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

Adaptive quantum state tomography improves accuracy quadratically

We introduce a simple protocol for adaptive quantum state tomography, which reduces the worst-case infidelity between the estimate and the true state from $O(N^{-1/2})$ to $O(N^{-1})$. It uses a single adaptation step and just one extra measurement setting. In a linear optical qubit experiment, we demonstrate a full order of magnitude reduction in infidelity (from $0.1$ to $0.01$) for a modest number of samples ($N=3\times10^4$).Comment: 8 pages, 7 figure

Scalable Spatial Super-Resolution using Entangled Photons

N00N states -- maximally path-entangled states of N photons -- exhibit spatial interference patterns sharper than any classical interference pattern. This is known as super-resolution. However, even with perfectly efficient number-resolving detectors, the detection efficiency of all previously demonstrated methods to measure such interference decreases exponentially with the number of photons in the N00N state, often leading to the conclusion that N00N states are unsuitable for spatial measurements. Here, we create spatial super-resolution fringes with two-, three-, and four-photon N00N states, and demonstrate a scalable implementation of the so-called ``optical centroid measurement'' which provides an in-principle perfect detection efficiency. Moreover, we compare the N00N-state interference to the corresponding classical super-resolution interference. Although both provide the same increase in spatial frequency, the visibility of the classical fringes decreases exponentially with the number of detected photons, while the visibility of our experimentally measured N00N-state super-resolution fringes remains approximately constant with N. Our implementation of the optical centroid measurement is a scalable method to measure high photon-number quantum interference, an essential step forward for quantum-enhanced measurements, overcoming what was believed to be a fundamental challenge to quantum metrology

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

Acid-Labile Traceless Click Linker for Protein Transduction

Intracellular delivery of active proteins presents an interesting approach in research and therapy. We created a protein transduction shuttle based on a new traceless click linker that combines the advantages of click reactions with implementation of reversible pH-sensitive bonds. The azidomethyl-methylmaleic anhydride (AzMMMan) linker was found compatible with different click chemistries, demonstrated in bioreversible protein modification with dyes, polyethylene glycol, or a transduction carrier. Linkages were stable at physiological pH but reversible at the mild acidic pH of endosomes or lysosomes. We show that pH-reversible attachment of a defined endosome-destabilizing three-arm oligo(ethane amino)amide carrier generates an effective shuttle for protein delivery. The cargo protein nlsEGFP, when coupled via the traceless AzMMMan linker, experiences efficient cellular uptake and endosomal escape into the cytosol, followed by import into the nucleus. In contrast, irreversible linkage to the same shuttle hampers nuclear delivery of nlsEGFP which after uptake remains trapped in the cytosol. Successful intracellular delivery of bioactive ß-galactosidase as a model enzyme was also demonstrated using the pH-controlled shuttle system

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

How sports clubs decide to adopt an outdoor smoke-free policy:A qualitative study applying the Garbage Can Model

Background Outdoor smoke-free policies (SFPs) at sports clubs can contribute to protecting people from second-hand smoke (SHS). However, in absence of national legislation, it is uncertain whether and how sports clubs decide to adopt an SFP. The aim of this study was to explore the decision-making process at sports clubs in relation to the adoption of an outdoor SFP. Methods Semi-structured interviews were held with key stakeholders at 20 Dutch sports clubs (in field hockey, football, tennis, or korfball) with an outdoor SFP. Thematic analysis was applied, and themes were defined in line with the four streams of the Garbage Can Model (GCM). Results We identified four motivating factors for sports clubs to start the decision-making process: 1) SHS as a problem, 2) intolerance of smoking behavior, 3) advantages of an outdoor SFP, and 4) external pressure to become smoke-free. The decision-making process involved a variety of participants, but the board, influential club members, and smokers usually played major roles. Decisions were discussed during both formal and informal choice opportunities, but only made during formal choice opportunities. With regard to solutions, sports clubs adopted a partial or total outdoor SFP. In addition, sports clubs followed different strategies with regard to the decision-making process, which we classified along two dimensions: 1) autocratic vs. democratic and 2) fast vs. slow. Conclusion A number of factors motivated sports clubs to start the decision-making process. These factors were mainly linked to a strong non-smoking norm. Decision-making involved different participants, with a key role for the board, influential club members, and smokers. Governments and other external organizations may contribute to SFP adoption at sports clubs in several ways. They may advise clubs on strategies of decision-making and how to involve smokers in this process

Stability of and change in substance use risk personality:Gender differences and smoking cigarettes among early adolescents

OBJECTIVE: Adolescents show a steadily increasing inclination toward health risk behaviors, including smoking cigarettes. There is ample evidence that personality traits are related to smoking behavior. However, less is known about the stability of and change in these personality traits during early adolescence and whether smoking behavior affects the developmental trajectories. Moreover, less is known about the influence of gender on the course of personality. METHOD: Longitudinal data of three waves were used from 1121 early adolescents. To measure personality, the Substance Use Risk Profile Scale was used. Individual growth curve models were conducted to measure the stability, mean-level change and individual differences in change for personality. RESULTS: Stability of personality was moderate for boys and ranged from moderate to high for girls. On average early adolescents became more impulsive and more sensation seeking over a period of 18 months. Furthermore, hopelessness for girls increased and the increase in sensation seeking was higher for girls than for boys. Third, smoking behavior was related to all personality traits, indicating that smoking adolescents are more anxious, hopeless, impulsive and sensation seeking than non-smoking adolescents. CONCLUSIONS: Our results are in line with the disruption hypothesis, i.e., during early adolescence there is a dip in personality maturity. There are clear differences between girls and boys in stability of and change in personality traits. Besides, although smoking behavior is related to personality, the change in personality is probably related to other variables

Nonlinear quantum logic with colliding graphene plasmons

Graphene has emerged as a promising platform to bring nonlinear quantum optics to the nanoscale, where a large intrinsic optical nonlinearity enables long-lived and actively tunable plasmon polaritons to strongly interact. Here we theoretically study the collision between two counter-propagating plasmons in a graphene nanoribbon, where transversal subwavelength confinement endows propagating plasmons with %large effective masses a flat band dispersion that enhances their interaction. This scenario presents interesting possibilities towards the implementation of multi-mode polaritonic gates that circumvent limitations imposed by the Shapiro no-go theorem for photonic gates in nonlinear optical fibers. As a paradigmatic example we demonstrate the feasibility of a high fidelity conditional $\pi$ phase shift (CZ), where the gate performance is fundamentally limited only by the single plasmon lifetime. These results open new exciting avenues towards quantum information and many-body applications with strongly-interacting polaritons.Comment: 13 pages, 4 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