Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption

Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evid ence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices

Suppressing quantum errors by scaling a surface code logical qubit

Practical quantum computing will require error rates that are well below what is achievable with physical qubits. Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. Here, we report the measurement of logical qubit performance scaling across multiple code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, both in terms of logical error probability over 25 cycles and logical error per cycle ($2.914\%\pm 0.016\%$ compared to $3.028\%\pm 0.023\%$). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a $1.7\times10^{-6}$ logical error per round floor set by a single high-energy event ($1.6\times10^{-7}$ when excluding this event). We are able to accurately model our experiment, and from this model we can extract error budgets that highlight the biggest challenges for future systems. These results mark the first experimental demonstration where quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references, Fig. S12, Table I

Non-Abelian braiding of graph vertices in a superconducting processor

Indistinguishability of particles is a fundamental principle of quantum mechanics. For all elementary and quasiparticles observed to date - including fermions, bosons, and Abelian anyons - this principle guarantees that the braiding of identical particles leaves the system unchanged. However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions. Hence, it can change the observables of the system without violating the principle of indistinguishability. Despite the well developed mathematical description of non-Abelian anyons and numerous theoretical proposals, the experimental observation of their exchange statistics has remained elusive for decades. Controllable many-body quantum states generated on quantum processors offer another path for exploring these fundamental phenomena. While efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasi-particles, superconducting quantum processors allow for directly manipulating the many-body wavefunction via unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons, we implement a generalized stabilizer code and unitary protocol to create and braid them. This allows us to experimentally verify the fusion rules of the anyons and braid them to realize their statistics. We then study the prospect of employing the anyons for quantum computation and utilize braiding to create an entangled state of anyons encoding three logical qubits. Our work provides new insights about non-Abelian braiding and - through the future inclusion of error correction to achieve topological protection - could open a path toward fault-tolerant quantum computing

Réadaptation cardio-pulmonaire après atteinte sévère de la COVID-19.

info:eu-repo/semantics/publishe

Incremental value of copeptin to highly sensitive cardiac Troponin I for rapid rule-out of myocardial infarction

The incremental value of copeptin, a novel marker of endogenous stress, for rapid rule-out of non-ST-elevation myocardial infarction (NSTEMI) is unclear when sensitive or even high-sensitivity cardiac troponin cTn (hs-cTn) assays are used.In an international multicenter study we evaluated 1929 consecutive patients with symptoms suggestive of acute myocardial infarction (AMI). Measurements of copeptin, three sensitive and three hs-cTn assays were performed at presentation in a blinded fashion. The final diagnosis was adjudicated by two independent cardiologists using all clinical information including coronary angiography and levels of hs-cTnT. The incremental value in the diagnosis of NSTEMI was quantified using four outcome measures: area under the receiver-operating characteristic curve (AUC), integrated discrimination improvement (IDI), sensitivity and negative predictive value (NPV). Early presenters (< 4h since chest pain onset) were a pre-defined subgroup.NSTEMI was the adjudicated final diagnosis in 358 (18.6%) patients. As compared to the use of cTn alone, copeptin significantly increased AUC for two (33%) and IDI (between 0.010 and 0.041 (all p < 0.01)), sensitivity and NPV for all six cTn assays (100%); NPV to 96-99% when the 99 th percentile of the respective cTnI assay was combined with a copeptin level of 9 pmol/l (all p < 0.01). The incremental value in early presenters was similar to that of the overall cohort.When used for rapid rule-out of NSTEM in combination with sensitive or hs-cTnI assays, copeptin provides a numerically small, but statistically and likely also clinically significant incremental value