment via non-homogeneous 3D acoustic simulations. The data demonstrates acoustic focusing beyond the skull bone, with the focus slightly broadened and shifted proximal to the skull. The fabricated design is capable of targeting regions within the S1 sensorimotor cortex of macaques.

physics.med-ph↗

arXiv2016

The 3rd Fermi GBM Gamma-Ray Burst Catalog: The First Six Years

Since its launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has triggered and located on average approximately two gamma-ray bursts (GRB) every three days. Here we present the third of a series of catalogs of GRBs detected by GBM, extending the second catalog by two more years, through the middle of July 2014. The resulting list includes 1405 triggers identified as GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux and fluence are derived. The latter two quantities are calculated for the 50-300~keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed, and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBM's low-energy NaI(Tl) detectors. Using statistical methods to assess clustering, we find that the hardness and duration of GRBs are better fitted by a two-component model with short-hard and long-soft bursts, than by a model with three components. Furthermore, information is provided on the settings and modifications of the triggering criteria and exceptional operational conditions during years five and six in the mission. This third catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

astro-ph.HE↗

arXiv2014

The 2nd Fermi GBM Gamma-Ray Burst Catalog: The First Four Years

This is the second of a series of catalogs of gamma-ray bursts (GRBs) observed with the Fermi Gamma-ray Burst Monitor (GBM). It extends the first two-year catalog by two more years, resulting in an overall list of 953 GBM triggered GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux and fluence are derived. The latter two quantities are calculated for the 50 - 300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10 - 1000 keV, exploiting the full energy range of GBMs low-energy detectors. Furthermore, information is given on the settings and modifications of the triggering criteria and exceptional operational conditions during years three and four in the mission. This second catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

astro-ph.HE↗

arXiv2013

Analytical modeling of pulse-pileup distortion using the true pulse shape; applications to Fermi-GBM

Pulse-pileup affects most photon counting systems and occurs when photon detections occur faster than the detector's registration and recovery time. At high input rates, shaped pulses interfere and the source spectrum, as well as intensity information, get distorted. For instruments using bipolar pulse shaping there are two aspects to consider: `peak' and `tail' pileup effects, which raise and lower the measured energy, respectively. Peak effects have been extensively modeled in the past. Tail effects have garnered less attention due to the increased complexity: bipolar tails mean the tail pulse-height measurement depends on events in more than one time interval. We leverage previous work to derive an accurate, semi-analytical prediction for peak and tail pileup, up to high orders. We use the true pulse shape from the detectors of the Fermi Gamma-ray Burst Monitor. The measured spectrum is calculated by writing exposure time as a state-space expansion of overlapping pileup states and is valid up to very high rates. This expansion models losses due to fixed and extendable deadtime by averaging overlap configurations. Additionally, the model correctly predicts energy-dependent losses due to tail subtraction (sub-threshold) effects. We discuss pileup losses in terms of the true rate of photon detections versus the recorded count rate.

astro-ph.IM↗

arXiv2013

Three years of Fermi GBM Earth Occultation Monitoring: Observations of Hard X-ray/Soft Gamma-Ray Sources

The Gamma ray Burst Monitor (GBM) on board Fermi Gamma-ray Space Telescope has been providing continuous data to the astronomical community since 2008 August 12. We will present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. Although the occultation technique is in principle quite simple, in practice there are many complications including the dynamic instrument response, source confusion, and scattering in the Earth's atmosphere, which will be described. We detect 99 sources, including 40 low-mass X-ray binary/neutron star systems, 31 high-mass X-ray binary/neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky monitors below 100 keV and is the only all-sky monitor above 100 keV. In our fourth year of monitoring, we have already increased the number of transient sources detected and expect several of the weaker persistent sources to cross the detection threshold. I will briefly discuss these new sources and what to expect from our five year occultation catalog.

astro-ph.HE↗

arXiv2012

Three years of Fermi GBM Earth Occultation Monitoring: Observations of Hard X-ray/Soft Gamma-Ray Sources

