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We are pleased to announce that the American Physical Society (APS) journal, *Physical Review Letters*, has selected the Station Q paper, Transport Signatures of Quasiparticle Poisoning in a Majorana Island, as an Editors' Suggestion. The paper details how, working with theorists in Copenhagen, we found a way to measure the quasiparticle poisoning rate of a Majorana wire by using the strength of a shadow of the main Coulomb blockade peaks. By operating with a nearly open device, the Coulomb energy was reduced, and we could see Coulomb peak motion much more clearly than in previous studies. Microsoft is supporting this fundamental science both for its intrinsic interest and as a stepping stone toward building a topological quantum computer.

*Physical Review Letters *editors highlight only one in six submitted papers as an Editors' Suggestion, based on the paper's particular importance, innovation, and/or broad appeal. Ranked first among physics and mathematics journals by the Google Scholar five-year h-index, *Physical Review Letters* accepts fewer than one quarter of the submissions it receives. We are honored and thank *Physical Review Letters* for highlighting our work.

Read the abstract of the paper.

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Working together, ETH Zurich and Microsoft QuArC researchers have provided the first application of machine-learning techniques to solve outstanding problems in quantum physics. The neural networks used in their study developed a genuine intuition of the bizarre behavior of quantum particles. For example, after the artificial intelligence is trained on the elementary rules of quantum mechanics, it can precisely predict the probability of the atoms being in a certain quantum state.

Predicting this probability, among other properties, is an extremely complex problem that, in most cases, even the best classical supercomputers available today are unable to exactly solve. However, taking an unconventional approach to this daunting problem, Giuseppe Carleo and Matthias Troyer have devised artificial neural networks that can learn how atoms behave in the quantum worldand correct themselves in the process.

The artificial intelligence has performed remarkably well when tested on problems that have long challenged the minds of brilliant quantum physicists. In the cases covered in the study, it has automatically found the few relevant patterns and correlations driving the behavior of interacting quantum particles. Applications of this approach hold the promise to help physicists understand the behavior of those molecules, materials, and devices where the effects of quantum mechanics seriously defy human intuition. A well-trained machine would provide great help to physicists and chemists working on such problems.

Read the full article.

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]]>As its name implies, the poisoning of Majorana devices by normal electrons is fatal to topological computation, so much effort is now focused on characterizing the degree of poisoning either by the creation of quasiparticle pairs within the device, or by electrons entering the device through the leads.

A recent experiment (see https://arxiv.org/abs/1612.05748), led by Sven Albrecht and carried out at Station Q Copenhagen, demonstrates that when a Majorana device is strongly coupled to normal-metal leads, poisoning has a distinct experimental signaturea set of "shadow" Coulomb blockade diamonds, offset from the main diamonds by one electron charge from the main Coulomb diamonds associated with Cooper-pair tunneling.

Detailed theoretical modeling by Esben Hansen, Jeroen Danon, and Karsten Flensberg, also presented in the paper, was in good quantitative agreement with the experiment, and allowed the strength of the shadow peaks to be converted into a poisoning rate. The rate was measured at, and calculated at, strong tunneling, which is not where one would operate a Majorana device. Extrapolating the theory to the point where the shadows would be invisible allows a bound to be placed on the poisoning rate from the leads, even when they are more closed than in the experiment. The fact that we don't see shadows in the more closed devices means that poisoning must occur with a characteristic time of around 10 microseconds, given the parameters of these nanowire devices. We expect that the situation is much better than this conservative bound, an assumption we will test in future experiments.

Read the full paper.

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]]>The post A clear view of emerging and hybridizing Majorana zero modes using epitaxial InAs-Al nanowires appeared first on Microsoft Azure Quantum Blog.

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The first signature of Majorana physics, identified experimentally at TU Delft in 2012, focused on a characteristic conductance peak at zero voltage. It bore many signatures of Majorana zero modes, but had a sizable background signal that obscured how the peak arose out of coalescing Andreev bound states. Recently, Mingtang Deng and a Station Q Copenhagen (QDev) team considered a similar geometrynow fabricated with epitaxial semiconductor-superconductor nanowires grown by Peter Krogstrup, also of QDev.

Published in *Science* (December 2016), this new material system provides a clearer view of how Majorana zero modes emerge, adding support for the Delft interpretation and exploring new, previously unconsidered regimes, including how the Majorana zero mode hybridizes with a quantum dot at the end of the wire. The measurements, led by postdoctoral fellow Mingtang Deng, along with a team of experimentalists and theorists, are complemented by extensive numerical simulations, showing very good agreement between theory and experiment. The case for Majoranas is stronger now, and furthers our understanding of the relationship between Andreev states and Majorana zero modes in proximitized nanowires.

Read the *Science *article.

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Topological materials can yield quasiparticles that behave in a manner similar to elementary particles that are part of the standard model of particle physics. In this paper, published in Physical Review X, we report on a new class of such quasiparticlestriple point fermionswhich represent fermions that have mixed properties of Dirac and Weyl fermions. The triple point fermions exhibit a variety of observable phenomena, including anomalous responses to magnetic fields that can possibly be used in future devices. We expect our results to pave the way for future studies that identify topological materials with technologically interesting properties.

Read the published version.

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]]>The post Direct from the 2016 Quantum Retreat in Redmond appeared first on Microsoft Azure Quantum Blog.

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The 2016 QRetreat took place on Microsoft's Redmond campus on April 28 and 29, 2016. QRetreat is an annual meeting of the Station Q Santa Barbara and Station Q Redmond teams. The goals of the meeting are to update each other on the recent research in an informal atmosphere and discuss current projects.

This retreat was organized as a series of short talks followed by discussion sessions. The range of topics was very broad, including recent developments in condensed matter physics, topological quantum computing, quantum algorithms, fault tolerance, quantum circuit design and compilers for quantum computers. This year's retreat also featured talks by experimentalists who collaborate with Station Q from TU Delft, University of Sydney and Niels Bohr Institute.

Station Q Redmond / QuArC team members presented two overview talks and three talks on ongoing projects. Nathan Wiebe gave an overview of the recent developments in quantum machine learning. It was interesting to hear about the different ways of thinking about both quantum machine learning and machine learning for quantum systems. You can find quite a few approaches to this in Nathan's recent papers. Martin Roetteler presented his results on developing new quantum circuit libraries. Alan Geller told us about new developments related to compilers and programming languages for quantum computers. Matt Hastings shared some new ideas on quantum algorithms for small quantum computers. Vadym Kliuchnikov gave a short tutorial on small surface codes.

Station Q Santa Barbara researchers chose to present their recent work on the theory of topological phases and many-body quantum systems. This kind of result usually gets less visibility at other meetings we have, and QRetreat is a great place to catch up on it. Maissam Barkeshli told us about his recent work on manipulating quantum information using topological charge projection. The work opens a new path towards achieving universal quantum computation using certain models of anyons that are not universal by braiding alone. Michael Freedman presented his result describing holographic entanglement. We learned that the min-flow max-cut principle, which is very familiar to computer scientists and graph theorists, can be applied to studying minimal surfaces in holographic systems and provide a new on holographic entanglement and the Ryu-Takayanagi formula. Michael Zaletel presented results on using DMRG to study physics of half-filled Landau level.

The retreat concluded with wine tasting and great food at DeLille Cellars!

Vadym Kliuchnikov

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