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"Jordan, Stephen"
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Quantum Algorithms for Quantum Field Theories
Quantum field theory reconciles quantum mechanics and special relativity, and plays a central role in many areas of physics. We developed a quantum algorithm to compute relativistic scattering probabilities in a massive quantum field theory with quartic self-interactions (ф⁴ theory) in spacetime of four and fewer dimensions. Its run time is polynomial in the number of particles, their energy, and the desired precision, and applies at both weak and strong coupling. In the strong-coupling and high-precision regimes, our quantum algorithm achieves exponential speedup over the fastest known classical algorithm.
Journal Article
Homerooms & hall passes
\"In the mystical realm of Brâiandalèor, every day the brave and the bold delve into hidden temples or forgotten dungeons, battling vile monsters and evil wizards to loot their treasure hoards for sweet, sweet magic items. But in their free time, our heroes ... need to relax and unwind. That's why they meet up once a week to play Homerooms & Hall Passes, a role-playing game where they assume the characters of average American eighth graders. But when the five young adventurers are magically transported into their H&H game by an ancient curse, they must band together to survive their toughest challenge yet: middle school\"--Publisher marketing.
Book
Polynomial-Time Quantum Algorithm for the Simulation of Chemical Dynamics
The computational cost of exact methods for quantum simulation using classical computers grows exponentially with system size. As a consequence, these techniques can be applied only to small systems. By contrast, we demonstrate that quantum computers could exactly simulate chemical reactions in polynomial time. Our algorithm uses the split-operator approach and explicitly simulates all electron-nuclear and interelectronic interactions in quadratic time. Surprisingly, this treatment is not only more accurate than the Born-Oppenheimer approximation but faster and more efficient as well, for all reactions with more than about four atoms. This is the case even though the entire electronic wave function is propagated on a grid with appropriately short time steps. Although the preparation and measurement of arbitrary states on a quantum computer is inefficient, here we demonstrate how to prepare states of chemical interest efficiently. We also show how to efficiently obtain chemically relevant observables, such as state-to-state transition probabilities and thermal reaction rates. Quantum computers using these techniques could outperform current classical computers with 100 qubits.
Journal Article
Efficient Quantum Algorithm for Nonlinear Reaction–Diffusion Equations and Energy Estimation
Nonlinear differential equations exhibit rich phenomena in many fields but are notoriously challenging to solve. Recently, Liu et al. (in: Proceedings of the National Academy of Sciences 118(35), 2021) demonstrated the first efficient quantum algorithm for dissipative quadratic differential equations under the condition
R
<
1
, where
R
measures the ratio of nonlinearity to dissipation using the
ℓ
2
norm. Here we develop an efficient quantum algorithm based on Liu et al. (2021) for reaction–diffusion equations, a class of nonlinear partial differential equations (PDEs). To achieve this, we improve upon the Carleman linearization approach introduced in Liu et al. (2021) to obtain a faster convergence rate under the condition
R
D
<
1
, where
R
D
measures the ratio of nonlinearity to dissipation using the
ℓ
∞
norm. Since
R
D
is independent of the number of spatial grid points
n
while
R
increases with
n
, the criterion
R
D
<
1
is significantly milder than
R
<
1
for high-dimensional systems and can stay convergent under grid refinement for approximating PDEs. As applications of our quantum algorithm we consider the Fisher-KPP and Allen-Cahn equations, which have interpretations in classical physics. In particular, we show how to estimate the mean square kinetic energy in the solution by postprocessing the quantum state that encodes it to extract derivative information.
Journal Article
Henry's crime
Released from prison for a crime he didn't commit, an ex-con targets the same bank he was sent away for robbing.
DVD
Wetlands as Sinks for Reactive Nitrogen at Continental and Global Scales: A Meta-Analysis
Wetlands support physical and ecological functions that result in valuable services to society, including removal of reactive nitrogen (Nr) from surface water and groundwater. We compiled published data from wetland studies worldwide to estimate total Nr removal and to evaluate factors that influence removal rates. Over several orders of magnitude in wetland area and Nr loading rates, there is a positive, near-linear relationship between Nr removal and Nr loading. The linear model (null hypothesis) explains the data better than either a model of declining Nr removal efficiency with increasing Nr loading, or a Michaelis-Menten (saturation) model. We estimate that total Nr removal by major classes of wetlands in the contiguous U.S. is approximately 20-21% of the total anthropogenic load of Nr to the region. Worldwide, Nr removal by wetlands is roughly 17% of anthropogenic Nr inputs. Historical loss of 50% of native wetland area suggests an equivalent loss of Nr removal capacity. Expanded protection and large-scale restoration of wetlands should be considered in strategies to re-balance the global nitrogen cycle and mitigate the negative consequences of excess Nr loading.
Journal Article
Automated design of pulse sequences for magnetic resonance fingerprinting using physics-inspired optimization
Magnetic resonance fingerprinting (MRF) is a method to extract quantitative tissue properties such as T₁ and T₂ relaxation rates from arbitrary pulse sequences using conventional MRI hardware. MRF pulse sequences have thousands of tunable parameters, which can be chosen to maximize precision and minimize scan time. Here, we perform de novo automated design of MRF pulse sequences by applying physics-inspired optimization heuristics. Our experimental data suggest that systematic errors dominate over random errors in MRF scans under clinically relevant conditions of high undersampling. Thus, in contrast to prior optimization efforts, which focused on statistical error models, we use a cost function based on explicit first-principles simulation of systematic errors arising from Fourier undersampling and phase variation. The resulting pulse sequences display features qualitatively different from previously used MRF pulse sequences and achieve fourfold shorter scan time than prior human-designed sequences of equivalent precision in T₁ and T₂. Furthermore, the optimization algorithm has discovered the existence of MRF pulse sequences with intrinsic robustness against shading artifacts due to phase variation.
Journal Article
An Adaptive Chlamydia trachomatis-Specific IFN-γ-Producing CD4+ T Cell Response Is Associated With Protection Against Chlamydia Reinfection in Women
Adaptive immune responses that mediate protection against
(CT) remain poorly defined in humans. Animal chlamydia models have demonstrated that CD4
Th1 cytokine responses mediate protective immunity against reinfection. To better understand protective immunity to CT in humans, we investigated whether select CT-specific CD4
Th1 and CD8
T cell cytokine responses were associated with protection against CT reinfection in women.
Peripheral blood mononuclear cells were collected from 135 CT-infected women at treatment and follow-up visits and stimulated with CT antigens. CD4
and CD8
T-cells expressing IFN-γ, TNF-α, and/or IL-2 were assessed using intracellular cytokine staining and cytokine responses were compared between visits and between women with vs. without CT reinfection at follow-up.
A CD4
TNF-α response was detected in the majority (77%) of study participants at the treatment visit, but a lower proportion had this response at follow-up (62%). CD4
IFN-γ and CD4
IL-2 responses occurred less frequently at the treatment visit (32 and 18%, respectively), but increased at follow-up (51 and 41%, respectively). CD8
IFN-γ and CD8
TNF-α responses were detected more often at follow-up (59% for both responses) compared to the treatment visit (30% for both responses). At follow-up, a CD4
IFN-γ response was detected more often in women without vs. with reinfection (60 vs. 33%,
= 0.005).
Our findings suggest that a CT-specific CD4
IFN-γ response is associated with protective immunity against CT reinfection and is thus an important component of adaptive immunity to CT in women.
Journal Article