The Gamma ray Burst Monitor (GBM) on board Fermi has been providing continuous data to the astronomical community since 2008 August 12. In this paper we present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. From this catalog, we detect 99 sources, including 40 low-mass X-ray binary/neutron star systems, 31 high-mass X-ray binary neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula, and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky-monitors below 100 keV and is the only all-sky monitor above 100 keV. Up-to-date light curves for all of the catalog sources can be found at http://heastro.phys.lsu.edu/gbm/.

astro-ph.HE↗

arXiv2012

The Fermi GBM Gamma-Ray Burst Catalog: The First Two Years

The Fermi Gamma-ray Burst Monitor (GBM) is designed to enhance the scientific return from Fermi in studying gamma-ray bursts (GRBs). In its first two years of operation GBM triggered on 491 GRBs. We summarize the criteria used for triggering and quantify the general characteristics of the triggered GRBs, including their locations, durations, peak flux, and fluence. This catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

astro-ph.HE↗

arXiv2012

The Fermi GBM Gamma-Ray Burst Spectral Catalog: The First Two Years

We present systematic spectral analyses of GRBs detected by the Fermi Gamma-Ray Burst Monitor (GBM) during its first two years of operation. This catalog contains two types of spectra extracted from 487 GRBs, and by fitting four different spectral models, this results in a compendium of over 3800 spectra. The models were selected based on their empirical importance to the spectral shape of many GRBs, and the analysis performed was devised to be as thorough and objective as possible. We describe in detail our procedure and criteria for the analyses, and present the bulk results in the form of parameter distributions. This catalog should be considered an official product from the Fermi GBM Science Team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

astro-ph.HE↗

arXiv2011

Searching for Unmodeled Sources Using the Earth Occultation Data from the Fermi GBM

Employing the 12 NaI detectors in the Fermi GBM, the Earth Occultation Technique (EOT) can be used to measure the fluxes of x-ray and gamma-ray sources. Each time a source passes behind the Earth (or emerges from behind the Earth), a step-like feature is produced in the detector count rate. With a predefined catalog of source positions, the times of the occultation steps can be calculated, the individual steps fit, and the fluxes derived. However, in order to find new sources and generate a complete catalog, a method is needed for generating an image of the sky. An imaging algorithm has been developed to generate all-sky images using the GBM data. Here we present imaging results from ~2.5 years of data in the 12-25 keV and 100-300 keV energy bands.

astro-ph.HE↗

arXiv2011

Temporal Deconvolution study of Long and Short Gamma-Ray Burst Light curves

The light curves of Gamma-Ray Bursts (GRBs) are believed to result from internal shocks reflecting the activity of the GRB central engine. Their temporal deconvolution can reveal potential differences in the properties of the central engines in the two populations of GRBs which are believed to originate from the deaths of massive stars (long) and from mergers of compact objects (short). We present here the results of the temporal analysis of 42 GRBs detected with the Gamma-ray Burst Monitor onboard the Fermi Gamma-ray Space Telescope. We deconvolved the profiles into pulses, which we fit with lognormal functions. The distributions of the pulse shape parameters and intervals between neighboring pulses are distinct for both burst types and also fit with lognormal functions. We have studied the evolution of these parameters in different energy bands and found that they differ between long and short bursts. We discuss the implications of the differences in the temporal properties of long and short bursts within the framework of the internal shock model for GRB prompt emission.

astro-ph.HE↗

arXiv2011

Burst and Persistent Emission Properties during the Recent Active Episode of the Anomalous X-ray Pulsar 1E 1841-045

Swift/BAT detected the first burst from 1E 1841-045 in May 2010 with intermittent burst activity recorded through at least July 2011. Here we present Swift and Fermi/GBM observations of this burst activity and search for correlated changes to the persistent X-ray emission of the source. The T90 durations of the bursts range between 18-140 ms, comparable to other magnetar burst durations, while the energy released in each burst ranges between (0.8 - 25)E38 erg, which is in the low side of SGR bursts. We find that the bursting activity did not have a significant effect on the persistent flux level of the source. We argue that the mechanism leading to this sporadic burst activity in 1E 1841-045 might not involve large scale restructuring (either crustal or magnetospheric) as seen in other magnetar sources.

astro-ph.HE↗

arXiv2011

Constraints on the Synchrotron Shock Model for the Fermi GBM Gamma-Ray Burst 090820A

