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

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

The association of adolescents' smoking with the physical activity levels of their friends

Funding Information: This study is part of the SILNE-R project (Enhancing the Effectiveness of Programs and Strategies to Prevent Smoking by Adolescents: A Realist Evaluation Comparing Seven European Countries), which is supported by the European Union‘s Horizon 2020 research and innovation programme, under grant agreement 635,056. The funder was not involved and did not have any input in the design, analysis and reporting of this study. Publisher Copyright: © 2023Background: Smoking is inversely related to people's Physical Activity Level (PAL). As the behavior of friends may affect the choices and behavior of adolescents, having friends with a high PAL may potentially protect against adolescent smoking. This study aims to assess whether adolescents' smoking is associated with the PAL of their friends. Methods: SILNE-R survey data of 11.918 adolescents from 55 different schools in 7 European cities was used to determine weekly smoking, individual PAL, PAL of friends, school PAL, and smoking of friends. Multilevel, multivariable logistic regression analysis were used to assess the association between the PAL of friends and weekly smoking. Several socio-demographic variables were included as covariates in the analysis. Results: Our results indicated that 10.8% of the respondents was smoking weekly. Weekly smoking was most common among adolescents whose friends had a PAL of 0–42.0 min per day (14.5%). Respondents were significantly more likely to be smoking weekly if their friends were on average 0–42 min vs. 80–180 min physically active (OR 1.27 [95% CI 1.04–1.55]). This association existed independently of the individual PAL of respondents. Stratification for smoking of friends yielded equal results, although the association appeared to be somewhat stronger for those with smoking friends (OR 1.38 [95% CI 1.06–1.82]). Conclusion: Adolescents are less likely to smoke weekly if they associate with friends who spend >80 min per day on physical activity. Initiatives aimed at the prevention of smoking among adolescents may benefit from organizing group-based physical activity programs.publishersversionpublishe

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

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

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

Interdisciplinary collaboration in the treatment of alcohol use disorders in a general hospital department:A mixed-method study

Background !nterdisciplinary collaborations (i.e., where various disciplines work coordinated and interdependently toward shared goals) are stated to yield higher team effectiveness than multidisciplinary approaches (i.e., where various disciplines work in parallel within their professional boundaries) in somatic health care settings. Nevertheless, research is lacking on interdisciplinary approaches for alcohol use disorder (AUD) treatment of hospitalized patients as these types of approaches are still uncommon. This study aims to evaluate an innovative interdisciplinary AUD treatment initiative at a general hospital department by 1) identifying which and to what extent network partners are involved and 2) to explore how network partners experienced the interdisciplinary collaboration. Methods A mixed-method study was conducted, using 1) measures of contact frequency and closeness in a social network analysis and 2) semi-structured interviews, which were analyzed thematically. Respondents were network partners of an interdisciplinary collaboration in a general hospital department, initially recruited by the collaborations' project leader. Results The social network analysis identified 16 network partners, including a 'core' network with five central network partners from both inside and outside the hospital. The project leader played an important central role in the network and the resident gastroenterologist seemed to have a vulnerable connection within the network. Closeness between network partners was experienced regardless of frequency of contact, although this was especially true for the 'core' group that (almost) always consisted of the same network partners that were present at biweekly meetings. Interview data showed that presence of the 'core' network partners was reported crucial for an efficient collaboration. Respondents desired knowledge about the collaborations' effectiveness, and one structured protocol with working procedures, division of responsibilities and agreements on information sharing and feedback. Conclusions The design of this interdisciplinary collaboration has potential in improving the treatment of hospital patients with AUD and was evaluated positively by the involved network partners. Interdisciplinary collaborations may offer a critical solution to increase treatment rates of patients with AUD and should be adopted in hospitals on a larger scale. Research towards the effectiveness of interdisciplinary collaborations in the treatment of hospitalized patients with AUD is needed. A correction to this paper has been published: https://doi.org/10.1186/s13011-022-00492-

Aanbevelingen uit onderzoek voor rookvrije onderwijsterreinen

Vanaf 1 augustus 2020 geldt in Nederland een rookverbod op alle terreinen van onderwijsinstellingen. Deze maatregel levert een belangrijke bijdrage aan een rookvrije omgeving voor kinderen en jongeren. Een omgeving waarin niet-roken vanzelfsprekend is, roken nauwelijks zichtbaar is en sigaretten en dergelijke voor jongeren moeilijk te verkrijgen zijn. Scholen hebben een groot aandeel in het bijdragen aan een rookvrije omgeving. Kinderen en jongeren brengen veel tijd op school door en worden sterk beïnvloed door leeftijdsgenoten en rolmodellen, zoals docenten. De wettelijke maatregel komt ook tegemoet aan de wens vanuit scholen blijkt uit onderzoek. Maar hoe kan een onderwijsinstelling het rookvrije onderwijsterrein nou het beste invoeren? Daar gaat deze infosheet over