Improved qubit bifurcation readout in the straddling regime of circuit QED

We study bifurcation measurement of a multi-level superconducting qubit using a nonlinear resonator biased in the straddling regime, where the resonator frequency sits between two qubit transition frequencies. We find that high-fidelity bifurcation measurements are possible because of the enhanced qubit-state-dependent pull of the resonator frequency, the behavior of qubit-induced nonlinearities and the reduced Purcell decay rate of the qubit that can be realized in this regime. Numerical simulations find up to a threefold improvement in qubit readout fidelity when operating in, rather than outside of, the straddling regime. High-fidelity measurements can be obtained at much smaller qubit-resonator couplings than current typical experimental realizations, reducing spectral crowding and potentially simplifying the implementation of multi-qubit devices.Comment: 9 pages, 6 figure

QuantMig:The use of migration scenarios in future characterisations: A systematic review and typology

BackgroundMigration plays an increasingly important role in shaping the demographic profiles of developed countries and receives ample attention in society at large as well as among policymakers. To understand how migration flows might evolve in the future, the QuantMig project set the goal of producing migration scenarios to support European migration policy. To do so, we need to make clear with what purpose scenarios are developed, how they are developed, and on which flows they focus. Other questions concern whether they are designed to describe the most likely future or a possible future, whether they are extrapolating trends observed in the past (assuming no fundamental changes in policies), or whether they are designed to describe desirable futures (migration as a panacea for ageing societies) or undesirable futures (massive inflow of immigration from developing countries). To produce the best possible migration scenarios, it is essential to get an overview of the literature. Migration scenarios have been used in a variety of future characterisations including forecasts, projections, and foresights. However, the term migration scenario is rarely well-defined or used consistently. Before developing a set of own scenarios, this document takes the necessary step of providing an overview of the existing literature and provide a definition and typology of migration scenarios. Based on this work, alternative ways of exploring the future of migration (for example in a vignette survey) will be discussed that lay out the bases for the extension of the work in the next deliverables of the work package. MethodsThis document looks at how migration scenarios are used in the literature presenting characterisations of societies’ futures. Relevant documents are systematically retrieved and assigned to one of six categories part of a pre-established typology. The typology rests on the focus (either migration or another aspect of societies influenced by migration) and purpose (either to predict the future, explore the future, or establish how a specific target can be reached) of each future characterisation. Subsequently, the techniques used for generating migration scenarios are described in terms of the approach taken (quantitative or qualitative) and how data is generated and transformed into meaningful output. Finally, the specific geographical context and characteristics of migration and migrants included in the scenarios are explored. ResultsA total of 107 documents were analysed. More than half presented migration scenarios that were developed to answer questions not about migration itself, but about its influence on a population’s future growth, age composition, or economic performance, among others. Future characterisations had most often prediction as purpose, being for example population forecasts, while many others had exploration as purpose, where the sensitivity of a given phenomenon to different migration assumptions is assessed. Most scenarios rest on a quantitative approach rather than on a narrative, but the latter has clearly expanded in the last years. Migration scenarios that follow a quantitative approach often rest on past migration trends to characterise the future, but seldom provide likelihoods that a given scenario will realise. Migration scenarios that follow a qualitative approach, on the other hand, often rest on experts and stakeholders’ views for input, or rely on previously developed storylines. Finally, quantitative scenarios often concentrate on net migration figures inside of a single, usually economically developed country, while qualitative scenarios are more likely to consider bidirectional flows between two (world) regions. ConclusionsThere was an increase over time in the use of qualitative scenarios to characterise the future of migration. However, these scenarios were seldom used to translate storylines into quantitative outputs that specifically aim at predicting future migration flows. Ways to achieve this are discussed, including more advanced data collection techniques among experts and stakeholders, and the consideration of multiple types of migration

QuantMig:The use of migration scenarios in future characterisations: A systematic review and typology

BackgroundMigration plays an increasingly important role in shaping the demographic profiles of developed countries and receives ample attention in society at large as well as among policymakers. To understand how migration flows might evolve in the future, the QuantMig project set the goal of producing migration scenarios to support European migration policy. To do so, we need to make clear with what purpose scenarios are developed, how they are developed, and on which flows they focus. Other questions concern whether they are designed to describe the most likely future or a possible future, whether they are extrapolating trends observed in the past (assuming no fundamental changes in policies), or whether they are designed to describe desirable futures (migration as a panacea for ageing societies) or undesirable futures (massive inflow of immigration from developing countries). To produce the best possible migration scenarios, it is essential to get an overview of the literature. Migration scenarios have been used in a variety of future characterisations including forecasts, projections, and foresights. However, the term migration scenario is rarely well-defined or used consistently. Before developing a set of own scenarios, this document takes the necessary step of providing an overview of the existing literature and provide a definition and typology of migration scenarios. Based on this work, alternative ways of exploring the future of migration (for example in a vignette survey) will be discussed that lay out the bases for the extension of the work in the next deliverables of the work package. MethodsThis document looks at how migration scenarios are used in the literature presenting characterisations of societies’ futures. Relevant documents are systematically retrieved and assigned to one of six categories part of a pre-established typology. The typology rests on the focus (either migration or another aspect of societies influenced by migration) and purpose (either to predict the future, explore the future, or establish how a specific target can be reached) of each future characterisation. Subsequently, the techniques used for generating migration scenarios are described in terms of the approach taken (quantitative or qualitative) and how data is generated and transformed into meaningful output. Finally, the specific geographical context and characteristics of migration and migrants included in the scenarios are explored. ResultsA total of 107 documents were analysed. More than half presented migration scenarios that were developed to answer questions not about migration itself, but about its influence on a population’s future growth, age composition, or economic performance, among others. Future characterisations had most often prediction as purpose, being for example population forecasts, while many others had exploration as purpose, where the sensitivity of a given phenomenon to different migration assumptions is assessed. Most scenarios rest on a quantitative approach rather than on a narrative, but the latter has clearly expanded in the last years. Migration scenarios that follow a quantitative approach often rest on past migration trends to characterise the future, but seldom provide likelihoods that a given scenario will realise. Migration scenarios that follow a qualitative approach, on the other hand, often rest on experts and stakeholders’ views for input, or rely on previously developed storylines. Finally, quantitative scenarios often concentrate on net migration figures inside of a single, usually economically developed country, while qualitative scenarios are more likely to consider bidirectional flows between two (world) regions. ConclusionsThere was an increase over time in the use of qualitative scenarios to characterise the future of migration. However, these scenarios were seldom used to translate storylines into quantitative outputs that specifically aim at predicting future migration flows. Ways to achieve this are discussed, including more advanced data collection techniques among experts and stakeholders, and the consideration of multiple types of migration

