5,795 research outputs found
Sensitivity optimization in quantum parameter estimation
We present a general framework for sensitivity optimization in quantum
parameter estimation schemes based on continuous (indirect) observation of a
dynamical system. As an illustrative example, we analyze the canonical scenario
of monitoring the position of a free mass or harmonic oscillator to detect weak
classical forces. We show that our framework allows the consideration of
sensitivity scheduling as well as estimation strategies for non-stationary
signals, leading us to propose corresponding generalizations of the Standard
Quantum Limit for force detection.Comment: 15 pages, RevTe
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A Formal Definition of Control Semantics in a Completely Visual Language ; CU-CS-673-93
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Control Constructs in a Completely Visual Imperative Programming Language ; CU-CS-672-93
Optimal control, geometry, and quantum computing
We prove upper and lower bounds relating the quantum gate complexity of a
unitary operation, U, to the optimal control cost associated to the synthesis
of U. These bounds apply for any optimal control problem, and can be used to
show that the quantum gate complexity is essentially equivalent to the optimal
control cost for a wide range of problems, including time-optimal control and
finding minimal distances on certain Riemannian, subriemannian, and Finslerian
manifolds. These results generalize the results of Nielsen, Dowling, Gu, and
Doherty, Science 311, 1133-1135 (2006), which showed that the gate complexity
can be related to distances on a Riemannian manifoldComment: 7 Pages Added Full Names to Author
Bellman equations for optimal feedback control of qubit states
Using results from quantum filtering theory and methods from classical
control theory, we derive an optimal control strategy for an open two-level
system (a qubit in interaction with the electromagnetic field) controlled by a
laser. The aim is to optimally choose the laser's amplitude and phase in order
to drive the system into a desired state. The Bellman equations are obtained
for the case of diffusive and counting measurements for vacuum field states. A
full exact solution of the optimal control problem is given for a system with
simpler, linear, dynamics. These linear dynamics can be obtained physically by
considering a two-level atom in a strongly driven, heavily damped, optical
cavity.Comment: 10 pages, no figures, replaced the simpler model in section
Blood, sweat, and tears: Implications for hydration testing in combat sports—Investigating body mass loss and biomarker changes
Combat sports athletes often undergo rapid body mass loss (BML), which presents health risks. Hydration testing has been proposed as a possible solution to reduce or eliminate rapid BML. However, combat sports athletes may exhibit distinct physiological characteristics due to repeated exposure to BML. Thus, traditional and emerging hydration biomarkers should be investigated to determine their potential suitability for field use in this cohort. This study examined whether BML can explain changes in serum and urine osmolality (SosmΔ, UosmΔ), tear osmolarity (TosmΔ), hematocrit (HctΔ), and urine-specific gravity (USGΔ) after mild–moderate passive dehydration. Biomarker reliability was also assessed across two trials. Fifteen male and female combat sports athletes (age: 26.3 ± 5.3 years, body mass: 67.7 ± 9.9 kg) underwent a sauna protocol twice (5–28 days apart) aiming for 4% BML. The average BML in Trials 1 and 2 was 3.0 ± 0.7%. Regression analysis revealed that BML explained HctΔ (R2 = 0.22, p = 0.009) but not SosmΔ (R2 = 0.11, p = 0.079) or other biomarkers. Intraclass correlation coefficients (ICCs) were significant for all biomarkers except TosmΔ (ICC = 0.06, p = 0.37) and post-Tosm (ICC = 0.04, p = 0.42); post-Hct performed best (ICC = 0.82, p \u3c 0.001). Contingency tables with post-Sosm (295 mOsm/kg) and post-USG (1.020) cutoffs revealed an 80% true negative rate (TNR) and a 62% true positive rate (TPR). Increasing the Sosm cutoff to 301 mOsm/kg decreased the TNR to 52% but increased the TPR to 83%. Although blood parameters were most sensitive to BML, they could only explain 11%–22% of biomarker variation. The typical USG cutoff misclassified 42% of athletes postdehydration, and reliability was generally poor-moderate. Alternative strategies should be pursued to manage rapid BML in combat sports
Information Effect of Entry Into Credit Ratings Market: The Case of Insurers\u27 Ratings
The paper analyzes the effect of competition between credit rating agencies (CRAs) on the information content of ratings. We show that a monopolistic CRA pools sellers into multiple rating classes and has partial market coverage. This provides an opportunity for market entry. The entrant designs a rating scale distinct from that of the incumbent. It targets higher-than-average companies in each rating grade of the incumbent\u27s rating scale and employs more stringent rating standards. We use Standard and Poor\u27s (S&P) entry into the market for insurance ratings previously covered by a monopolist, A.M. Best, to empirically test the impact of entry on the information content of ratings. The empirical analysis reveals that S&P required higher standards to assign a rating similar to the one assigned by A.M. Best and that higher-than-average quality insurers in each rating category of A.M. Best chose to receive a second rating from S&P
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