1,365 research outputs found
Resource frugal optimizer for quantum machine learning
Quantum-enhanced data science, also known as quantum machine learning (QML),
is of growing interest as an application of near-term quantum computers.
Variational QML algorithms have the potential to solve practical problems on
real hardware, particularly when involving quantum data. However, training
these algorithms can be challenging and calls for tailored optimization
procedures. Specifically, QML applications can require a large shot-count
overhead due to the large datasets involved. In this work, we advocate for
simultaneous random sampling over both the dataset as well as the measurement
operators that define the loss function. We consider a highly general loss
function that encompasses many QML applications, and we show how to construct
an unbiased estimator of its gradient. This allows us to propose a shot-frugal
gradient descent optimizer called Refoqus (REsource Frugal Optimizer for
QUantum Stochastic gradient descent). Our numerics indicate that Refoqus can
save several orders of magnitude in shot cost, even relative to optimizers that
sample over measurement operators alone.Comment: 22 pages, 6 figures - extra quantum autoencoder results adde
Unifying and benchmarking state-of-the-art quantum error mitigation techniques
Error mitigation is an essential component of achieving practical quantum
advantage in the near term, and a number of different approaches have been
proposed. In this work, we recognize that many state-of-the-art error
mitigation methods share a common feature: they are data-driven, employing
classical data obtained from runs of different quantum circuits. For example,
Zero-noise extrapolation (ZNE) uses variable noise data and Clifford-data
regression (CDR) uses data from near-Clifford circuits. We show that Virtual
Distillation (VD) can be viewed in a similar manner by considering classical
data produced from different numbers of state preparations. Observing this fact
allows us to unify these three methods under a general data-driven error
mitigation framework that we call UNIfied Technique for Error mitigation with
Data (UNITED). In certain situations, we find that our UNITED method can
outperform the individual methods (i.e., the whole is better than the
individual parts). Specifically, we employ a realistic noise model obtained
from a trapped ion quantum computer to benchmark UNITED, as well as
state-of-the-art methods, for problems with various numbers of qubits, circuit
depths and total numbers of shots. We find that different techniques are
optimal for different shot budgets. Namely, ZNE is the best performer for small
shot budgets (), while Clifford-based approaches are optimal for larger
shot budgets (), and for our largest considered shot budget
(), UNITED gives the most accurate correction. Hence, our work
represents a benchmarking of current error mitigation methods, and provides a
guide for the regimes when certain methods are most useful.Comment: 13 pages, 4 figure
Cadherin-26 (CDH26) regulates airway epithelial cell cytoskeletal structure and polarity.
Polarization of the airway epithelial cells (AECs) in the airway lumen is critical to the proper function of the mucociliary escalator and maintenance of lung health, but the cellular requirements for polarization of AECs are poorly understood. Using human AECs and cell lines, we demonstrate that cadherin-26 (CDH26) is abundantly expressed in differentiated AECs, localizes to the cell apices near ciliary membranes, and has functional cadherin domains with homotypic binding. We find a unique and non-redundant role for CDH26, previously uncharacterized in AECs, in regulation of cell-cell contact and cell integrity through maintaining cytoskeletal structures. Overexpression of CDH26 in cells with a fibroblastoid phenotype increases contact inhibition and promotes monolayer formation and cortical actin structures. CDH26 expression is also important for localization of planar cell polarity proteins. Knockdown of CDH26 in AECs results in loss of cortical actin and disruption of CRB3 and other proteins associated with apical polarity. Together, our findings uncover previously unrecognized functions for CDH26 in the maintenance of actin cytoskeleton and apicobasal polarity of AECs
The battle of clean and dirty qubits in the era of partial error correction
When error correction becomes possible it will be necessary to dedicate a
large number of physical qubits to each logical qubit. Error correction allows
for deeper circuits to be run, but each additional physical qubit can
potentially contribute an exponential increase in computational space, so there
is a trade-off between using qubits for error correction or using them as noisy
qubits. In this work we look at the effects of using noisy qubits in
conjunction with noiseless qubits (an idealized model for error-corrected
qubits), which we call the "clean and dirty" setup. We employ analytical models
and numerical simulations to characterize this setup. Numerically we show the
appearance of Noise-Induced Barren Plateaus (NIBPs), i.e., an exponential
concentration of observables caused by noise, in an Ising model Hamiltonian
variational ansatz circuit. We observe this even if only a single qubit is
noisy and given a deep enough circuit, suggesting that NIBPs cannot be fully
overcome simply by error-correcting a subset of the qubits. On the positive
side, we find that for every noiseless qubit in the circuit, there is an
exponential suppression in concentration of gradient observables, showing the
benefit of partial error correction. Finally, our analytical models corroborate
these findings by showing that observables concentrate with a scaling in the
exponent related to the ratio of dirty-to-total qubits.Comment: 27 pages, 15 figures, (v2) minor change
Inference-Based Quantum Sensing
In a standard Quantum Sensing (QS) task one aims at estimating an unknown
parameter , encoded into an -qubit probe state, via measurements of
the system. The success of this task hinges on the ability to correlate changes
in the parameter to changes in the system response (i.e.,
changes in the measurement outcomes). For simple cases the form of
is known, but the same cannot be said for realistic
scenarios, as no general closed-form expression exists. In this work we present
an inference-based scheme for QS. We show that, for a general class of unitary
families of encoding, can be fully characterized by only
measuring the system response at parameters. In turn, this allows us to
infer the value of an unknown parameter given the measured response, as well as
to determine the sensitivity of the sensing scheme, which characterizes its
overall performance. We show that inference error is, with high probability,
smaller than , if one measures the system response with a number of
shots that scales only as . Furthermore, the
framework presented can be broadly applied as it remains valid for arbitrary
probe states and measurement schemes, and, even holds in the presence of
quantum noise. We also discuss how to extend our results beyond unitary
families. Finally, to showcase our method we implement it for a QS task on real
quantum hardware, and in numerical simulations.Comment: 5+10 pages, 3+5 figure
Free energy barrier for melittin reorientation from a membrane-bound state to a transmembrane state
An important step in a phospholipid membrane pore formation by melittin
antimicrobial peptide is a reorientation of the peptide from a surface into a
transmembrane conformation. In this work we perform umbrella sampling
simulations to calculate the potential of mean force (PMF) for the
reorientation of melittin from a surface-bound state to a transmembrane state
and provide a molecular level insight into understanding peptide and lipid
properties that influence the existence of the free energy barrier. The PMFs
were calculated for a peptide to lipid (P/L) ratio of 1/128 and 4/128. We
observe that the free energy barrier is reduced when the P/L ratio increased.