Quantum trajectory approach to circuit QED: Quantum jumps and the Zeno effect

We present a theoretical study of a superconducting charge qubit dispersively coupled to a transmission line resonator. Starting from a master equation description of this coupled system and using a polaron transformation, we obtain an exact effective master equation for the qubit. We then use quantum trajectory theory to investigate the measurement of the qubit by continuous homodyne measurement of the resonator out-field. Using the same porlaron transformation, a stochastic master equation for the conditional state of the qubit is obtained. From this result, various definitions of the measurement time are studied. Furthermore, we find that in the limit of strong homodyne measurement, typical quantum trajectories for the qubit exhibit a crossover from diffusive to jump-like behavior. Finally, in the presence of Rabi drive on the qubit, the qubit dynamics is shown to exhibit quantum Zeno behavior.Comment: 20 pages, 12 figure

Single-shot qubit readout in circuit Quantum Electrodynamics

The future development of quantum information using superconducting circuits requires Josephson qubits [1] with long coherence times combined to a high-fidelity readout. Major progress in the control of coherence has recently been achieved using circuit quantum electrodynamics (cQED) architectures [2, 3], where the qubit is embedded in a coplanar waveguide resonator (CPWR) which both provides a well controlled electromagnetic environment and serves as qubit readout. In particular a new qubit design, the transmon, yields reproducibly long coherence times [4, 5]. However, a high-fidelity single-shot readout of the transmon, highly desirable for running simple quantum algorithms or measur- ing quantum correlations in multi-qubit experiments, is still lacking. In this work, we demonstrate a new transmon circuit where the CPWR is turned into a sample-and-hold detector, namely a Josephson Bifurcation Amplifer (JBA) [6, 7], which allows both fast measurement and single-shot discrimination of the qubit states. We report Rabi oscillations with a high visibility of 94% together with dephasing and relaxation times longer than 0:5 \mu\s. By performing two subsequent measurements, we also demonstrate that this new readout does not induce extra qubit relaxation.Comment: 14 pages including 4 figures, preprint forma

Realistic loophole-free Bell test with atom-photon entanglement

The establishment of nonlocal correlations, obtained through the violation of a Bell inequality, is not only important from a fundamental point of view, but constitutes the basis for device-independent quantum information technologies. Although several nonlocality tests have been performed so far, all of them suffered from either the locality or the detection loopholes. Recent studies have suggested that the use of atom-photon entanglement can lead to Bell inequality violations with moderate transmission and detection efficiencies. In this paper we propose an experimental setup realizing a simple atom-photon entangled state that, under realistic experimental parameters available to date, achieves a significant violation of the Clauser-Horn-Shimony-Holt inequality. Most importantly, the violation remains when considering typical detection efficiencies and losses due to required propagation distances.Comment: 21 pages, 5 figures, 3 table, to appear in Nature Com

Backaction of a driven nonlinear resonator on a superconducting qubit

We study the backaction of a driven nonlinear resonator on a multi-level superconducting qubit. Using unitary transformations on the multi-level Jaynes-Cummings Hamiltonian and quantum optics master equation, we derive an analytical model that goes beyond linear response theory. Within the limits of validity of the model, we obtain quantitative agreement with experimental and numerical data, both in the bifurcation and in the parametric amplification regimes of the nonlinear resonator. We show in particular that the measurement-induced dephasing rate of the qubit can be rather small at high drive power. This is in contrast to measurement with a linear resonator where this rate increases with the drive power. Finally, we show that, for typical parameters of circuit quantum electrodynamics, correctly describing measurement-induced dephasing requires a model going beyond linear response theory, such as the one presented here.Comment: 17 pages, 7 figure

Genome-Wide Mapping of DNA Strand Breaks

Determination of cellular DNA damage has so far been limited to global assessment of genome integrity whereas nucleotide-level mapping has been restricted to specific loci by the use of specific primers. Therefore, only limited DNA sequences can be studied and novel regions of genomic instability can hardly be discovered. Using a well-characterized yeast model, we describe a straightforward strategy to map genome-wide DNA strand breaks without compromising nucleotide-level resolution. This technique, termed “damaged DNA immunoprecipitation” (dDIP), uses immunoprecipitation and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin end-labeling (TUNEL) to capture DNA at break sites. When used in combination with microarray or next-generation sequencing technologies, dDIP will allow researchers to map genome-wide DNA strand breaks as well as other types of DNA damage and to establish a clear profiling of altered genes and/or intergenic sequences in various experimental conditions. This mapping technique could find several applications for instance in the study of aging, genotoxic drug screening, cancer, meiosis, radiation and oxidative DNA damage