Identification of Decoherence-Free Subspaces Without Quantum Process Tomography

Characterizing a quantum process is the critical first step towards applying such a process in a quantum information protocol. Full process characterization is known to be extremely resource-intensive, motivating the search for more efficient ways to extract salient information about the process. An example is the identification of "decoherence-free subspaces", in which computation or communications may be carried out, immune to the principal sources of decoherence in the system. Here we propose and demonstrate a protocol which enables one to directly identify a DFS without carrying out a full reconstruction. Our protocol offers an up-to-quadratic speedup over standard process tomography. In this paper, we experimentally identify the DFS of a two-qubit process with 32 measurements rather than the usual 256, characterize the robustness and efficiency of the protocol, and discuss its extension to higher-dimensional systems.Comment: 6 pages, 5 figure

Political Ideology and Judicial Administration: Evidence from the COVID-19 Pandemic

We study the effect of political ideology on the administration of the judiciary by investigating how the chief judges of federal district courts set courthouse policies in response to the COVID-19 pandemic. To do so, we use novel data on the geographic boundaries of federal courts and on the contents of pandemic orders. We account for state and local conditions and policies by leveraging district courts in states that have multiple judicial districts and that have courthouses in multiple counties, and we isolate the effect of chief ideology by using simulations that difference out unobserved district-level effects. We find no consistent evidence that the ideology of chief judges influenced courthouse closures and the authorization of a law allowing for remote proceedings, but we find strong evidence that Republican-appointed chief judges were less likely to require masks and more likely to suspend in-person trials

Personalized Optical Designs and Manipulating Optics: Applications on the Anterior Segment of the Eye

The image-forming properties of the eye can be described in terms of wave aberration. Understanding the link between aberrations and the anterior segment geometry is therefore of crucial importance for (i) comprehending how the eye works, (ii) modelling the optics of individual eyes, (iii) optimizing optical solutions, or (iv) designing surgical strategies. The eye has many innate adaptations that minimize optical aberrations. In most normal young eyes, the magnitude of aberrations of the cornea is significantly larger than for the whole eye, indicating a significant role of the crystalline lens in compensating corneal aberrations. However, due to geometrical and structural changes, this ocular compensation gets disturbed in different anterior segment conditions, such as keratoconus, presbyopia, or cataract. Keratoconus progressively degrades the corneal shape and, consequently, vision in the adolescence, with a prevalence of 0.05% in the general population. Meanwhile, presbyopia and cataract are conditions related to aging that affect the structure of the crystalline lens, one referring to a loss in accommodative amplitude (presbyopia) and the other to a progressive loss of transparency (cataract). Presbyopia affects 100% of the population older than 45¿years of age, ..

Cross-verification of independent quantum devices

Quantum computers are on the brink of surpassing the capabilities of even the most powerful classical computers. This naturally raises the question of how one can trust the results of a quantum computer when they cannot be compared to classical simulation. Here we present a verification technique that exploits the principles of measurement-based quantum computation to link quantum circuits of different input size, depth, and structure. Our approach enables consistency checks of quantum computations within a device, as well as between independent devices. We showcase our protocol by applying it to five state-of-the-art quantum processors, based on four distinct physical architectures: nuclear magnetic resonance, superconducting circuits, trapped ions, and photonics, with up to 6 qubits and 200 distinct circuits

On the correct formula for the lifetime broadened superconducting density of states

We argue that the well known Dynes formula [Dynes R C {\it et al.} 1978 {\it Phys. Rev. Lett.} {\bf 41} 1509] for the superconducting quasiparticle density of states, which tries to incorporate the lifetime broadening in an approximate way, cannot be justified microscopically for conventional superconductors. Instead, we propose a new simple formula in which the energy gap has a finite imaginary part $-\Delta_2$ and the quasiparticle energy is real. We prove that in the quasiparticle approximation 2$\Delta_2$ gives the quasiparticle decay rate at the gap edge for conventional superconductors. This conclusion does not depend on the nature of interactions that cause the quasiparticle decay. The new formula is tested on the case of a strong coupling superconductor Pb$_{0.9}$Bi$_{0.1}$ and an excellent agreement with theoretical predictions is obtained. While both the Dynes formula and the one proposed in this work give good fits and fit parameters for Pb$_{0.9}$Bi$_{0.1}$, only the latter formula can be justified microscopically.Comment: 6 pages, 4 figure

Diagnostic accuracy of physical examination findings for midfacial fractures:a systematic review and meta-analysis