Discerning the radiative dissipation mechanism for prompt emission in Gamma-Ray Bursts (GRBs) requires detailed spectroscopic modeling that straddles the $νF_ν$ peak in the 100 keV - 1 MeV range. Historically, empirical fits such as the popular Band function have been employed with considerable success in interpreting the observations. While extrapolations of the Band parameters can provide some physical insight into the emission mechanisms responsible for GRBs, these inferences do not provide a unique way of discerning between models. By fitting physical models directly this degeneracy can be broken, eliminating the need for empirical functions; our analysis here offers a first step in this direction. One of the oldest, and leading, theoretical ideas for the production of the prompt signal is the synchrotron shock model (SSM). Here we explore the applicability of this model to a bright {\it Fermi} GBM burst with a simple temporal structure, GRB {\it 090820}A. Our investigation implements, for the first time, thermal and non-thermal synchrotron emissivities in the RMFIT forward-folding spectral analysis software often used in GBM burst studies. We find that these synchrotron emissivities, together with a blackbody shape, provide at least as good a match with the data as the Band GRB spectral fitting function. This success is achieved in both time-integrated and time-resolved spectral fits.

astro-ph.HE↗

arXiv2011

Fermi/GBM Observations of SGR J0501+4516 Bursts

We present our temporal and spectral analyses of 29 bursts from SGR J0501+4516, detected with the Gamma-ray Burst Monitor onboard the Fermi Gamma-ray Space Telescope during the 13 days of the source activation in 2008 (August 22 to September 3). We find that the T90 durations of the bursts can be fit with a log-normal distribution with a mean value of ~ 123 ms. We also estimate for the first time event durations of Soft Gamma Repeater (SGR) bursts in photon space (i.e., using their deconvolved spectra) and find that these are very similar to the T90s estimated in count space (following a log-normal distribution with a mean value of ~ 124 ms). We fit the time-integrated spectra for each burst and the time-resolved spectra of the five brightest bursts with several models. We find that a single power law with an exponential cutoff model fits all 29 bursts well, while 18 of the events can also be fit with two black body functions. We expand on the physical interpretation of these two models and we compare their parameters and discuss their evolution. We show that the time-integrated and time-resolved spectra reveal that Epeak decreases with energy flux (and fluence) to a minimum of ~30 keV at F=8.7e-6 erg/cm2/s, increasing steadily afterwards. Two more sources exhibit a similar trend: SGRs J1550-5418 and 1806-20. The isotropic luminosity corresponding to these flux values is roughly similar for all sources (0.4-1.5 e40 erg/s).

astro-ph.HE↗

arXiv2011

When A Standard Candle Flickers

The Crab Nebula is the only hard X-ray source in the sky that is both bright enough and steady enough to be easily used as a standard candle. As a result, it has been used as a normalization standard by most X-ray/gamma ray telescopes. Although small-scale variations in the nebula are well-known, since the start of science operations of the Fermi Gamma-ray Burst Monitor (GBM) in August 2008, a ~ 7% (70 mcrab) decline has been observed in the overall Crab Nebula flux in the 15 - 50 keV band, measured with the Earth occultation technique. This decline is independently confirmed with three other instruments: the Swift Burst Alert Telescope (Swift/BAT), the Rossi X-ray Timing Explorer Proportional Counter Array (RXTE/PCA), and the INTErnational Gamma-Ray Astrophysics Laboratory Imager on Board INTEGRAL (IBIS). A similar decline is also observed in the ~3 - 15 keV data from the RXTE/PCA and INTEGRAL Joint European Monitor (JEM-X) and in the 50 - 100 keV band with GBM and INTEGRAL/IBIS. Observations from 100 to 500 keV with GBM suggest that the decline may be larger at higher energies. The pulsed flux measured with RXTE/PCA since 1999 is consistent with the pulsar spin-down, indicating that the observed changes are nebular. Correlated variations in the Crab Nebula flux on a ~3 year timescale are also seen independently with the PCA, BAT, and IBIS from 2005 to 2008, with a flux minimum in April 2007. As of August 2010, the current flux has declined below the 2007 minimum.

astro-ph.HE↗