In addition, we study the cooperative effect; specifically we investigate if
the barrier is smaller for a second melittin reorientation, given that another
neighboring melittin was already in the transmembrane state. We observe that
indeed the barrier of the PMF curve is reduced in this case, thus confirming
the presence of a cooperative effect
In the dedicated pursuit of dedicated capital: restoring an indigenous investment ethic to British capitalism
Tony Blair’s landslide electoral victory on May 1 (New Labour Day?) presents the party in power with a rare, perhaps even unprecedented, opportunity to revitalise and modernise Britain’s ailing and antiquated manufacturing economy.* If it is to do so, it must remain true to its long-standing (indeed, historic) commitment to restore an indigenous investment ethic to British capitalism. In this paper we argue that this in turn requires that the party reject the very neo-liberal orthodoxies which it offered to the electorate as evidence of its competence, moderation and ‘modernisation’, which is has internalised, and which it apparently now views as circumscribing the parameters of the politically and economically possible
Mitiq : a software package for error mitigation on noisy quantum computers
We introduce Mitiq, a Python package for error mitigation on noisy quantum computers. Error mitigation techniques can reduce the impact of noise on near-term quantum computers with minimal overhead in quantum resources by relying on a mixture of quantum sampling and classical post-processing techniques. Mitiq is an extensible toolkit of different error mitigation methods, including zero-noise extrapolation, probabilistic error cancellation, and Clifford data regression. The library is designed to be compatible with generic backends and interfaces with different quantum software frameworks. We describe Mitiq using code snippets to demonstrate usage and discuss features and contribution guidelines. We present several examples demonstrating error mitigation on IBM and Rigetti superconducting quantum processors as well as on noisy simulators
What does inflation really predict?
If the inflaton potential has multiple minima, as may be expected in, e.g.,
the string theory "landscape", inflation predicts a probability distribution
for the cosmological parameters describing spatial curvature (Omega_tot), dark
energy (rho_Lambda, w, etc.), the primordial density fluctuations (Omega_tot,
dark energy (rho_Lambda, w, etc.). We compute this multivariate probability
distribution for various classes of single-field slow-roll models, exploring
its dependence on the characteristic inflationary energy scales, the shape of
the potential V and and the choice of measure underlying the calculation. We
find that unless the characteristic scale Delta-phi on which V varies happens
to be near the Planck scale, the only aspect of V that matters observationally
is the statistical distribution of its peaks and troughs. For all energy scales
and plausible measures considered, we obtain the predictions Omega_tot ~
1+-0.00001, w=-1 and rho_Lambda in the observed ballpark but uncomfortably
high. The high energy limit predicts n_s ~ 0.96, dn_s/dlnk ~ -0.0006, r ~ 0.15
and n_t ~ -0.02, consistent with observational data and indistinguishable from
eternal phi^2-inflation. The low-energy limit predicts 5 parameters but prefers
larger Q and redder n_s than observed. We discuss the coolness problem, the
smoothness problem and the pothole paradox, which severely limit the viable
class of models and measures. Our findings bode well for detecting an
inflationary gravitational wave signature with future CMB polarization
experiments, with the arguably best-motivated single-field models favoring the
detectable level r ~ 0.03. (Abridged)Comment: Replaced to match accepted JCAP version. Improved discussion,
references. 42 pages, 17 fig
Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields: Technical Summary and Data Release
The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained
five-band optical-wavelength imaging near the Galactic plane outside of the
nominal survey boundaries. These additional data were obtained during
commissioning and subsequent testing of the SDSS observing system, and they
provide unique wide-area imaging data in regions of high obscuration and star
formation, including numerous young stellar objects, Herbig-Haro objects and
young star clusters. Because these data are outside the Survey regions in the
Galactic caps, they are not part of the standard SDSS data releases. This paper
presents imaging data for 832 square degrees of sky (including repeats), in the
star-forming regions of Orion, Taurus, and Cygnus. About 470 square degrees are
now released to the public, with the remainder to follow at the time of SDSS
Data Release 4. The public data in Orion include the star-forming region NGC
2068/NGC 2071/HH24 and a large part of Barnard's loop.Comment: 31 pages, 9 figures (3 missing to save space), accepted by AJ, in
press, see http://photo.astro.princeton.edu/oriondatarelease for data and
paper with all figure
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