OBJECTIVES: To conduct a systematic review and meta-analysis to assess the diagnostic accuracy of physical examination findings and related clinical decision aids for midfacial fractures in comparison to computed tomography and cone beam computed tomography. MATERIAL AND METHODS: A systematic review was performed by searching the MEDLINE, Cochrane, EMBASE, and CINAHL databases. Risk of bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. Pooled sensitivity, specificity, and diagnostic odds ratios with the corresponding 95% confidence intervals were calculated for each physical examination finding and reported clinical decision aids. RESULTS: After screening 2367 records, 12 studies were included. High risk of patient selection bias was detected in three studies (25%). Additionally, high concerns regarding applicability were found for the patient selection in five studies (41.7%), and for the reference standard in eleven studies (91.7%). Of the total 42 individual physical examination findings, only 31 were suitable for a meta-analysis. High specificity and low sensitivity were found for most findings. The pooled diagnostic odds ratio ranged from 1.07 to 11.38. Clinical decision aids were reported by 8 studies, but none were constructed specifically for midfacial fractures. CONCLUSION: Based on the current available evidence, the absence of physical examination findings can successfully identify patients who do not have a midfacial fracture, but the presence of individual findings does not necessarily mean that the patient has a midfacial fracture. Although various clinical decision aids were presented, none focused on exclusively midfacial fractures. CLINICAL RELEVANCE: The diagnostic accuracy of physical examination findings can be used to diagnose a midfacial fracture so as to reduce unnecessary imaging, health care costs, and exposure to ionizing radiation

Genuine Counterfactual Communication with a Nanophotonic Processor

In standard communication information is carried by particles or waves. Counterintuitively, in counterfactual communication particles and information can travel in opposite directions. The quantum Zeno effect allows Bob to transmit a message to Alice by encoding information in particles he never interacts with. The first suggested protocol not only required thousands of ideal optical components, but also resulted in a so-called "weak trace" of the particles having travelled from Bob to Alice, calling the scalability and counterfactuality of previous proposals and experiments into question. Here we overcome these challenges, implementing a new protocol in a programmable nanophotonic processor, based on reconfigurable silicon-on-insulator waveguides that operate at telecom wavelengths. This, together with our telecom single-photon source and highly-efficient superconducting nanowire single-photon detectors, provides a versatile and stable platform for a high-fidelity implementation of genuinely trace-free counterfactual communication, allowing us to actively tune the number of steps in the Zeno measurement, and achieve a bit error probability below 1%, with neither post-selection nor a weak trace. Our demonstration shows how our programmable nanophotonic processor could be applied to more complex counterfactual tasks and quantum information protocols.Comment: 6 pages, 4 figure

Enhanced Photonic Maxwell's Demon with Correlated Baths

Maxwell's Demon is at the heart of the interrelation between quantum information processing and thermodynamics. In this thought experiment, a demon extracts work from two thermal baths at equilibrium by gaining information about them at the single-particle level and applying classical feed-forward operations. Here we implement a photonic version of Maxwell's Demon with active feed-forward in a fiber-based system using ultrafast optical switches. We experimentally show that, if correlations exist between the two thermal baths, the Demon can extract over an order of magnitude more work than without correlations. Our work demonstrates the great potential of photonic experiments -- which provide a unique degree of control on the system -- to access new regimes in quantum thermodynamics.Comment: 23 pages with appendix, 6 figure

Impeding and facilitating factors for the implementation of alcohol interventions in hospitals:A qualitative and exploratory study among Dutch healthcare professionals

BACKGROUND: Non-moderated alcohol use is more prevalent among hospitalized patients compared to the general population. However, many hospitals fail to find and intervene with people with alcohol problems. We aimed to conduct an exploration of impeding and facilitating factors experienced by healthcare professionals in implementation of alcohol interventions in Dutch general hospitals. In addition, we explored the alcohol interventions used in the selected hospitals and involved stakeholders. METHODS: Through a qualitative study, semi-structured telephone interviews were conducted with twenty healthcare professionals working in or in collaboration with six different general hospitals. RESULTS: Healthcare professionals indicated impeding and facilitating factors in the areas of motivation, knowledge and skills, patient characteristics, protocol, internal and external collaboration/support, resources, role suitability and societal support. Five different categories of approaches to identify and intervene with non-moderated alcohol use and 18 involved stakeholders from both inside and outside the hospital were found. CONCLUSIONS: Implementation of alcohol interventions for patients in Dutch general hospitals still seems to be in its infancy. Respondents emphasized the importance of one clear protocol on how to tackle alcohol problems within their hospital, repeated training on alcohol-related knowledge and skills, (clinical) “champions” that support healthcare professionals and developing and maintaining collaborations with stakeholders within and outside the hospital